A DICTIONARY OF ELECTRICAL WORDS, TERMS AND PHRASES. BY EDWIN J. HOl|,STON, A.M., PROFESSOR OF NATURAL PHILOSOPHY AND PHYSICAL GEOGRAPHY IN THE CENTRAL HIGH SCHOOL OF PHILADELPHIA ; PROFESSOR OF PHYSICS IV THE FRANKLIN INSTITUTE OF PENNSYLVANIA ; ELECTRICIAN OF THE INTERNATIONAL ELECTRICAL EXHIBITION, ETC., ETC. SECOND EDITION. RE WRITTEN AND GREA TL Y ENLARGED. NEW YORKv: THE W. J. JOHNSTON COMPANY, LIMITED, 167-176 TIMES BUILDING. 1892; stri COPYRIGHT, 1889 AND 1892, BY THE W. J. JOHNSTON COMPANY, LIMITED. PREFACE TO THE FIRST EDITION. THE rapid growth of electrical science, and the almost daily addition to it of new words, terms and phrases, coined, as they too frequently are, in ignorance of those already existing, have led to the production of an electrical vocabulary that is already bewildering in its extent. This multiplicity of words is extremely discourag- ing to the student, and acts as a serious obstacle to a general dissemination of elec- trical knowledge, for the following reasons : 1. Because, in general, these new terms are not to be found eve-, in the unabridged editions of dictionaries. 2. The books or magazines, in which they were first proposed, are either inac- cessible to the ordinary reader, or, if accessible, are often written in phraseology un- intelligible except to the expert. 3. The same terms are used by different writers in conflicting senses. 4. The same terms are used with entirely different meanings. 5. Nearly all the explanations in the technical dictionaries are extremely brief as regards the words, terms and phrases of the rapidly growing and comparatively new science of electricity. In this era of extended newspaper and periodical publication, new words are often coined, although others, already in existence, are far better suited to express the same ideas. The new terms are used for a while and then abandoned ; or, if retained, having been imperfectly defined, their exact meaning is capable of no little ambiguity; and, subsequently, they are often unfortunately adopted by different writers with such varying shades of meaning, that it is difficult to understand their true and exact significance. Then again, old terms buried away many decades ago and long since forgotten, are dug up and presented in such new garb that their creators would most certainly fail to recognize them. It has been with a hope of removing these difficulties to some extent that the author has ventured to present this Dictionary of Electrical Words, Terms and Phrases to his brother electricians and the public generally. He trusts that this dictionary will be of use to electricians, not only by showing the wonderful extent and richness of the vocabulary of the science, but also by giving the general consensus of opinion as to thi significance of its different words, terms or phrases. It is, however, to the general public, to whom it is not only a matter of interest but also one of necessity to fully understand the exact meaning of electrical literature, that the author believes the book will be of the greatest value. In order to leave no doubt concerning the precise meaning of the words, terms and phrases thus defined, the following plan has been adopted of giving : (i.) A concise definition of the word, term or phrase. (2.) A brief statement of the principles of the science involved in the definition. (3.) Whew possible and advisable, a cut of the apparatus described or employed in connection with the word, term or phrase defined. It will be noticed that the second item of the plan makes the Dictionary ap- proach to some extent the nature of an Encyclopedia. It differs, however, from an Encyclopedia in its scope, as well as in the fact that its definitions in all cases are concise. Considerable labor has been expended in the collection of the vocabulary, for which purpose electrical literature generally has been explored.' In the alphabetical arrangement of the terms and phrases defined, much perplexity has arisen as to the proper catch-word under which to place them. It is believed that part of the difficulty in this respect has been avoided by the free use of cross references. In elucidating the exact meaning of terms by a brief statement of the principles of the science involved- therein, the author has freely referred to standard textbooks on electricity, and to periodical literature generally. He is especially indebted to works or treatises by the following authors, viz. : S. P. Thompson, Larden, Gumming, Hering, Prescott, Ayrton, Ayr ton and Perry, Pope, Lock wood. Sir William Thom- son, Fleming, Martin and Wetzler, Preece, Preece and Sivewright, Forbes, Max- well, De Watteville, J. T. Sprague, Culley, Mascart and Joubert, Schwendler, Fontaine, Noad, Smee, Depretz, De la Rive, Harris, Franklin, Cavallo, Grove, Hare, Daniell, Faraday and very many others. The author offers his Dictionary to his fellow electricians as a starting point only. He does not doubt that his book will be found to contain many inaccuracies, ambig- uous statements, and possibly doubtful definitions. Pioneer work of this character must, almost of necessity, be marked by incompleteness. He, therefore, invites the friendly criticisms of electricians generally, as to errors of omission and commis- sion, hoping in this way to be able finally to crystallize a complete vocabulary of electrical words, terms and phrases. The author desires in conclusion to acknowledge his indebtedness to his friends, Mr. Carl Hering, Mr. Joseph Wetzler and Mr. T. C. Martin, for critical exami- nation of the proof sheets ; to Dr. G. G. Faught for examination of the proofs of the parts relating to the medical applications of electricity, and to Mr. C. E. Stump for valuable aid in the illustration of the book ; also to Mr. George D. Fowle, Engineer of Signals of the Pennsylvania Railroad Company, for information concern- ing their System of Block Signaling, and to many others. EDWIN J. HOUSTON. CENTRAL HIGH SCHOOL, PHILADELPHIA, PA., SEPTEMBER, 1889. PREFACE TO THE SECOND EDITION. THE first edition of the "Dictionary of Electrical Words, Terms and Phrases" met with so favorable a reception that the entire issue was soon exhausted. Although but a comparatively short time has elapsed since its publication, electrical progress has been so marked, and so many new words, terms and phrases have been introduced into the electrical nomenclature, that the preparation of a new edition has been determined on rather than a mere reprint from the old plates. The wonderful growth of electrical science may be judged from the fact that the present work contains more than double the matter and about twice the number of definitions that appeared in the earlier work. Although some of this increase has been due to words which should have been in the first edition, yet in greater part it has resulted -from an actual multiplication of the words used in electrical literature. To a certain extent this increase has been warranted either by new applications of electricity or by the discovery of new principles of the science. In some cases, how- ever, new words, terms or phrases have been introduced notwithstanding the fact that other words, terms or phrases were already in general use to express the same ideas. The character of the work is necessarily encyclopedic. The definitions are given in the most concise language. In order, however, to render these definitions intel- ligible, considerable explanatory matter has been added. The Dictionary has been practically rewritten, and is now, in reality, a new book based on the general lines of the old book, but considerably changed as to order of arrangement and, to some extent, as to method of treatment. As expressed in its preface, the author appreciates the fact that the earlier book was tentative and incomplete. Though the wide scope of the second edition, the vast number of details included therein, and the continued growth of the electrical vocabulary must also necessarily make this edition incomplete, yet the author ventures to hope that it is less incomplete than the first edition. He again asks kindly criti- cisms to aid him in making any subsequent edition more nearly what a dictionary of so important a science should be. The order of arrangement in the first edition has been considerably changed. The initial letter under which the term or phrase is defined is in all cases that of the noun. For example, "Electric Light " is defined under the term " Light, Electric " ; " Diameter of Commutation " under "Commutation, Diameter of ," "Alter- nating Current Dynamo-Electric Machine" under "Machine, Dynamo-Electric, Alternating Current . " As before, the book has numerous cross references. Although the arrangement of the words, terms and phrases under the initial letter of the first word, term or phrase, as, for example, " Electric Light" under the letter E, might possess some advantages, yet, in the opinion of the author, the educational value of the work would be thereby considerably decreased, since to a great extent such an arrangement would bring together incongruous portions of the science. Frequent cross references render it possible to use the Dictionary as a text-book in connection with lectures in colleges and universities. With such a book the student need make notes only of the words, terms or phrases used, and afterwards, by the use of the definitions and explanatory matter connected therewith, work up the general subject matter of the lecture. The author has successfully used this method in his teaching. In order to separate the definitions from the descriptive matter, two sizes of type have been used, the definitions being placed in the larger sized type. In the descriptive matter the author has not hesitated to quote freely from standard electrical works, electrical magazines, and periodical literature generally. Among the numerous works consulted, besides those to which reference has already been made in the preface to the first edition, he desires to acknowledge his indebtedness espe- cially to "The Alternating Current Transformer," by J. A. Fleming ; to various works of John W. Urquhart; to "Modern Views of Electricity," by Prof. O. J. Lodge; to "A Text-book of Human Physiology," by Landois & Sterling; and to "Practical Application of Electricity in Medicine and Surgery," by Liebig & Rohe. . The cuts or diagrams used in the book have either been drawn especially for the work or have been taken from standard electrical publications. The chart of standard electrical symbols and diagrams has been taken from Prof. F. B. Crocker's paper on that subject. The definition of terms used in systems of electric railways have been taken mainly from a paper on " Standards in Electric Railway Practice," by O. T. Crosby. The author desires especially to express his obligations to Prof. F. B. Crocker of the Electrical Engineering Department, Columbia College, New York, and to Carl Hering, of Philadelphia, for critical examination of the entire manuscript and for many valuable suggestions ; also to The Electrical World and the Electrical Engineer of New York, and to Prof. Elihu Thomson, Edward Caldwell, T. C. Martin, Dr. Louis Bell, Joseph Wetzler, Nikola Tesla, Wm. H. Wahl, Prof. Win. D. Marks, Prof. A. E! Dolbear, C. W. Pike, John Hoskin, and numerous others, for aid in connection with new words or phrases. So far as they relate to the medical applications of electricity, the proof sheets were revised by Dr. G. G. Faught, of Philadelphia. The author desires to thank critics of the first edition and the electrical fraternity in general for valuable suggestions. He presents this second edition of his Dictionary in the hope that it may to some extent properly represent the vocabulary of electrical science. CENTRAL HIGH SCHOOL, EDWIN J. HOUSTON PHILADELPHIA, May, 1892. A DICTIONARY OF ELECTRICAL WORDS, TERMS AND PHRASES. A. or An. An abbreviation sometimes used in medical electricity for anode. (See Anode.) A. C. C. An abbreviation used in medical electricity for Anodic Closure Contraction. (See Contraction, Anodic Closure.) A. D. C. An abbreviation used in medical electricity for Anodic Duration Contraction. (See Contraction, Anodic Duration?) A. 0. C. An abbreviation used in medical electricity for Anodic Opening Contraction. (See Contraction, Anodic Opening?) Abscissa of Rectilinear Co-ordinates. A line or distance cut off along axis of abscissas. The abscissa of the point D, Fig. i, on the curve O D R, is the distance D i, or its equal A 2, measured or cut off on the line A C, the axis of abscissas; or, briefly, A 2, is the abscissa of the point D. Abscissas, Axis of One of the axes of co-ordinates used for determining the position of points on a curved line. Thus the position of the point D, Fig. i, on the curved line O D R, is determined by the per- pendicular distances, D I and D 2, of such point from two straight lines, A B and A C, called the axes of co-ordinates. AC, is called the axis of A 2 C _ Fig. i. Axes of Co-ordinates, scissas, and AB, the axis of ordinates. The point A, where the lines are considered as starting or originating, is called the point of origin, or, gen- erally, the origin, The use of co-ordinates was first introduced by the famous mathematician, Des Cartes. Absolute. Complete in itself. The terms absolute and relative are used in electricity in the same sense as ordinarily. Thus, a galvanometer is said to be calibrated absoluttly when the exact current strengths re- quired to produce given deflections aie known ; or, in other words, when the absolute current strengths are known ; it is said to be calibrated relatively when only the relative current strengths required to produce given deflections are known. The word absolute, as applied to the units em- ployed in electrical measurements, was introduced by Gauss to indicate the fact that the values of such units are independent both of the size of the instrument employed and of the value of gravity at the particular place where the instrument is used. The word absolute is also used with reference to the fact that the values of the units could readily be redetermined from well known con- stants, in case of the loss of the standards. The absolute units of length, mass, and time are more properly called the C. G. S. units, or the centimetre-gramme-second units. (See Units, Absolute.) An absolute system of units based on the milli- gramme, millimetre, and second, was proposed by Weber, and was called the millimetre milli- gramme-second units. It has been replaced by Aba.] [Ace. the C. G. S. units. (See Units, Centimetre- Gramme-Second. Units, Fundamental.) Absolute Block System for Railroads. (See Block System for Railroads, Absolute?) Absolute Calibration. (See Calibration, Absolute) Absolute Electrometer. (See Electrome- ter, Absolute?) Absolute Galvanometer. (See Galva- nometer, Absolute?) Absolute Unit of Current, (See Current, Absolute Unit of.) Absolute Unit of Electromotive Force. (See Force, Electromotive, Absolute Unit of.) Absolute Unit of Inductance. (See In- ductance, Absolute Unit of.) Absolute Unit of Resistance. (See Re- sistance, Absolute Unit of.) Absolute Unit of Self-induction. (See Induction, Self, Absolute Unit of.) Absolute Units. (See Units, Absolute) Absolute Vacuum. (See Vacuum, Ab- solute?) Absorption. The taking, or, literally, drinking in, of one form of matter by another, such as a gas, vapor or liquid by a solid ; or of the energy of sound, light, heat, or elec- tricity by ordinary matter. Absorption, Acoustic The taking in of the energy of sound waves produced by one sounding or vibrating body by another vibrating body. Acoustic absorption may result in the dissipa- tion of the absorbed energy, as heat, or in sym- pathetic vibrations. (Bee nitrations, Sympathetic.} Absorption, Electric The appar- ent soaking of an electric charge into the glass or other solid dielectric of a Leyden jar or, condenser. (See Condenser?) The capacity of a condenser varies with the time the condenser remains charged and with the time taken in charging. Some of the charge acts as if it soaked into the solid dielectric, and this is the cause of the residual charge. (See Charge, Residual.) Therefore, when the con- denser is discharged, less electricity appears than was passed in ; hence the term electric absorption. Absorption, Luminous The ab- sorption of the energy of light in its passage through bodies. When sunlight falls on an opaque colored body, such for example as a red body, all the colors but the reds are absorbed. The reds are then thrown off and thus cause the color. In the same manner, when sunlight falls on a transparent colored body, such for example as red, all colors but the reds are absorbed, and the reds are transmitted. When sunlight falls on a phosphorescent body, a part of the light is absorbed as heat ; another part is absorbed by the molecules being set into motion sufficiently rapid to cause them to emit light or to become luminous. A mass of glowing gas or vapor absorbs waves of light of the same length as those it itself emits. This is the cause of the dark lines of the solar spectrum, called the Fraunhoffer lines. The amount of light absorbed by the glass globe of an incandescent lamp, according to Urquhart, is as follows, viz.: Clear glass 10 per cent. Ground glass 35 " Opalescent glass 50 " Absorption, Selective The absorp- tion of a particular or selected character of waves of sound, light, heat, or electricity. Absorption, Thermal The ab- sorption of heat energy in its passage through a body. The phenomena of thermal absorption are similar to those of luminous absorption. A sub- stance that is transparent to heat, or which allows heat waves to pass through without absorption, is called diathermanous, or diathermanic, or is said to be transparent to heat. Absorptive Power. (See Power, Absorp- tive?) Acceleration. The rate of change of velocity. Acceleration is thus distinguished from velocity: velocity expresses in time the rate-of-change of position, as a velocity of three metres per second; acceleration expresses in time the rate-of-change of velocity, as an acceleration of one centimetre per second. Since all matter is inert, and cannot change its Ace.] [Ace. condition of rest or motion without the applica- tion of some force, acceleration is necessarily due to some force outside the matter itself. A force may therefore be measured by the acceleration it imparts to a given mass of matter. Acceleration is positive when the velocity is in- creasing, and negative when it is decreasing. Acceleration, Dimensions of The value of the acceleration expressed in terms of the length or of distance by the time. (See Acceleration, Unit of.) Acceleration, Unit of That ac- celeration which will give to a body unit- velocity in unit-time; as, for example, one centimetre-per-second in one second. Bodies falling freely in a vacuum, and ap- proximately so in air, acquire an acceleration which in Paris or London, at the end of a second, amounts to about 981 centimetres per second, or nearly 32.2 ft. per second. V A = , or, in other words, The acceleration equals the velocity divided by the time. But, since velocity equals the Distance, or the Length traversed in a Unit of Time, V = - . Therefore, A := = L TV r The acceleration equals the length, or the dis- tance passed through, divided by the square of the time in seconds. These formulae represent the Dimensions of Acceleration. Accumulated Electricity. (See Electri- city, Accumulated^ Accumulating Electricity. (See Electri- city, Accumulating^) Accumulation of Electricity. (See Elec- tricity, Accumulation of.} Accumulator. A word sometimes applied to any apparatus in which the strength of a current is increased by the motion past it of a conductor, the currents produced in which tend to strengthen and increase the current which causes the induction. The word accumulator is sometimes applied to Sir Wm. Thomson's Electric Current Accumu- lator. Current accumulators operate on the reaction principle of dynamo-electric machines. In this sense, therefore, a dynamo-electric machine is an accumulator. (See Machine, Dynamo-Electric, Reaction Principle of.} Fig. 2. Barlow's Wheel. The copper disc D, Fig. 2, has freedom of rotation, on a horizontal axis at O, in a magnetic field, the lines of force of which, represented by the dotted lines in the drawing, pass downward perpendicularly into the plane of the paper. If, now, a current from any source be passed in the direction A, O, B, C, A, through the circuit A, O, B, C, A, which is provided with spring contacts at O, and A, the disc will rotate in the direction of the curved arrow. This motion is due to the current acting on that part of the disc which lies between the two contacts A and O. This apparatus is known as Barlow's Wheel. If, when no current is passing through the circuit, the disc be turned in the direction of the arrow, a current is set up in such a direction as would oppose the rotation of the disc. (See Law, Lenz's.) If, however, the disc be turned in the opposite direction to that of the arrow, induction currents will as before be produced in the circuit. As this rotation of the disc tends to move the circuit O A, towards the parallel but oppositely directed circuit B C, these two circuits being parallel and in opposite directions tend to repel one another, and there will thus be set up induced currents that tend to oppose the motion of rotation, and the current of the circuit will therefore increase in strength. (See Dynamics, Electro.) Should then a current be started in the circuit, and the original field be removed, the induction will be continued, and a current which, up to a certain extent, increases or accumulates, is maintained in the circuit during rotation of the disc. (LarJen. } Barlow's Wheel, when used in this manner, is known as TJiomfbn's Electric Current Accumu- lator. Ace.] [Ace. Accumulator. A word often applied to a Leyden jar or condenser, which permits the gradual collection from an electric source of a greater charge than it would otherwise be capable of containing. A condenser. (See Condenser) The ability of a source to accumulate an in- creased charge when connected to a condenser is due to the increased capacity which a plate or other conductor acquires when placed near another plate or conductor. (See Condenser. y.,r, Leyden.) Accumulator, Capacity of The capacity of a condenser, expressed in micro- farads. (See Condenser, Capacity of) Accumulator or Condenser ; Laws of Ac- cumulation of Electricity. Sir W. Snow Harris, by the use of his Unit-Jar and Elec- tric Thermometer, deduced the following laws for the accumulation of electricity, which we quote from Noad's " Student's Text-Book of Electricity," revised by Preece : (I.) "Equal quantities of electricity are given off at each revolution ot the plate of an electrical machine to an uncharged surface, or to a surface charged to any degree pf saturation. ' ' (2. ) "A coated surface receives equal quantities of electricity in equal times ; and the number of revolutions of the plate is a fair measure of the relative quantities of electricity, all other things remaining the same." (3. ) " The free action of an electrical accumula- tion is estimated by the interval it can break through, and is directly proportional to the quan- tity of electricity." (4.) " The free action is inversely proportional to the surface." (5.) " When the electricity and the surface are increased in the same ratio, the discharging in- terval remains the same ; but if, as the electricity is increased, the surface is diminished, the dis- charging interval is directly as the square of the quantity of electricity." (6.) "The resistance of air to discharge is as the square of the density directly. " According to some later investigations, the quantity a plane surface can receive under a given density depends on the linear boundary of the surface as well as on the area of ihe surface. " The amount of electrical charge depends on surface and linear extension conjointly. There exists in every plane surface what may be termed an electrical boundary, having an important rela- tion to the grouping or disposition of the electric particles in regard to each other and to surrounding matter. This boundary in circles or globes is represented by their circumferences. In plane rectangular surfaces, it is by their linear extension or perimeter. If this boundary be constant, their electrical charge varies with the square root of the surface. If the surface be constant the charge varies with the square root of the boundary. If the surface and boundary both vary, the charge varies with the square root of the surface multi- plied into the square root of the boundary," These laws apply especially to continuous sur- faces taken as a whole, and not to surfaces divided into separate parts. By electrical charge Harris meant the quantity sustained on a given surface under a given elec- trometer indication ; by electrical intensity, he meant the indication of the electrometer corre- sponding to a given quantity on a given surface. (See Condenser, Capacity of. Capacity, Elec- trostatic. Capacity, Specific Inductive. ) Accumulators of this character are now generally called Condensers. (For more modern principles concerning their construction and capacity see Condenser. Condenser, Capacity of. ) Accumulator, Secondary or Storage Cell Two inert plates partially sur- rounded by a fluid incapable of acting chem- ically on either of them until after the passage of an electric current, when they become capable of furnishing an independent electric current. This use of the term accumulator is the one most commonly employed. A better term for such a cell is a secondary or storage cell. (See Cell, Secondary or Storage.) Commercially, an accumulator consists of a single jar and its electrolyte, in which a single set of positive and negative plates is properly placed. Accumulator, Water-Dropping An apparatus devised by Sir W. Thomson for increasing the difference of potential between two electric charges. The tube X Y, Fig. 3, connects with a reser- voir of water which is maintained at the zero potential of the earth. The water escapes from Ach.] [Act. IB ' I! ally x il Y re |"~ aallA.Jf if the openings at C and D, in small drops and falls on funnels provided, as shown, to receive the separate drops and again discharge them. The vessels A, A', and B, B', which are electrically connected as shown, a : maintained at a certain small A f. difference of potential, as indicated by the respective + and signs. -f){j Under these c i r c u m - stances, therefore, C and U, A ' will be charged inductively Fig. 3. Water-Drop- with charges opposite to **** Accumulator. those of A and B, or with and -f- electricities respectively. As the drops of water fall on the funnels, the charges which the funnels thus con- stantly receive are given up to B' and A', before the water escapes. Since, therefore, B, B', and A, A', are receiving constant charges, the differ- ence of potential between them must continually increase. This apparatus operates on the same principle as the replenisher. The drops of water act as the carriers, and A, A', and B, B', as the hollow vessels. (.See Replenisher.'] Achromatic. Free from false coloration. Images formed by ordinary lenses do not pos- sess the true colors of the object, unless the edges of the lenses are cut off by the use of a diaphragm ; i. e., an opaque plate with a central circular opening. The edges of the lenses disperse the light like an ordinary prism, and so produce rain- bow colored (prismatic) fringes in the image. The use of an achromatic lens is to obviate this false coloration. Achromatizable.->-Capable of being freed from false coloration. Achromatize. To free from false color- ation. Achromatizing. Freeing from false color- ation. Acid, Spent A battery acid, or other acid, that has become too weak for efficient action. In a voltaic cell the acid of the electrolyte becomes spent by combining with the metal of the positive plate. Acidometer. A special form of hydrom- eter used in determining the specific gravity of the acid liquid in a secondary or storage cell. (See Areometer or Hydrometer. Cell, Storage!) The scale on the acidometer tube is made to in- dicate the density according to the distance the floating instrument sinks in the liquid. Aclinic Line. (See Line, Aclinic) Acoustic Absorption. (See Absorption, Acoustic) Acoustic Engraving. (See Engraving, Acoustic?) Acoustic Telegraphy. (See Telegraphy, Acoustic) Acoustic Tetanus. (See Tetanus, Acous- tic) Acoutemeter, Electric An ap- paratus for electrically testing the delicacy of hearing. The Acoutemeter is one of the many applica- tions of Hughes' sonometer. It consists of three flat coils placed parallel to one another on a grad- uated rod, passing through their axes. The central coil, which is used as the primary of an induction coil, is fixed. The other two, which are employed as secondary coils, are movable. (See Sonometer, Hughes' 1 . Coil, Induction. Micro- phone.} A microphone, electrical tuning fork, switches, plugs, and other accessories, are suitably placed and connected. The subject whose hear- ing is to be tested is placed with his back to the apparatus, and with two telephone receivers tightly fixed to his ears. As various sounds are produced, the outer or movable coils are moved gradually away from the central coil, until no sound is heard in the telephone receivers. This distance is in the inverse ratio of the delicacy of hearing of the individual. Actinic Photometer. (See Photometer, Actinic) Actinic Ray. (See Ray, Actinic) Actinism. The chemical effects of light, as manifested by the decomposition of various substances. Under the influence of the sun's light, the car- bonic acid absorbed by the leaves of plants is de- composed in the living leaves into carbon, which is retained by the plant for the formation of its woody fibre or ligneous tissue, and oxygen, which is thrown off. Act] The bleaching of curtains, carpets, and other fabrics exposed to sunlight is caused by the actinic power of the light. The photographic picture is impressed by the actinic power of light on a plate covered with some sensitive metallic salt. Actinograph. An apparatus for measur- ing and recording the intensity of the chemi- cal effects of light. Actinography. The method of measuring and recording the intensity of the chemical effects of light. Actinometer. A word sometimes applied to a pyrheliometer. (See Pyrheliometer) Actinometer, Electric An appa- ratus for electrically measuring the intensity of the chemically active rays present in any luminous radiation. The rays from the luminous source are per- mitted to fall on a selenium resistance, and their intensity determined by the change observed in the resistance as indicated by the deflections of a galvanometer placed in circuit with the selenium resistance. Or, a thermo-electric pile is employed, and the amount of heat present determined by the indications of a galvanometer placed in its circuit. Action, Cataphoric - The action of electric osmose or cataphoresis. (See Cataphoresis.) Action Currents. (See Currents, Action?) Action, Inductive, Lines of Lines within the space, separating a charge and a neighboring body, along which elec- trostatic inductive action takes place. Lines of electrostatic force. Lines of inductive action pass through the dielectric, separating the two bodies, and termi- nate on the surfaces of the conductor. According to the now generally received notions, the elec- trostatic charge exists in the mass of the dielectric, and not in that of the conductor. The lines of inductive action terminate against the surfaces, one at the positive, and the other at the negative surface. A true E. M. F. exists in the space traversed by lines of inductive action. A con- ductor brought into this space becomes electri- fied, or is strained in such a manner that a momentary current is produced by the rearrange- 8 [Act. ment of the electrification brought about b)r electrostatic induction. Action, Local, of Dynamo-Electric Ma- chine : The loss of energy in a dy- namo-electric machine by the setting up of eddy currents in its pole pieces, cores, or other conducting masses. (See Currents, Eddy.} In a dynamo-electric machine local action is obviated by a lamination of the pole pieces, arma- ture core, etc. (See Core, Lamination of.) Action, Local, of Voltaic Cell An irregular dissolving or consumption of the zinc or positive element of a voltaic battery, by the fluid or electrolyte, when the circuit is open or broken, as well as when closed, or in regular action. Local action is due to small particles of such impurities as carbon, iron, arsenic, or other negative elements, in the positive plate. These impurities form with the positive element minute voltaic couples, and thus direct the corrosive action of the liquid to portions of the plate near them. Local action causes a waste of energy. It may be avoided by the amalgamation of the zinc. (See Zinc, Amalgamation of.) Action, Magne-Crystallic A term. proposed by Faraday to express differences in the action of magnetism on crystalline bodies in different directions. A needle of tourmaline, if hung with its axis horizontal, is no longer paramagnetic, as usual, but diamagnetic. The same is true of a crystal of bismuth. Faraday concluded from these ex- periments that a force existed distinct from either the paramagnetic or the diamagnetic force. He called this the magne -cry stallic force. PlUcker infers from these phenomena that a definite relation exists between the ultimate form of the particles of matter and their magnetic be- havior. The subject may be regarded as yet somewhat obscure. (See Polarity, Diamagnetic.') Action of a Current on a Magnetic Pole. (See Current, Action of, on a Magnetic Pole) Action, Refreshing, of Current The restoration, after fatigue, of muscular and nervous excitability obtained by the action of Act.] [Aer. voltaic alternatives. (See Alternatives, Vol- taic) Activity. The work done per second by any agent. (This term is but seldom used.) Work-per-second, or, as generally termed in the United States, Power, or Rate of Doing Work. (See Power.) Activity, Unit of A rate of work- ing that will perform one unit of work per second. In C. G. S. units, the activity of one erg per second. The C. G. S. unit of activity is very small. One Watt, the practical unit of activity or power, is equal to ten million ergs per second. (See Watt.) The unit of activity generally used for mechan- ical power is the horse-power, or 746 watts. {See Horse-Power.) Actual Cautery. (See Cautery, Actual.) Acute Angle. (See Angle, Acute?) Adapter. A screw nozzle fitted to an elec- tric lamp, provided with a screw thread to en- able it to be. readily placed on a gas bracket or chandelier in place of an ordinary gas burner. Adherence. The quality or property of adhering. (See Adhesion) Adherence, Magnetic Adhesion be- tween surfaces due to magnetic attraction. Magnetic adhesion has been applied, among other things, to a brake action on car wheels, either by causing them to adhere directly to the track or to a brake-block. Adhesion. The mutual attraction which exists between unlike molecules. (See At- traction, Molecular?} The phenomena of adhesion are due to the mutual attraction of dissimilar molecules. Adhesion, Electric - Adhesion be- tween surfaces due to the attraction of unlike electrostatic charges. Molecular adhesion must be distinguished from the attraction which causes a piece of dry and warmed writing paper, that has been rubbed by a piece of india-rubber, to stick to a papered wall. In this latter case the attraction between the wall and the paper is due to the mutual attraction of two dissimilar electrostatic charges. Molecular adhesion must also be distinguished from the at- traction of opposite magnetic poles. Adhesion, Galvanoplastic The ad- hesion of a galvanoplastic deposit or coating to surfaces subjected to electroplating. (See Plating, Electro) Adiathermancy. Opacity to heat. A substance is said to be dtathermanous when it is transparent to heat. Clear, colorless crys- tals of rock salt are very transparent both to light and to heat. Rock salt, covered with a layer or deposit of lampblack or soot, is quite transparent to heat. An adiathermanous body is one which is opaque to heat. Heat transparency varies not only with differ- ent substances, but also with the nature of the source from which the heat is derived. Thus, a substance may be opaque to heat from a non- luminous source, such as a vessel filled with boil- ing water, while it is comparatively transparent to heat from a luminous source, such as an incan- descent solid or a voltaic arc. A similar difference exists as regards transpar- ency to light. A colorless glass will allow light of any color to pass through it. A blue glass will allow blue light to pass freely through it, but will completely prevent the passage of any red light; and so with other colors. Adiathermanie. Possessing the quality of adiathermancy. (See Adiathermancy) Adjustable Condenser. (See Condenser, Adjustable) Adjuster, Cord A device for ad- justing the length of a pendant cord. Adjustment. Such a regulation of any apparatus as will enable it to properly perform its functions. JEpinns' Condenser. (See Condenser, sEptnus') Aerial Cable. (See Cable, Aerial) Aerial Cable, Suspending \Vire of (See Wire, Suspending, of Aerial Cable) Aerial Line. (See Line, Aerial) Aerolites. A name sometimes given to meteorites. Meteorites are masses of solids which pass Aff.] through the upper portions only of the earth's atmosphere on their approach to the orbit of the earth, or which fall through the air on the earth's surface from the sky. They are luminous at night and are followed by a train of fire. The luminosity is due to heat produced by friction through the air. Meteors frequently burst from the sudden expansion of their outer portions. Some meteorites are composed of nearly pure iron alloyed with nickel. The majority of them, however, are merely stones or oxidized sub- stances. Their average velocity is about 26 miles a second. Affinity, Chemical Atomic attrac- tion. The force which causes atoms to unite and form chemical molecules. Atomic or chemical attraction generally results in a loss of the characteristic qualities or proper- ties which distinguish one kind of matter from another. In this respect chemical affiniiy differs from adhesion, or the force which holds unlike molecules together. (See Adhesion. Attraction, Molecular.) If, for example, sulphur is mixed with lampblack, no matter how intimate the mixture, the separate particles, when examined by a magnifying glass, exhibit their peculiar color, lustre, etc. If, however, the sulphur is chemi- cally united with the carbon, a colorless, transpar- ent, mobile liquid, called carbon bisulphide, re- sults, that possesses a disagreeable, penetrating odor. Chemical affinity, or atomic combination, is in fluenced by a variety of causes, viz. : (I.) Cohesion. Cohesion, by binding the mole- cules more firmly together, opposes their mutual atomic attraction. A solid rod of iron will not readily burn in the flame of an ordinary lamp; but, if the cohesion be overcome by reducing the iron rod to filings, it burns with brilliant scintillations when dropped into the same flame. In this case the increase of surface and the increased temperature, of the smaller particles aly is now extensively em- ployed for resistance coils from the fact that changes in temperature of the alloy produce but comparatively small changes in its electrical re- sistance. (See Alloy, German Silver.) Alphabet, Telegraphic - An arbi- trary code consisting of dots and dashes, sounds.deflections of a magnetic needle, flashes of light, or movements of levers, following one another in a given predetermined order, to represent the letters of the alphabet and the numerals. Alphabet, Telegraphic: International Code The code of signals for letters, etc., employed in England and on the Euro- pean continent generally. Similar symbols are employed for the numerals and the punctuation marks. It will be observed that it is mainly in the characters of the American Morse, in which spaces are used, that the Continental characters differ from the American. This is due to the use of the needle instrument with which a space cannot well be represented. A movement or deflection of the International Telegraphic Code. needle to the left signifies a dot; a movement to the right, a dash. Alphabet, Telegraphic : Morse's Various groupings of dots and dashes, or deflections of a magnetic needle to the right and left, which represent the letters of the alphabet or other signs. In the Morse alphabet dots and dashes are em- ployed in recording systems, and sounds of varying intervals, corresponding to the dots and dashes, in the sounder system. A dash is equal in length of time to three dots. The space between the separate characters of a single letter is equal to one dot, except in the American Morse, in which the following letters contain longer spaces: C, O, R, Y, and Z. The lengthened spaces are equal to two dots. L is one and a half times the length of T. The sound produced by the down stroke of the sounding lever in the Morse sounder is readily distinguishable from the up stroke. When these differences are taken in connection with the inter- vals between successive sounds there is no diffi- culty in reading by sound. (For methods of receiving the alphabet, see Sounder, Morse Telegraphic. Recorder, Morse* Recorder, Bain's Chemical. Recorder, Siphon* Relay. Magnet, Receiving. ) In the needle ttle- graph, the code is similar to that used in the Morse Alphabet. (See Telegraphy, Single- Needle.} Alt] 16 AMERICAN MORSE CODE. ALPHABET. NUMERALS. i 6 2 7 3 8 4 5 PUNCTUATION MARKS. Period Comma Interrogation Exclamation Period Comma Jnterrogation_ Exclamation __ . Colon Semicolon Alteration Theory of Muscle or Nerve Current (See Theory, Alteration, of Muscle or Nerve Current?) Alternating Arc. (See Arc, Alternat- ing.} Alternating Current Circuit. (See Cir- cuit, Alternating Current} [Alt. Alternating Current Condenser. (See Condenser, Alternating Current?) Alternating Current Dynamo-Electric Machine. (See Machine, Dynamo-Electric, Alternating Current?) Alternating Current Electric Motor. (See Motor, Electric, Alternating Current?) Alternating Currents. (See Currents, Alternating?) Alternating Currents, Distribution of Electricity by (See Electricity, Dis- tribution of, by Alternating Currents?) Alternating Discharge. (See Discharge, Alternating?) Alternating Dynamo-Electric Machine. (See Machine, Dynamo-Electric, Alternat- ing Current?) Alternating Electrostatic Field. (See Field, Alternating Electrostatic} Alternating Electrostatic Potential. (See Potential, Alternating Electrostatic} Alternating Field. (See Field, Alternat- ing} Alternating Influence Machine, Wims- hurst's (See Machine, Wimshurst's Alternating Influence?) Alternating Magnetic Field. (See Field, Alternating Magnetic?} Alternating Magnetic Potential. (See Potential, Alternating Magnetic} Alternating Potential. (See Potential, Alternating?) Alternating Primary Currents. (See Currents, Alternating Primary?) Alternating Secondary Currents. (See Currents, Alternating Secondary?) Alternation. A change in direction or phase. Alternations. Changes in the direction of a current in a circuit. A current that changes its direction 300 times per second is said to possess 300 alternations per second. Alternations, Complete A change in the direction of a current in a circuit from its Alt.] 17 \inin. former direction and back again to that direction. A complete to-and-fro change. Complete alternations are sometimes indicated by the symbol ~. Alternations, Frequency of A phrase employed to denote the number of al- ternations per second. Alternative Path. (See Path, Alterna- tive) Alternatives, Voltaic A term used in medical electricity to indicate sudden re- versals in the polarity of the electrodes of a voltaic battery. An alternating current from a voltaic bat- tery, obtained by the use of a suitable com- mutator. Sudden reversals of polarity produce more energetic effects of muscular contraction than do simple closures or completions of the circuit. The muscular contraction produced by a voltaic current is much stronger when the direction of the current is rapidly reversed by means of a com- mutator than when the current is more slowly broken and the poles then reversed. The effect of voltaic alternatives is to produce quick contractions that are in strong contrast to the prolonged contractions that result from the faradic curr.ent. In the faradic machine, the reversals are so rapid that the muscle fails to return to rest before it is again contracted. Voltaic alternatives are sometimes indicated by the contraction V. A. Alternator. A name commonly given to an alternate current dynamo. (See Machine, Dynamo- Electric, Alternating Current?) Alternator, Compensated Excitation of An excitation of an alternating current dynamo-electric machine, in which the field is but partfally excited by separate excitement, the remainder of its exciting current being derived from the commuted currents of a small transformer placed in the main circuit of the machine. The object of compensated excitation of nn alternator is to render the machine self-governing. Amalgam. A combination or mixture of a metal with mercury. A'nalgain, Electric A substance with which the rubbers of the ordinary fric- tional electric machines are covered. Electric amalgams are of various compositions. The following formula produces an excellent amalgam : Melt together five parts of zinc and three of tin, and gradually pour the molten metal into nine parts of mercury. Shake the mixture until cold, and reduce to a powder in a warm mortar. Apply to the cushion by means of a thin layer of stiff grease. Mosaic gold, or bisulphide of tin, and powdered graphite, both act as good electric amalgams. An electric amalgam not only acts as a con- ductor to carry off the negative electricity, but, being highly negative to the glass, produces a far higher electrification than would mere leather or chamois. Amalgamate. To form into an amalgam. Amalgamating. Forming into an amal- gam. Amalgamation. The act of forming into an amalgam, or effecting the combination of a metal with mercury. Amalgamation of Zinc Plates of Voltaic Cell. (See Plates, Zinc, of Voltaic Cell, Amalgamation of.) Amber. A resinous substance, generally of a transparent, yellow color. Amber is interesting electrically as being be- lieved to be the substance in which the proper- ties of electric attractions and repulsions, imparted by friction or rubbing, were first noticed. It was called by the Greeks ij\.EKTpov, from which the word electricity is derived. This property was mentioned by the Greek, Thales of Miletus, 600 B. c., as well as by Theophrastus. American System of Telegraphy. (See Telegraphy, American System of.) American Twist-Joint. (See Joint, American Twist.) American Wire Gtauge. (See Gauge, Wire, American.)^ Ammeter. A form of galvanometer in which the value of the current is measured directly in amperes. (See Galvanometer) An ampere-meter or ammeter is a commercial form of galvanometer in which the deflections of Amm.j 18 [Amp. a magnetic needle are calibrated or valued in am- peres. As a rule the coils of wire in an ammeter are of lower resistance than in a voltmeter. The magnetic needle is deflected from its zero position by the field produced by the current whose strength in amperes is to be measured. This needle is held in the zero position by the action of a magnetic field, either of a permanent or an electro-magnet, by the action of a spring, or by a weight under the influence of gravity. There thus exist a variety of ammeters, viz.: permanent -magnet ammeters, electro-magnetic ammeters, spring ammeters and gravity ammeters. In the form originally devised by Ayrton and Perry, the needle came to rest almost imme- diately, or was dead-beat in action. (See Damp- ing.} It moved through the field of a permanent magnet. The instrument was furnished with a number of coils of insulated wire, which could be connected either in series or in muldple-arc by means of a commutator, thus permitting the scale reading to be verified or calibrated by the use of a single voltaic cell. (See Circuits, Varieties of. Commutator. Calibration, Absolute. Calib>a- tion, Relative.) In this case the coils were turned to series, and a plug pulled out, thus intro- ducing a resistance of one ohm. c Fig. T2. Ayrton and Perry Ammeter. Fig. 12 represents an ampere-meter devised by Ayrton and Perry. A device called a commutator for connecting the coils either in series or parallel is shown at C. Binding posts are provided at P, PS, and S. The dynamo terminals are con- nected at the posts P, PS, and the current will pass only when the coils are in multiple, thus avoiding accidental burning of the coils. In this case the entire current to be measured passes through the coils so coupled. The posts S and PS, are for connecting the single battery cell cur- rent. A great variety of ampere-meters, or ammeters, have been devised. They are nearly all, how- ever, constructed on essentially the same general principles. Commercial ammeters are made in a ^reat va- riety of forms. When the currents to be meas- ured are large, as is generally the case in electric light or power stations, they consist of a coil of insulated wire, often of a single turn, or even of but a part of a turn, having a balanced coie of iron or steel capable of moving freely within it. Ammeter, Electro-Magnetic A form of ammeter in which a magnetic needle is moved against the field of an electro-magnet by the field of the current it is measuring. (See Ammeter.) Ammeter, Gravity A form of am- meter in which a magnetic needle is moved against the force of gravity by the field of the current it is measuring. (See Ammeter?) Ammeter, Magnetic- Vane An ammeter in which the strength of a magnetic field produced by the current that is to be measured is determined by the repulsion ex- erted between a fixed and a movable iron vane, placed in said field and magnetized thereby. (See Voltmeter, Magnetic- Vane.) Ammeter, Permanent-Magnet A form of ammeter in which a magnetic needle is moved against the field of a permanent mag- net by the field of the current it is measuring. (See Ammeter) Ammeter, Redncteur for (See Re- ducteur, or Shunt for Ammeter?) Ammeter, Spring A form of am- meter in which a magnetic needle is moved against the action of a spring by the field of the current it is measuring. (See Ammeter) Amorphous. Having no definite crys- talline form. Mineral substances have certain crystalline forms, that are as characteristic of them as are the forms of animals or plants. Under certain cir- cumstances, however, they occur without definite crystalline form, and are then said to be amor- phous solids. Amperage. The number of amperes pass- ing in a given circuit. The current strength in any circuit as indi- cated by an ampere-meter placed in the circuit. Amp.] 19 [Am . Ampere. The practical unit of electric current. Such a rate-of-flow of electricity as trans- mits one coulomb per second. Such a current (or rate-of-flow or trans- mission of electricity) as would pass with an electromotive force of one volt through a cir- cuit whose resistance is equal to one ohm. A current of such a strength as would deposit .005084 grain of copper per second. A current of one ampere is a current of such definite strength that it would flow through a cir- cuit of a certain resistance and with a certain electromotive force. (See Force, Electromotive. Volt. Resistance. Ohm.) Since the ohm is the practical unit of resistance, and the volt the practical unit of electromotive force, the ampere, or the practical unit of current, is the current that would flow through unit resist- ance, under unit pressure or electromotive force. To make this clearer, take the analogy of water flowing through a pipe under the pressure of a column of water. That which causes the flow is the pressure or head ; that which resists the flow is the friction of the water against the pipe, which will vary with a number of circumstances. The rate-of-flow may be represented by so many cubic inches of -water per second. As the pressure or head increases, the flow in- crea-es proportionally; as the resistance increases, the flow diminishes. Electrically, electromotive force corresponds to the pressure or head of the water, and resistance to the friction of the water and the pipe. The ampere, which is the unit rate-of-flow per second, may therefore be represented as follows, p viz. : C = , as was announced by Ohm in his R law. (See Law of Ohm.} This expression signifies that C, the current in amperes, j.s equal to E, the electromotive force in volts, divided by R, the resistance in ohms. We measure the rate-of-flow of liquids as so many cubic inches or cubic feet per second that is, in units of quantity. We measure the rate-of-flow of electricity as so much electricity per second. The electrical unit of quantity is called the Coul- omb. (See Coulomb.) The coulomb is such a quantity as would pass in one second through a circuit in which the rate-of-flow is one amp6re. An ampere is therefore equal to one coulomb per -St-c, nd. The electro-magnetic unit of current is such a current that, passed through a conducting wire bent into a circle of the radius of one centimetre, would tend to move perpendicular to its plane a unit magnetic pole htld at its centre, and sufficiently long to practically remove the other pole from its influence, with unit force, i. e., the force of one dyne. (See Dyne.) The ampere, or practical electro-magnetic unit, is one-tenth of such a current ; or, in other words, the absolute unit of current is ten amperes. An ampere may also be defined by the chemical decomposition the current can effect as measured by the quantity of hydrogen liberated, or metal deposited. Defined in this way, an ampere is such a cur- rent as will deposit .00111815 gramme, or .017253 grain, of silver per second on one of the plates of a silver voltameter, from a solution of silver nitrate containing from 15 to 30 per cent, of the salt (See Voltameter), or which will decompose .00009326 gramme, or .001439 grain of dilute sulphuric acid per second, or pure su'phuric acid at 59 degrees F. diluted with about 15 per cent, of water, that is, dilute sulphuric acid of Sp. Gr. of about i.i. The present scientific and commercial practice is to take the ampere to be such a current as will deposit 4 024 grammes of silver in one hour. Ampdre Arc. (See Arc, Ampere?) Ampere-Feet. (See Feet, Ampere.) Ampere-Hour. (See Hour, Ampere.) Ampere-Meter. An ammeter. (See Am- meter.) Ampere-Meter, Balance or Neutral Wire An ampere-meter placed in the cir- cuit of the neutral wire, in the three-wire sys- tem of electric distribution, for the purpose of showing the excess of current passing over one side of the system as compared with the other side, when the central wire is no longer neutral. Ampdre-Minnte. (See Minute, Ampere.) Ampdre Ring. (See Ring, Ampere.) Ampere-Second. (See Second, Ampere.) Ampere Tap. (See Tap, Ampere.) Ampere-Turn. (See Turn, Ampere.) Ampere-Turn, Primary (See Turn, Ampere, Primary?] Amp.] Ampdre-Tnrn, Secondary - - (See Turn, Ampere, Secondary) Ampere- Volt. A watt, or the TJ* of a horse-power. This term is generally written volt-ampere. (See Volt- Ampere.} Ampere-Winding. (See Winding, Am- pere) Ampere's Rule for Effect of Current on Needle. (See Rule, Amperes, for Effect of Current on Needle.} Ampere's Theory of Magnetism. (See Magnetism, Ampere s Theory of.) Ampcrian Currents. (See Currents, Am- jterian.) Amplitude of Vibration or Wave. (See Vibration or Wave, Amplitude of.) Ammunition-Hoist, Electric An electrically operated hoist for raising ammu- nition to the deck of a ship. In Ihe electric ammunition-hoist the electric motor which moves the hoist is made to follow the motions of the operator's hand, both as regards direction and speed. The motion of a crank, or wheel, causes a switch to start an electric motor in a certain direction, which tends to close the switch, thus necessitating a race between the operator and the motor. Should the operator begin to close the switch more slowly, the m tor will over- take him, will partially close the switch, and thus lower the speed of the motor. Analogous Pole. (See Pole, Analogous) Analysis. The determination of the com- position of a compound substance by separ- ating it into the simple or elementary sub- stances of which it is composed. Analysis, Electric The determin- ation of the composition of a substance by electrical means. Various processes have been proposed for elec- tric analysis; they consist essentially in decompos- ing the substance by means of electric currents, and are either qualitative or quantitative. (See Electrolysis.) Analysis, Electrolytic A term sometimes used instead of electric analysis, (See Analysis, Electric.) Analysis, Qualitative A chemical 20 [A ne. analysis which merely ascertains the kinds of elementary substances present. Analysis, Quantitative A chemical analysis which ascertains the relative propor- tions in which the different components enter into a compound. Analyzable. Separable into component parts. Analyze. To separate into component parts. Analyze, Electrically To separate electrically into component parts. Analyzer, Electric A gridiron of metallic wires which is transparent to electro- magnetic waves, when its length is perpendic- ular to them, but opaque to them i. od of the crater." The crater in the end of the positive car- bon is seen in Fig. 18. On the opposed end of the negative carbon a projection or nipple i formed by the de- posit of the electrical- ly volatilized carbon. Fig. 18. Voltaic Arc. The rounded masses or globules that appear on the surface of the elec- trodes are due to deposits of molten foreign mat- ters in the carbon. The carbon, both of the crater and its opposed nipple, is converted into pure, soft graphite. Arc, Yoltaic, Resistance of The resistance offered by the voltaic arc to the passage of the current. As in all other conductors, the ohmic resistance of the arc increases with its length, and decrea^es with its area of cross section. The apparent resistance, however, is not directly proportional to the length. An increase of temperature de- creases the icsistance of the voltaic arc. Arc.] [Arm* The total apparent resistance of the voltaic arc is composed of two parts, viz. : (I.) The true ohmic resistance. (See Resist- ance, Ohmic.} (2.) The counter electromotive force, or spuri- ous resistance. (See Resistance, Spurious.) Arc, Watt A voltaic arc, the elec- tric power of which is equal to a given number of watts. The ordinary long-arc, as employed in arc lighting, has a difference of potential of about 45 volts and a current strength of about 10 amperes. It is, therefore, a 45o-watt arc. Arch, Auroral The archlike form sometimes assumed by the auroral light. (See Aurora Borealis?) Arcing. Discharging by means of voltaic arcs. (See Arc, Voltaic.} Arcing at the commutator of a dynamo-electric machine not only prevents the proper operation of the machine, but eventually leads to the de- struction of the brushes and the commutator. Areometer, Bead A form of are- ometer suitable for rapidly testing the density of the liquid in a storage cell. The bead aieometer consists of a glass tube, open at both top and bottom, containing a few glass beads, so weighted as to float at liquid densities such as 1.105, I - I 7> r - 1 9 and 1. 200. To use the instrument, it is immersed in the liquid of the storage cell, and then withdrawn. The finger being kept in the upper opening, the liquid does not escape through the small opening at the bottom. The density is then ascer- tained by noting the beads that float. Areometer or Hydrometer. An instrument for determin- ing the specific gravity of a liquid. A common form of hydrometer consists, as shown in Fig. 19, of a closed glass tube, provided with a bulb, and filled at the lower end with mercury or shot, so as to in- sure its vertical position when Fig. 19. ffy- floating in a liquid. When placed drometer. in different liquids, it floats with part of the tube out of the liquid. The lighter the liquid, the smaller is the portion that remains out of the liquid when the instrument floats. The specific gravity is determined by observing the depth to which the instrument sinks when placed in different liquids, as compared with the depth it sinks when placed in water. Areometry. The measurement of specific gravity by means of an areometer. Argand Burner, Electric Hand-Lighter (See Burner, Argand, Electric Hand- Lighter?) Argand Burner, Electric Plain-Pendant (See Burner, Plain Pendant, Argand, Electric?) Argand Burner, Electric Ratchet-Pen- dant (See Burner, Ratchet-Pendant, Argand, Electric?) Argyrometry. The art of determining the weight of .electrolytically deposited silver. (See Balance, Plating?) Arm, Balance One of the resist- ances of an electric balance. (See Arms, Bridge or Balance. Bridge, Electric?) Arm, Bridge A bridge arm. (See Arms, Bridge or Balance?) Arm, Cross A horizontal beam at- tached to a pole for the support of the in- sulators for telegraph, electric light or other electric wires. A telegraphic arm. (See Arm, Tele- graphic?) Arm, Rocker An arm on which the brushes of a dynamo or motor are mounted for the purpose of shifting their position on the commutator. Arm, Semaphore The movable arm of the signal apparatus employed in block systems for railroads, for the purpose of in- forming engineers of trains of the condition of the road as regards other trains. In the absolute block system, as used on some roads, there are two positions for the semaphore arm, viz.: (I.) For Danger when in a horizontal position, or at 90 degrees with the vertical supporting pole. (2.) Clear when dropped below the horizontal position through an angle of 75 degrees. In the Permissive Block System, a third position Arm.] [Ann. intermediate between the 1st and the 2d, or at an angle of 37 degrees 30 minutes with the horizontal position, is used for caution. (See Block System for Railroads.) Arm, Signal A semaphore arm. (See Arm, Semaphored) Arm, Telegraphic A cross-arm placed on a telegraphic pole for the support of the insulators. These arms are generally called cross-arms. Armature. A mass of iron or other magnetizable material placed on or near the pole or poles of a magnet. In the case of a permanent magnet, the arma- ture, when used as a keeper, is of soft iron and is placed directly on the magnet poles. In this case it preserves or keeps the magnetism by closing the lines of magnetic Jorce of the magnet through the soft iron of the armature, and is then called a keeper. (See Force, Magnetic, Lines of.) In the case of an electro-magnet, the armature is placed near the poies, and is moved toward them whenever the magnet is energized by the passage of the current through the magnetizing coils. This movement is made against the action of a spring or weights, so that on the loss of magnetism by the magnet, the armature moves from the magnet poles. (See Magnet, Permanent. Magnet, Keeper of. ) When the armature is of soft iron it moves to- ward the magnet on the completion of the circuit through its coils, no matter in what direction the current flows, and is then called a non-polar- ized armature. (See Armature, Non-Poiarized. ) When made of steel, or of another electro-mag - Fig. 20. Bi-polar Armature. net, it moves from or toward the poles, accord- ing to whether the poles of the armature are of the same or of a different polarity from those of the magnet. Such an armature is called a polarized armature. (See Armature, Polarized. ) Armature, Bi-polar An armature of a dynamo-electric machine the polarity of which is reversed twice in every revolution through the field of the machine. A form of bi-polar armature is shown in Fig. 20. The word bi-polar armature is not generally employed. The term applies rather to the field- magnet poles than to the armature. Armature Bore. (See Bore, Armature?) Armature Bore, Elliptical (See Bore, Elliptical Armature?) Armature Chamber. (See Chamber, Armature?) Armature Coils, Dynamo - (See Coils, Armature, of Dynamo-Electric Ma- chine?) Armature Core, Dynamo (See Core, Armature, of Dynamo-Electric Ma- chine?) Armature, Cylindrical A term sometimes applied to a drum armature. (See Armature, Drum. Armature, Dy- namo-Electric Machine?) Armature, Cylindrical King. A ring armature with a core in the shape of a com- paratively long cylinder. Armature, Disc An armature of a dynamo-electric machine, in which the arma- ture coils consist of flat coils, supported on the surface of a disc. (See Armature, Dy- namo-Electric Machine?) Armature, Dissymmetrical Induction of Any induction produced in the arma- ture of a dynamo-electric machine that is un- equal in amount on opposite halves, or in sym- metrically disposed portions of the armature. Dissymmetrical induction in the armature may cause annoying or injurious sparking at the com- mutator. It may arise (i.) From a lack of symmetry in the amount of the armature windings. (2.) From a lack of symmetry in the arrange- ment of the armature windings on the armature core. (3. ) From a lack of symmetry of the pole pieces of the machine. (4.) From an improper position of the brushes Arm.] [Arm. as regards the neutral point on the commutator, causing a temporary short-circuiting of one or 'more of the armature coils. Armature, Drum An armature of a dynamo-electric machine, in which the armature coils are wound longitudinally over the surface of a cylinder or drum. (See Armature, Dynamo-Electric Machine?) A form of drum- armature is shown in Fig. 21. Fig. 21. Drum- Armature. Armature, Dynamo-Electric Machine The coils of insulated wire together with the iron armature core, on or around which the coils are wound. That part of a dynamo-electric machine in which the differences of potential which cause the useful currents are generated. Generally, that portion of a dynamo-elec- tric machine which is revolved between the pole pieces of the field magnets. The armature of a dynamo-electric machine usually consists of a series of coils of insulated wire or conductors, wrapped around or grouped on a central core of iron. The movement of these wires or conductors through the magnetic field of the machine produces an electiic cur- rent by means of the electromotive forces so gen- erated. Sometimes the field is rotated ; some- times both armature and field rotate. The armatures of dynamo-electric machines are of a great variety of forms. They may for convenience be arranged under the following heads, viz.: Cylindrical or drum-armatures, disc -or ma- tures, pole-or-radial armatures, ring armatures, and spherical. armatures. For further particulars see above terms. Armatures are also divided into classes according to the character of the magnetic field through which they move viz.: unipolar, bipolar, and multipolar armatures. The English sometimes use the word cylindrical armature as a synonym of ring-armature. A unipolar-armature is one whose polarity is never reversed. A bipolar-armature is one in which the polarity is reversed twice in every rotation; multipolar armatures have their po- larity reversed a number of times in every rota- tion. The term armature as applied to a dynamo- electric machine was derived from the fact that the iron core acts to magnetically connect the two poles of the field magnets in the same manner that an ordinary armature connects the poles of a magnet Armature, Flat Ring A ring-arma- ture with a core in the shape of a short cylin- drical ring. Armature, Girder An armature with an H -shaped or girder-like core. An H -shaped armature. Armature, Intensity An old term for an armature with coils of many turns and of a comparatively high resistance. Armature, Lamination of Core of A division of the iron core of the armature of a dynamo-electric machine or motor, so as to avoid the formation of eddy-currents therein. (See Core, Lamination of. Cur- rents, Eddy?) Armature, Multipolar A dynamo- electric machine armature whose polarity is reversed more than twice during each rotation in the field of the machine. Armature, Neutral A non-polarized armature. (See Armature, Non-Polarized?) Armature, Neutral-Relay A relay armature, consisting of a piece of soft iron, which closes a local circuit whenever its elec- tro-magnet receives an impulse over the main line. (.See Armature, Polarized?) This term is applied in contradistinction to a polarized relay armature. Armature, Non-Polarized An armature of soft iron, which is attracted toward the poles of an electro-magnet on the comple- Arm.] tion of the circuit, no matter in what direc- tion the current passes through the coils. The term non-polarized is used in contradistinc- tion to polarized armature. (See Armature, Polarized.) Th non-polarized armature of a relay magnet is generally called the neutral-relay armature. Armature of a Cable, or Cable-Armature. A term sometimes employed for the sheath- ing or protecting coat of a cable. The term armor sheathing or coating is prefer- able.\ Armature of a Condenser, or Condenser Armature. A term sometimes applied to the metallic plates of a condenser or Leyden jar. The use of this term is unnecessary and ill- advised. The term coating or plate would appear to be preferable. Armature of Holtz Machine, or Holtz- Machine Armature. The pieces of paper that are placed on the stationary plate of the Holtz and other similar electrostatic induction machines. Armature Pockets. (See Pockets, Arma- ture?) Armature, Polarized An armature which possesses a polarity independent of that imparted by the magnet pole near which it is placed. In permanent magnets the armatures are made of soft iron, and therefore, by induction, become of a polarity opposite to that of the magnet poles that lie nearest them. They have, therefore, only a motion of at'raction toward such poles. (See Induction, Magnetic.) In electro-magnets the armatures may either be made of soft iron, in which case they are attracted only on the passage of the current; or they may be formed of permanent steel magnets, or may be electro-magnets themselves, in which case the pas- sage of the current through the coils of the elec- tro-magnet, or electro-magnets, may cause either attraction or repulsion, according as the adjacent poles are of opposite polarity or are of the same polarity. Armature, Pole An armature the coils of which are wound on separate poles [Arm. that project radially from the periphery of a. disc, drum or ring. A pole-armature showing the arrangement of Fig, 22. Pole-Armature, the coils and their connection to the commutator segments is seen in Fig. 22. Armature, Quantity An old term for an armature wound with but a few coils of comparatively low resistance. Armature, Radial A term some- times used instead of pole-armature. (See Armature, Pole.} Armature, Ring A dynamo-electric machine armature, the coils of which are wound on a ring-shaped core. Fig. 23. Ring-Armature, A ring-armature is shown in Fig. 23, together with the disposition of the coils and their connec- tion to the segments of the commutator. Armature, Shuttle A variety of drum armature in which a single coil of wire is wound in an H -shaped groove formed in a bobbin shaped core. The old form of Siemens-armature. Armature, Single-Loop A closed conducting circuit consisting of a single loop, capable of revolving in a magnetic field so as to cut its lines of force. Armature, Spider. (See Spider, Arma- ture^ Arm.J 31 [Arr. Armature, Spherical A dynamo- electric machine armature, the coils of which are wound on a spherical iron core. The Thomson -Houston dynamo, which is the only machine employing an armature of this type, has its armature formed by wrapping three coils of insulated wire on a core of iron so shaped as to insure an approximately spherical armature when wrapped. Armature, Toothed-Ring An ar- mature, the core of which is in the shape of a ring, provided with a number of teeth in the spaces between which the armature coils are placed. Armature, Unipolar A dynamo- electric machine armature whose polarity is not reversed during its rotation in the field of the machine. Armature, Ventilation of A pro- cess for insuring the free passage of air through the armature of a dynamo-electric machine in order to prevent overheating. Armor of Cable. (See Cable, Armor of.) Armored Cable. (See Cable, Armored.) Armored Conductor. (See Conductor, Armored.) Arms, Bridge or Balance The electric resistances, in the electric balance or bridge. (See Bridge, Electric) HI Zn G Fig. 24. Arms of Balance. An unknown resistance, such, for example, as D, Fig. 24, is measured by proportioning the known resistances, A, C and B, so that no current flows through the galvanometer G, across the circuit or bridge M G N. Arms, Proportionate The two re- sistances or arms of an electric bridge whose relative or proportionate resistances only are required to be known in order to determine, in connection with a known resistance, the value of an unknown resistance placed in the remaining arm of the bridge. Thus is Fig. 24, A and B, are the proportionate arms. Arrangement or Deyice, Electromotiye A term sometimes employed to rep- resent a dynamo-electric machine, voltaic cell or other electric source, by means of which electromotive force can be produced. Electric sources do not produce electric cur- rents, but differences of potential or electro- motive force. Electric sources are therefore very properly termed electromotive devices. Arrester, Lightning A device by means of which the apparatus placed in any . electric circuit is protected from the destruc- tive effects of a flash or bolt of lightning. In the phenomena of lateral induction and alternative path, we have seen the tendency of a. disruptive discharge to take a short-cut across an intervening air space, rather than through a. longer though better conducting path. Most lightning arresters are dependent for their opera- tion on this tendency to lateral discharge. (See Induction, Lateral. Path, Alternative.) A form of lightning arrester is shown in Fig. 25. Fig. 25. Comb Lightning- Arrester. The line wires, A and B, are connected by two metallic plates to C and D, respectively. These plates are provided with points, as shown, and placed near a third plate, connected to the ground by the wire G. Should a bolt strike the line, it is discharged to the earth through the wire G. Various forms are given to lightning arresters of this type. The projections are sometimes placed on the ground-connected plate as well as on the plates connected to line wires. This form is. sometimes called a comb arrester, or pro'eclo*. Arr.] fist. Arrester, Lightning, Comb - A term sometimes applied to a lightning ar- rester in which both the line and ground plates are furnished with a series of teeth, like those on a comb. (See Arrester, Light- ning) Arrester, Lightning, Counter-Electro- motive Force A lightning arrester, in which the passage of the discharge through the instruments to be protected is opposed by a counter-electromotive force, generated by induction on the passage of the discharge of the bolt to earth. The counter-electromotive force lightning ar- rester is an invention of Professor Elihu Thomson. It assumes a variety of forms. In the shape shown in Fig. 26, the line circuit of the dynamo, p:g. 26. Counter-Electromotive Force Lightning Arrester. D, has one end connected to ground, and the other end has two conducting paths to giound. One of these paths is through the ordinary comb- protector at P, by the ground plate E; this cir- cuit includes a few turns of wire C'. The other path is through a corres- ponding coil C, either interior or exterior to C', so as to be within its in- ductive field. As will be [ E | seen from the figure, C, is Fig. 27. Counter-Elec- connected through the tromotive Force Light- machine to the ground. ning Arrester. The induction coils C and C', are thoroughly insulated from each other. Should a lightning flash or other static discharge pass' through the circuit C', which is of compara- tively low self-induction, a counter-electromotive force is produced in the other coil C, which protects the line circuit. In the form of lightning arrester shown in Fig. 27, the coil in the path of the direct light- ning discharge is formed into an exterior mesh or net work surrounding the dynamo to be pro- tected. In this case, the coils of the dynamo act as the secondary coils in which the counter elec- tromotive force is set up. Arrester, Lightning, Transformer A form of lightning arrester designed for the protection of transformers. The Thomson arrester for transformers oper- ates on the same principle as his arc-line pro- tector. In the latter the arc, when formed, is blown out by the action of the field of an electro-magnet. This arc is formed on curved metallic bows, one of which is connected to line and the other to earth. The arc is formed at the smallest interval between the bows, and is extin- guished by being driven by action of a magnetic field toward greatest interval. Arrester Plate of Lightning Protector. (See Plate, Arrester, of Lightning Pro- tector^) Arrester Plates. (See Plates, Arrester) Articulate Speech. (See Speech, Articu- late) Artificial Carbons. (See Carbons, Arti- ficial) Artificial Illumination. (See Illumina- tion, Artificial) Artificial Line. (See Line, Artificial) Artificial Magnet. (See Magnet, Arti- ficial) Asphyxia. Suspended respiration, result- ing eventually in death, from non-aeration of the blood. In cases of insensibility by an electric shock a species of asphyxia is sometimes brought about. This is due, probably, to the failure of the nerves and muscles that carry on respiration. The exact manner in which death by electrical shock results is not known. (See Death, Electric.} Assymmetrical Resistance. (See Resist- ance, Assymmetrical) Astatic. Possessing no directive power. Usually applied to a magnetic or electro-mag- netic device which is free from any tendency to take a definite position on account of the earth's magnetism. Ast.] [Ato. Astatic Circuit (See Circuit, Astatic) Astatic Couple. See Couple, Astatic.} Astatic Galvanometer. (See Galvanom- eter, Astatic.) Astatic Needle. (See Needle, Astatic) Astatic Pair. (See Pair, Astatic) Astatic System. (See System, Astatic.) Astronomical Meridian. (See Meridian, Astronomical) Asymptote of Curve. (See Curve, Asymp- tote of.) Atmosphere, An A unit of gas or fluid pressure equal to about 1 5 pounds to the square inch. At the level of the sea the atmosphere exerts a pressure of about 15 pounds avoirdupois, or, more accurately, 14.73 pounds, on every square inch of the earth's surface. This value has there- fore been taken as a unit of fluid pressure. For more accurate measurements pounds to the square inch are employed. In the metric system of weights and measures an atmosphere is considered equal to 1,033 grammes per square centimetre. Atmospheric pressures are measured by instru- ments called Manometers. (See Manometer.) Atmosphere, Residual The traces of air or other gas remaining in a space which has been exhausted of its gaseous contents by a pump or other means. It is next to impossible to remove all traces of air from a vessel by any known form of pump or other appliance. (See Vacuum, Absolute.) Atmosphere, The The ocean of air which surrounds the earth. The atmosphere is, approximately, composed, by weight, of oxygen 23 parts, and nitrogen 77 parts. Besides these there are from 4 to 6 parts in 10,000 of carbonic acid gas (or about a cubic inch of carbonic acid to a cubic foot of air), and varying proportions of the vapor of water. '\ he oxygen, nitrogen and carbonic acid form the constant ingredients of the atmosphere, the vapor of water the variable ingredient. There are in most localities a number ot other variable ingredients present as impurities. Atmospheric Electricity. (See Electric- ity, Atmospheric) Atmospheric Electricity, Origin of (See Electricity, Atmospheric, Origin of) Atom. The smallest quantity of elemen- tary or simple matter that can exist. An ultimate particle of matter. Atom means that which cannot be cut. It is generally believed that material atoms are abso- lutely unalterable in size, shape, weight and den- sity ; that they can neither be cut, scratched, flattened, nor distorted ; and that they are un- affected in size, density, or shape, by heat or cold, or by any known physical force. Although almost inconceivably small, atoms nevertheless possess a definite size and mass. According to Sir William Thomson, the smallest visible organic particle, I 4000 of a millimetre in diameter, will contain about 30,000,000 atoms. Atom, Closed-Magnetic Circuit of (See Circuit, Closed-Magnetic, of Atom) Atom, Gramme Such a number of grammes of any elementary substance as is numerically equal to the atomic weight of the substance. The gramme-atom of a substance represents the number of calories required to raise the tem- perature of one gramme ot that substance through I degree C. (See Heat, Atomic. Calorie) Thus, in the case of chlorine, whose atomic weight is 35.5, its gramme-atom is 35.5 ; consequently 35.5 small calories of heat would be required to raise one gramme-atom of chlorine through I degree C. Atom of Electricity. (See Electricity, Atom of) Atom, Vortex A number of particles of the universal ether moving in the manner of a vortex ring. The theory of vortex atoms, so formed from vortex rings, was propounded by Sir William Thomson in order to explain how a readily mov- able substance, like the universal ether, could be made to possess the properties of a rigid solid. If it be granted that a vortex motion has once been imparted to the universal ether, Thomson shows that such rings would be indestructible. (See Matter, Thomson's Hypothesis of.) Atomic Attraction. (See Attraction, Atomic) Ato.] [Att. Atomic Capacity. (See Capacity, Atom- ic) Atomic Currents. (See Currents, Atom- ic) Atomic Energy. (See Energy, Atomic) Atomic Heat. (See Heat, Atomic) Atomic or Molecular Induced Currents. (See Currents, Induced, Molecular or Atomic) Atomic Weight. (See Weight, Atomic) Atomicity. The combining capacity of the atoms. The relative equivalence of the atoms or their atomic capacity. The elementary atoms do not always combine atom for atom. Some single atoms of certain elements will combine with two, three, four, or even more atoms of another element. The value of the atomic capacity of an atom is also called its quantivalence or valency. Elements whose atomic capacity is One, are called Monads, or Univalent. Two, " Dyads, " Bivalent. Three, " Triads, " Trivalent Four, " Tetrads, " Quadrivalent. Five, " Pentads, " Quinquivalent Six, " Hexads, " Sexivalent. Seven, " Hep tads, " Septivalent. Atomization. The act of obtaining liquids in a spray of finely divided particles. In most cases the term is not literally correct, as each of the smallest particles so obtained usu- ally consist of many thousands of atoms. Atomize. To separate into a fine spray by means of an atomizer. (See Atomizer) Atomizer. An apparatus for readily ob- taining a finely divided jet or spray of liquid. A jet of steam, or a blast of air, is driven across the open end of a tube that dips below the surface of the liquid to be atomized. The partial vacuum so formed draws up the liquid, which is then blown by the current into a fine spray. Attract. To draw together. Attracted-Disc Electrometer. (See 'Elec- trometer, Attracted-Disc) Attracting. Drawing together. Attraction. Literally the act of drawing together. In science the name attraction is given to a series of unknown causes which effect, or are as- sumed to effect, the drawing together of atoms, molecules or masses. Attraction and repulsion underlie nearly all natural phenomena. While their effects are well known, it is doubtful if anything is definitely known of their true causes. Since attraction, pure and simple, necessitates the belief in action at a distance, an action which is now generally discredited, we must, strictly speaking, regard the term attraction as being but a convenient substitution cf the effect for the cause. It would appear much more reasonable to -re- gard the effects of attraction as produced by a true push exerted from the outside of the bodies. According to this notion, two masses of matter undergoing attraction are pushed together rather than drawn or attracted together. It has been suggested that gravitation may per- haps be an effect of a longitudinal motion or vibra- tory thrust in the universal ether. If this is the case, and the ether is sensibly incompressible, the velocity of gravitation, it would appear, should be almost infinite. Attraction, Atomic The attraction which causes the atoms to combine. (See Affinity, Chemical) In the opinion of Lodge, atomic attraction is the result of the attraction of dissimilar charges of electricity possessed by all atoms, which are capa- ble of uniting or entering into chemical combi- nation. (See Electricity, Atom of) Attraction, Capillary The molec- ular attractions that are concerned in capillary phenomena. (See Capillarity) Attraction, Electro-Dynamic The mutual attraction of electric currents, or of conductors through which electric currents are passing. (See Dynamics, Electro) Attraction, Electro-Magnetic The mutual attraction of the unlike poles of electro-magnets. (See Magnet, Electro.} Attraction, Electrostatic The mutual attraction exerted between unlike electric charges, or bodies possessing unlike "lectric charges. Alt.] 35 [Aur. For example, the pith ball supported on an in- sulated string is attracted, as shown at A, Fig. 28, Fig. 28. E'ictrostatic Attraction. Fig. ZQ. Electrostatic Repulsion. by a bit of sulphur which has been briskly rubbed by a piece of silk. As soon, however, as the ball touches the sulphur and receives a charge, it is repelled, as shown at B, Fig. 29. These attractions ai d repulsions are due to the effects of electrostatic induction. (See Induction, Electrostatic. ) Attraction, Magnetic The mutual attraction exerted between unlike magnet poles. Magnetic attractions and repulsions are best shown by means of the magnetic needle N S, Fig. 30. The N. pole of an approached magnet 3 N Fig, 30. Magnetic Attraction. attracts the S. pole of the needle but repels the N. pole. The laws of magnetic attraction and repulsion may be stated as follows, viz.: (I.) Magnet poles of the same name repel each other; thus, a north pole repels another north pole, a south pole repels another south pole. Fig. 31. Floating Magnet. (2.) Magnet poles of unlike names attract each other; thus a north pole attracts a south pole, or a south pole attracts a north pole. A small bar magnet, N S, Fig. 3 1 , laid on the top of a light vessel floating on the surface of a liquid, may be readily employed to illustrate the laws of magnetic attraction and repulsion. Attraction, Mass -- The mutual at- traction exerted between masses of matter. (See Gravitation.) Attraction, Molar -- A term some- times employed for mass attraction. Gravitation is an example of mass attraction, where the mass of the earth attracts the mass of some body placed near it. (See Gravitation.) Attraction, Molecular -- The mutual attraction exerted between neighboring molecules. The attraction of like molecules, or those of the same kind of matter, is called Cohesion ; that of unlike molecules, Adhesion. The tensile strength of iron or steel is due to the cohesion of its molecules. Paint adheres to wood, or ink to paper, by cohesion or the attrac- tion between the unlike molecules. Attraction of Gravitation. A term gen- erally applied to the mutual attraction be- tween masses. (See Gravitation.) Attractions and Repulsions of Currents. (See Currents, Attractions and Repulsions of.) Audiphone. A thin plate of hard rubber held in contact with the teeth, and maintained at a certain tension by strings attached to one of its edges, for the purpose of aiding the hearing. The plate is so held that the sound-waves from a speaker's voice impinge directly against its flat surface. It operates by means of some of the waves being transmitted to the ear directly through the bones of the head. The audiphone is sometimes called a denti- phons. Aural Electrode. (See Electrode, Aural.) Aurora Australia. The Southern Light. A name given to an appearance in the south- Aur.] 36 [Aut. ern heavens similar to that of the Aurora Borealis. (See Aurora Borealis} Aurora Borealis. The Northern Light. Luminous sheets, columns, arches, or pillars of pale, flashing light, generally of a red color, seen in the northern heavens. The auroral light assumes a great variety of ap- pearances, to which the terms auroral arch, bands, coronas, curtains and streamers are applied. The exact cause of the aurora is not as y,t known. It would appear, however, beyond any reasonable doubt, that the auroral flashes are due to the passage of electrical discharges through the upper, and therefore rarer, regions of the atmos- phere. The intermittent flashes of light are prob- ably due to the discharges being influenced by the earth's magnetism. Auroras are frequently accompanied by mag- netic storms. (See Storm, Magnetic. ) The occurrence of auroras is nearly always simultaneous with that of an unusual number of sun spots. Auroras are therefore probably con- nected with outbursts of the solar energy. (See Spots, Sun.) The auroral light examined by the spectroscope gives a spectrum characteristic of luminous gaseous matter, i. e , contains a few bright lines; but, ac- cording to S. P. Thompson, this spectrum is pro- duced by matter that is not referable with cer- tainty to that of any known substance. Whatever may be the exact causi of auroras, their appearance is almost exactly reproduced by the passage of electric discharges through vacua. Aurora Polaris. A general term some- times applied to aurora in the neighborhood of either pole, or in either the northern or the southern hemisphere. Auroral Arch. (See Arch, Auroral.") Auroral Bands. ^See Bands, Auroral?) Auroral Coronae. (See Corona, Au- roral^ Auroral Curtain. (See Curtain, Au- roral.} Auroral Flashes. (See Flashes, Auroral.} Auroral Light. (See Light, Auroral} Auroral Storm. (See Storm, Auroral} Auroral Streamer. v See Streamer, Au- roral} Auroras and Magnetic Storms, Peri- odicity of Observed coincidences be- tween the occurrence of auroras, magnetic storms, and sun-spots. The occurrence of auroras, or magnetic storms, at periods of about eleven years apart, corre- sponds to the well-known eleven-year sun-spot period. The period also agrees with a variation in the magnetic declination of any place, which, accord- ing to Sabine, occurs once in every eleven years. Austral Magnetic Pole. (See Pole, Mag- netic, Austral} Autographic Telegraphy. (See Teleg- raphy, Autographic} Automatic Annunciator Drop. (See Drop, Annunciator, Automatic} Automatic Bell. ,See Bell, Automatic Electric} Automatic Contact Breaker. (See Con- tact Breaker, Automatic} Automatic Cut-Out (See Cut-Out, Au- tomatic} Automatic Cut-Out for Multiple-Connect- ed Electro-Receptive Devices. (See Cut- Out, Automatic, for Multiple-Connected Electro-Receptive Devices} Automatic Cut-Out for Series-Connected Electro-Receptive Devices. (See Cut-Out* Automatic , for Series-Connected Electro-Re- ceptive Devices} Automatic Drop. (See Drop, Auto- matic} Automatic Electric Burner. (See Burn- er, Automatic Electric} Automatic Electric Safety System for Railroads. (See Railroads, A utomatic Elec- tric Safety System for} Automatic Fire- Alarm. (See Alarm*. Fire, Automatic} Automatic Gas Cut-Off. (See Cut-Off, Automatic Gas} Automatic Indicator. (See Indicator, Automatic} Automatic Make-and-Break. (See Make- and-Break, Automatic} Automatic Oiler. (See Oiler, Automatic^ Aut. 37 [B. A. U. Automatic Paper-Winder. (See Winder, Telegraphic Paper.} Automatic Regulation. ( See Regulation, Automatic.} Automatic Regulator. (See Regulator, Automatic?) Automatic Search-Light. (See Light, Search, Automatic} Automatic Switch for Incandescent Elec- tric Lamp. (See Switch, Automatic, for Incandescent Electric Lamp.} Automatic Telegraphy. (S e e Teleg- raphy, Automatic.} Automatic Telephone Switch. (See Switch, Telephone, Automatic?) Automatic Time Cut-Outs. (See Cut- Out, Automatic Time.} Automatic Variable Resistance. (See Resistance, Variable, Automatic.} Automatically Regulable. (See Regula- ble, Automatically.} Automobile Torpedo. (See Torpedo, Au- tomobile} Average or Mean Electromotive Force. (See Force, Electromotive, Average, or Mean?) Axes of Co-ordinates. (See Co-ordinates, Axes of.} Axial Magnet. (See Magnet, Axial.} Axis, Magnetic The line around which a magnetic needle, free to move, but which has come to rest in a magnetic field, can be turned without changing the set or direction in which it has come to rest. Axis, Magnetic, of a Straight Needle A straight line drawn through the magnet, joining its poles. The magnetic axis of a straight needle may be regarded as a straight line passing through the poles of the needle and its point of support. The magnetic axis may not correspond with the geometric axis of the needle. This leads to an error in reading the true direct on in which the needle is pointing, which must be cor- rected. Thus, the nee- dle N S, Fig. 32, points to 31 degrees on the scale. In reality, if the magnetic axis of the needle lies in the line N' S', the true deflec- tion of the needle is only 28 degrees. 25 30 35 Magnet ; Axis of Abscissas. (See Abscissas, Axis of} Axis of Ordinates. (See Ordinates, Axis of.} Azimuth. In astronomy, the angular dis- tance between an azimuth circle and the meridian. The azimuth of a heavenly body in the Nonh- ern Hemisphere is measured on the arc of the horizon intercepted between the north point of the horizon and the point where the great circle that passes through the heavenly body cuts the horizon. Azimuth Circle. (See Circle, Azimuth) Azimuth Compass. (See Compass, Azi- muth?) Azimuth, Magnetic The arc inter- cepted on the horizon between the magnetic meridian and a great circle passing through the observed body. B. A contraction used in mathematical writings for the internal magnetization, or the magnetic induction, or the number of lines of force per square centimetre in the magnetized material. This contraction for internal magnetization is, in most mathematical treatises, printed in bold- faced type. B. A. Ohm. (See Ohm, B. A.} B. A. TJ. A contraction sometimes em- ployed for the British Association unit or ohm. B. W. 0.] 38 B. ^y. G. A contraction for Birmingham wire gauge. (See Gauge, Birmingham Wire) A contraction sometimes used for the new British wire gauge. Back Electromotive Force. (See Force, Electromotive, Back) Back-Stroke of Lightning. (See Light- ning, Back- Stroke of.) Bain's Chemical Recorder. (See Re- corder, Chemical, Bain's.) Bain's Printing Solution. (See Solution, Bain's Printing) Balance Arms. (See Arms, Bridge or Balance) Balance, Si-filar Suspension An instrument similar in construction to Cou- lomb's torsion balance, but in which the needle is hung by two separate fibres instead of by a single one. (See Balance, Coulomb's Torsion. Suspension. Bi-filar) Balance, Centi- Ampere An am- meter in the form of a balance, whose scale is graduated to give direct readings in centi- amperes. Ampere balances giving readings in various decimals or multiples of amperes have been de- vised by Sir William Thomson. The strength of current passing is determined by the action on a movable ring or coil, placed between two fixed rings or coils. The movable ring is. in a horizontal plane nearly midway between the two fixed rings. The fixed rings are traversed by the current in opposite directions, so that one attracts and the other repels the movable ring. The movable ring is attached to one end of a horizon- tal balance arm, and a similar movable ring, also provided with attracting and repelling fixed rings, is attached to the opposite end of the balance arm. In order to avoid disturbance of horizontal com- ponents of terrestrial, or of local magnetic force, the current is sent in the same direction through the two movable rings. The balancing is effected by means of a weight, sliding on a nearly hori- zontal arm attached to the balance. A counter- poise weight is used in connection with the sliding weight. [Bal. A standard Thomson centi-ampere balance is shown in Fig. 33. In measuring a current, Fig' 33- CtHti-Amplre Balance. the weight is moved along the scale until the balance comes to rest. Balance, Composite A balance form of ammeter devised by Sir William Thom- son, which can be used for an ampere-meter, a watt-meter, or a volt-meter, according to the manner in which its sets of fine and coarse wire coils are connected. (See Balance, Centi- Ampere) Balance, Coulomb's Torsion An apparatus to measure the force of electric or magnetic repulsion between two similarly charged bodies, or between two similar mag- net poles, by opposing to such force the tor- sion of a thin wire. The two forces balance each other ; hence the origin of the name. Fff. 34. Coulomb's Torsion Balance. Fig. 34 represents a Coulomb torsion bal- ance, adapted to the measurement of the force Bal.J 39 [Bal. of electrostatic repulsion. A delicate needle of shellac, having a small gilded pith ball at one of its ends, is suspended by a fine metallic wire. A proof -plane, B, is touched to the electrified surface whose charge is to be measured, and is then placed as shown in the figure. (See Plane, Proof.} There is a momentary attraction of the needle, and then a repulsion, which causes the needle to be moved a certain distance from the ball on the proof-plane. This distance is measured in degrees on a graduated circle a a, marked on the in-tru- ment. The force of the repulsion is calculated by determining the amount of torsion required to move the needle a certain distance toward the ball of the electrified proof-plane. This torsion is obiained by the movement of the torsion head D, the amount of which motion is measured on a graduated circle at D. The measurement is based on the fact that the force re- quired to twist a wire is proportional to the angle of torsion. Balance, Deci-Ampere An ammeter in the form of a balance, whose scale is graduated to give direct readings in deci- amperes. (See Balance, Centi-Ampere^) Balance, Deka- Ampere An am- meter in the form of a balance, whose scale is graduated to give direct readings in deka- amperes. (See Balance, Centi-Ampere^) Balance, Electric A term fre- quently used for Wheatstone's electric bridge. (See Bridge, Electric^ The electric bridge is sometimes called a balance because, when in use in measuring resistances, one resistance or set of resistances balances an- other resistance or set of resistances. Balance, Hekto-Ampdre An am- meter in the form of a balance, whose scale is graduated to give direct readings in hekto- amperes. (See Balance, Centi-Ampere.) Balance Indicator. (See Indicator, Bal- ance.) Balance, Induction, Hughes' An apparatus for the detection of the presence of a metallic or conducting substance by the aid of induced electric currents. Hughes' induction balance is shown in Fig. 35. A, B, C and D are bobbins, wound with about 300 feet of No. 32 copper wire. The coils are connected as shown, A and B, in the circuit of a battery, and C and D, in the circuit of a telephone.- The coils, A and B, and C and D, are placed at F 'f- 35- Hughes' Induction Balance. such a distance apart as to prevent any mutual induction occurring between them. The coils are so joined that the direction of the induction of A, on C, is opposite to that of B, on D. The coils, A and B, then act as primaries, and C and D, as secondaries. In Ihe battery circuit is an interrupter I, which is caused to continually make and break the circuit. The coils are so adjusted that the opposing secondary coils produce but little noise to one listening at the telephone. This can readily be done by the adjusting of a single pair of coils. If a single coin or mass of metal be introduced between either A and C, or B and D, or even above one of the coils, as at d, the balance will be disturbed, since some of the induction is now expended in producing electric currents in the interposed metal, and a sound will therefore be heard in the telephone. But if precisely similar metals are placed in similar positions, between A and C, and B and D, no sound is heard in the telephone, since the inductive effects due to the two metals are the same. The slightest difference, however, either in composition, size or position, destroys the balance, and causes a sound to be heard in the telephone. A spurious coin is thus readily detected when compared with a genuine coin. A somewhat similar instrument has been em- ployed to detect and locate a bullet or other for- eign metallic substance in the human body. In order to determine the amount of the dis- turbance, an instrument called a sonometer is used (See Sonometer, Hughes'), in which a single secondary coil, placed in the circuit of a telephone, slides on a graduated bar between two fixed primary coils, so wound as to exert equal and op- posite inductions on the secondary. When, there- fore, the secondary is exactly in ihe middle of the Hal.] graduated bar, and consequently exactly midway between the two fixed primary coils, no sounds are heard in the telephone, but when moved to one side or the other the sounds are heard. Switches are so arranged that the telephone can be readily switched from the induction balance to the tele- phone, or vice versa. When, therefore, a metallic disc is placed in one of the coils of the induction balance, and a noise is heard in the telephone, the coil of the sonometer is shifted so that the noise heard in this telephone is judged by the ear to be equal, and the comparison can then be made by means of simple calculations. The following table gives, in arbitrary values, the results of various experiments as to the sensi- tiveness in this respect of discs of different metals, of various sizes and shapes : Silver, chemically pure 125 Gold "7 Silver, commercial 115 Aluminium 1 12 Copper ico Zinc 80 Bronze 75 Tin 74 Irqp, ordinary 53 German silver 50 Iron, pure 40 Copper, alloyed 40 Lead 58 Antimony 35 Bismuth 10 Zinc, alloyed 6 Carbon 2 (Fleming.) An inspection of this table shows that the values found for different metals do not correspond with their electric conducting power, although, roughly speaking, the best conductors stand at the top of the table, and the worst at the bottom. The effects appear to be dependent for their action on the phenomena of magnetic screening, for (i.) If slots are cut in the middle of the plate its disturbing action is either removed or very much decreased. (2.) If a flat coil of copper wire replaces a disc of metal no effect is produced on the induction balance when its ends are open, but when closed the coil acts just like a disc, or continuous plate of metal. (3.) The difference between various metals in- [BaU serted as discs in the induction balance is less at high speeds ot reversal than at low speeds. Balance, Kilo-Ampere An am- meter in the form of a balance, whose scale is graduated to give direct readings in kilo-am- peres. (See Balance, Centi- Ampere?) Balance of Induction in Cable. (See Induction, Balance of, in Cable?) Balance, Plating An automatic device for disconnecting the current from the article to be plated, as soon as a certain increase in weight has been obtained. The objects to be plated are suspended at one end of a balance, and when a certain increase in weight has been gained, the balance tips and breaks the circuit Edison's electric meter is based on this principle. Balance, Thermic, or Bolometer. An apparatus constructed on the principle of the differential galvanometer, devised by Professor Langley for determining small differences of temperature. (See Galvanometer, Differen- tial?) A coil composed of two separately insulated wires, wound together, is suspended in a mag- netic field, and has a current sent through it. Under normal conditions, this current separates into two equal parts, and runs through the wires in opposite directions. It therefore produces no sensible field, and suffers no deflection by the field in which it is suspended. Any local application of heat producing a dif- ference in temperature in these coils, causing a- difference in resistance, prevents this equality. A field is therefore produced in the suspended coil, which, though extremely small, is rendered meas- urable by means of the powerful field produced in the coil, within which the double coil is sus- pended. Differences of temperature as small as one- fourteen thousandth of a degree Fahrenheit are detected by the instrument. Balance, Wheatstone's Electric A name often given to the electric bridge or balance. (See Bridge, Electric) Balanced-Metallic Circuit (See Circuit, Balanced-Metallic?) Balanced Resistances. (See Resistances, Balanced?) Bal.] 41 [Bar. Balata. An insulating material. Balata, when prepared for use as an insulating material, is somewhat like gutta-percha. Ball, Electric Time A ball, sup- ported in a prominent position on a tall pole, and caused to fall at the exact hour of noon, or at any other predetermined time, for the purpose of thus giving correct time to an entire neighborhood. The release of the ball is effected by the closing of an electric circuit, either automatically, or through the agency of an observer. Ball, Fire A term sometimes ap- plied to globular lightning. (See Lightning, Globular^ Ball Lightning. (See Lightning, Sail.} Ballistic Curve. (See Curve, Ballistic.} Ballistic Galvanometer. (See Galva- nometer, Ballistic.} Balloon, Electric A balloon, or air ship, provided with electric power so as to be able to be steered or moved against the direction of the wind. Electric balloons have been moved against the wind and steered with a certain amount of success, by the use of electric motors driven by storage batteries. All that is needed to make aerial navi- gation a commercial success is the ability to ob- tain great power with a small weight. The storage battery does this to a limited extent. Bearing in mind the high efficiency of the elec- tric motor, it would appear that the problem of successful aerial navigation will be solved when the discovery is made of means for directly con- verting the chemical potential energy of coal into electrical energy. Balloon Signaling for Military Pur- poses. (See Signaling, Balloon, for Mil- itary Purposes?) Balls, Pith Two balls of pith, sus- pended by conducting threads of cotton to insulated conductors, employed to show the electrification of the same by their mutual repulsion. The pith balls connected with the insulated cylinder A B, Fig. 36, not only show the electri- fication of the cylinder, but Serve also to roughly indicate the peculiarities of distribution of the charge thereon. Fig. 36. Pith Ball Cylinder. Bands, Auroral Approximately parallel streaks of light sometimes seen during the prevalence of the aurora. (See Aurora Borealis.) Bank of Lamps. (See Lamps, Bank of.} Banked Battery. (See Battery, Banked.} Bar, Detorsion A bar placed in a magnetic instrument called a declinometer for the purpose of removing the torsion of the suspending thread of the magnet. The detorsion _,ar of the declinometer is gen- erally made of gun metal of the same weight as that of the suspended magnet. A small magnet is placed in a rectangular aperture in the middle of the bar. Bar Electro-Magnet. (See Magnet, Electro, Bar.} Barad. A unit of pressure proposed by the British Association. One barad equals one dyne per square centi- metre. Barometer. An apparatus for measuring the pressure or weight of the atmosphere. Barometric Column. (See Column, Baro- metric?) Bars, Bus Omnibus bars. (See Bars, Omnibus.) Bars, Krizik's Cores of various shapes, provided for solenoids, in which the distribution of the metal in the bar is so pro- portioned as to insure as nearly as possible a uniform attraction or pull while in different positions in the solenoid. Bar.] 42 [Bat. Krizik's bars of various shapes are shown in Fig. 37. It will be observed that in all cases the Fig- 37- Krizik's Bars. mass of metal is greater toward the middle of the core than near the ends. When a core of uniform diameter is drawn into a solenoid, the attraction or pull is not uniform in strength for different positions of the bar. When the bar is just entering the solenoid, the pull is strongest ; as soon as the end passes the middle of the core the attraction decreases, until, when the centres of the bar and core coincide, the motion ceases, since both ends of the solenoid attract equally in opposite directions. By proportioning the bars, as shown in the figure, a fairly uniform pull for a considerable length may be obtained. Bars, Negative-Omnibus The bus-bars that are connected with the negative terminal of the dynamos. (See Bars, Omni- bus.} Bars, Neutral-Omnibus The bus- bars that are connected with the neutral dynamo terminal in a three-wire system of distribution. Bars, Omnibus Heavy bars of con- ducting material connected directly to the poles of dynamo-electric machines, in electric incandescent light or electric railway installa- tions, and therefore receiving the entire current produced by the machine. Main conductors common to two or more dynamos in an electrical generating plant. The terms bus and omnibus bars refer to the fact that the entire or whole current is carried by them. Bars, Positive-Omnibus The bus- bars that are connected with the positive terminal of the dynamos. Bath, Bi-polar An electro-thera- peutic bath, the current applied to which enters at one part of the tub, and leaves at another part. The electrodes for the bi-polar bath consist of suitably shaped copper plates, generally called shovel electrodes. Bath, Copper An electrolytic bath containing a readily electrolyzable solution of a copper salt, and a copper plate acting as the anode, and placed in the liquid near the object to be electro-plated, which forms the kathode. (See Plating, Electro) The sulphate, the cyanMe and the acetate of cop- per are used for copper baihs. The use of the sul- phate is objectionable. The cyanide is expensive. The acetate is therefore very generally employed. Wahl gives the following formula for a copper bath, viz.: Water 1,000 parts. Acetate of copper, crystal- lized 20 " Carbonate of soda ao " Bisulphite of soda 20 " Cyanide of potassium (pure) 20 " Bath, Electro-Plating Tanks con- taining metallic solutions in which articles are placed so as to be electro-plated. (See Plating, Electro?) Strictly speaking a plating bath includes not only the vessel and its metallic solution, but also the metallic plate acting as the anode and the article to be plated forming the kathode. Bath, Electro-Therapeutic A bath furnished with suitable electrodes and used in the application of electricity to curative purposes. Such baths should be used only under the advice of a regular physician. Bath, Gold An electrolytic bath containing a readily electrolyzable solution of a gold salt and a gold plate acting as the anode, and placed in the liquid opposite the object to be plated, which forms the kathode. (See Plating, Electro) Electro gilding may beaccomp.ished cither with or without the aid of heat. Hot gilding appears to give a smoother and cleaner deposit. The following is a fairly good solution for a. gold bath: Water i.coo parts. Cyanide of potassium, pure. . 20 " Gold 10 " (Wahl.\ Bat] [Bat. The gold is first converted into neutral chloride by dissolving it in 25 parts of pure hydrochloric acid to which 12.5 parts of pure nitric acid has been added. When the gold is completely dis- solved, the liquid is heated until of a dark red color, in order to expel any excess of acid. Bath, Head, Electric A variety of electric breeze, applied therapeutically to the head of the patient. The patient is placed on an insulating stool and connected with one pole of an electrostatic induc- tion machine, the other pole of which is con- nected to a circle of insulated points suspended over the head. Bath, Hydro-Electric A bath in which electro-therapeutic treatment is given by applying one electrode to the metallic lining of the tub, and the other electrode to the body of the bather. Bath, Multipolar-Electric An electro-therapeutic bath, in which more than two electrodes are employed. It is not clear that the multipolar-electric bath possesses any decided advantages over the bi-polar bath. Bath, Nickel An electrolytic bath containing a readily electrolyzable salt of nickel, a plate of nickel acting as the anode of a battery and placed in the liquid near the object to be coated, which forms the kathode. (See Plating, Electro?) The double sulphate of nickel and ammonium (from 5 to 8 parts dissolved in 100 parts of water) is used for the bath. Some prefer to add sulphate of ammonium and citric acid to the above solution. Bath, Shower, Electric A shower bath in which the falling drops carry electric charges to the patient subjected thereto. The water is rendered slightly alkaline. One pole is immersed in the alkaline water and the other connected to a metallic stool on which the patient is placed. Bath, Silver An electrolytic bath containing a readily electrolyzable salt of silver and a plate of silver acting as the anode of an electric source and placed in the liquid near the object to be coated, which forms the kathode. v See ^fating, Electro?) The double cyanide of silver and potassium is the salt usually employed in the silver bath. The following bath is recommended by Rose- leur: Water 1,000 parts. Cyanide of potassium (pure) 50 " Pure silver 25 " The silver (granulated) is treated with pure nitric acid (43 degrees Beaum) and converted into nitrate of silver. The solution is then heated to dryne>sand subsequently fused. The fused nitrate so obtained is dissolved in fifteen times its weight of distilled water and treated with a solution of cyanide of potassium (10 per cent, of the cyanide), by means of which silver cyanide is thrown down as a precipitate. This precipitate is then sepa- rated and washed. It is added to the 1,000 parts of water, dissolved, and the cyanide of potassium afterward added, thus forming the double cyan- ide required for the bath. Bath, Stripping A bath for remov- ing an electro-plating of gold, silver, or other metal, either by simple dipping or by electric action. Bath, Ungilding A stripping bath suitable for the removal of a coating of gold. (See Bath, Stripping) Bath, Unipolar-Electric An electro- therapeutic bath, the water of which forms one of the electrodes of the source, and the other electrode is attached to a metallic rod fixed at a convenient height above the tub. The bath tub is formed of non conducting sub- stances. The terminals of the electrode con- nected with the water terminate in metal plates located at suitable points in the tub. The cur- rent is applied by the patient making and break- ing contact at the vertical metal rod with his hands. The unipolar-electric bath is employed instead of local galvanization where it is desired to limit the application to especial organs or particular parts of the body. In general galvanization the patient is placed on an electrode of large sur- face, formed of a large sponge- covered metallic plate, on which he sits or rests. This electrode is connected with the kathode of the battery. The anode is connected with a large sponge electrode, which is moved regularly over the body of the patient; sometimes the moistened hand of the operator is used in place of the sponge electrode. Bat.] [Bat. Bath, Unsilyering A stripping bath suitable for the removal of a coating of silver. (See Bath, Stripping) Bathometer. An instrument invented by Siemens for obtaining deep-sea soundings without the use of a sounding line. The bathometer depends for its operation on the varied attraction of the earth for a suspended weight in parts of the ocean differing in depth. As the vessel passes over deep portions of the ocean, the solid land of the bottom, being further from the ship, exerts a smaller attraction than it would in shallow parts, where it is nearer; for, although in the deep parts of the ocean the water lies between the ship and the bottom, the smaller density of the water as compared with the land causes it to exert a smaller attraction than in the shallower parts, where the bottom is nearer the ship. The varying attraction of the earth is caused to act on a mercury column, the reading of which is effected by means of an electric con- tact. Battery, Banked A term some- times applied to a battery from which a num- ber of separate circuits are supplied with cur- rents. The term banked battery is sometimes ap- plied to a multiple-arc connected battery. Battery, Cautery A term some- times employed in electro-therapeutics, for a multiple connected voltaic battery adapted for producing electric incandescence for cautery effects. Battery, Closed-Circuit A voltaic battery which may be kept constantly on closed-circuit without serious polarization. The gravity battery is a closed circuit battery. As employed for use on most telegraph lines, it is maintained on a closed circuit. When an operator wishes to use the line he opens his switch, thus breaking the circuit and calling his correspondent. Such batteries should not polarize. (See Cell, Voltaic, Polarization of, ) Battery, Connection of, for Quantity A term, now generally in disuse, formerly employed to indicate the grouping of voltaic cells, now known as parallel or multiple. The arrangement or coupling of a number of voltaic cells in multiple reduces the internal resist- ance of the battery, and thus permits a greater current, or quantity, of electricity to pass ; hence the origin of the term. Battery, Dynamo The combina- tion or coupling together of several separate dynamo-electric machines so as to act as a single electric source. The dynamos may be connected to the leads either in series, in multiple, in multiple-series or in series-multiple. Battery, Dynamo, Electric Machine A dynamo battery. (See Battery,' Dy- namo.) Battery, Electric A general term applied to the combination, as a single source, of a number of separate electric sources. The separate sources may be coupled either in series, in multiple, in multiple-series, or in series- multiple. ( See Circuits, Varieties of.) The term battery is sometimes incorrectly ap- plied to a single voltaic couple or cell. Battery, Floating, De la Rive's A floating voltaic cell, the terminals of which are connected with a coil of insulated wire, em- ployed to show the attractions and repul- sions between magnets and movable electric circuits. The cell, shown in Fig. 38, consists of a vol- Fig. 38. Floating Cell. taic couple of zinc and copper, the terminals of which are connected to the circular coil of insu- lated wire, as shown, and the whole floated by means of a cork, in a vessel containing dilute sul- phuric acid. When the current flows through the coil in the direction shown by the arrows, the approach of the N-seeking pole of a magnet will cause the cell to be attracted or to move towards the mag- net pole, since the south face or end of the coil is nearer the north pole of the magnet. If the other Bat] [Bat. nd were nearer, repulsion would occur, the cell turning round until the south face is nearer the magnet, when attraction occurs. This is, strictly speaking, a floating cell, and not a battery. (See Battery ; Voltaic.) Battery, Galvanic Two or more separate voltaic cells so arranged as to form a single source. This is more correctly called a Voltaic Battery. (See Battery, Voltaic.} Battery, Gas A battery in which the voltaic elements are gases as distinguished from solids. The electrodes of a gas battery generally con- sist of plates of platinum, or other solid substance which possesses the power of occluding oxygen and hydrogen. The lower parts of these plates dip into dilute sulphuric acid, and the upper parts are respectively surrounded by oxygen and hydro- gen gas derived from the electrolytic decompo- sition of the dilute acid. A gas battery consisting of plates of platinum dipping below into acid liquid, and surrounded in the space above the liquid by hydrogen and oxygen H, H' and O, O', etc., respectively is shown in Fig. 39. Battery, Leyden Jar The combina- tion of a number of separate Leyden jars so as to act as one single jar. A Leyden jar battery is shown in Fig. 40, Fig. 39. Gas Battery. In charging this battery an electric current is sent through it until a certain quantity of the gases has been produced. If, then, the charging current be discontinued, a current in the oppo- site direction is produced by the battery. The gas battery is in reality a variety of storage bat- tery. (See Electricity, Storage of. Cell, Secon- dary. Cell, Storage.) Gas batteries can also be made by feeding con- tinually into the cell a gas capable of acting on the positive elements. Battery Gauge. (See Gauge, Battery) Fig. 40. Leyden Jar Battery. vrhere nine separate Leyden jars are connected as a single jar by joining their outer coatings by placing them in the box P, the bottom of which is lined with tin foil. The inner coatings are connected together by the metal rods B, as shown. A discharging rod A, may be employed for connecting the opposite coatings. The handles are made of glass or any other good insulating material. A number of Leyden jars can be coupled in series by connecting the inner coating of the first jar to the outer coating of the second, the inner coating of the second to the outer coating of the third, and so on. The battery so obtained is then discharged by connecting the outer cr>at- ing of the first jar with the inner coating of the last. Battery, Local A voltaic battery used at a station on a telegraph line to operate the Morse sounder, or the register- ing or recording apparatus, at that point only. (See Telegraphy, American or Morse System of) The local battery is thrown into or out of action by the telegraphic relay. (See A-.Vy.) Battery, Magnetic The combina- tion, as a single magnet, of a number of sep- arate magnets. A magnetic battery, or compound magnet, is Bat] 4C [Bat. Fig. 41, Magnetic Battery, or Com- pound Magnet. shown in Fig. 41. It consists of straight bars of steel, p, p, p, with their similar poles placed near together and inserted in masses of soft iron, N and S, as shown. Battery, Main The battery, in a system of telegraphic communi- cation, that is employed for sending the signals over the main line, as dis- tinguished from any bat- tery employed for any other particular work, such, for example, as that of the local battery. (See Battery, Local.) Battery, Multiple-Con- nected A battery the single cells of which are connected to one another and to the mains or conductors in multiple. (See Cir- cuit, Multiple) Battery, Open-Circuit A voltaic battery which is normally on open-circuit, and which is used continuously only for com- paratively small durations of time on closed- circuit. Leclanche"-cells form an excellent open-circuited battery. They have a comparatively high electro- motive force, but rapidly polarize. They cannot therefore be economically used for furnishing currents continuously for long durations of time. When left on open-circuit, however, they readily depolarize. They therefore form an excellent battery for such work as annunciator bells, burg- lar alarms, etc., where the current is only required for short periods of time, separated by comparatively long intervals of rest. (See Cell, Voltaic, Leclanche.) Battery Plates of Secondary or Storage Cell, Forming of (See Plates of Secondary or Storage Cell, Forming of.) Battery, Plunge A number of separate voltaic cells connected so as to form a single cell or electric source, the plates of which are so supported on a horizontal bar as to be capable of being simultaneously placed in, or removed from, the exciting liquid. The plunge battery shown in Fig. 42, consists Fig. 42. Plunge Battery, of a number of zinc-carbon elements immersed in an electrolyte of dilute sulphuric acid, or in elec- tropoion liquid, contained in separate jars, J, J. (See Liquid, Electropoion.) The mode of support to the horizontal bar' will be understood from an inspection of the drawing. Battery, Primary The combina- tion of a number of separate primary cells so- as to form a single source. The term primary battery is used in order to distinguish it from secondary or storage battery. (See Cell, Secondary. Cell, Storage.) Battery, Secondary The combina- tion of a number of separate secondary or storage cells, so as to form a single electric source. (See Electricity, Storage of.) Battery, Selenium The combina- tion of a number of separate selenium cells so as to form an electric source. (See Cell, Selenium.) Battery, Series-Connected A bat- tery, the separate cells of which are con- nected to one another and to the line or conductor in series. (See Circuit, Series!} Battery Solution. (See Solution, Bat- tery) Battery, Split A voltaic battery connected in series, but having one of its middle plates connected with the ground. By the employment of the device of a split- battery, the poles of the battery are maintained at potentials differing in opposite directions from the potential of the earth. Battery, Storage A number of separate storage cells connected so as to* form a single electric source. Bat.] [Bel. A cell of a storage battery is shown in Fig. 43- Fig. 43- Storage Battery. Battery, Storage, Element of A single set of positive and negative plates of a storage cell connected so as to be ready for placing in the acid liquid of the jar or cell. A term sometimes applied to one of the storage cells in a storage battery. This latter use of the term element is unfortu- nate, since from the analogous case of a pnmary cell, an element would consist of a single plate, either positive or negative, and not of both. That is, every voltaic couple consists of two elements, the positive and the negative. Battery, Thermo A term often applied to a thermo-electric battery. (See Battery, Thermo- Electric!) Battery, Thermo-Electric The combination, as a single thermo-electric cell, of a number of separate thermo-electric cells or couples. (See Couple, Thermo-Electric!) Battery, Voltaic The combina- tion, as a single source, of a number of sepa- rate voltaic cells. Battery, Water A battery formed cf zinc and copper couples immersed in an electrolyte of ordinary water. Any voltaic couple can be used, the positive element of which is slightly acted on by water. When numerous couples are employed consider- able difference of potential can be obtained. Water batteries are employed for charging electrometers. They are not capable of giving any considerable current, owing to their great in- ternal resistance. Bead Areometer or Hydrometer. (See Areometer, Bead.} Bec-Carcel. The Carcel, or French unit of light. (See Carcel) Bell, Automatic-Electric An elec- tric bell furnished with an automatic contact- breaker. (See Contact-Breaker, Automatic) A form of automatic-electric bell is shown in Fig. 44. The relation of the electro-magnet, its armature and the bell lever, will be readily understood from an in- spection of the draw- ing. Bell, Call An electric bell used to call the attention of an operator to the fact that his corre- spondent wishes to communicate with him. Bell, Circular A bell so construct- ed that all its moving parts are contained in Fig . 44 , Automa tic Electee the gong. Bell. Bell, Continuous-Sounding Electric An electric bell, which, on the completion of the circuit, continues striking until stopped either by hand or automatically. On the completion of the circuit, the attraction of an armature throws a catch off from a lever, and thus permits the lever to fall and complete a contact and allows the current to ring the bell ; or the bell is rung by clockwork, which is thrown into action by the passage of a current through an electro-magnet. (See Bell, Electro-Mechanical.) Bell, Differential Electric - An electric bell, the magnetizing coils of which are differentially wound. Differential winding is ot advantage where a very strong current is required, as this winding decreases the sparking at the contacts, on the opening of the circuit. Bell, Electro-Magnetic, Siemens-Anna' tare Form A form of electro-mag- Bel.] 48 [Bel. netic bell in which the movements of the bell armature are obtained by the reversal of polarity that takes place when alternating cur- rents are pass- ed through the coils of a sim- ple, single coil, Siemens - arma- ture> Fig. 4$. Semens-Armature Form The details of Electro- Magnetic Dell. will be readily understood from an examination of Fig. 45. Bell, Electro-Mechanical A bell, the striking apparatus of which is driven by a weight or spring, called into action by the movement of the armature of an electro- magnet. (See Alarm, Electric?) Bell, Extension-Call A device for prolonging the sound of a magneto call. An alarm bell is automatically connected with Fig. 46. Extension-Call Bell. the circuit of a local battery by means of the cur- rent generated by the magneto-call, and continues sounding after the current of the magneto call has ceased. A form of extension-call bell is shown in Fig. 46. Bell, Indicating An electric bell in which, in order to distinguish between different bells in the same office, a number is displayed by each bell when it rings. Bell, Magneto-Electric An electric bell, the current employed to operate or strike which is obtained by the motion of a magneto-electric machine. Bell, Night In a telephone ex- change, a bell, switched into connection with the shunted circuit of an annunciator case, and intended, by its constant ringing, to call the attention of the night operator to the falling of a drop. Bell, Relay, Electric An electric bell m which a relay magnet is employed to switch a local battery into the circuit of the sounding apparatus of the bell. The relay bell is suitable for use when the bell to be sounded is situated at a great distance. As the current from the line, when this is long, is too weak to ring the be'.l, it throws into action a local battery by the action of a relay. Relay bells were used in the early forms of acoustic telegraphs as employed in England with relay sounders. The dots and dashes of the Morse alphabet were indicated by the sounds of two bells, a tap on one bell indicating a dot, and a tap on the other a dash. This system is now practically aban- doned. Bell-Shaped Magnet (See Magnet, Bell- Shaped^ Bell, Shnnt, Electric An electric bell, the magnetizing coils of which are placed on the line in shunt. In the case of shunt-connected electric bells, one of the bells must make and break the circuit for all the rest. The series-connected electric bell is used where the distance between the sepa- rate bells is great, in order to save the expense of multiple connections. In most cases, where a number of electric bells are to be simultaneously sounded, connection in multiple is adopted^ Bell, Single-Stroke Electric An electric bell that gives a single stroke only for each make of the circuit. Fig. 47. Single- Stroke Bell. Since the bell gives a single stroke for each completion of the circuit, its use permits of ready communication between any two places by any JBcl.] 49 [Bla. system of prearranged signals. A buzzer may be used for the same purpose. A form of single- stroke bell is shown in Fig. 47. On completing the c'rcuit, the current, through its coils, attracts the armature and causes a single stroke of the bell. Bell, Telephone-Call - A call bell used to call a correspondent to the telephone. The telephone-call bell is generally a magneto- electric bell. Bell, Trembling A name some- times given to a vibrating or an automatic make-and-break bell. (See Make-and-Break, Automatic?) Bell, Vibrating A trembling bell. (See Bell, Trembling) Bias of Relay Tongue. (See Tongue, Relay, Bias of.) Bichromate Voltaic Cell. (See Cell, Vol- taic, Bichromate^ Bi-fllar Suspension. (See Suspension, Bi-JUar) Bi-fllar Suspension Balance. (See Bal- ance, Bi-filar Suspension?] Bi-fllar Winding. (See Winding, Bi- filar.) Binary Compound. (See Compound, Bi- nary) Binding Coils. (See Coils, Binding) Binding-Post (See Post, Binding) Binding-Screw. (See Screw, Binding) Binding Wire for Telegraph Lines. (See Wire, Binding, for Telegraph Lines) Biology, Electro That branch of electric science which treats of the electric conditions of living animals and plants, and the effects of electricity upon them. Electro-Biology includes : (i.) Electro-Physiology. (2.) Electro-Therapy, or Electro-Therapeutics. Bioplasm. Any form of living matter pos- sessing the power of reproduction. Bioscopy, Electric The determina- tion of the presence of life or death by the passage of electricity through the nerves and muscles. Bi-polar. Having two poles. Bi-polar Armature. (See Armature, Bi-polar) Bi-polar Bath. (See Bath, Bi-polar) Birmingham Wire Gauge. (See Gauge, Wire, Birmingham) Bi-Telephone. (See Telephone, i.) Bitite. A variety of insulating material. Black Electro-Metallurgical Deposit. (See Deposit, Black Electro- Metallurgical.) Black Lead. A variety of carbon em- ployed in various electrical processes. Black lead is also termed plumbago or graphite. (See Plumbago. Graphite.) The term black lead is a misnomer, since the substance is carbon and not lead. The term is an old one, and is still very generally used. Blasting, Electric The electric ignition of powder or other explosive material in a blast. (See Fuse, Electric.) The current required for the ignition of the fuse is generally obtained by means of a magneto- electric machine. In the form of magneto-blast- ing machine, shown in Fig. 48, the movement Fig. 48. Magneto-Blasting Machine, of the handle shown at the top of the figure causes the rapid rotation of a cylindrical armature constructed on the Wheatstone and Siemens prin- ciple. The magnets are of iron, and are furnished file.] so with coils of insulated wire. On the rotation of the armature the current developed therein in- creases the field of the field magnet, and, when of the proper degree of intensity, is thrown into the outer circuit, and ignites the fuse. Bleaching, Electric Bleaching pro- cesses in which the bleaching agents are liberated, as required, by the agency of electro- lytic decomposition. In the process of Naudin and Bidet, the cur- rent from a dynamo-electric machine is passed through a solution of common salt between two closely approached electrodes. The chlorine and sodium thus liberated react on each other and form sodium hypochloride, which is drawn off by means of a pump and used for bleaching. (See Electrolysis.'] Block, Branch A device em- ployed in electric wiring for taking off a branch from a main circuit. (See Wiring?) A form of branch -block, with its fuses attached, is shown in Fig. 49. Fig. 49. Branch-Block. Block, Cross-Over A device to permit the safe crossing of one wire over another in molding or cleat wiring. Block, Fuse A block containing a safety fuse or fuses for incandescent light circuits. (See Fuse, Safety?) Block System for Railroads. (See Rail- roads, Block System for?) Block Wire. (See Wire, Block?) Blow-Pipe, Electric A blow-pipe in which the air-blast is obtained by a stream of air particles produced at the point of a [Boa. charged conductor by a convection dis- charge. The candle flame, Fig. 50, is blown in the di- Fig. SO. Convection Blow-Pipe. rect ; on of the stream of air particles passing off from the point P. (See Convection, Electric.} Blow-Pipe, Electric-Arc - A de- vice of Werdermann for cutting rocks, or other refractory substances, in which the heat of the voltaic arc is directed, by means of a magnet, or a blast of air, against the substance to be cut. The carbons are placed parallel, so as to readily enter the cavity thus cut or fused. This inven- tion has never been introduced into extensive practice. In the welding process of Benardos and Olzewski, the welding temperature is obtained by means of an electric arc taken between two suit- ably shaped electrodes. In the electric-arc blow - pipe, shown in Fig. 51, the voltaic arc, taken between two ver- tical carbon electrodes, is deflected into a hori- zontal position under the influence of the inclined poles of a powerful elec- tro-magnet. The highly heated car- bon vapor which consti- tutes the voltaic arc is deflected by the magnet in the same direction as would be any other mov- able circuit or current. Board, Cross-Connecting In a system of telegraphic or telephonic communi- cation, a board to which the line terminals are run before entering the switchboard, so as to Fig. S ' - Electric- Arc Blmu-Pifee. Boa.] 51 [Boa. readily place any subscriber in connection with any desired section of the switchboard. Board, Fuse A board of slate or other incombustible material on which all the safety fuses in an installation are as- sembled. The fuse board is used for avoiding accidents from the firing of the fuses. Board, Hanger A form of board provided for the ready placing or removal of an arc lamp from a circuit. Fig. 32, Hanger-Board. A hanger-board contains a switch or cut-out for ihe ready opening or closing of the circuit. A form of hanger-board is shown in Fig. 52. Board, Key Any board to which are connected electric keys or switches. Board, Legging-Key A key board employed for the purpose of legging an operator into a circuit connecting two or more subscribers. (See Leg?) Board, Multiple Switch A board to which the numerous circuits employed in systems of telegraphy, telephony, annunciator or electric light and power circuits are con- nected. Various devices are employed for closing these circuits, or for connecting or cross-connecting them with one another, or with neighboring cir- cuits. A multiple switchboard, for example, for a tele- phone exchange, will enable the operator to con- nect any subscriber on the line with any other subscriber on that line, or on another neighbor. ing line provided with a multiple switchboard. To this end the following parts are necessary: (i.) Devices whereby each line entering the ex- change can readily have inserted in its circuit a loop connecting it with another line. This is accomplished by placing on the switchboard a separate spring-jack connection for each sepa- rate line. This connection consists essentially of one or two springs made of any conducting metal, which are maintained in metallic contact when the plug key is not inserted, but which are readily separated from one another by the introduction of the plug- key, Fig. 53, the terminals, a and b, of which are insulated from each other, and are connected to the ends of a loop coming from another line. As the key is in- *"* serted, the metallic spring or springs of the spring-jack are separated and the metallic pieces, a and b, are brought into good sliding contact therewith, thus introducing the loop into the circuit. (See Spring- Jack.} (2.) As many separate annunciator-drops as there are separate subscribers. These are pro- vided so as to notify the Central Office of the par- ticular subscriber who desires a. connection. Alarm-bells to call the operator's attention to the calling subscriber, or to the falling of a drop, are generally added. (See Bell, Call.) (3.) Connecting cords and keys for connecting the operator's telephone, and means for ringing subscribers' bells, and clearing out drops. Fig. S4> Multiple Switchboard for Electric Light. In Multiple Switchboards for the Electric Light or Distributing Switches, spring-jack contacts are connected with the terminals of different circuits. Boa.] [Bod. and plug switches with the dynamo terminals. By these means, any dynamo can be connected with any circuit, or a number of circuits can be connected with the same dynamo, or a number of separate dynamos can be placed in the same circuit without interference with the lights. Board, Switch A board provided with a switch or switches, by means of which electric circuits connected therewith may be opened, closed, or interchanged. Board, Switch, Telegraphic A device employed at a telegraph station by means of which any one of a number of tele- graph instruments, in use at that station, may be placed in or removed from any line con- nected with the station, or by means of which one wire may be connected to another. The ability to readily connect one wire with another is of use in case of interruption to tele- graph lines, in which case a through circuit may be made up of sections of different circuits. In the switchboard shown in Fig. 55, the upper left- hand binding -post is con- nected to earth; the four remaining binding - posts are connected to two sepa- Fig. 35. Telegraphic rate instruments the sec- Switchboard, ond and third from the top to one instrument, and the fourth and fifth to another instrument. The four posts at the top of the figure are con- nected to two lines running east and west. Various connections are made by the insertion of plug keys in the various openings. Board, Switch, Trnnking A switchboard in which a few subscribers only are connected with the operator, thus enabling him to obtain any other subscriber by means of trunk wires extending to the other sections. (See Wire, Trunk) Boat, Electric A -boat provided with electric motive power. Electric power has been applied both to ordi- nary vessels and to submarine torpedo boats. Boat, Submarine Electric A boat capable of being propelled and steered while entirely under water. The motive power of such boats is generally electricity. The requisite buoyancy is obtained by means of an air chamber. Artificial ventila- tion is maintained, the fresh air requisite for breathing being derived from a compressed air cylinder. Boat, Torpedo A boat used for carrying and discharging torpedoes. (See Torpedo) Bobbin, Electric An insulated coil of wire for an electro-magnet. Body, Charged A body containing an electric charge. Charges are bound or free. (See Charge,. Sound. Charge, free.) Body, Electrified A body con- taining an electric charge. Body, Human, Resistance of The resistance which the human body offers to- the passage of an electric current. The resistance of the human body to the passage 1 of a current varies with the time. The re- sistance rapidly decreases after a short time. " The resistance diminishes because of the con- duction of water in the epidermis under the action of the constant current and the congestion of the cutaneous blood vessels in consequence of the stimulation. ' ' ( Landois and Stirling. ) The resistance also varies markedly with the condition of the surface, the condition of the skin, and with the shape, area, position and material of the electrodes by which the current is led into and carried out of the parts. It very seldom is less than I, coo ohms under the most favorable conditions, and with ordinary contacts is many times that amount. The muscles offer nearly nine times the resist- ance in a direction transverse to the fibres than longitudinally to them. (Hermann.'] The resistance of the epidermis is greater than that of any other tissue of the bo 'y. The human body probably possesses a true assymmetrical resistance; that is to say, when taken after the current has been passing for some time, its resistance is different in different direc- tions. This variation in the apparent resistance is believed by some to be due to polarization effects. Body, Insulated A body sup- ported on an insulator, or non-conductor of. electricity. Bod. 53 [Box. Fig: $b. Electric Body- Protector. Body-Protector, Electric A de- vice for protecting the human body against the accidental passage of an electric discharge. To protect the human body from the acciden- tal passage through it of dangerous electric cur- rents, Delany places a light, flexible, conducting wire, A A B L L, in the posi- tion shown in Fig. 56, for the purpose of leading the greater part of the current around instead of through the body. The body-pro- tector thus provides a by- path, or shunt of low resist- ance, around the body, and protects it from the effects of an accidental discharge. The resistance of the con- tacts of the protecting conductor with the skin may interfere somewhat with the efficacy of the device. Inside insulating shoe-soles for lessening the danger from accidental contacts through grounded circuits have also been proposed. Boiler-Feed, Electric A device for automatically opening a boiler-feed appar- atus electrically when the water in the boiler falls to a certain predetermined point. Boiling of Secondary or Storage Cell. (See Cell, Secondary, or Storage, Boiling of.} Bole. A unit, seldom or never used, pro- posed by the British Association. One bole is equal to one gramme-kine. (See Kine.} Bolometer. An apparatus devised by Langley for measuring small differences of temperature. A thermal balance. (See Balance, Ther- mic^ Bombardment, Molecular The forcible rectilinear projection from the nega- tive electrode, of the gaseous molecules of the residual atmospheres of exhausted vessels on the passage of electric discharges. (See Matter, Radiant, or Ultra-Gaseous?) Bonsalite. An insulating substance. Bore, Armature The space pro- vided between the pole pieces of a dynamo or motor for the rotation of the armature. Boreal Magnetic Pole. (See Pole, Mag- netic, Boreal} Bot. A term sometimes used as a con- traction for Board of Trade unit of electric supply, or the energy contained in a current of i ,000 amperes flowing in one hour under a pressure of one volt. The term appears inadmissible. If used at all, it should be B. O. T. The usage of giving the names of distinguished dead electricians to new- units is a good one, and should be followed here. Boucherize. To subject to the boucheriz- ing process. (See Boucherizing} Boucherizing. A process for the preser- vation of wooden telegraph poles, by inject- ing a solution of copper sulphate into the pores of the wood. (See Pole, Telegraphic^} Bound Charge. (See Charge, Bound} Box Bridge. (See Bridge, Box} Box, Cable A box placed on a large terminal pole and provided to receive the separate conductors where the air-line wires join a cable. The wires are distributed in the cable box so as to be readily attached to the air-line wires. Box, Cooling, of Hydro-Electric Ma- chine. A box provided in Armstrong's hydro-electric machine for the steam to pass through before leaving the nozzle. In passing through the cooling-box some of the steam suffers condensation. The cooling-box, therefore, always contains some water, the pres- ence of which seems to be necessary to the opera- tion of the machine. Box, Distributing, of Conduit A name generally applied to a handhole of a conduit. (See Handhole of Conduit.} Box, Distribution, for Arc Light Cir- cuits. A device by means of which arc and incandescent lights may be simultane- ously employed on the same line from a con- stant-current dynamo-electric machine or other source of constant currents. A portion of the line circuit, whose difference of potential is sufficient to operate the electro- receptive device, as, for example, an incandescent lamp, is divided into such a number of multiple Box.] [Box. circuits as will provide a current of the requisite strength for each of the devices. For example, if the normal current on the line is seven amperes, then each of the seven multiple-connected electro- Fig. J?. Series- Multiple Circuit. receptive devices shown in Fig. 57 will have a cur- rent of one ampere passing through it, provided the resistance of each branch is the same. In order to protect the remaining devices from variations in the current on the extinguishment of any of the devices, automatic cut-outs are pro- vided, which divert the current thus cut off through a resistance equivalent to that of the -device. A variety of distribution boxes are in use. (See Circuits, Varieties of.) Box, District-Call A box by means of which an electric signal is auto- matically sent over a telegraphic line and received by an electro-magnetic device at the other end of the line. motion by the pulling of a lever, makes and breaks an electric circuit and sends over the line a succession of electric impulses of varying length, separated from one another by varying intervals of time. These impulses may be received at the central station as a series of dots and dashes, or may, by means of a Morse sounder, produce suc- cessive sounds. By pulling the lever or handle through different distances, different signals may be sent to the central station and serve as calls for various services, such as messenger boys, fire alarm, police, special, etc. The general appearance of a four-call district box is shown in Fig. 58. In order to transmit a call for any particular one of these four services the handle is pulled until it comes opposite to the letters indicating the required service, and is then released. The service required is then indicated at the receiving, or central station, through the varying signals sent over the line by the move- ment of the break-wheel, on the release of the handle. Box, Fire-Alarm Signal A signal box provided for the purpose of automatically sending an alarm of fire. The fire-alarm box shown in Fig. 59, operates Fig. 38. District Call Box. Fig. j-0. Fire- Alarm Signal-Box. on the same principle as the district call box. The movement of the handle in the direction of the A system of district calls includes a number of arrow drives a wheel that makes and breaks a call boxes connected by telegraphic lines with a circuit at certain intervals, central station. A wheel, or its equivalent, set in The fire-alarm signal boxes are connected Box.] 55 [Box. -either with a central station, or with the engine houses of the district in which the alarm is sounded, or with both. Box, Fire-Alarm Telegraph An automatic-call signal-box employed for send- ing an alarm of fire to a central station. A form of fire-alarm telegraph box is shown in Fig. 60. It consists essentially of a circuit-breaker Fig. bo. Fire-Alarm Telegraph Box. that is moved by pulling down a lever. The release of the lever repeats the signal to the fire department at the central station a certain number of times. The box also contains a relay bell, lightning arrester and signal-bell key. Box, Fishing A term sometimes used instead of junction box. (See Box, Junction. ) Box, Flush A box or space, flush with the surface of a road-bed, provided in a system of underground wires or conduits, to facilitate the introduction of the conduct- ors into the conduit, or for the examination of the conductors. Box, Fuse The box in which the fuse-wire of a safety-fuse is placed. The fuse-box should be formed of moisture- proof, incombustible, insulating materials. Box, Junction A moisture-proof box provided in a system of underground con- the feeders and the mains, and from which the current is distributed to the individual consumer. (See Feeder. Main, Electric?) A form of junction box for coupling lengths of conductors is shown in Fig. 61. Box, Patrol Alarm An automatic- signal call-box provided for use on the out- side of buildings. The call-box is placed inside a box, the outer door of which is furnished with a Yale lock. Fig. 6f. Junction Box, ductors to receive the terminals of the feed- ers, in which connection is made between Fig. 62. Patrol Box. A iorm of patrol box is shown in Fig. 62. Box, Resistance A box containing a number of separate coils of known resist- ances employed for determining the value of an unknown resistance, and for other pur- poses. (See Bridge, Electric, Box Form of.) Box-Sounding Relay. (See Relay, Box- Sounding) Box-Sounding Telegraphic Relay. (See Relay, Box-Sounding Telegraphic) Box, S;>lice A box provided for holding splice joints and loops, and so ar- ranged as to be readily accessible for exami- nation, re-arranging, cross-connecting, etc. Splice-boxes vary in shape and construction according to the purposes for which they are designed. Box, Splice, Four-way A splice- box piovided with four ways or tubular con- duits. Box, Splice, Two Way- -A splice- Box.J [Bra. box provided with but two tubular conduits or ways. Box, Tumbling A rotating box in which metallic articles that are to be electroplated are placed so as to be polished by attrition against one another. Boxing the Compass. (See Compass, Boxing the?) Bracket, Lamp, Electric A de- vice similar to a bracket for a gas burner for holding or supporting an electric lamp. Fig. 63. Lamp Bracket. Fig. 6 4. Lamp Bracket. Lamp brackets are either fixed cr movable. Fig. 6j. Lamp Bracket, Movable Arms. Those shown in Figs. 63 and 64 are fixed. That shown in Fig. 65 is movable. Bracket, Telegraphic A support or cross piece placed on a telegraph pole for the support of the insulators of tele- graphic lines. Telegraphic insulators are supported either on wooden arms, or on iron or metal brackets, Fig. 66 shows a form of iron bracket. Fig. 67 shows a form of wooden arm. I- Fig. 66. Telegraphic Fig. 67. Telegraphic Bracket. Cross-Arm. Various well known modifications of these shapes are in common vise. (For details, see Pole, Telegraphic.) Braid, Tubular A braid of fibrous insulating material, woven in the form of a tube, and provided for drawing over a splice after two wires have been connected. Braided Wire. (See Wire, Braided.} Brake, Electro-Magnetic A brake for car wheels, the braking power for which is either derived entirely from electro-magnet- ism, or is thrown into action by electro-mag- netic devices. Electro-magnetic car brakes are of a great va- riety of forms. They may, however, be arranged in two classes, viz. : (l.) Those in which magnetic adhesion, or the magnetic attraction of the brake to the wheels, is employed. (2.) Ordinary brake mechanism in which the force operating the brake is thrown into action by an electro-magnet. Brake, Friction A name some- times given to a Prony brake. (See Brake, Prony?) Brake, Magneto-Electric A device for checking the swing of a galvanometer, in which a slight inverse current is sent through the coils of the galvanometer. The Frey magneto-electric brake, as shown in Fig. 68, consists of a small coil, connected by a. Fig. 68. Electric . contact-key with the galvanometer terminals. A small adjustable magnet coil is provided for regulating the action of the inverse current. To avoid disturbance, the brake is placed at least 4 or 5 feet from the galvanometer. Manipulation of the ordinary galvanometer key attains the same end in a much simpler manner. Brake, Prony A mechanical de- vice for measuring the power of a driving shaft. Bra.] 57 [Bre. An inflexible beam, Fig. 69, is provided at one end with a clamping device for clamping the driving shaft or pulley, and at the other end A, with a pan for holding weights. If the brake be arranged as shown in Fig. 69, and the shaft rotate in the direction of the arrow, the tendency will be to carry the beam around with the shaft, placing it at some given moment Fig. 6$. Prany Brake. in the position shown by the dotted line. If a sufficiently heavy weight be placed at x, in a pan hung at A, the beam will assume a position ver- tically downwards. If, however, the torque, or Fig. 70. Prony Brake. twisting force of the driving shaft, be balanced by the weight, the bar will remain horizontal. The power can then be calculated by multiplying the weight in pounds by the circumference in feet of the circle of which the bar is a radius, and this product by the number of turns of the driving shaft per minute. The product will be the num- Fig. 7 1, Prony Brake. ber of foot-pounds per minute, and, when divided by 33,000, will give the horse-power. Some modified forms of the Prony brake are shown in Figs. 70 and 71. A simple form of brake consists of a cord passed over the pulley of the machine to be tested. A weight is hung at one end of the cord. The other end of the cord is attached to the top of a spring balance, the other end of which is fastened to the floor. A reading of the spring balance is taken while the pulley is at rest and when it is in motion, and the result calculated. Branch. A term applied to any principal distributing conductor from which outlets are taken or taps made. Branch-Block. (See Block, Branch) Branch Conductors. (See Conductor, Branch) Branch Fuse. (See Fuse, Branch) Branch, Snb A distributing con- ductor taken from a branch. Branding, Electric A process whereby the branding tool is heated by elec- trical incandescence instead of by ordinary heat. The branding tool consists essentially of a small transformer with devices for regulating the cur- rent strength by switches and choking coils. Brassing, Electro Coating a sur- face with a layer of brass by electro-plating. (See Plating, Electro) The plating bath contains a solution of copper and zinc ; a brass plate is used as an anode. Break. A want of continuity in a circuit. Break, Circuit Loop A device for introducing a loop in any part of a line circuit. A form of circuit loop-break is shown in Fig. 72. Fig. 7 2. Circuit Loop Break. It consists essentially of a rigid frame with two porcelain or other suitable insulators for the sup- port of the loop wires. Bre.] 58 [Bru Break-Down Switch. (See Switch,Break- Down.) Break-Induced Current. (See Current, Break-Induced?) Break, Mercury A form of circuit breaker operated by the removal of a conduc- tor from a mercury surface. Mercury breaks assume a variety of forms. One end of the circuit is connected with the mercury, and the other with the conductor. Break Shock. (See Shock, Break.) Breaker, Circuit Any device for breaking a circuit. Breaking the Primary. (See Primary, Breaking the.] Breaking Weight of Telegraph Wires. (See Wires, Telegraph, Breaking Weight /) Breath Figures. (See Figures, Breath?) Breeze, Electric A term some- times employed in electro-therapeutics for a brush discharge. One of the electrodes, consisting of a single point or a number of points, is held near the parts to be treated so that the convective discharge is received thereon. The other electrode is con- nected to the body of the patient. Breeze, Electro-Therapeutic An electric breeze. (See Breeze, Electric?) Breeze, Head, Electro-Therapeutic A form of electric convective discharge, or electric breeze, applied to the head. (See Breeze, Electric?) Breeze, Static An electric breeze obtained by the convective discharge of an electrostatic charge. Bridge-Arms. (See Arms, Bridge or Balance?) Bridge, Box A box of resistance coils so arranged as to be capable of being used directly as a Wheatstone electric balance. (See Bridge, Electric, Box Form of?) The commercial form of Wheatstone's balance. Bridge, Electric A device for measuring the value of electric resistances. The electric bridge is also called the Electric Balance. This is called a bridge because the wire M, G, N, bridges or joins points of equal potential. A, B, C and D, Fig. 73, are four electric re- sistances, any one of which can be determined in ohms, provided the absolute value of one of the others, and the relative values of any two of the remaining three are known in ohms. A voltaic battery, Zn C, is connected at Q and P, so as to branch at P, and again unite at - 73- Electric Balance. Q, after passing through the conductor D C, and B A. A sensitive galvanometer, G, is connected at M N, as shown. The passage of a current through any resistance is attended by a fall of potential proportional to the resistance. (See Potential, Electric.') If, then, the resistances A, C and B, are so proportioned to the value of the unknown resistance D, that no current passes through the galvanometer G, the two points, M and N, in the two circuits, Q M P and Q N P, are at the same potential. That isto- say, the fall of potential along Q MP and Q N P, at the points M and N, is equal. Since the fall of potential is proportional to the resistance, it follows that A : B : : C : D, or A X D = B X C, If then we know the values of A, B and C, the value of D, can be readily calculated. T) By making the value _, some simple ratio, the A. value of D, is easily obtained in terms of C. The resistances A, B and C, may consist of coils of wire whose resistance is known. To avoid their magnetism affecting the galvanometer needle during the passage of the current through them, they should be made of wire bent into two- Bri.] 5 ( J [Bru parallel wires and wrapped in coils called resist- ance coils; or a resistance box may be used. (See Coil, Resistance. Box, Resistance,") There are two general forms of Wheatstone's Bridge, the box form, and the sliding form. Bridge, Electric, Arms of The resistances of an electric bridge or balance. (See Bridge, Electric) Bridge, Electric, Box Form of A commercial form of bridge or balance in which all the known arms or branches of the bridge, except the unknown arm, consist of standardized resistance coils, whose values are given in ohms. (See Coil, Resistance^) The box form of bridge or balance is shown in Fig. 74. Box Balance, perspective in Fig. 74, and in plan in Fig. 75. The bridge arms, corresponding to the resistances F'S- 7S' R x Balance, A and B, of Fig. 73, consist of resistance coils of 10, 100 and 1,000 ohms each, inserted in the arms q z, and q x, of Fig. 75. These are called the proportional coils. The arm corre- sponding to resistance C, of Fig. 73, is composed of separate resistances of I, 2, 2, 5, 10, 10, 20, 50, ico, 100, 200, 500, i,oco, i, coo, 2,000 and 5,000 ohms. In some forms of box bridges additional decimal resistances are added. The resistance coils are wound', as shown in Fig. 76, after the wire has been bent on itself in the middle. This is done in order to avoid the effects of induction, among which are a disturb- ing action on a galvanometer used near them, and the introduction of a spurious resistance in the coils themselves. (See Resistance, Spurious.) To avoid the effects of changes of resistance oc- casioned by changes of temperature, the coils are made of German silver, or, preferably, of alloys called Platinoid or Platinum silver. Even when these alloys are used, care should be taken not to allow the currents to pass continuously through the resistance coils longer than a few moments. The coils, C, C , are connecte 1 with one another in series by soldering their ends to the short Fig. 76. Resistance Coils. thick pieces of brass, E, E, E, Fig. 76. On the in- sertion of the plug-keys, at S, S, the coils are cut- out by short-circuiting. Care should be taken to see that the plug-keys are firmly inserted and free from grease or dirt, as otherwise the coil will not be completely cut out. As each plug-key is inserted it should be turned slightly in the opening, so as to insure good contact. The following are the connections, viz.: The galvanometer is inserted between q and r, Fig. 77, Zi, 'f Fig. 77. Electric Balance. the unknown resistance between z and r ; the bat- tery is connected to x and z. A convenient pro- portion being taken for the value of the propor- tional coils, resistances are inserted in the arm C, until no deflection is shown by the galvanometer G. The similarity between these connections and those shown in Fig. 75 will be seen from an inspection of Fig. 77. The arms, A and B, corre- spond to q x and q z, of Fig. 75; C, to the arm Bri.] GO [Bri. x r, Fig. 75 j and D, to the unknown resistance. We then have as before: A:B::C:D,orAxD . .-. D = \ C. The advantage of the simplicity of the ratios, A and B, or 10, 100 and 1,000 of the bridge box, will therefore be manifest. The battery terminals may also be connected to q and r, and the gal- vanometer terminals to x and z, without disturb- ing the proportions. Bridge, Electric, Commercial Form of -- A name sometimes given to the box form of Wheatstone's electric balance. (See Bridge, Electric, Box Form of.} Bridge, Electric Duplex -- An ar- rangement of telegraphic circuits in the form of a Wheatstone electric bridge for the pur- poses of duplex telegraphy. (See Teleg- raphy, Duplex, Bridge Method ridge is to measure the value of this inductance. I, is an interrupter placed in the circuit of the battery B. Suppose the interrupter, I, be placed in the tele- phone circuit between T and c. By shifting the sliding contact so as to alter the value of R, a bal- ance can be effected and silence obtained in the telephone. Now remove the interrupter and place it in the battery circuit between b and a, as shown in Fig. 80. If now, the interrupter, I, be made to rapidly interrupt the battery current, this balance is destroyed, and cannot be again obtained by any variation in the value of the resistance, R. The reason of this is evident. On the closing or opening of the battery current, the inductance of P, produces a counter electromotive force in P, which produces differences of potential between a and c. If an attempt be made to prevent this, Fig. Si. HugJies? Inductance Bridge. by altering the value of R, the steady balance is destroyed, and the telephone will be traversed by a current during the time the currents have be- come steady. In order to obtain a balance during rapid alternations of the battery current, Professor Hughes placed a pair of mutually in- ductive coils in the battery and the telephone circuits, as shown in Fig. 81. The resistances, Q, S, R and P, are the same as already described. The mutually inductive coils, M t and M 2 , are placed respectively in the telephone and batti ry circuits in the manner shown. The coil M,, in the battery circuit is fixed, while that in the telephone circu.t is so arranged that it can be maintained, with its centre coincident with that of M 8 , while its axis can be placed at any desired angle with M g . When the axes of the coils are at right angles, the inductance is zero. When they are co-linear, the inductance is at its maximum. When the coils M I} and M,, are in any inter- mediate position, the inductive electromotive force produced in the telephone circuit can, if the value of R, be changed, be made to balance the impulsive electromotive force due to the in- ductance of P, a:;d the value of this latter can, therefore, be inferred. Bridge, Magnetic An apparatus in- vented by Edison for measuring magnetic resistance, similar in principle to Wheatstone's electric bridge. The magnetic bridge is based on the fact that two points at the same magnetic potential, when connected, fail to produce any action on a mag- netic needle. The magnetic bridge consists, as shown in Fig. 82, of four arms or sides made of Fig. 82. Magnetic Bridge. pure, soft iron. The poles of an electro-magnet are connected to projections at the middle of the short side of the rectangle. By this means a difference of magnetic potential is main- tained at these points. The two long sides are formed of two halves each, which form the four arms of the balance. Two of these only are movable. Two curved bars of soft iron, of the same area of cross-section as the arms of the bridge, rest on the middle of the long arms, in the arched shape shown. Their ends approach near the top of the Bri.] [Briu arch within about a half inch. A space is hol- lowed out between these ends, for the reception of a short needle of well-magnetized hardened steel, suspended by a wire from a torsion head. The movements of the needle are measured on a scale by a spot of light reflected from a mirror. The electro-magnet maintains a constant dif- ference of magnetic potential at the two shorter ends of the rectangle. If, therefore, the four bars, or arms of the bridge, are magnetically identical, there will be no deflection, since no difference of potential will exist at the ends of the bars between which the needle is suspended. If, however, one of the bars or arms be moved even a trifle, the needle is at once deflected, the motion becoming a maximum when the bar is entirely removed. If replaced by another bar, differing in cross-section, constitution, or molecular struc- ture, the balance is likewise disturbed. The magnetic bridge is very sensitive. It was designed by its inventor for testing the magnetic qualities of the iron used in the construction of dynamo-electric machines. Bridge Method of Duplex Telegraphy. (See Telegraphy, Duplex, Bridge Method of.) Bridge Method of Quadruplex Teleg- raphy. (See Telegraphy, Quadruple*, Bridge Method of.) Bridge, Metre A slide form of Wheatstone's electric bridge, in which the slide wire is one metre in length. (See Bridge, Electric, Slide Form of.) Bridge, Resistance A term some- times applied to an electric bridge or balance. (See Bridge, Electric.) Bridge, Reversible A bridge or balance so arranged that the proportionate coils can be readily interchanged, thus per- mitting the bridge coils to be readily tested by reversing. Bridge, Wheatstone's Electric A name given to the electric bridge or balance. (See Bridge, Electric.) Bridges. Heavy copper wires suitably shaped for connecting the dynamo-electric machines in an incandescent light station to the bus-rods or wires. Bright Dipping. (See Dipping, Bright.) Bright Dipping Liquid. (See Liquid* Bright Dipping.) Britannia Joint. (See Joint, Britannia.) Broken Circuit. (See Circuit, Broken) Bronzing, Electro Coating a sur- face with a layer of bronze by electro-plating. (See Plating, Electro.) The plating bath contains a solution of tin and copper. Brush-and-Spray Discharge. (See Dis- charge, Brush-and- Spray) Brush Discharge. (See Discharge, Brush.) Brush Electrode. (See Electrode, Brush.) Brush, Faradic An electrode in the form of a brush employed in the medical application of electricity. The bristles are generally made of nickelized copper wire. Brush-Holders for Dynamo-Electric Ma- chines. Devices for supporting the collecting brushes of dynamo-electric machines. As the brushes require to be set or placed on the commutator in a position which often varies with the speed of the machine, and with changes in the resistance of the external circuit, all brush- holders are provided with some device for moving them concentrically with the commutator cylin- der. Brush Rocker. (See Rocker, Brush) Brush, Scratch A brush made of wire or stiff bristles, etc., suitable for clean- ing the surfaces of metallic objects before placing them in the plating bath. Scratch brushes are made of various shapes and are provided with wires or bristles of varying coarseness. Some forms of scratch v and finishing brushes- are shown in Fig. 83 . They are circular in outline Fig. Sj. Scratch Brushes. and are adapted for use in connection with a lathe. Bru.J 63 [Bui. Brnsh, Scratch, Circular A scratch brush of a circular shape, so fitted as to be capable of being placed in a lathe and set in rapid rotation. Brush, Scratch, Hand A scratch brush operated by hand, as distinguished from a circular scratch brush operated by a lathe. Brushes, Adjustment of Dynamo-Electric Machines Shifting the brushes into the required position on the commutator cylinder, either non-automatically by hand, or automatically by the current itself. (See Regulation, Automatic, of Dynamo-Electric Machines?) Brushes, Carbon, for Electric Motors Plates of carbon for leading current to electric motors. (See Brushes of Dynamo- Electric Machine?) These are generally known simply as brushes. Brushes, Collecting, of Dynamo-Electric Machine Conducting brushes which bear on the commutator cylinder, and take off the current generated by the difference of potential in the armature coils. (See Brushes of Dynamo-Electric Machine?) Brushes, Lead of The angle through which the brushes of a dynamo-electric ma- chine must be moved forward, or in the direction of rotation, in order to diminish sparking and to get the best output from the dynamo. The necessity for the lead arises from the coun- ter magnetism or magnetic reaction of the arma- ture, and the magnetic lag of its iron core. (See Lead, Angle of.) The position of the brushes on the commutator to insure the best output is practically the same in a series dynamo for any current strength. In shunt and compound dynamos it varies with the lead. Brushes of Dynamo-Electric Machine. Strips of metal, bundles of wire, slit plates of metal, or plates of carbon, that bear on the commutator cylinder of a dynamo-electric machine, and carry off the current generated. Rotary brushes consisting of metal discs are sometimes employed. Copper is almost univer- Fig. 84. Brushes. sally used for the brushes of dynamo-electric machines. Carbon brushes are often used for dynamo-electric motors. The brush shown at B, Fig. 84, is formed of copper wires, soldered together at the non- bearing end. A copper plate, slit at the bear- ing end, is shown at C, and bundles of copper plates, soldered together at the non -bearing end, are shown at D. The brushes should bear against the com- mutator cylinder with sufficient force to pre- vent jumping, and con- sequent burning, and yet not so hard as to cause excessive wear. Brushes, Rotating, of Dynamo-Electric Machines Discs of metal, employed in place of the ordinary brushes for carry- ing off the current from the armatures of dynamo-electric machines. Brushing, Scratch Cleansing the surface of an article to be electroplated, by friction with a scratch brush. Scratch brushing is generally done with the brushes wet by various solutions. Buckling. Irregularities in the shape of the surfaces of the plates of storage cells, fol- lowing a too rapid discharge. Bug. A term originally employed in quad- ruplex telegraphy to designate any fault in the operation of the apparatus. This term is now employed, to a limited extent, for faults in the operation of any electric appa- ratus. Bug-Trap. A device employed to over- come the " bug " in quadruplex telegraphy. Bulb, Lamp The chamber or globe in which the filament of an incan- descent electric lamp is placed. The chamber or globe of a lamp must be of such construction as to enable the high vacuum necessary to the operation of the lamp to be main- tained. Bun.] 64 [Bur. Bunched Cable.-(See Cable, Bunched?) Bunched Cable, Straightaway (See Cable, Bunched, Straightaway?) Bunched Cable, Twisted - (See Cable, Bunched, Twisted?) Bunsen Voltaic Cell. (See Cell, Voltaic, Bunsen's?) Buoy, Electric A buoy on which Iumin9us electric signals are displayed. Burglar Alarm. (See Alarm, Burglar?) Burglar Alarm Annunciator. (See An- nunciator, Burglar Alarm?) Burglar Alarm Contacts. (See Contacts, Burglar Alarm?) Burglar Alarm, Tale Lock Switch for (See Alarm, Yale-Lock-Switch Burglar?) Burner, Argand Electric An ar- gand gas-burner that is lighted by means of an electric spark. The argand electric burner assumes a variety of forms, such as the plain pendant, the ratchet- pmdant and the automatic. They are also used in systems of multiple gas lighting. Burner, Argand Electric, Automatic An argand burner arranged for automatic electric lighting. (See Burner, Automatic- Electric?) Burner, Argand Electric, Hand-Lighter A plain-pendant electric burner adapted for lighting an argand gas-burner. (See Burner, Plain-Pendant Electric?) Burner, Argand-Electric, Plain-Pendant A plain-pendant electric burner adapted for lighting an argand gas burner. (See Burner, Plain-Pendant Electric?) Burner, Argand-Electric, Ratchet-Pend- ant A ratchet-pendant electric burner adapted for lighting an argand gas-burner. (See Burner, Ratchet-Pendant Electric?) Burner, Automatic-Electric An electric device for both turning on the gas and lighting it, and turning it off, by alter- nately touching different buttons. The gas-cock is opened or closed by the motion of an armature, the movements of which are con- trolled by two separate electro-magnets. One push-button, usually a white one, turns the gas on by energizing one of the electro-magnets and, at the same time, lights it by means of a suc- cession of sparks from a spark coil. Another push-button, usually a black one, turns the gas off by energizing the other electro-magnet. The turning on or off of the gas is accom- plished by positive motions. Automatic burners are also made with a single button. An Argand Electric Burner is shown in Fig. 85. Burner, Electric Candle A device for electri- cally lighting a gas jet in a burner sur- rounded by a por- celain tube in imita- tion of a candle. Electric candle bur- ners are either simple or ratchet candle bur- ners. Burner, Hand- Lighting Electric A name sometimes applied to a plain- pendant electric burner. (See Burner, Plain- Pendant Electric?) Burner, Jump-Spark A term sometimes applied to a gas burner in which the issuing gas is ignited by a spark that jumps be- tween the metallic points placed on it. Jump-spark burners are used in systems of multiple gas lighting. (See Light- ing, Electric Gas.) Burner, Plain-Pen- dant Electric A gas - burner provided with a pendant for the purpose of lighting the gas by means of a spark, pig, 86. Plain-Pendant after the gas has been Burner, turned on by hand. The gas is first turned on by hand at the ordi- Fig. 83- Argand Electric Burner. Bur.] 65 [But. nary key, and is then lighted by pulling the pend- ant C, Fig. 86. A spark from a spark coil ignites the gas. This is sometimes called an electric hund- lighting burner. Burner, Ratchet-Pendant Candle Elec- tric A burner for both lighting and extinguishing a candle gas jet. Burner, Ratchet-Pendant Electric A gas-burner in which one pulling of a pendant turns on the gas and ignites it by means of an electric spark from a spark coil, and the next pulling of the pendant turns off the gas. A ratchet-wheel and pawl are operated by the motion of the pendant. The first pull of the pendant chain moves the ratchet so as to open a four-way gas cock, and at the same time light the gas at the burner tip by a wipe-spark from a spark coil. On the next pull ot the pendant, the four- way cock is turned so as to turn off the g?s. Alternate pulls, therefore, light and extinguish the gas. Burner, Simple Candle Electric A plain-pendant electric burner. (See Bur- ner, Plain Pendant Electric.) Burner, Thumb-Cock Electric An electric gas- burner, in which the turning of an ordinary thumb- cock turns on the gas, and ignites it by a spark pro- duced by a wiping contact actuated by the motions of the thumb-cock. A form of thumb- cock burner is shown in Fig. 87. Burner, Ti- brating-Elec- tric An Fig. 87. Thumb-Cock Burner. electric gas-burner in which the gas is lighted after it is turned on by hand, by means of the spark from a spark coil produced on the rapid making and breaking of the circuit by a vibrating contact. The vibrating-electric burner has a single elec- tro-magnet. It is operated by means of a button or switch, and may be used on single lights or on groups of lights. It bears the same relation to the automatic burner that the plain-pendant burner does to the ratchet burner. Burnetize. To subject to the Burnetizing process. (See Burnetizing?) Burnetizing. A method adopted for the preservation of wooden telegraph poles by injecting a solution of zinc chloride into the pores of the wood. (See Pole, Telegraphic?) Burning at Commutator of Dynamo. An arcing at the brushes of a dynamo-elec- tric machine, due to their imperfect contact, or improper position, which results in loss of energy and destruction of the commutator segments. Bus. A word generally used instead of omnibus. (See Omnibus?) Bus-Bars. (See Bars, Bus.} Bus-Rod Wires. (See Wires Bus-Rod.) Bus-Wire. (See Wire, Bus.) Butt Joint. (See Joint, Butt.) Button, Carbon A resistance of carbon in the form of a button. A button of carbon is used as an electric resist- ance in a variety of apparatus; its principal use, however, is in the transmitting instrument of the electric telephone. In the telephone Iransmitter, the button is so placed between contact-plates that when the plates are pressed together by the sound-waves, the electrical resistance is decreased by a decrease in the thickness of the carbon button, an increase in its density, and an increase in the number of points where the carbon touches the plates. Rheostats, or resistances, have been made by the use of a number of carbon buttons or discs piled one on another and placed in a glass tube. Discs of carbonized cloth form excellent resistances lor such purposes. Button, Press A push button. (See Button, Push.) Button, Push A device for closing But.] 66 [Cab. in electric circuit by the movement of a Buzzer, Electric A call, not as button, loud as that of a bell, produced by a rapid A button, when pushed by the hand, closes the Fig. 88. Push Button. Fig. 89 contact, and thus completes a circuit in which some electro- receptive device is placed. This circuit is opened by a spring, on the removal of the pressure. Some forms of push-buttons are shown in Figs. 88, 89 and 90. A. floor-push, for dining-rooms and offices is shown in Fig. 90. Fig. 88 shows the general appearance of an ordinary bell- push. The arrangement of the p . interior spring contacts will be understood by an inspection of Fig. 91. Fig. 9 I. Spring Contact of Bell Push. automatic make-and-break. (See Make-and- Break, Automatic!) The buzzer is generally pkced inside a resonant Fig. 92. case of wood in order to strengthen the sound by resonance. A form of buzzer is shown in Fig. 92. C. An abbreviation for centigrade. T hus, 20 degrees C. means 20 degrees of the centigrade thermometric scale. (See Scale, Cen- tigrade Thermometer.) C. A contraction for current. Generally a contraction for the current in amperes, as C = ^. C. C. A contraction for cubic centimetre. (See Weights and Measures, Metric System "/} C. G. S. Units. A contraction for centi- timetre-gramme-second units. (See Units, Centimetre-Gramme-Second) C. P. A contraction for candle power. (See Candle, Standard) Cable. An electric cable. (See Cable, Electric) Cable. To send a telegraphic dispatch, by means of a cable. Cable, Aerial A cable suspended in the air from suitable poles. Cable, Anti-Induction, Waring A form of anti-induction cable. In the Waring an ti- induction cable the separate conductors are covered with a fibrous insulator, from which all air and moisture is expelled, and the fibre then saturated with an insulating ma- Cab.] 67 [Cab. terial called ozite. The conductors are then pro- tected from the inductive effects of neighboring conductors by a continuous sheath of lead alloyed with tin. Where the cables are bunched, the bunches are sometimes again surrounded by insulating material, and the whole then covered by a con- tinuous lead sheathing ; generally, however, the separately insulated conductors are bunched, and then covered by a single sheathing of lead alloyed with tin. Cable, Armature of The armor of a cable. (See Armature of a Cabled) Cable, Armor of The protecting sheathing or metallic covering on the outside of a submarine or other electric cable. Cable, Armored An electric cable provided, in addition to its insulating coat- ing, with a protective coating or sheathing, generally of metal tubing or wire. Cable-Box. (See Box, Cable) Cable, Bunched A cable contain- ing more than a single wire or conductor. Some forms of bunched, lead-covered cables, are shown in Fig. 93. Fig. cable containing two wires. Cable-Grip. (See Grip, Cable.) Cable-Hanger. (See Hanger, Cable) Cable-Hanger Tongs. (See Tongs, Cable- Hanger.) Cable Laid-TJp in Layers. A term applied to a cable, all the conducting wires of which are in layers. Cab.] [Cab. Cable Laid-Up in Reversed Layers. A term applied to a cable in which the conduct- ors, in alternate layers, are twisted in opposite directions. (See Cable, Bunched, Straight- away^) Cable Laid-Up in Twisted Pairs. A term applied to a cable in which every pair of wires is twisted together. (See Cable, Bunched, Twisted?) Cable Lead. (See Lead, Cable). Cable, Multiple-Core A cable con- taining more than a single core. Cable-Protector. (See Protector, Cable.) Cable-Serving. (See Serving, Cable.) Cable, Single-Wire A cable con- taining a single wire or conductor. Cable, Sub- Aqueous An electric cable designed for use under water. The term submarine is more frequently em- ployed. Cable, Submarine A cable designed for use under water. Submarine cables are either shallow-water, or deep-sea cables. Gutta-percha answers admirably for the insulating material of the core. Various other insulators are also used. Strands of tarred hemp or jute, known as the cable- serving, are wrapped around the insulated core in order to protect it from the pressure of the galvanized iron wire armor afterwards put on. To prevent corrosion the iron wire is covered with tarred hemp, galvanized, or otherwise coated. Submarine cables' are generally employed for telegraphic or telephonic communication. (See Cable, Electric.) Cable, Submarine, Deep-Sea A submarine cable designed for use in deep water. This form of cable is not so heavily armored as the shallow-water submarine cable. Cable, Submarine, Shallow- Water A submarine cable designed for use in shallow water. This cable is provided with a heavier armor or sheathing than a deep-sea cable to protect it from chafing due to the action of the waves and tides in shallow water. (See Cable, Submarine.} Cable Support, Underground (See Support, Underground Cable) Cable Tank. (See Tank, Cable) Cable, Telegraphic A cable de- signed to establish telegraphic communication between different points. Telegraphic cables may be aerial, submarine, or underground. (See Cable, Electric.) Cable, Telephonic A cable de- signed to establish telephonic communication between different points. Telephonic cables may be aerial, submarine, or underground. (See Cable, Electric.) Cable-Terminal. (See Terminal, Cabled Cable, Torpedo A cable, in the circuit of which a torpedo is placed. (See Torpedo, Electric) Cable, Twisted-Pair - A cable containing a single twisted pair, suitable for use as a lead and return, thus affording a metallic circuit. Cable, Two, Three, Four, etc., Conductor A cable containing two, three, four, or more separate conducting wires. Cable, Underground An electric cable placed underground. The conducting wires of an underground cable are surrounded by a good insulating, water-proof substance, and protected by a sheathing or armor. A coating of lead is very generally employed for the sheathing or armor. Underground cables, in order to be readily accessible, should be placed in an underground conduit or subway. (See Cable, Electric. Conduit, Underground Electric. Subway, Electric) Cable- Worming. (See Worming, Cable) Cablegram. A message received by means of a submarine telegraphic cable. Cables, Laying-Up The placing or disposing of the separate cables or conduc- tors in a bunched cable. The separate conductors in cables may be laid- up "straightaway" or "twisted." (See Cable, Bunched, Twisted. Cable, Bunched, Straight- away. ) Cabling. Sending a telegraphic dispatch bv means of a cable. Cal.] 70 [Cal. Calahan's Stock Printer. (See Printer, Stock, Calahan's) Calamine, Electric A crystalline variety of silicate of zinc that possesses pyro- electric properties. (See Electricity, Pyro) Cal-Electricity. (See Electricity, Cal.) Calibrate. To determine the absolute or relative value of the scale divisions, or of the indications of any electrical instrument, such as a galvanometer, electrometer, vol- tameter, wattmeter, etc. Calibrating. The act of determining the absolute or relative value of the deflections, or indications of an electric instrument. Calibration, Absolute The deter- mination of the absolute values of the read- ing of an electrometer, galvanometer, volt- meter, amperemeter, or other similar instru- ment. The calibration of a galvanometer, for ex- ample, consists in the determination of the law which governs its different deflections, and by which is obtained in amperes, either the absolute or the relative currents required to produce such deflections. For various methods of calibration, see stan- dard works on electrical testing, or on elec- tricity. Calibration, Invariable, of Galvanom- eter In galvanometers with absolute calibration, a method for preventing the oc- currence of variations in the intensity of the field of the galvanometer, due to the neigh- borhood of masses of iron, etc. Calibration, Relative The deter- mination of the relative values of the reading of an electrometer, voltmeter, amperemeter, or other similar instrument. Caliper, Mi- B cronieter - A name some- times given to a vernier wire gauge. (See Gauge, Vernier Call-Bell, Extension (See Bell, Extension Call.) Call-Bell, Magneto-Electric An electric call-bell operated by currents pro- duced by the motion of a coil of wire before the poles of a permanent magnet. A well known form of magneto call-bell is shown Fig, 9S- Micrometer Caliper. A form of micrometer caliper is shown in Fig. q Fig.qb. Magneto Call Bell. in Fig. 96. The armature is driven by the rota- tion of the handle. Call-Bell, Telephone An electric bell, the ringing of which is used to call a person to a telephone. Call, Electric Bell An electric bell sometimes used to call 'the attention of an operator to the fact that his correspondent wishes to communicate with him, or to notify an attendant that some service is desired. Call, Messenger A district call- box. (See Box, District Call) Call, Thermo-Electric An instru- ment for sounding an alarm when the tem- perature rises above, or falls below, a fixed point. In one form of thermo-electric call a needle is moved over a dial by a simple thermic device and rings a bell when the temperature for which it has been se is attained. The thermo-call is appli- cable to the regulation of the temperature ol Cal.J 71 [Cal. dwellings, incubators, hot houses, breweries, dry- ing rooms, etc. Callaud Yoltaic Cell. (See Celt, Vol- taic, Callaud's.) Calling-Drop. (See Drop, Calling.) Calorescence. The transformation of invisible heat-rays into luminous rays, when received by certain solid substances. The term was proposed by Tyndall. The light from a voltaic arc is passed through a hollow glass lens filled with a solution of iodine in bisul- phide of carbon. This solution is opaque to light but quite trans- parent to heat. If a piece of charred paper, or thin platinum foil, is placed in the focus of these invisible rays, it will be heated to brilliant incandescence. (See Focus.) Caloric. A term formerly applied to the fluid which was believed to be the cause or essence of heat. The use of the word caloric at the present time is very unscientific, since heat is now known to be an effect of a wave motion and not a material thing. (See Meat.) Calorie. A heat unit. There are two calories, the small and the large calorie. The amount of heat required to raise the tem- perature of one gramme of water from o degree C. to I degree C. is called the small calorie. The amount of heat required to raise 1,000 grammes, or a kilogramme, of water from o de- gree C. to I degree C. is called the great calorie. The first usage of the word is the commoner. This word is sometimes spelled calory. Calorie, Great The amount of heat required to raise the temperature of one kilogramme of water from o degree C. to I degree C. Calorie, Small The amount of heat required to raise the temperature of one gramme of water from o degree C. to I degree C. Calorimeter An instrument for measur- ing the amount of heat or thermal energy contained or developed in a given body. Thermometers measure temperature only. A thermometer plunged in a cup full of boiling water shows the same temperature that it would in a tub full of boiling water. The quantity of heat energy present in the two cases is of course greatly different, and can be measured by a cal- orimeter only. Various forms of calorimeters are employed. In order to determine the quantity of heat in a given weight of any body, this weight may be heated to a definite temperature, such as the boil- ing point of water, and placed in a vessel con- taining ice. The quantity of ice melted by the body in cooling to the temperature of the ice, is determined by measuring the amount of water derived from the melting of the ice. Care must be observed to avoid the melting of the ice by ex- ternal heat. In this way the amount of heat required to raise the temperature of a given weight of a body a certain number of degrees, or the capacity of the body for heat, may be compared with the capacity of an equal weight of water. This ratio is called the specific heat. (See Heat, Specific.) The heat energy, present in a given weight of any substance at a given temperature, can be de- termined by means of a calorimeter; for, since a pound of water heated i F. absorbs an amount of energy equal to 772 foot-pounds, the energy can be readily calculated if the number of pounds of water and the number of degrees of temperature are known. (See Heat, Mechanical Equivalent '/) Calorimeter, Electric An instru- ment for measuring the heat developed in a conductor or any piece of electrical apparatus, in a given time, by an electric current. Fig. 97. Electric Calorimeter. A vessel containing water is provided with a thermometer T, Fig. 97. The electric current Cal.] [Can. passes for a measured time through a wire im- mersed in the liquid. The quantity of heat is determined from the increase of temperature, and the weight of the water heated. According to Joule, the number of heat units developed in a conductor by an electric current is proportional: (i.) To the resistance of the conductor. (2.) To the square of the current passing. (3.) To the time the current is passing. (See Heat Unit, English.) The heating power of a current is as the square of the current only when the resistance remains the same. (See Heat, Electric.) Calorimetric. Pertaining to or by means of the calorimeter. Calorimetric measurement is the measurement of heat energy made by means of the calorimeter. (See Calorimeter.) Caloriinetrically. In a Calorimetric man- ner. Calorimetric Photometer. (See Photom- eter, Calorimetric.) Calorimotor. A name applied to a defla- grator. (See Deflagrator?* Calory. A term used for calorie. Calorie is the preferable orthography. (See Calorie.) Cam, Electro-Magnetic A form of magnetic equalizer, which depends for its operation on the lateral approach of a suita- bly shaped polar surface. (See Equalizer, Magnetic?) . Cam, listening In a telephone exchange system, a metallic cam by means of which an operator is placed in circuit with a subscriber. Candle. The unit of photometric intensity. Such a light as would be produced by the consumption of two grains of a standard candle per minute. An electric lamp of 16 candle-power, or one of 2,000 candle-power, is a light that gives respect- ively 16 or 2,000 times as much light as one stand- ard candle. Candle Burner, Electric (See Bur- ner, Electric Candle?) Candle, Electric A term applied to the Jablochkoff candle, and other similar devices. (See Candle, Jablochkoff.') Candle, Foot A unit of illumina- tion equal to the illumination produced by a standard candle at the distance of i foot. According to this unit, the illumination pro- duced by a standard candle at the distance of 2 feet would be but the one-fourth of a foot- candle; at 3 feet, the one-ninth of a foot-candle, etc. The advantage of the proposed standard lies in the fact that knowing the illumination in foot- candles required lor the particular work to be done, it is easy to calculate the position and intensity of the lights required to produce the illumination. Candle, Jablochkoff An electric arc light in which the two carbon electrodes are placed parallel to each other and maintained a constant distance apart by means of a sheet of insulating material placed between them. The Jablochkoff electric candle consists of two parallel carbons, separated by a layer of kaolin or other heat-resisting insulating material, as shown in Fig. 98. The current is passed into and out of the carbons at one end of the candle, and forms a voltaic arc at the other end. In order to start the arc, a thin strip called the igniter, consisting of a mixture of some readily ignitable substance, connects the upper ends of the carbons. An alternating current is em- ployed with these candles, thus avoiding the difficulty which Ft 'f- <> 8 Ja ~ would otherwise occur from the ***** CandU ' more rapid consumption of the positive than the negative carbon. (See Current ', Alternating.') Candle, Metre The illumination pro- duced by a standard candle at the distance of one metre. (See Candle, Foot?) Candle-Power. (See Power, Candle?) Candle-Power, Rated (See Power, Candle, Rated) Candle- Power, Spherical (See Power, Candle, Spherical?) Candle, Standard A candle of Cao.] 73 [Cap. definite composition which, with a given con- sumption in a given time, will produce a light of a fixed and definite brightness. A candle which burns 120 grains of sperma- ceti wax per hour, or 2 grains per minute, will give an illumination equal to one standard candle. Unless considerable care is taken, erroneous re- sults will be obtained from the use of the stand- ard candle. According to Slingo and Brooker the following are among the most important causes of these errors : (i.) Defective forms of candle which cause a varying consumption of the material per second, and consequently a varying light for the standard candle. (2. ) Variations in the composition of the sper- maceti of which the candle is composed. Sper- maceti is not a definite chemical compound, but consists of a mixture of various substances ; therefore, even if the consumption is maintained constant, the light-giving power is not necessarily constant. (3.) Variations in the composition and charac ter of the wick, such as the number and size of the threads of which it is formed and the closeness Dfthe strands, all of which circumstances influence the amount of light given off by the candle. (4.) The light emitted in certain directions va- ries in a marked degree with the shape of the wick. The mere bending of a wick may, there- fore, cause the amount of light to vary consider ably. (5.) The light varies with the thickness of the wick. Thick wicks give less light than thin wicks. (6.) The light given by the standard candle va- ries with the temperature of the testing-room. As the temperature rises the light given by the standard candle increases. (7.) Currents of air. by producing variations in the amount of melting wax in the cup of the candle, vary the amount of light emitted. These difficulties in obtaining a fixed amount of light from a standard candle, together with the difficulty of comparing the feeble light of a single candle with the light of a much more powerful source, such as an arc lamp, coupled with the additional difficulty arising from the difference in the colors of the lights, have led to the use of other standards of light than those furnished by the standard candle. Caontchouc. or India-Rubber. A resin- ous substance obtained from the milky juices of certain tropical trees. Caoutchouc possesses high powers of electric insulation, and is used either pure or combined with sulphur. Cap, Insulator A covering or cap placed some distance above an insulator, but separated from it by an air space. Insulator caps are intended for protection of the insulators from injury by the throwing of stones or other malicious acts. Insulator caps are gen- erally made of iron. They are highly objection- able, owing to the facility they offer for the ac- cumulation of dust and dirt. Capacity, Atomic The quantiva- lence or valency of an atom. (See Atomi- city) Capacity, Dielectric A term em- ployed in the same sense as specific inductive capacity. (See Capacity, Specific Inductive?) Capacity, Electro-Dynamic A term formerly employed by Sir William Thomson for self-induction. (See Induction, Self.) Capacity, Electrostatic The quan- tity of electricity which must be imparted to a given body or conductor as a charge, in order to raise its potential a certain amount. (See Potential, Electric.) The electrostatic capacity of a conductor is not unlike the capacity of a vessel filled with a liquid or gas. A certain quantity of liquid will fill a given vessel to a level dependent on the size or capacity of the vessel. In the same manner a given quantity of electricity will produce, in a conductor or condenser, a certain difference of electric level, or difference of potential, dependent on the electrical capacity of the conductor or condenser. Or, taking the analogous case of a gas-tight vessel, the quantity of gas that can be firced into such a vesssl depends on the size of the vessel and the pressure with which it is forced in. A tension or pressure is thus produced by the gas on the walls of the vessel, which is greater the smaller the size of the vessel and the greater the quantity of gas forced in. In the same manner, the smaller the capacity of a conductor, the smaller is the charge required Cap.] to raise it to a given potential, or the higher the potential a given charge will raise it. The capacity K, of a conductor or condenser, is therefore directly proportional to the charge Q, and inversely proportional to the potential V; or, From which we obtain Q = KV; or, The quantity of electricity required to charge a conductor or condenser to a given potential is equal to the capacity of the conductor or condenser multiplied by the potential through which it is raised, Capacity, Electrostatic, Unit of -- Such a capacity of a conductor or condenser that an electromotive force of one volt will charge it with a quantity of electricity equal to one coulomb. The farad. (See Farad} Capacity of Cable. (See Cable, Capacity of.} Capacity of Condenser. (See Condenser, Capacity of} Capacity of Leyden Jar. (See Jar, Leyden, Capacity of.} Capacity of Line. (See Line, Capacity of.} Capacity of Polarization of a Toltaic Cell. (See Cell, Voltaic, Capacity of Polar- ization of.} Capacity, Safe Carrying, of a Conductor -- The maximum electric current the conductor will carry without becoming unduly heated. Capacity, Specific Inductive -- The ability of a dielectric to permit induction to take place through its mass, as compared with the ability possessed by a mass of air of the same dimensions and thickness, under precisely similar conditions. The relative power of bodies for trans- mitting electrostatic stresses and strains analogous to permeability in metals. The ratio of the capacity of a condenser whose coatings are separated by a dielectric of a given substance to the capacity of a similar condenser whose plates are separated by a plate or layer of air. 74 [Cap. The inductive capacity of a dielectric is com- pared with that of air. According to Gordon and others, the specific inductive capacities of a few substances, com- pared with air, are as follows: Air ..................... I. oo Glass ................... 3.013 to 3.258 Shellac ................. 2.740 Sulphur ............... 2.580 Gutta-percha ............ 2.462 Ebonite ................ 2.284 India-rubber ............ 2.220 to 2.497 Turpentine .............. 2.160 Petroleum .............. 2.030 to 2.070 Paraffin (solid) .......... 1.994 Carbon bisulphide ....... 1.810 Carbonic acid ........... 1.00036 Hydrogen .............. 0.99967 Vacuum ................ -9994i Faraday, who proposed the term specific in- ductive capacity, employed in his experiments a condenser consisting of a metallic sphere A, Fig. 99, placed inside a large hollow sphere B. The concentric space between A and B was filled with the substance whose specific inductive capacity was to be determined. Capacity, Specific Magnetic -- A term sometimes employed in the sense of magnetic permeability. Conductibility for lines of magnetic force in the same sense that specific inductive capacity is con- ductibility for lines of electrostatic force. This term has received the name of specific mag- Fig netic capacity in order to distinguish it from specific inductive capacity. The velocity of propagation of waves in any elastic medium is proportional to the quotient obtained by extracting the square root of the elasticity of the medium divided by the square root of its density ; or, IT D Cap.] [Car. Similarly, the speed with which inductive waves travel depends on the relation between the elas- ticity and the density of the medium. Calling =^ 5 the electric elasticity, then its reciprocal, K, corre- sponds with the dielectric capacity. The elec- trical density, /u, corresponds with the magnetic permeability. The velocity of wave transmission is therefore, Capacity, Storage, of Secondary Cell (See Cell, Secondary or Storage, Capa- city of.} Capillarity. The elevation or depression of liquids in tubes of small internal diameter. The liquid is elevated when it wets the walls, and depressed when it does not wet the walls of the tube. The phenomena of capillarity are due to the mutual attractions existing between the mole- cules of the liquid for one another, and the mutual attraction between the molecules of the liquid and those of the walls of the tube. In capillarity, therefore, the approximately level surface caused by the equal attraction of all the molecules towards the earth's centre is dis- turbed by the unequal attraction exerted on each molecule by the walls of the tube and by the re- maining molecules. Capillarity, Effects of, on Voltaic Cell Effects caused by capillary action which disturb the proper action of a voltaic cell. These effects are as follows: (i.) Creeping, or efflorescence of salts. (See Creeping, Electric. Efflorescence. ) (2. ) Oxidation of contacts and consequent in- troduction of increased resistance into the battery circuit. The liquid enters the capillary spaces between the contact surfaces and oxidizes them. Capillary. Of a small or hair-like diame- ter or size. A capillary tube is a tube of small hair-like di- ameter. (See Capillarity.) Capillary Attraction. (See Attraction, Capillary.) Capillary Contact-Key. (See Key, Cap- illary Contact.) Capillary Electrometer. (See Electrom- eter, Capillary.) Carbon. An elementary substance which occurs naturally in three distinct allotropic forms, viz.: charcoal, graphite and the dia- mond. (See Allotropy.) Carbon-Brushes for Electric Motors. (See Brushes, Carbon, for Electric Motors.} Carbon Button. (See Button, Carbon.) Carbon-Clutch or Clamp of Arc Lamp. (See Clutch, Carbon, of Arc Lamp} Carbon-Electrodes for Arc Lamps. (See Electrodes, Carbon, for Arc Lamps.) Carbon-Holders for Arc Lamps. (See Holders, Carbon, for Arc Lamps} Carbon Points. (See Points, Carbon^ Carbon Transmitter for Telephones. (See Transmitter, Carbon, for Telephones} Carbonic Acid Gas. (See Gas, Carbonic Acid.) Carboning Lamps. (See Lamps, Carbon- ing) Carbonizable. Capable of being carbon- ized. (See Carbonization, Processes of.) Carbonization. The act of carbonizing. (See Carbonization, Processes of.) Carbonization, Processes of Means for carbonizing material. The carbonizable material is placed in suitably shaped boxes, covered with powdered plumbago or lamp black, and subjected to the prolonged action of intense heat while out of contact with air. The electrical conducting power of the carbon which results from this process is increased by the action ot the heat, and, probably, also, by the de- posit in the mass, ot carbon resulting from the subsequent decomposition of the hydro-carbon gases produced during carbonization. When the carbonization is for the purpose of producing conductors for incandescent lamps, in order to obtain the uniformity of conducting power, electrical homogeneity, purity and high refractory power requisite, selected fibrous ma- terial, cut or shaped in at least one dimension ar.J [Car. prior to carbonization, must be taken, and sub- jected to as nearly uniform carbonization as pos- sible. Carbonize. To reduce a carbonizable ma- terial to carbon. (See Carbonization, Pro- cesses of) Carbonized Cloth Discs for High Resist- ances. (See Cloth Discs Carbonized, for High Resistances^) Carbonizer. Any apparatus suitable for reducing carbonizable material to carbon. Carbonizing. Subjecting a carbonizable substance to the process of carbonization. (See Carbonization, Processes of.) Carbons, Artificial Carbons ob- tained by the carbonization of a mixture of pulverized carbon with different carbonizable liquids. Powdered coke, or gas-retort carbon, some- times mixed with lamp-black or charcoal, is made into a stiff dough with molasses, tar, or any other hydro-carbon liquid. The mixture is molded into rods, pencils, plates, bars or other desired shapes by the pressure of a powerful hydraulic press. After drying, the carbons are placed in crucibles and covered with lamp-black or pow- dered plumbago, and raised to an intense heat at which they are maintained for several hours. By the carbonization of the hydro-carbon liquids, the carbon paste becomes strongly coherent, and by the action of the heat its conducting power in- creases. To give increased density after baking, the carbons are sometimes soaked in a bydro-carbon liquid, and subjected to a re-baking. This may be repeated a number of times. Carbons, Concentric-Cylindrical A cylindrical rod of carbon placed inside a hol- low cylinder of carbon but separated from it by an air space, or by some other insulating, refractory material. Jablochkoff candles sometimes are made with a solid cylindrical electrode, concentrically placed in a hollow cylindrical carbon. Carbons, Cored A cylindrical carbon electrode for an arc lamp that is molded around a central core of charcoal, or other softer carbon. Much of the unsteadiness of the arc light is due to changes in the position of the arc. Cored car- bons, it is claimed, render the arc light steadier, by maintaining the arc always at the softer carbon a-.id hence at the central point of the electrode. A core of harder carbon, or other refractory material, is sometimes provided for the negative carbon. Carbons, Flashed Carbons which have been subjected to the flashing pro- cess, (See Carbons, Flashing Process for.) Carbons, Flashing Process for A process for improving the electrical uniformity of the carbon conductors employed in in- candescent lighting, by the deposition of car- bon in their pores, and over their surfaces at those places where the electric resistance is relatively great. The carbon conductor or filament is placed in a vessel filled with the vapor of a hydrocarbon liquid called rhigolene, or any other readily de- composable hydrocarbon liquid, and gradually raised to electric incandescence by the passage through it of an electric current A decomposi- tion of the hydrocarbon vapor occurs, the car- bon resulting therefrom being deposited in and on the conductor. As the current is gradually increased, the parts of the conductor first rendered incandes- cent are the places where the electric resist- ance is the highest, these parts, therefore, and practically these parts only, receive the deposit of carbon. As the current increases, other portions become successively incandescent and receive a deposit of carbon, until at last the filament glows with a uniform brilliancy, in- dicative of its electric homogeneity. A carbon whose resistance varies considerably at different parts could not be successfully em- ployed in an incandescent lamp, since if heated by a current sufficiently great to render the points of comparatively small resistance satisfactorily incandescent, the temperature of the points of high resistance would be such as to lower the life of the lamp, while if only those portions were safely heated, the lamp would not be economical. The flashing process is therefore of very great value in the manufacture of an incandescent lamp. The name " flashing " was applied to the pro- cess by reason of the flashing light emitted by the Car.] 77 [Cas. carbons when they have been sufficiently treated. The process requires so little time that the dull red which first appears soon flashes to the full lumin- osity required. The term "flashing" is sometimes applied to the electrical heating to incandescence, while the carbons are in the lamp chambers, and on the pumps. This flashing is for the purpose of driving off all the gases occluded by the carbon, so that these gases may be carried off by the operation of pumping. This process is more properly called the process for driving off the occluded gases. The carbons are sometimes flashed in the liquid itself instead of in its vapor. Carbons, Paper Carbons, of textile or fibrous origin, obtained from the carboniza- tion of paper. The carbonization of paper is readily effected by submitting the paper to the prolonged action of a high temperature while out of contact with air. For this purpose the paper is packed in retorts or crucibles, and covered with lamp-black, or powdered plumbago, in order to exclude the air. Since paper consists of a plane of material uni- formly thin in one direction, formed almost en- tirely of fibres of pure cellulose, the greatest length of which extends in a direction nearly par- allel to that in which the paper is uniformly thin, it is clear that sheets of this substance, when car- bonized, should yield flexible carbons of unusual purity and electrical homogeneity, since such carbons are structural in character, and are uni- formly affected by the heat of carbonization to an extent that would be impossible by the carboniza- tion of any material in a mass. Carcase of Dynamo-Electric Machine. (See Machine, Dynamo-Electric, Carcase of.) Carcel. The French unit of light. The light emitted by a lamp burning 42 grammes of pure colza oil per hour, with a flame 40 millimetre? in height. The bec-carceL One carcel = 9.5 to 9.6 stand- ard candles. Carcel Lamp. (See Lamp, Carcel} Carcel Standard Gas Jet. (See Jet, Gas, Carcel Sta ndard} Card, Compass A card used in the mariner's compass, on which are marked the four cardinal points of the compass N, S, E and W, and these again divided into thirty- two points called Rhumbs. (See Compass, Azimuth} Cardew Voltmeter. (See Voltmeter, Cardew} Carriage, Pen The carriage in an electric chronograph which holds the pen and moves over the sheet of paper on which the record is made. (See Chronograph, Elec- tric.} Carriers of Replenishes (See Replen- isher, Carriers of} Cascade, Charging Leyden Jars by A method of charging jars or condensers by means of the free electricity liberated by induction from one coating, when a charge is passed into the other coating. The jars are p'acel as shown in Fig. 100, with the inside coating of the first jar connected with the outside coa.ing of the one next it. There is in Q f Fig. 100. Cascade Charging of Leyden Jars. reality no increase in the entire charge obtained in charging by cascade, since the sum of the charges given to the separate jars is equal to the same charge given to a single jar separately charged. The energy of the discharge in cascade can be shown to be less than that of the same charge when confined to a single jar. This is of course to be expected, since it is energy that is charged in the jar and not electricity, and, of course, the energy charged in the jar can never exceed the energy employed in charging the jar. There is a small loss for each jar, and this increases ne- cessarily with each jar added. Cascade, Connection of Electric Sources in A term sometimes used for series- connection of electric sources. The term series -connection is the preferable one. (See Connection, Series.) Case-Hardening, Electric Super- ficially converting a piece of wire into steel by electrically produced heat. Cas.] 78 [Can. In electric case-hardening, the superficial layers of a piece of iron are converted into steel by electrically heating the same, while surrounded by a layer of case-hardening flux and carbonaceous substances such as animal charcoal, shavings of horn, leather cuttings or other similar substances. In the case of a readily oxidizable metal like iron, oxidation is prevented by surrounding the metal by a hydrocarbon gas, which, when suffi- ciently heated, deposits on the surfaces a pro- tective coating of carbon. This layer of carbon gradually carbonizes the iron. Case Wiring. (See Wiring, Case.) Cataphoresis. A term sometimes em- ployed in place of electric osmose. (See Os- mose, Electric.) The word cataphoresis applies to the cases where medicinal substances, such as iodine, cocoaine, quinine, etc., are caused to pass through organic tissues in the direction of flow of an electric cur- rent, or from the anode to the kathode. This action is probably due to an electrolytic action. Cataphoric Action. (See Action, Cata- phoric) Catch, Safety A wire, plate, strip, or box of readily fusible metal, capable of con- ducting, without fusing, the current ordinarily employed on the circuit, but which fuses and thus breaks the circuit on the passage of an abnormally large current. Safety -catches are generally placed on multiple- arc and multiple-series circuits. (See fuse, Safety.) Catelectrotonus. An orthography some- times applied to Kathelectrotonus. (See Kathelectrotonus) Cathetometer. An instrument for the ac- curate measurement of vertical height. The cathetometer consists essentially of an accurately divided vertical rod which carries a sliding support for a telescope. The telescope is provided with two spider lines at right angles to one another, so placed as to be seen in front of the object whose height is to be measured. From observations taken in different positions, the measurement of the true vertical height is readily obtained. Cathion. A term sometimes used instead of Kathion. More correctly written Kathion. (See Kathion) Cathode. A term sometimes used instead of Kathode. Catoptrics. That branch of optics which treats of the reflection of light. Causty, Oalvano A term some- times used for galvano-cautery. (See Cautery, Galvano) Cauterization. The act of cauterizing, or burning with a heated solid or caustic sub- stance. Cauterization, Electric Subject- ing to cauterization by means of a wire elec- trically heated. (See Cautery, Electric) Cauterize. To subject to cauterization, or burning with a heated solid or caustic sub- stance. Cauterizer, Electric A term some- times applied to an electric cautery. (See: Cautery, Electric) Cautery, Actual A burning or sear- ing with a- white-hot metal. Cautery Battery. (See Battery, Cautery) Cautery, Electric An instrument used for electric cauterization. In electro-therapeutics, the application of variously shaped platinum wires heated to in- candescence by the electric current in place of a knife, for removing diseased growths, or for stopping hemorrhages. The operation, though painful during applica- tion, is afterward less painful than that with a- knife, since secondary hemorrhage seldom occurs, and the wound rapidly heals. Electric cautery is applicable in cases where the knife would be inadmissible owing to the situation of the parts or their surroundings. Cautery, Galvano A term fre- quently employed in place of electric cautery. (See Cautery, Electric) Cautery, Galvano Electric An electric cautery. (See Cautery, Electric) Cautery, Oalyano Thermal A term sometimes used for an electric cautery- (See Cautery, Electric^ Cau.] 79 [Cel. Cautery-Knife Electrode. (See Electrode Cautery- Knife.} Cautery, Thermal A cautery heated by heat other than that of electric ori- gin, as distinguished from an electric cautery. (See Cautery Electric!) Ceiling Rose. (See Rose, Ceiling} Cell, Depositing An electrolytic cell in which an electro-metallurgical deposit is made, (See Metallurgy. Electro} Cell, Electrolytic - A cell or vessel containing an electrolyte, in which electrolysis is carried on. An electrolytic cell is called a voltameter when the value of the current passing is deduced from the weight of the metal deposited. Cell, Impulsion A photo-electric cell whose sensitiveness to light may be re- stored or destroyed by slight impulses given to the plates, such as by blows or taps, or elec- tro-magnetic impulses. An impulsion cell may be prepared by pasting pieces of tin-foil, the opposite faces of which are respectively polished and dull, on the opposite faces of a plate of glass, so as to expose dissimi- lar sides to the light, when the cells are dipped in alcohol. Cell, Photo-Electric - A cell capa- ble of producing differences of potential when its opposite faces are unequally exposed to radiant energy. Photo-voltaic cells are made in a variety of forms, both with selenium and with different me- tallic substances. (See Cell, Selenium.} Cell, Porous A jar of unglazed earthenware, employed in double-fluid voltaic cells, to keep the two liquids separated. The use of a porous cell necessarily increases the internal resistance of the cell, from the de- crease it produces in the area of cross section of liquid between the two elements. When the bat- tery is dismantled, the porous cells should be kept under water, otherwise the crystallization of the zinc sulphate or other salt is apt to produce serious exfoliation, or scaling off, or even to crumble the porous cell. A porous cell is sometimes called a diaphragm, but only properly so when the cell is reduced to a single separating plate. (See Cell, Voltaic.} Cell, Secondary A term sometimes used instead of storage cell. The term secondary cell is used in contradis- tinction to primary or voltaic cell. Cell. Secondary or Storage. Boiling of A term sometimes applied to the gassing of a storage cell, (See Cell, Storage, Gassing of} Cell, Secondary or Storage, Capacity of The product of the current in am- peres, by the number of hours the battery is capable of furnishing said current, when fully charged, until exhausted. The capacity of storage cells is given in ampere- hours. A storage battery with a capacity of i,oco ampdre-hours can furnish, say a current of fifty amperes for twenty hours, or a current of one hundred ampdres for ten hours; or a current of twenty -five amperes for forty hours. Cell, Secondary or Storage, Gassing of An escape of gas due to the decom- position ot water on passage of too strong a charging current. Cell, Secondary or Storage, Renovation of The revivifying or recharging of a run-down, or discharged storage cell. Cell, Secondary or Storage, Time-Fall of Electromotive Force of (See force. Electromotive of Secondary or Storage Cell, Time-Fall, of.} Cell, Secondary or Storage, Time-Rise of Electromotive Force of (See force, Electromotive of, Secondary or Storage Cell, Time-Rise, , of "} Cell, Selenium A cell consisting of a mass of selenium fused in between two conducting wires or electrodes of platinized silver or other suitable metal. A convenient manner of forming a selenium cell is to wind two separate spirals of platinized silver wire around a cylinder of hard wood, tak- ing care to maintain them a constant distance apart, so as to avoid contact between them. The space between these wires is filled with fused sele- nium, which is allowed to cool gradually. Exposure to sunlight reduces the resistance of a selenium cell to about one-half its resistance in Cel.] the dark, but neither the resistance nor the reduc- tion ratio long remains constant. A selenium cell produces a difference of poten- tial, or electromotive force, when one of its elec- trode faces is exposed to light, while the other is kept in darkness. According to Von Uljanin, who experimented with se'.enium melted in between two parallel platinized plates, cooled under pressure, and then reduced from the amorphous to the sensitive crys- talline variety by gradual cooling alter two or three heatings in a paraffme bath up to 195 de- grees, the following peculiarities were observed: (i.) Exposure of one of the electrodes to sun- light produced an electromotive force which causes a current to flow from the dark to the illumined electrode. (2.) The maximum electromotive force was o. 12 volt. (3.) The electromotive force disappeared instan- taneously and completely on the darkening of the electrodes. (4.) A slight difference in the electromotive force was observed when the positive and nega- tive electrodes were alternately exposed to the light, the maximum electromotive force being attained by the exposure of the negative electrode. (5.) If both electrodes are similarly illumined the resulting current strength is decreased and may reach zero. (6.) The action of light is instantaneous. (7.) Most of the selenium cells experimented with exhibited an electromotive force of polariza- tion. (8.) The electromotive force of polarization is diminished by exposure to light. (9.) The electrical resistance and sensitive- ness to light as regards the production of an electromotive force decrease with time. This is probably due to a gradual change in the allo- tropic state of the selenium. (See State, Allo- tropic.} (10.) The electromotive force produced is pro- portional to the intensity of the illumination only when the obscure rays or heat rays are absent. (n.) Of different wave lengths the orange-yel- low rays in the diffraction spectrum, and the greenish-yellow in the prismatic spectrum pro- duced the greatest effect. Among some of the more recent applications of selenium cells are the following: (i.) A selenium cell is so placed in a circuit containing an electro-magnet and switch, that on [Cel. one of its electrodes being exposed to the de- creased illumination of coming night it automat- ically turns on an electric lamp, and, conversely, on the approach of daylight, and the consequent illumination of the electrode, turns it off. (2.) A device whereby the presence of light, as for example that carried by a burglar, auto- matically rings an alarm and thus calls the atten- tion of the watchman of the building. Cell, Standard (See Cell, Voltaic, Standard?) Cell, Storage Two relatively inert plates of metal, or of metallic compounds, immersed in an electrolyte incapable of acting considerably on them until after an electric current has been passed through the liquid from one plate to the other and has changed their chemical relations. A single one of the cells required to form a secondary battery. Sometimes, the jar containing a single cell is called a storage cell. This latter use of the word is objectionable. A storage cell is also called an accumulator. On the passage of an electric current through the electrolyte, its decomposition is effected and the electro-positive and electro-negative radicals are deposited on the plates, or unite with them, so that on the cessation of the charging current, there remains a voltaic cell capable of generating an electric current. A storage cell is charged by the passage through the liquid from one plate to the other of an elec- tric current, derived from any external source. The charging current produces an electrolytic de- composition of the inert liquid between the plates, depositing the electro-positive radicals, or kathions, on the plate connected with the negative terminal of the source, and the electro-negative radicals, or anions, on the plate connected with the positive terminal. On the cessation of the charging current, and the connection of the charged plates by a con- ductor outside the liquid, a current is produced, which flows through the liquid from the plate covered with the electro-positive radicals, to that covered with the electro -negative radicals, or in the opposite direction to that of the charging cur- rent. The simplest storage cell is Plante's cell, which, as originally constructed, consists of two plates of Cel.] si [Cel. lead immersed in dilute sulphuric acid, H 2 SO 4 . On the passage of the charging current, the plates A andB, Fig 101, dipped in H 2 SO 4 , are covered respectively with lead peroxide, PbO 2 , and finely divided, spongy lead. The peroxide is formed on the positive plate, and the metallic lead on the negative plate. The acid and water should have a specific gravity of about 1.170. When the cell is fully charged the acid solution loses its c eir- ness and becomes milky in appearance, and the Figs ioiandiO2. Storage Cell. specific gravity increases to 1. 195. This increase is a good sign of a full charge. When the charging current ceases to pass, the cell discharges in the opposite direction, viz., from B' to A , that is, from the spongy lead plate to the peroxide plate through the electrolyte, as shown in Fig. 102. As a result of this discharging current the per- oxide, PbO a , on A', gives up one of its atoms of oxygen to the spongy lead on B', thus leaving both plates coated with a layer of PbO, lead monoxide, or litharge. When this change is thoroughly effected, the cell becomes inert, and will furnish no further current until again charged by the passage of a current from some external source. In order to increase the capacity of the storage cells, and thus prolong the time of their discharge, the coating of lead monoxide thus left on each of the plates, when neutral, is made as great as possible. To effect this, a process called ' 'forming the plates" is employed, which con ists in first charging the plates as already described, and then reversing the direction of the charging cur- rent, the currents being sent through the cell in alternately opposite directions, until a consider- able depth of the lead plates has been acted on. It will be noticed that during the action of the charging current, the oxygen is transferred from the PbO, on one plate, to the PbO, on the other plate, thus leaving one Pb, and the other PbO 2 ; and that on discharging, one atom of oxygen is transferred from the PbO z , to the Pb, thus leav- ing both plates covered with PbO. In reality this is but the final result of the action, hydrated sulphate of lead, PbO, H 4 SO 4 , being formed and subsequently decomposed. Other com pounds are formed that are but imperfectly un- derstood. In order to decrease the time required for form- ing, accumu.ators, or secondary cells, have been constructed, in which metallic plates covered with red lead Pb 3 O 4 replace the lead p'ates in the original Plante cell. On charging, the Pb 8 O 4 is peroxidized at the anode, i. e., converted into PbO 2 , and deoxidized, and subsequently con- verted into metallic lead at the kathode. Or, in place of the above Pb 3 O 4 , red lead is placed on the anode and PbO, or litharge, on the kathode. Plates of compressed litharge have also been recently used for this purpose. Storage cells so formed have a greater storage capacity per unit weight than those in which a grid is employed, but a higher resistance. In all cases where a metal plate is employed various irregularities of surface are given to the plates, in order to increase their extent of surface and to afford a means for preventing the separa- tion of the coatings. The metallic form thus provided is known technically as a grid. Unless care is exercised, the plates will bucklt from the difference in the expansion of the lead and its filling of oxide. This buckling is attended with an increase in the resistance of the cell and the gradual separation of the oxides that cover or fill it. Cell, Thermo-Electric - A name applied to a thermo-electric couple. (See Couple, Thermo-Electric^ Cell, Voltaic The combination of two metals, or of a metal and a metalloid, which, when dipped into a liquid or liquids called electrolytes, and connected outside the liquid or liquids by a conductor, will produce a current of electricity. Different liquids or gases may take the place of the two metals, or of the metal and metalloid. (See Battery, Gas.) Plates of zinc and copper dipped into a solu- tion of sulphuric acid and water, and connected outside the liquid by a conductor, form a simple voltaic cell. If the zinc be of ordinary commercial purity, Cel.] [Cel. and is not connected outside the liquid by a con- ductor, the following phenomena occur: (I.) The sulphuric acid or hydrogen sul- phate, H 4 SO 4 , is decomposed, zinc sulphate, ZnSO 4 , being formed, and hydrogen, H 2 , liber- ated. (2.) The hydrogen is liberated mainly at the surface of the zinc plate. (3.) The entire mass of the liquid becomes heated. If, however, the plates are connected outside the liquid by a conductor of electricity, then the phenomena change and are as follows, viz.: (i.) The sulphuric acid is decomposed as be- fore ; but, (2.) The hydrogen is liberated at the surface of the copper plate only. (3.) The heat no longer appears in the liquid only, but in all parts of the circuit. (4.) An electric current now flows through the entire circuit, and will continue so to floiv as long as there is any sulphuric acid to be decomposed, and zinc with which to form zinc sulphate. The energy which previously appeared as heat only, now appears in part as electric energy. Therefore, although the mere contact of the two metals with the liquid will produce a differ- ence of potential, it is the chemical potential energy which became kinetic during chemical combination that supplies the energy required to maintain the electric current. (See Energy, Kinetic. Energy, Potential.') A voltaic cell consists of two plates of different nv ta'.s, or of a metal and a metalloid (or of two gases, or two liquids, or of a liquid and a gas), each of which is called a voltaic element, and which, taken together, form what is called a voltaic couple. The voltaic couple dips in- to a liquid called an electro- lyte, which, as it transmits the electric current, is de- composed by it. The ele- ments are connected outside the electrolyte by any con- ducting material. Fig. 103. Voltaic Couple. Direction of the Current. In any voltaic cell the current is assumed to flow through the liquid, from the metal most acted on to the metal least acted on, and outside the liquid, through the out- side circuit, from the metal least acted on to the metal most acted on. In Fig. 103 a zinc-copper voltaic couple is shown, immersed in dilute sulphui ic acid. Here, since the zinc is dissolved by the suiphuric acid, the zinc is positive, and the copper negative in the liquid. The zinc and copper are of opposite polarities out of the liquid. There is still a considerable difference of opinion as to the exact cause of the potential difference of the voltaic cell. There can be no doubt that a true contact force exists, but the chemical poten- tial energy of the positive plate is the source of energy which maintains the potential differ- ence. The difference in the polarity of the zinc and copper in and out of the liquid is generally de- nied by most of the later writers on electricity, since tests by a sufficiently delicate electrometer show that the entire zinc plate is negative and the entire copper plate positive. Remembering, however, the convention as to the direction of the flow of the current, since the current flows from the zinc to the copper through the liquid, we may still fairly regard the zinc as positive and the copper as negative in the liquid. It will be remembered, that in every source the polarity within the source is necessarily opposite to the polarity outside it. The copper plate is there- fore called the negative plate, and the wire con- nected to its end out of the liquid, the positive electrode. Similarly, the zinc plate is called the positive plate, and the wire connected to it the negative electrode. It wiJ of course be understood that- in the above sketch the current flows only on the com- pletion of the circuit outside the cell; that is, when the conductors attached to fie zinc and copper phtes a e electrically connected. Amalgamation of the Zinc Plate. When zinc is used for the positive ele.ncnt, it will, unkss chemically pure, be dissolved by the electrolyte when the circuit is open, or will be irregularly dissolved when the circuit is closed, p-oducing currents in little closed circuits fiom minute vol- taic couples formed by the zinc and such impuri- ties as carbon, lead, or iron, etc., always found in commercial zinc. (See Action, Local, of Vol- taic Ceil.) As it is practically impossible to ob- tain chemically pure zinc, it is necessary to amal- gamate the zinc plate; that is, to cover it with a thin layer of zinc amalgam. Polarization of the Negative Plate. Since the evolved hydrogen appears at the surface of the negative plate, the surface of this plate, unless Cel.] 83 [CeL means are adopted to avoid it, will, after a while, become coated with a film of hydrogen gas, or .as it is technically called, will become polarized. {See Cell, Voltaic, Polarization of.) The effect of this polarization is to cause a fall- ing off or weakening of the current produced by the battery, due to the formation of a counter- .electromotive force produced by the hydrogen- covered plate; that is to say, the negative plate, now being covered with hydrogen, a very highly electro-positive element, tends to produce a current in a direction opposed to that of the cell proper. (See force, Electromotive, Coun- ter.) This 'decrease in current strength is rendered still greater by the increased resistance in the ctll, due to the bubbles of hydrogen, and to the de- creased electromotive force, due to the increase in the density of the zinc sulphate, in the case of zinc in hydrogen sulphate. In the case of storage cells, the counter-elec- tromotive force of polarization is employed as the source of secondary currents. (See Electricity, Storage of. Cell, Secondary. Cell, Storage.) In order to avoid the effects of polarization in voltaic cells, and thus insure constancy of cur- rent, the bubbles of gas at the negative plate are mechanically carried off either by roughening its surface, by forcing the electrolyte against the plate as by shaking, or by a stream of air; or else the negative plate is surrounded by some liquid or solid substance which will remove the hydro- gen, by entering into combination with it. (See Cell, Voltaic, Polarization of.) Voltaic cells are therefore divided into cells with one or with two fluids, or electrolytes, or into: (I.) Single-fluid cells; and (2.) Double-fluid cells. Very many forms of voltaic cells have been de- vised. The following are among the more im- portant, viz. : Of the Single-Fluid Cells, the Grenet, Poggendorff, or Bichromate, the Zinc- Copper, the Zinc- Carbon and the Smee. Of the Double-Fluid Cells, Grove's, Bunsen's, Callaud or Gravity, Daniels, Leclanche, Siemens -Halske and the Mcidinger. Of all the voltaic cells that have been devised two only, viz., the Gravity, a modified Daniell, and the Leclanche, have continued until now in very general use, the gravity cell being used on closed-circuited lines, and the Leclanche on open- circuited lines ; the former being the best suited of all cells to furnish the continuous constant cur- rents employed in most systems of telegraphy, and the latter for furnishing the intermittent cur- rents required for ringing bells, operating annun- ciators, or for similar work. Cell, Yoltaic, Absorption and Genera- tion of Heat in -- (See Heat, Absorption and Generation of, in Voltaic Cell.} Cell, Voltaic, Bichromate A zinc- carbon couple used with an electrolyte known as electropoion, a solution of bichro- mate of potash and sulphuric acid in water. (See Liquid, Electropoion} Bichromate of sodium or chromic acid are sometimes used instead of the bichromate of potassium. T he zinc, Fig. 104, is amalgamated and placed between two carbon plates. The terminals connected with the zinc and carbon are respectively negative and. positive. In the form shown in the figure, the zinc p ate can be lifted out of the liquid when the cell is not in action. The bichromate cell is excellent for purposes re- quiring strong currents where long action is not necessary. As this cell readily polarizes it cannot be advantageously employ- ed continuously for any considerable period of time. It becomes depolar- ized, however, when left for some time on open circuit. The following chemical reaction probably takes place when the cell is furnishing current, viz. : Fig. jo 4. Bichromate Cell. K 2 S0 4 + 3 ZnS0 4 -f Cr 8 3(So 4 ) + 7 H 2 O. This cell gives an electromotive force of about 1. 9 volts. Cell, Toltaic, Bunsen's -- A zinc- carbon couple, the elements of which are immersed respectively in electrolytes of dilute sulphuric and strong nitric acids. Bunsen's cell is the same as Grove's, except that the platinum is replaced by carbon. The zinc surrounds the porous cell containing the car- Cel.] 84 [CeL bon. The polarity is as indicated in Fig. 105. (See Cell, Voltaic, Grove.) F&. i OS' Bunsen Cell. The Bunsen cell gives an electromotive force of about 1.96 volts. Cell, Voltaic, Callaud's A name sometimes given to the gravity cell. (See Cell, Voltaic, Gravity.} Cell, Voltaic, Capacity of Polarization of The quantity of electricity required to be discharged by a voltaic cell in order to produce a given polarization. (See Cell, Vol- taic, Polarization of.) During the discharge of a voltaic cell an electro- motive force is gradually set up that is opposed to that ot the cell. The quantity of electricity required to produce a given polarization de- pends, of course, on the condition and size of the plates. Such a quantity is called the capacity of polarization. Cell, Voltaic, Closed-Circuit A voltaic cell that can be left for a considerable time on a closed circuit of comparatively small resistance without serious polarization. The term closed-circuit voltaic cell is used in contradistinction to open-circuit cell, and applies to a cell that can only be kept on closed circuit for a comparatively short time. Daniell's cell and the gravity cell are clo c ed-cir- cuit cells. Leclanche's is an open-circuit cell. Cell, Voltaic, Contact Theory of A theory which accounts for the production of difference of potential or electromotive force in the voltaic cell by the contact of the elements of the voltaic couple with one an- other by means of the electrolyte. The mere contact of two dissimilar substances through the electrolyte will produce a difference of potential, but the cause of the current which a- voltaic cell is able to maintain is the chemical potential energy which becomes kinetic during combination. (See Cell, Voltaic. Series, Contact.}* Most authorities explain the difference of potential produced by the contact of different metals by the fact that the metals are sur- rounded by air. They point out the fact that the order of the metals in the contact-series is almost identical with the order of their electro- chemical power as deduced from their chemical equivalents, and their heat of combination with oxygen. It would appear, therefore, that the difference of potential between a metal and the air which surrounds it, is a measure of the tend- ency of the metal to become oxidized. The origin of the electromotive force of a zinc- copper couple, in an electrolyte of hydrogen sul- phate, is the superior affinity of the zinc for the oxygen, over that of the copper for the oxygen. Cell, Voltaic, Creeping in The formation, by efflorescence, of salts on the sides of the porous cup .of a voltaic cell, or on the walls of the vessel containing the electrolyte. Paraffining the portions of the walls out of the liquid, or covering the surface of the liquid with a neutral oil, obviates much of this difficulty. (See Efflorescence.} Cell, Voltaic, Daniell's A zinc- copper couple, the elements of which are im- mersed respectively in electrolytes of dilute sulphuric acid, and a saturated solution of. copper sulphate. In the form of Daniell's cell, shown in Fig. 106, the copper element is made in the form of a cylin- der c, and is placed in a porous cell. The cop- per cylinder is provided with a wire basket near" the top, filled with crystals of blue vitriol, or cop- per sulphate, so as to maintain the strength of the solution while the cell is in use. The zinc is ir. the shape of a cylinder and is placed so as to sur- round the porous cell. This cell gives a nearly constant electromotive force. The constancy of action of Daniell's cell depends on the fact that for every molecule o< sulphuric acid decomposed in the outer cell, an- additional molecule of sulphuric acid is supplied by the decomposition of a molecule of copper sul- phate in the inner cell. This will be better un- Cel.] 85 [Cel. derstood from the following reactions which take place, viz.: Zn + H 2 SO 4 = ZnSO 4 -f H 8 The H 8 SO 4 , thus formed in the inner cell, passes through the porous cell, and the copper is deposited on the surface of the copper plate. Fig rob. Daniell s Cell. The Daniell cell gives an electromotive force of about 1.072 volts. A serious objection to this form of cell arises from the fact that the copper is gradually de- posited over the surface and in the pores of the porous cell, thus greatly increasing its resistance. This difficulty is avoided in the gravity cell. (See Cell, Voltaic, Gravity.} Cell, Voltaic, Double-Fluid A voltaic cell in which two separate fluids or elec- trolytes are employed. One of the elements of the voltaic couple is dipped into one of the fluids and the other ele- ment into the other fluid. In order to keep the fluids separate and distinct, they are either sep arated by means of porous cells, or by the action of gravity. (See Cell, Porous. Ctll, Voltaic^ Gravity.') In the double-fluid cell the negative element is surrounded by a liquid which is capable ot pre- venting polarization by combining chemically with the substance that tends to collect on its surface. In the Daniell cell this substance is the same as that of the negative plate. (See Cell, Voltaic^ Polarization of^ Cell, Toltaic, Dry A voltaic cell in which a moist material is used in place of the ordinary fluid electrolyte. The term dry cell is in reality a misnomer, since all such cells are moistened with liquid electrolytes. The dry cell, like other cells, is made in a variety of forms. The ab- sence of free liquid permits the cell to be closed. A well known form of dry cell shown in Fig. 107. Cell, Voltaic, Effects of I Capillarity iu (See Capillarity, Effects of, in \ Voltaic Cell.) Cell, Voltaic, Exciting Liquid of The elec- trolyte Of a Voltaic Cell. Fig. 107. Dry Cell A voltaic cell may have a single electrolyte, in which case it is called a single-fluid cell, or it may have two electrolytes, in which case it is called a double-fluid cell. Cell, Voltaic, Fuller's Mercury Bichro mate A zinc-carbon couple im- mersed in an electrolyte of electropoion liquid. The zinc is attached to a copper rod by being cast thereto, and is placed at the bottom of a porous cell, where it is covered by a layer of mercury. The carbon plate is placed in electro- Fig. 108 Fuller's Mercury BUhromate Cell. poion liquid, diluted with water in the proportion of three ot the former to two of the latter. The zinc is generally placed in pure water, which rapidly becomes acid. The mercury effects the continuous amalgama- tion of the zinc. A Fuller mercury bichromate cell is showtt in Fig. 108. Cel.] 86 Cell, Toltaic, Gravity A zinc- copper couple, the elements of which are em- ployed with electrolytes of dilute sulphuric acid or dilute zinc sulphate, and a concentrated solution of copper sulphate respectively. The use of a porous cell is open to the objection of increased internal resistance. Moreover, the porous cell is apt to receive a coating of copper Which often deposits on the cell instead of on the .copper plate. The gravity cell was devised in order to avoid the use of a porous cell. As its name indicates, the two fluids are separated from each other by gravity. The copper plate is the lower plate, and is sur- rounded by crystals of copper sulphate. The 7inc, generally in the form of an open wheel, or crow -foot, is sus- pended near the top -. . of the liquid, as shown in Fig. 109. When the cell is set up with sul- phuric acid, the re- actions are the same as in the Daniell cell. When copper sulphate and zinc sulphate alone are used, zinc replaces = the copper in the copper sulphate. The action is then **'"" The Gra ^ CM ' merely a substitutioii process. (See Cell, Voltaic, Danieirs.) A dilute solution of zinc sulphate is generally used to replace the dilute sulphuric acid. It gives a somewhat lower electromotive force, but ensures a greater constancy for the cell. Cell, Voltaic, Grenet A name sometimes given to the bichromate cell. (See Cell. Voltaic, Bichromate^ Cell, Voltaic, Grove A zinc-plati- num couple, the elements of which are used with electrolytes of sulphuric and nitric acids respectively. The zinc, Z, Fig. no, is amalgamated and placed in dilute sulphuric acid, and the platinum, P, in strong nitric add (HNO 8 ) in a porous cell to separate it from the sulphuric acid. (See ( ell, Porous.) In the Grove cell the current is moder- ately constant, since the polarization of the plati- [Cel. num plate is prevented by the nitric acid, which oxidizes and thus removes the hydrogen that tends to be liberated at its surface. The con- stancy of the current is not maintained for any considerable time, since the two liquids are rapidly decom- posed, or consumed, zinc sulphate forming in the sulphuric acid, and water in the nitric acid. The chemical reac- tions are as follows, viz.: Zn 4- H 2 S0 4 = ZnSO 4 -f H 8 ; 6H 4. 2 HNO,= 4H 2 O 4- 2ND; 2NO 4- 8 = N 8 4 . Nitrate of ammo- nium is sometime i formed when the nitric acid becomes dilute by decomposition. The reaction is as follows : 2HNO, 4- 4H 8 = 3H 8 O -f NH 4 NO. The cell gives an electromotive force of 1.93 volts. When the porous cell is good, the resistance of the Grove cell may be calculated according to the following formula of Ayrton: Cell. where d, is the distance in inches between the platinum and zinc plates, and A, the square inches of the immersed portion of the platinum plate. Cell, Toltaic, Leclanche" - A zinc- carbon couple, the elements of which are used in a solution of sal-ammoniac and a finely divided layer of black oxide of manganese respectively. The zinc is in the form of a slender rod and dips into a saturated solution of sal-ammoniac, NH 4 C1. The negative element consists of a plate of car- bon, C, Fig. in, placed in a porous cell, in which is a mixture of black oxide of manganese and broken gas-retort carbon, tightly packed around the carbon plate. By this mean? a greatlv ex tended surface of carbon surrounded by black CeL] oxide of manganese, MnO,, is secured. The entire outer jar, and the spaces inside the porous cell are filled with the solution ot sal-ammoniac. 87 Fig. i IT. The Leclanche Cell. This cell, though containing but a single fluid, belongs, m reality, to the class or type of double- fluid cells, being one in which the negative ele- ment is surrounded by an oxidizing substance, the black oxide of manganese, which replaces the nitric acid or copper sulphate in the other double- fluid cells. This reaction is generally given : Zn + 4NH 4 C1 + 2Mn0 2 = ZnCl a -f 2NH 4 C1 -f 2NH 8 + Mn a 8 + H 8 0. This reaction is denied by some, who believe the following to take place : Zn + 2(NH 4 C1) = ZnCl 8 + 2NH 8 + H 2 . The ZnCl 2 and NH 8 react as follows : ZnCl 2 -f 2(NH 3 ) = 2 (NH 2 ) ZnCl 2 + H 8 . 2H + 2(Mn 2 O 2 ) = H 8 O + Mn 2 O 3 ; or, possibly, 4H -f- 3MnO 8 = Mn 2 O -f- 2H 2 O. The Leclanche cell gives an electromotive force of about 1.47 volts. It rapidly polarizes, and cannot, therefore, give a steady current for any prolonged time. When left on open circuit, how- ever, it quickly depolarizes. Cell, Toltaic, Local Action of (See Action, Local, of Voltaic Cell.) Cell, Yoltaic, Meidin^er A zinc- copper couple, the elements of which are em- ployed with dilute sulphuric acid, or solution of sulphate of magnesia, and strong nitric acid, respectively. The Meidinger cell is a modification of the Daniell cell. The zinc-copper couple is thus ar- ranged : Z Z, Fig. 112, is an amalgamated zinc ring placed near the walls of the vessel, A A, constricted nt b b. The copper element, c, is similarly placed with respect to the walls of the vessel d d. The glass cylinder h, filled with [Cel. crystals of copper sulphate, has a small hole in s bottom, and keeps the vessel, d d, supplied ith saturated so- ution of copper ulphate. The cell charged with di- .te sulphuric acid, or a dilute solution of Epsom salts, or magnesium sul- phate. Cell, Voltaic, Open-Circuit A voltaic cell that cannot be kept on closed cir- cuit, with a com- .^= paratively small resistance, for any Fig. 112. The Meidinger Cell. considerable time without serious polariza- tion. A Leclanche cell is an open-circuit cell. The term open-circuit cell is used in contradistinc- tion to closed-circuit cell, such as the Daniell. (SeeCV//, Voltaic, Closed-Circuit.} Cell, Toltaic, Poggendorff - -A name sometimes given to the Grenet cell. (See Cell, Voltaic, Grenet?) Cell, Voltaic, Polarization of The collection of a gas, generally hydrogen, on the surface of the negative element of a voltaic cell. The collection of a positive substance like hydro- gen on the negative element or plate of a voltaic cell sets up a counter -electromotive force, which tends to produce a current in the opposite direc- tion to that produced by the cell. (See Force, Electromotive, Counter.} Polarization causes a decrease in the normal current of a voltaic cell: (I.) On account of the increased resistance of the cell from the bubbles of gas which form part of its circuit. (2.) On account of the counter-electromotive force, produced by polarization. There are three ways in which the ill effects of the polarization of a voltaic cell can be avoided. These are : (i.) Mechanical. The. negative plate is fur- nished with a roughened surface which enables the Cel.] 88 [Cel. bubbles of gas to escape from the points on such sur- face ; or, a stream of gas, or air, is blown through the liquid against the plate and thus mechanically brushes the bubbles off. (2.) CAemicat.The surface of the negative plate is surrounded by some powerful oxidizing substance, such as chromic or nitric acid , which is capable of oxidizing the hydrogen, and thus thoroughly removing it from the plate. The oxidizing substance may form the entire electrolyte, as is the case of the bichromate solution employed in the zinc-carbon couple. Generally, however, it has been found preferable to employ a separate liquid, like nitric acid, to completely surround the negative plate, and another liquid for the positive plate, the two liquids being generally kept from mixing by a porous cell, or diaphragm. Such cells are called double -fluid cells. (See Cell, Voltaic, Double- Fluid.} (3.) Electro-Chemical. This also necessitates a double-fluid cell. The negative element is im- mersed in a solution of a salt of the same metal as that forming the negative plate. Thus, a cop- per plate, immersed in a solution of copper sul. phate, cannot be polarized, since metallic copper is deposited on its surface by the action of the hydrogen which tends to be liberated there. The constancy of action of a Daniell cell depends on a deposition of metallic copper on its copper plate as well as on the formation of hydrogen sulphate, and the solution of additional copper sulphate from the crystallized salt placed in the cell. (See Cell, Voltaic, Daniell "s.) Cell, Yoltaic, Primary, Exhaustion of The inability of a primary voltaic cell to furnish any further current, unless fresh electrolyte, or fresh positive element, or both, are supplied to it. In the case of exhaustion of a primary voltaic cell the stock of fresh energy is supplied to the cell from the chemical potential energy of the positive element, or of the electrolyte or elec- trolytes. (See Energy, Chemical Potential.} In most voltaic cells a marked decrease in the current strength is observed soon after the cir- cuit is closed, and, therefore, long before the cell is exhausted. This decrease is due (i.) To the increased internal resistance due to the bubbles of hydrogen on the negative plate. (2.) To the counter-electromotive force of po- larization, where zinc is employed with an elec. trolyte of sulphuric acid. (3.) To the decrease in the electromotive fores due to an increase in the density of the zinc sul- phate. Cell, Voltaic, Secondary, Exhaustion of The inability of a secondary cell to furnish any further current, unless fresh electro-positive and electro-negative materials are formed in it by the passage of the charging current. In the case of the exhaustion of a secondary voltaic cell, the stock of fresh energy supplied to the cell is derived from the electric energy of the charging current. (See Energy, Electric. \ Cell, Voltaic, Siemens-Halske A zinc-copper couple, the elements of which are employed with dilute sulphuric acid and saturated solution of copper sulphate respect- ively. The Siemens-Halske cell is a modification of Darnell's. A ring of zinc, Z Z, Fig. 113, sur- Fig. IT 3. Siemens-Ilahke Cell. rounds the glass cylinder, c c. The porous cell is replaced by a diaphragm, f f, of porous- paper, formed by the action of sulphuric acid on. a mass of paper pulp. Crystals of copper sul- phate are placed in the glass jar, c c, and rest on the copper plate, k, formed of a close copper spiral. Terminals are attached at b and h. The entire cell is charged with dilute sulphuric acid. The resistance of the cell is high . Cell, Voltaic, Silver Chloride A zinc and silver couple immersed in electro- lytes of sal-ammoniac or common salt and silver chloride. Cel.] [Cel, The zinc acts as the positive element, and a silver wire, around which a cylinder of fused silver chloride is cast, as the negative element. The zinc, and the silver wire and silver chloride, are placed in a small glass test-tube and covered with the sal-ammoniac or common salt, and the tube closed by a cork of paraffin, to prevent the evaporation of the electrolyte. When sal- ammoniac is used, the strength of the solution is that obtained by dissolving 23 grammes of pure sal-ammoniac in I litre of water. The silver chloride acts as a depolarizer. This cell is used as a standard cell, known as De la Rue's standard cell, from its inventor, Warren De la Rue. Its electromotive force is 1. 068 volts. Cell, Yoltaic, Simple Any voltaic cell formed of a single couple immersed" in a single exciting liquid. Cell, Voltaic, Single-Fluid A vol- taic cell in which but a single fluid or elec- trolyte is used. Single-fluid voltaic cells possess the disadvan- tage of polarizing during action. This polariza- tion is due to the electro-positive element of the electrolyte collecting on the surface of the nega- tive plate, or within its ma?s. For example, where dilute sulphuric acid is the electrolyte, hydrogen gas collects on the negative plate and lowers the electromotive Jorce produced by the cell, by a counter-electromotive force thereby generated. (See Force, Electromotive. Force, Electromotive, Counter. ) Cell, Voltaic, Smee A zinc-silver couple used with an electrolyte of dilute sul- phuric acid, HoSO 4 . A form of Smee cell is shown in Fig. 1 14. Here the plate of silver is placed between two zinc plates. The silver plate is roughened and covered with a coating of metallic platinum, in the condition known as platinum black. (See Platinum Black. ) This cell was formerly extensively employed in electro-metallurgy but is now replaced by dynamo- electric -machines. (See Metallurgy, Electro. Machine, Dynamo Electric. ) A zinc carbon couple is sometimes used to re- place the zinc-silver couple. A couple of zinc- lead is also used, though not very advanta- geously. The Smee cell was one of the earliest forms of voltaic cells. In the zinc-silver couple the chemical reaction that takes place when the cell is furnishing current is as follows, viz.: Zn + H g SO 4 = ZnSO 4 + H 2 . The Smee cell gives an electromotive force of about .65 volt. Cell, Voltaic, Stand- ard A voltaic cell the electromotive force of which is constant, and Fig. 114. Smee Cell. which, therefore, may be used in the measure- ment of an unknown electromotive force. Absolute constancy of electromotive force is impossible to attain, but if the current of the standard cell is closed but for a short time the electromotive force may be regarded as practically invariable. Cell, Voltaic, Standard, Clark's The form of standard cell shown in Fig. 1 1 5. Latimer Clark's standard cell assumes a variety of forms. The H-form is arranged as shown in Fig. 115. The vessel to the left con- tains, at A, an amal- gam of pure zinc. The other vessel contains, at M, mercury covered with pure mercurous sulphate, Hg 8 SO 4 . Both vessels are then filled, above the level of the cross tube, with a saturated solution of zinc sulphate Z, Z, to which a few crystals of the same are added. Tightly fitting corks C, C, prevent loss by Fig. 113. Clark's Stand- evaporation. *rd Cell. The voltage of this cell in legal volts is 1.438 [i 0.00077 (t 15 degrees C.)] (Ayrton.) The value t, is the temperature in degrees of the centigrade scale. Cell, Voltaic, Standard, Rayleigh's Form of Clark's A modified form of Clark's cell. Cel.] 90 [CeL Fig. lib. Rayleigh's Its value in true Form of Clark's Lord Rayleigh's form of Clark's standard cell is shown in Fig. 1 16. The electrodes pass respect- ively through the bottom and top of the test tube of glass. On the lower electrode a layer of mer- cury, Hg, is placed. On this rests a layer of mercu- rous sulphate paste made sufficiently semi-fluid with a solution of zinc sulphate to form an approximately level surface. The zinc, Zn, is attached to the up- per electrode and is im- mersed in this semi-fluid paste. The mercurous sulphate appears to act to keep the mercury free from impuri- ties. The electromotive force ; of this cell has been care- fully determined by Ray- leigh. volts is : Standard Cell. E= 1.435 C 1 .00077 It 15)] when t, is the temperature in degrees Centigrade. This cell is often called Clark's normal element. Cell, Voltaic, Standard, De la Rue's A form of silver-chloride cell. (See Cell, Voltaic, Silver-Chloride '.) Cell, Voltaic, Stand- ard, Fleming's The form of standard cell shown in Fig. 117. The U-tube, Fig. 117, is connected, as shown, by means of taps, with two vessels filled with chemically pure solutions of copper sulphate of sp. gr. i. tat 15 degrees C., and zinc sulphate of sp. gr. 1.4 at 15 degrees C. respectively. To use the cell the zinc rod Zn, con- nected with a wire pass- ing through a rubber stopper, is placed in the left-hand branch. The tap A, is opened and the entire U-tube is filled with the denser zinc sulphate solution. The tap at C, is then Fig. ii 7. Fleming's Standard Cell. opened, and the liquid in the right-hand branch above the tap is discharged into the lower vessel, but, from this part only. The tap C, is then closed, and the tap B, opened, and the lighter copper sulphate allowed to fill the right-hand branch above the tap C. The copper rod Cu, fitted to a rubber stopper and connected with a con- ducting wire, is then placed in the copper solution. Tubes are provided at L and M, for the recep- tion of the zinc and copper rods when not in use. The copper rod is prepared for use by freshly electro-plating it with copper. The electro- motive force of this cell is 1.074 volts. If the line of demarkation between the two liquids is not sharp, the arms of the vessels are emptied, and fresh liquid is run in. Cell, Voltaic, Standard, Lodge's A for.m of standard Daniell cell. Lodge's standard cell is shown in Fig. 118* Through the tube T, in a wide mouthed bottle, is passed the glass tube, in the mouth of which is placed a zinc rod. To the bottom of the tube T, a small test-tube t, containing crystals of cop per sulphate, is fastened by means of a string or rubber band. The uncovered end of a gutta-percha insulated copper wire projects at the bottom of t, through a tube ***' *' 8 ' L ?, sf * . , , ' & , , Form of Daniel's Cell. in a tightly httmg cork, and forms the copper electrode. The bottle is partly filled as shown with a solution of zinc sulphate. The internal resistance of this cell is so high that it is only employed in the use of zero methods with a condenser. Cell, Voltaic, Standard, Sir William Thomson's - A form of standard Daniell cell. Fig. 1 19. Thomson's Form of Danull's Cell. Sir Wm. Thomson's standard cell is shown in Fig. 119. A zinc disc is placed at the bottom of the Cel.] 91 [Cha. cylindrical vessel and a solution of zinc sulphate of sp. gr. 1.2 poured over it. By means of the funnel F, a half-saturated solution of copper sulphate is carefully poured over this and floats on it owing to its smaller density. The etectro- motive force of this cell is 1.072 true volts at 15 degrees C. Cell, Voltaic, Standardizing a De- termining the exact value of the electromotive force of a voltaic cell, in order to enable it to be used as a standard in determining the electromotive force of any other electric source. Cell, Voltaic, Two-Fluid A term sometimes employed in place of double-fluid cell. (See Cell, Voltaic, Double-Fluid) Cell, Voltaic, Water A voltaic cell in' which the exciting liquid is merely water. Any voltaic couple can be used, the positive element of which is acted on by water. (See Battery, Voltaic.} Cell, Voltaic, Zinc-Carbon A cell in which zinc and carbon form the posi- tive and negative elements respectively. A name sometimes given to the bichro- mate cell. Cell, Voltaic, Zinc-Copper A cell in which zinc and copper form the posi- tive and negative elements respectively. Cell, Voltaic, Zinc-Lead A zinc- lead couple sometimes used, though not very advantageously, to replace the zinc-silver couple in a Smee cell. (See Cell, Voltaic, Smee.) Cells, Coupled A number of sep- arate cells connected in any way so as to form a single source. Cells, Voltaic, Series-Connected A number of separate voltaic cells connected in series so as to form a single source. (See Circuit, Series,?) Cement-Lined Conduit. (See Conduit. Cement-Lined?) Cements, Insulating Various mixtures of gums, resins and other substances, possessing the ability to bind two or more substances together and yet to electrically in- sulate one from the other. Centi. (As a prefix) The one-hundredth part of. Centi-Ampgre. One-hundredth of an am- pere. Centi-Ampere Balance. (See Balance, Centi- Ampere.) Centigrade Thermometer Scale. (See Scale, Centigrade Thermometer?) Centigramme. The hundredth of a gramme One centigramme equals 0.1544 grains avoir- dupoise. (See Weights and Measures, Metric System of.) Centilitre. The hundredth of a litre. One centilitre equals 0.6102 of a cubic inch. (See Weights and Measures, Metric System of.) Centimetre. The hundredth of a metre. One centimetre equals 0.3937 inch. (See Weights and Measures, Metric System of. ) Centimetre-Gramme-Second Units. (See Units. Centimetre-Gramme-Second.) Central Galvanization. (See Galvaniza- tion, Central.) Central Station. (See Station, Central.) Central Station Burglar Alarm. (See Alarm, Burglar, Central Station.) Central Station Lighting. (See Light- ing, Electric Central Station?) Centre of Gravity. (See Gravity, Centre of) Centre of Oscillation. (See Oscillation, Centre of.) Centre of Percussion. (See Percussion, Centre of?) Centrifugal Force. (See Force, Centrifu- gal.) Centrifugal Governor. (See Governor, Centrifugal?) Chain Lightning. (See Lightning, Chain?) Chain, Linked Magnetic and Electric A chain of three links, the separate links of which consist of the primary circuit. Cha.J [Cha. the magnetic circuit, and the secondary cir- cuit respectively, of an induction coil. The conception of a linked magnetic and elec- tric chain, in studying the action of an induction coil, was first developed by Kapp. A linked magnetic and electric chain is shown in Fig. 120. Fig. 120. Linked Magnetic and Electric Chain. If, in such a case, the magnetic core or circuit is of varying magnetization, when one of the electric circuits has a periodic current passed through it, the'various phenomena of the induction coil are produced. (See Coil, Induction.) Chain, Molecular A polarized chain of molecules that is supposed to exist in an electrolyte during its electrolytic decomposi- tion, or in a voltaic cell on closing its circuit. (See Hypothesis, Grotthus.) Chain Pull. (See Pull, Chain.) Chamber, Armature The armature bore. (See Bore. Armature?) Chamber of Lamp. (See Lamp, Cham- ber of.) Change, Chemical Any change in matter resulting from atomic combination and the consequent formation of new mole- cules. Some chemical changes are caused by atomic combinations and the formation of new molecules. They are necessarily attended by 3 loss of the spe- cific identity of the substances involved in the change. Thus carbon, a black solid, combined with sulphur, a yellow solid, produces carbon disulphide, a colorless, odorous liquid. (See Atom.) Change, Physical Any change in matter resulting from a change in the relative position of its molecules, without the forma- tion of new molecules. Ice, when heated, is turned into water; steel, when stroked by a magnet, is rendered perma- nently magnetic; a piece of vulcanite or hard rubber stroked by a piece of cat skin becomes electrified. In all these cases, which are instances of physical changes, the substances retain their specific identity , This is true in all cases of phys- ical changes. (See Molecule.) Changing-over Switch. (See Switch, Changing-over) Changing Switch. (See Switch, Chang- ing.) Characteristic Curve. (See Curve, Characteristic!) Characteristic Curve of Parallel Trans- former. (See Curve, Characteristic, of Parallel Transformer) Characteristic Curve of Series Trans- former. (See Curve, Characteristic, of Series Transformer) Characteristics of Sound. (See Sound, Characteristic of.) Charge, Bound The condition of an electric charge on a conductor placed near another conductor, but separated from it by a medium through which electrostatic induc- tion can take place. (See Induction, Elec- trostatic) When a charged conductor is placed near an- other conductor, but separated from it by a di- electric or medium through which induction can take place, a charge of the opposite name is in- duced in the neighboring conductor. This charge is so held or bound on the conductor by the mu- tual attraction of the opposite charge that it is not discharged on connection with the eai n i unless both conductors are simultaneously touched by any good conductor. The bound charge was formerly called dissimulated or latent electricity. (See Electricity, Dissimulated or Latent.) Charge, Density of The quantity of electricity per unit of area at any point on a charged surface. Coulomb used the phrase surface density to mean the quantity of electricity per unit of area at any point on a surface. Charge, Dissipation of The gradual but final loss of any charge by leakage, which occurs even in a well insulated conductor. This loss is more rapid with negatively charged conductors, than with those positively charged. ha.] [Cha. Crookes, of England, has retained a charge on conductors for years, without appreciable leakage, by placing the conductors in vessels in which a high vacuum was maintained. (See Vacuum, Charge, Distribution of - -- The vari- ations that exist in the density of an electrical charge at different portions of the surface of all insulated conductors except spheres. The density of charge varies at different points of the surface of conductors of various shapes. It is uniform at all points on the surface of a sphere. It is greater at the extremities of the longer axis of an egg-shaped body, and greatest at the sharper end. It is greater at the corners of a cube than at the middle of a side. It is greatest around the edge of a circular disc. It is greatest at the apex ot a cone. Charge, Electric -- The quantity of electricity that exists on the surface of an in- sulated electrified conductor. When such a conductor is touched by a good conductor connected with the earth, it is dis- charged. (See Condenser.) Charge, Free -- The condition of an electric charge on a conductor isolated from any other conductor. It is impossible to obtain a perfectly free charge, since it is impossible to completely isolate an insulated conductor. The charge, however, can be comparatively free. The charge, on a completely isolated conductor readily leaves it when iti> put in contact with a good conductor connected with the ground. (See Charge, Bound.') Charge, Induced Electrostatic ---- The charge produced by bringing a body into an electrostatic field. In order to obtain a permanent charge, i. e., a charge which will be maintained when the body is withdrawn from an electrostatic field, it is nec- essary to connect the body with the earth so that it may lose, or part with a charge of the same name as the inducing charge. Then, on the with- drawal of this charge, it wiM possess a charge op- posite in name to the inducing charge. (See Condenser.) Charge, Influence -- A charge pro- duced by electrostatic induction. (See In- duct ion, Electrostatic) Charge, Negative According to the double-fluid hypothesis, a charge of negative electricity. According to the single-fluid hypothesis, any deficit of an assumed electrical fluid. Charge, Positive According to the double-fluid hypothesis, a charge of positive electricity. According to the single-fluid hypothesis, any excess of an assumed electrical fluid. Charge, Residual The charge pos- sessed by a charged Leyden jar for a few moments after it has been disruptively dis- charged by the connection of its opposite coatings. The residual charge is probably due to a species of dielectric strain, or a strained position of the molecules of the glass caused by the charge. Such residual charge is not present in air con- densers. In other words, a Leyden jar does not give up all the electric energy charged in it, on a single disruptive discharge. Charge, Return A charge induced in neighboring conductors by a discharge of lightning. Under the influence of induction a lightning stroke produces during its discharge an electric shock in the human body, or a charge in neigh- boring bodies, which is called the back or re- turn stroke of lightning. (See Stroke, Light- ning^ Back or Return.") Charged Body. (See Body. Charged) Charging Accumulators. Sending an electric current into a storage battery for the purpose of rendering it an electric source. There is, strictly speaking, no accumulation of electricity in a storage battery, such, for example, as takes place in a condenser, but a mere storage of chemical energy, which may afterward become electric. (See Cell, Storage.) Charging Leyden Jars by Cascade. (See Cascade, Charging Leyden Jars by) Chart, Inclination A map or chart on which the isoclinic lines are marked. (See Map or Chart, Inclination. Lines Isoclinic^ Cha.] [Chr. Chart, Isodynamic A map or chart on which the isodynamic lines are marked. (See Map or Chart, Isodynamic. Lines, Isodynamic?) Chart, Isogonal An isogonic chart. (See Map or Chart, Isogonal.} Chart, Isogonic A map or chart on which the isogonic lines are marked. (See Map or Chart, Isogonic. Lines, Isogonic?) Chatterton's Compound. (See Com- pound, Chatter ton's.) Chemical Change. (See Change, Chem- ical) Chemical Effect. (See Effect, Chemical?) Chemical Equivalent. (See Equivalent, Chemical?) Chemical Galvano-Cautery. (See Cau- tery, Galvano-Chemical) Chemical Phosphorescence. (See Phos- phorescence, Chemical) Chemical Photometer. (See Photometer, Chemical) Chemical Potential Energy. (See En- ergy, Chemical Potential) Chemical Recorder, Bain's (See Recorder, Chemical, Bain's) Chemistry, Electro That branch of electric science \\tfiich treats of chemical compositions and decompositions effected by the electric current. (See Electrolysis. De- composition, Electrolytic?) That branch of chemistry which treats of combinations and decompositions by means of electricity. Electro-chemistry treats of the formation of new molecules, by the combination of atoms under the electric force, as well as the decomposition of molecules by electricity. The action of a series of sparks passed through air, in forming nitric acid, is an instance of the former, and electrolytic decompositions in gen- eral afford instances of the latter. Chimes, Electric Bells rung by the attractions and repulsions of electrostatic charges. The bells B and B, Fig. 121, are conductively connected to \hsprime or positive conductor +, of a frictional machine. The bell C, is insulated from this conductor by means of a silk thread, but is connected with the ground by the metallic chain. Under these circumstances the clappers, 1, 1, insu- lated by silk threads, t, t, are attracted to B, B, by an induced charge and repelled to C, where they lose their charge only to be again attracted to B, B. In this way the bells will con- tinue ringing as long as the electric ma- chine is in operation. Choking Coil. (See Coil, Choking?) Chronograph, Electric An elec- tric apparatus for automatically measuring", and registering small intervals of time. Chronographs, though of a variety of forms, generally register small intervals of time by causing a tuning fork or vibrating bar of steel, whose rate of motion is accurately known, to trace a sinuous line on a smoke-blackened sheet of paper, placed on a cylinder driven at a uni- form rate of motion by clockwork. If the fork is known to produce, say, 256 vibrations per second be used, each sinuous line will represent g^ part of a second. Fig. ISZ. Electric Chimes, Ch ronograph . An electro-magnet is used to make marks on the line at the beginning and the end of the observation, and thus permit its duration to be measured. In the form of electric chronograph shown Chr.] 95 [Cir. in Fig. 1.22, an electro-magnet, the armature of which carries a pen, is supported on a carriage moved by clockwork over a sheet of paper wrapped on a rotating cylinder. A clock is so connected with the circuit of the electro-magnet that it makes or breaks the circuit at the end of every second second, and so moves, or displaces, the armature, as to cause an elevation or depres- sion in the otherwise continuous sinuous line, that would be drawn on the paper by the double motion of its rotation and the movement of the pen-carriage. When it is desired to know with great precision the exact time of occurrence of any event, such, for example, as the transit of a star over the meridian, the observer, who carries in his hand a push button, or other form of electric key, closes or opens the circuit at the exact moment and so superposes an additional mark on the sinuous line. Since the exact time of starting the clock is known, and the intervals between the regular successive marks are two seconds each, it is easy to estimate from its position between any two such marks the exact value of the additional mark inter- posed. Fig. 122, taken from Young, shows a form of chronograph by Warner & Swasey. The de- tails of this apparatus will be understood from an inspection of the drawing. Chronograph Record. (See Record, Chronograph) Chronoscope, Electric An appa- ratus for electrically indicating, but not necessarily recording, small intervals of time. This term is ofteu used for chronograph. The interval of time required for a rifle ball to pass between two points may be determined by causing the ball to pierce two wire screens placed a known distance apart. As the screens are successively pierced, an electric circuit is thus made or broken, and marks are registered electrically on any apparatus moving with a known velocity. Cigar-Lighter, Electric (See Lighter, Cigar, Electric?) Cipher Code. (See Code, Cipher.) Circle, Azimuth - The arc of a great circle passing through the point of the heavens directly overhead, called the Zenith, and the point directly beneath, called the Nadir. Circle, Dipping A term some- times applied to an inclination compass. (See Compass, Inclination.'} Circle, Galvanic A term some- times used for galvanic circuit. (See Circuit, Galvanic.") Circle of Reference. The circle, by refer- ence to which simple harmonic motion may be studied, by comparison with uniform mo- tion around such circuit. (See Motion, Simple Harmonic.) Circle, Voltaic A name formerly employed for voltaic cell or circuit. (See Cell, Voltaic. Circuit, Voltaic.) Circuit, Air-Magnetic That part of the path of a line of magnetic induction which takes place wholly through air. Circuit, Alternating Current A circuit in which an alternating current of electricity is flowing. (See Current, Alter- nating^) Circuit, Astatic A circuit consist- ing of two closed curves enclosing equal sur- faces. Such a circuit is not deflected by the action of the earth's field. The circuit dis- posed, as shown in Fig. 123, is astatic and produces two equal and opposite fields at S and S'. (See Mag- Fig- '23. Astatic Circuit, netism, Ampere's Theory of.) Circuit, Balanced-Metallic A me- tallic circuit, the two sides of which have similar electrical properties. Circuit Breaker. (See Breaker, Circuit) Circuit, Broken An open circuit. A circuit, the electrical continuity of which has been disturbed, and through which the current has therefore ceased to pass. Circuit, Closed A circuit is closed, completed, or made when its conducting continuity is such that the current can pass. Circuit, Closed Iron-Magnetic The name applied to the path of any line dr.] of magnetic force, which takes place entirely through iron, steel, or other paramagnetic sub- stance. Circuit, Closed-Loop Parallel A variety of parallel circuit in which the lead and the return circuit are arranged in the form of concentric circuits, with the recep- tive devices placed radially between them. Circuit, Closed-Magnetic A mag- netic circuit which lies wholly in iron or other substance of high magnetic permeability. All lines of magnetic force form closed circuits. The term closed-magnetic circuit is used in con- tradistinction to a divided circuit, or one in which an air gap exists in the substance of high mag- Fig. 124. Closed-Magnetic Circuit. netic permeability forming the remainder of the circuit. This introduces so high a resistance that such a circuit is sometimes called an open-mag- netic circuit. An iron ring, such as shown in Fig. 124, forms a closed -magnetic circuit. Circuit, Closed-Magnetic, of Atom A closed-magnetic circuit, or closed lines of magnetic force supposed to lie entirely in the atom itself. The assumption of closed lines of magnetic force in atoms or molecules was made in order to explain the original polarity of the same, and to account for some of the other phenomena of magnetism. When the atom is subjected to a magnetizing force, such, for example, as the field of an electric current, these closed lines of force are assumed to open out and produce lines of polarized atoms. According to Lodge, for every single line of force produced by the current passing through a coil of wire surrounding an iron core, some 3,000 lines of magnetic force are added to it from the iron. Therefore an iron core greatly increases the magnetic strength of a hollow coil of wire. J [Cir. Circuit, Closed-Magnetic, of Molecule A closed-magnetic circuit assumed to lie wholly within the molecule. As it is not known whether the assumed mag- netic circuit lies within the atom or the molecule, it is called indifferently the closed-atomic or closed-molecular circuit. (See Circuit, Closed- Magnetic, of Atom.) Circuit, Completed A closed circuit. A circuit, the conducting continuity of which is unbroken. A completed circuit is also called a made or closed circuit. Circuit, Compound A circuit con- taining more than a single source, or more than a single electro-receptive device, or both, connected by conducting wires. The term compound circuit is sometimes ap- plied to a series circuit. (See Circuit, Series.) The term, however, is a bad one, and is not generally adopted. Circuit, Constant-Current A cir- cuit in which the current or number of am- peres is maintained constant notwithstanding changes occurring in its resistance. The series-circuit, as maintained for arc-lamps, is a constant-current circuit. (See Regulation, Automatic.) Circuit, Constant-Potential A circuit, the potential or number of volts of which is maintained approximately constant. The multiple-arc or parallel circuit is an ap- proximately constant-potential circuit. Circuit, Derivative A derived or shunt circuit. (See Circuit, Shunt.) Circuit, Derived Q A term applied to a shunt circuit. If, in addition to the galva- nometer G, the conductor S, Fig. 125, be connected with the circuit of the battery B, a derived circuit will thus be established, and a current will flow through S, diminishing '*" the current in the galvanom- eter. (See Circuit, Shunt.) Cir.] 9? [Cir. Circuit, Divided-Magnetic A magnetic circuit which lies partly in iron, or other substance of high magnetic perme- ability, and partly in air. A divided-magnetic circuit is shown in Fig. 126. Fig. 126. Divided Magnetic Circuit. Where the iron ring is separated by the air gap, a high magnetic resistance is introduced, owing to the fact that the iron is at these points replaced by air, whose magnetic reluctance is great. Circuit, Double-Wire A term sometimes used for a simple multiple circuit with two conductors or wires. (See Circuit, Multiple.) The term double-wire circuit is used in contra- distinction to single-wire circuit. (See Circuit, Single-Wire.} Circuit, Earth A circuit in which the ground or earth forms part of the con- ducting path. Circuit, Earth, Telegraphic That portion of a telegraphic circuit which is completed through the earth or ground. Circuit, Electric The path in which electricity circulates or passes from a given point, around or through a conducting path, back again to its starting point. All simple circuits consist of the following parts, viz.: (I.) Of an electric source which may be a voltaic battery, a thermopile, a dynamo-electric machine, or any other means for producing elec- tricity. (2.) Of leads or conductors for carrying the electricity out from the source, through whatever apparatus is placed in the line, and back again to the source. (3.) Various electro-receptive devices, such as electro-magnets, electrolytic baths, electric motors, electric heaters, etc., through which passes the current by which they are actuated or operated. Circuit, Electrostatic The circuit formed by lines of electrostatic force. Lines of electrostatic force, like lines of mag- netic force, form closed circuits. Hence the origin of the phrase electrostatic circuit. (See Force, Electrostatic, Lines of.) Circuit, External - That part of a circuit which is external to, or outside the elec- tric source. The circuit external to the source consists of two distinct parts, viz. : (I.) The conductors or leads. (2 ) The electro-receptive or translating de- vices. It is in the external circuit only that useful work is done by the current. Circuit, Forked A term sometimes used in telegraphy for a number of circuits that radiate from a given central point. Circuit, Galvanic A tern some- times employed instead of voltaic circuit. The term galvanic in place of voltaic is unwar- ranted by the facts of electric science. (See Cir- cuit, Voltaic. ) Galvani thought he had discovered the vital fluid or source of animal life. Volta first pointed out the true explanation of the phenomena ob- served in Galvani's frog, and devised means for producing electricity in this manner. The terms voltaic battery, cell, circuit, etc., are there- fore preferable. Circuit, Ground A circuit in which the ground forms part of the path through which the current passes. As the ground is not always a good conductor, the terminals should be connected with the gas or water pipes, or with metallic plates, called ground plates. Such connection, or any similar ground connection, is usually termed the ground or earth. Circuit, Ground, Telegraphic - An earth circuit used in any system of telegra- phy. (See Circuit, Earth, Telegraphic!) Circuit, Grounded A ground cir- cuit. Circuit, Incomplete An open or broken circuit. Cir.] 98 [Cir. A circuit whose conducting continuity is incomplete. Circuit, Inductive Any circuit in which induction takes place. Circuit, Internal That part of a circuit which is included within the electric source. The electric current passing through the inter- nal circuit does no useful work. Circuit, Leg of One part of a twisted or metallic circuit. Circuit, Line The wire or other conductors in the main line of any telegraphic or other electric circuit. Circuit, Line, Telegraphic The conductor or line connecting different tele- graphic stations. Circuit, Local-Battery The cir- cuit, in a telegraphic system, in which is placed a local battery as distinguished from a main battery. (See Telegraphy, American or Morse System of.) Circuit, Loop A term sometimes applied to a circuit in parallel or multiple-arc. (See Circuit, Multiple.} Circuit Loop Break. (See Break, Circuit Loop.} Circuit, Made A completed circuit. A circuit, whose conducting continuity is unbroken. A made circuit is often called a completed or closed circuit. (See Circuit, Closed.) Circuit, Magnetic The path through which the lines of magnetic force pass. All lines of magnetic force form closed circuits. is often placed around the magnet. The magnet is then said to be iron-clad. The armature of a magnet lowers the magnetic resistance by affording a better path for the line 5 of magnetic force than the air between the poles. The magnetic circuit always tries to shorten its path, or to render itself as compact as possible. This is seen in the action of an armature drawn towards a magnet pole. Circuit, Main-Battery A term sometimes used for line circuit. (See Circuit, Line.} Circuit, Metallic A circuit in which the ground is not employed as any part of the path of the current, metallic conductors being employed throughout the entire circuit. Circuit, Multiple A compound cir- cuit, in which a number of separate sources or separate electro-receptive devices, or both, have all their positive poles connected to a single positive lead or conductor, and all their negative poles to a single negative lead or conductor. The connection of three Bunsen cells, in mul- tiple, is shown in Fig. 128, where the three car- Fig. 127. Magnetic Circuit. In the bar magnet, shown in Fig. 127, part of this path is through the air. In order to reduce or lower the resistance of a magnetic circuit, iron Fig. 128. Batteries connected in a Multiple Circuit. bons, C, C, C, are connected together so as to form the positive, or -\- terminal of the battery, and the three zincs, Zn, Zn, Zn, are similarly con- nected together so as to form the negative, or terminal. The electromotive force is the same as that of a single cell, or source. The internal resistance of the source is as much less than the resistance of any single source as the area of the combined negative or positive plates is greater than that of any single negative or positive plate ; or, in other words, is less in proportion to the number of cells, or other separate sources so coupled. The connection of six cells in multiple or parallel circuit, is shown in Fig. 129. Cir.j In the case of the six cells, the current would be, E where E, is the electromotive force, r, the in- ternal, and r', the external resistance. [Cir. sources, or separate electro-receptive devices, or both, are connected in a number of sepa- rate groups in series, and these separate groups subsequently connected in multiple. In Fig. 130, a multiple-series circuit of six Fig. 129. Six Cells Connected in Multiple. In the case of voltaic cells the effect of multiple connection on the internal resistance of the source is to increase the area of cross-section of the liquid in the direct proportion of the number of cells added, and consequently to decrease the re- sistance in the same proportion. When strong or large currents of low electro- motive force are required, connections in multi- ple-arc are generally employed. The multiple-arc connection was formerly called connection-far -quantity. This term is now abandoned. The total resistance for the parallel circuit is obtained as follows: calling the separate resist- ances of the separate electro-receptive devices, R', R", R'", etc., etc., etc., total resistance, _ R' X R" X R'" R' R" -f- R" R"' R' R' or, what is the same thing, the conductivity is the sum of the reciprocal of the separate resistances, i. e. : Conductivity = -^-r -f -j^r The joint resistance of only two separate resist- ances joined in a multiple-circuit is equal to the product of the separate resistances divided by their sum. When the separate resistances joined in multiple arc are all of the same value, the joint resistance is equal to the resistance of one of them divided by their number. Circuit, Multiple-Arc A term often used for multiple circuit. (See Circuit, Mul- tiple.} Circuit, Multiple-Series -- A com- pound circuit in which a number of separate J Fig. 130. Mulliple-Series-Connected ails. sources is shown, in which three separate groups of two series-connected cells are coupled in multi- ple. The current takes the paths indicated by the arrows. The electromotive force of the source will be increased in proportion to the number of cells in series, and the internal resistance de- creased in proportion to the number in parallel. Fig. 131. Cells Connected in Multiple- Series. _ 3E In Fig. 131, six cells are arranged in two groups of three series-connected cells, and these three groups connected in parallel. Calling r, the resistance of each separate cell, the total resistance for the multiple-series circuit for a circuit containing three cells in parallel and two in series is, T, 2r 3 for three in series and two in parallel, R= -7- If, therefore, the circuit of this battery be closed by a resistance equal to r, the current would be in the case of Fig. 130, c _ 2E +r". Cir.l 100 [Cir, Circuit, Negative Side of The side of a circuit opposite to the positive side. (See Circuit, Positive Side of.) That side or half of a circuit connected to or leading from the positive terminal of the source of current. Circuit, Open A broken circuit. A circuit, the conducting continuity of which is broken. Circuit, Open-Iron Magnetic The path of a line of magnetic induction, which passes partly through iron, and partly through an air space. The magnetic circuit is always closed, that is the lines of magnetic force always form closed paths. The term "open" is used in contradis- tinction only to "closed " iron magnetic circuit, in which the entire path of a line of force passes through iron. (See Circuit, Magnetic.) Circuit, Parallel A name some- times applied to circuits connected in mul- tiple. (See Circuit, Multiple.) Circuit, Parallel-Tree A form of parallel circuit in which the receptive devices are placed in parallel between the leads and returns, and the branches and sub-branches arranged in a tree-like form. Circuit, Positive Side of That side of a circuit, bent in the form of a circle, in which, if an observer stood with his head in the positive region, he would see the current pass round him from his right hand towards his left. (Daniell) Circuit, Recoil A term sometimes applied to the circuit that lies in the alterna- tive path of a discharge. (See Path, Alter- native.} Circuit, Return - That part of a circuit by which the electric current returns to the source. In . multiple-circuit the lead that is con- nected to the negative terminals of the separate sources. Circuit, Series A compound cir- cuit in which the separate sources, or the sep- arate electro-receptive devices, or both, are so placed that the current produced in each, or passed through each, passes successively through the entire circuit from the first to the last. The six cells, shown in Fig. 132, are connected in series by joining the positive pole of each cell with the negative pole of the succeeding cell, the negative and positive poles at the extreme ends Fig. 132. Series Circuit. being connected by conductors with the external circuit. The connection of three Leclanche cells in series is clearly shown in Fig. 133. The carbons, -- C +Zn- C > . Voltaic Cells Connected in Series. C, C, of the first and second cells are connected to- the zincs, Zn, Zn, of the second and third cells, thus leaving the zinc, Zn, of the first cell, and the carbon, C, of the third cell, as the terminals of the battery. The direction of the current is shown by the arrows. The resistance of such a connection is equal to the sum of the resistances of all of the separate sources. The electromotive force is equal to the sum of the separate electromotive forces. If the electromotive force of a single cell is equal to E, its internal resistance to r, and the resistance of the leads and electro -receptive de- vices to r', then the current in the circuit, If six of such cells are coupled in series, the cur- rent becomes 6E If, however, the internal resistance of each cell be so small as to be neglected, the formula becomes c-f, Cir.] 101 [Cir. or the current is six times as great as with one cell. The total resistance of the separate sources or electro-receptive devices of the series circuit is as follows, calling R', R", R' , etc., the separate resistance and R, the total resistance, R = R' + R" -f R '', etc. The series connection of battery cells is used on telegraph lines, where a high electromotive force is required in order to overcome a consider- able resistance in the circuit, or in simil ir cases where the resistance in the external circuit is great, on account of a number of electro receptive devices being connected to the line in series. The series connection was formerly called connection for intensity. The term is now aban- doned. Circuit, Series-Multiple -- A com- pound circuit, in which a number of separate sources, or separate electro-receptive devices, or both, are connected in a number of sepa- rate groups in multiple-arc, and these sepa- rate groups subsequently connected in series. In the series multiple circuit the resistance of each multiple group is equal to the resistance of a single branch divided by the number of branches. If, for example, r, is the resistance of each sepa- rate branch of say seven parallel circuits in each of the separate groups of multiple circuits, then the resistance, R, of each separate multiple group is The total resistance of the series-multiple cir- cuit is equal to the sum of the resistances of the separate multiple groups. The total resistance of the three groups is R = - + L + L = JL 7777 An example of the series-multiple circuit is shown in Fig. 134, which is the method adopted f'ff- 134- Series-Multifile Circuit. in the use of distribution boxes. Here a number of multiple groups or circuits are connected with each other in series, as shown. (See Box, Dis- tribution, for Arc Light Circuits.) Circuit, Short A shunt, or by-path. of comparatively small resistance, around the poles of an electric source, or around any portion of a circuit, by which so much of the current passes through the new path, as vir- tually to cut out the part of the circuit around which it is placed, and so prevent it from re- ceiving an appreciable current. Circuit, Shunt A branch or addi- tional circuit provided at any part of a cir- cuit, through which the current branches or divides, part flowing through the original cir- cuit, and part through the new branch. A shunt circuit is in multiple circuit with the circuit it shunts. In the case of branch circuits each of the cir- cuits acts as a shunt to the others. Any number of additional or shunt circuits may be thus pro- vided. (See Laws, Kirchhofs.) Circuit, Simple A circuit containing a single electric source, and a single electro- receptive device, connected by a conductor. The term simple circuit is sometimes applied to a multiple circuit. The term is not, however, a good one, and is not in general use. Circuit, Single- Wire A term some- times used for a grounded circuit. (See Circuit, Grounded?) The single-wire circuit is sometimes used in the distribution of incandescent lamps in multiple-arc. One pole of the dynamo is put to ground, and the other pole to a single wire or lead. The electro- receptive devices have one of their poles con- nected to th s lead and the other pole to earth. The single-wire circuit is a very objectionable circuit so far as safety is concerned. It is frequently u^ed, however, in the wiring of ships. Circuit, Through A telephonic or telegraphic circuit that has been completed through to a given station by cutting out inter- ruptions or breaks in the line by the connec- tion together of sections of different wires. Circuit, Time-Constant of The time in which a current due to a constant electromotive force will rise in a conductor to a definite fraction of its maximum value. The ratio of the inductance of a circuit to its resistance. Cir.] 102 [Cle. The time required from the moment of closing the circuit, for a current to rise to a value equal to e of the full value, or .632 of the maximum value. In the above, e, equals 2.71828, or the base of the Napierian system of logarithms. The time-constant is proportional to the con- ductivity of the circuit and its formal resistance. Approximately the time constant of a circuit is the time from closing the circuit, in which the current rises to two-thirds of its maximum value, this maximum value being determined by the formula, C = ?. R Thetime-constant of a circuit may be reduced (i.) By decreasing the self-induction of the cir- cuit. (2.) By increasing the resistance. In the case of a magnetic conductor the time- constant is proportional to a quantity (the perme- ability) which is determined by the capacity of the conductor to utilize part of the energy in producing magnetization of its substance. (Flem- ') Circuit, Voltaic The path through which the current flows out from a voltaic cell or battery, through the translating devices and back again to the cell or battery. Circuits, Forked A term employed in telegraphy to indicate circuits that radiate from any single point. Forked circuits are employed in simultaneously transmitting messages to several stations. Circuits, Varieties of Conducting paths provided for the passage of an electric current. Electric circuits may be divided, according to their complexity, into (I.) Simple. (2.) Compound. According to the peculiarities of their connec- tions, into (i.) Shunt or derived. (2.) Series. (3.) Multiple, multiple-arc or parallel. ' (4.) Multiple-series. {5.) Series-multiple. Either the circuits, the sources, or the electro- receptive devices may be connected in series, in multiple, in multiple-series or in series-multiple. According to their resistance, circuits are divided into (i.) High-resistance. (2.) Low-resistance. According to their relation to the electric source, into (i.) Internal circuits. (2.) External circuits. According to their position, or the work done, circuits are divided into very numerous classes; thus, in telegraphy, we have the following, viz.: (i.) The line-circuit. (2.) The earth or ground circuit. (3.) The local-battery circuit. (4.) The main-battery circuit, etc. Circular Bell. (See Sell, Circular.} Circular Units. (See Units, Circular) Circular Units (Cross-Sections), Table of (See Units, Circular (Cross-Sec- tions), Table of.) Clamp, Carbon A carbon clutch. (See Clutch, Carbon, of Arc Lamp?) Clamp for Arc Lamps. A clamp for gripping the lamp-rod, /. e., the rod that sup- ports the carbon electrodes of arc lamps. (See Lamp, Electric, Arc.) Clamp, Rod A carbon clutch. (See Clamp for Arc Lamps?) Clark's Compound. (See Compound, Clark's?) Clark's Standard Voltaic Cell. (See Cell, Voltaic, Standard, Clark's) Clark's Standard Voltaic Cell, Ray- leigh's Form of (See Cell, Voltaic, Standard, Ray leigh's Form of Clark's?) Clay Electrode. (See Electrode, Clay) Cleansing, Fire The removal of grease from metallic articles, that are to be electro-plated, by subjecting them to the action of heat. This cleansing is for the purpose of obtaining a uniform, adherent coating. Clearance-Space. (See Stace. Clearance} le.] 103 [Clo. Cleariiig-Out Drops. (See Drops, Clear- ing-Out) Cleat, Crossing A cleat so arranged as to permit the crossing of one pair of wires under or over another pair without contact with each other. Cleat-Wiring 1 . (See Wiring, Cleat) Cleats, Electric Suitably shaped pieces of wood, porcelain, hard rubber or other non-conducting material used for fasten- ing and supporting electric conductors to ceilings, walls, etc. A simple form of wooden cleat is shown in Fig- 135- Fig. 135. Wooden Cleat. Clepsydra, Electric An instrument ior measuring time by the escape of water or other liquid under electrical control. Climbers, Pole Devices employed by linemen for climbing wooden telegraph poles. A climber with straps for attachment to the leg and foot is shown in Fig. 136- Clip, Cable A term sometimes used for cable hanger. (See Hanger, Cable.) Clock, Electric A clock, the works of which are moved, COn- Fig. 136. Climber and trolled, regulated or straps. wound, either entirely or partially, by the elec- tric current. Electric clocks may be divided into three classes, viz.: (i.) Those in which the works are moved en- tirely or partially by the electric current. (2.) Those which are controlled or regulated by the electric current. (3-) Those which are merely wound by the current. A clock moving independently of electric power is prevented from gain- ing or losing time, by means of a slight re- tardation or acceleration electrically imparted . The entire motion of the balance wheel sometimes imparted by electricity. An example of one oi many forms of controll- ing electric clocks is shown in Fig. 137, where the split battery (See Battery, Split), P N, is connected, as Fig. 137- Controlling: shown, to the spring Clock. contacts S and S'. In this way currents are sent into the circuit in alternately opposite directions. The pendulum bob, Fig. 138, of the con- trolled clock is formed of a hollow coil of insu- lated wire, which encircles one or both of two permanent magnets, A and A', placed with their opposite poles facing each other. When the pendulum of the controlling clock is in the position shown in Fig. 137, the current passes in the direction E P Sn W, etc. , and through the coil C, Fig. 138. When the pendulum of the controlling clock is in con- tact with S', the current flows through Wn S' N E, etc., and through the coil C in the opposite direc- tion. In this manner a slight motion forwards or backwards is imparted to the pendulum, which is thus kept in time with the controlling clock. Mercury contacts are sometimes employed in place of the springs S and S'. Induction currents may A also be employed. Clocks of non-electric ac- Fig. 138. Controlled tion may be electrically Clock ' controlled, or correctly set at certain intervals, either automatically by a central clock, or by the depression of a key operated by hand from an astronomical observatory. > . Clo.] 104 [Clo. In a system of time-telegraphy, the controlling clock is called the master clock, and the con- trolled clocks, the secondary clocks. Secondary clocks are generally mere dials, con- . T39' Mechanism of Secondary Clock. taining step-by-step movements, for moving the hour, minute and second hands, as shown in Fig- 139- In Spellier's clock, a series of armatures H, Fig. 140, mounted on the circumference of a Fig. 140. Spellier's Electric Clock, wheel, connected with the escapement wheel, pass successively, with a step-by-step movement, over the poles of electro-magnets. On the com- pletion of the circuit, they are attracted towards the magnet, and on the breaking of the circuit they are drawn away by the fall of the weight F, placed on the lever D, pivoted at E. A pulley at E, runs over the surface of a peculiarly shaped cog on the escapement wheel. Clock, Electric Annunciator A clock, the hands or works of which, at cer- tain predetermined times, make electric con- tacts and thus ring bells, release drops, trace records, etc. Clock, Electrical-Controlling In a system of time telegraphy, the master clock, whose impulses move or regulate the second- ary clocks. (See Clock, Electric) Clock, Electrically-Controlled In a system of time telegraphy, a secondary clock, that is either driven or controlled by the master clock. (See Clock, Electric) Clock, Electrolytic, Tesla's A time piece in which the rotation of the wheel work is obtained by the difference in weight of the two halves of a delicately pivoted and well- balanced wheel placed in an electrolytic bath. In the electrolytic clock of Nikola Tesla, a deli- cately formed and balanced disc of copper is sup- ported on a horizontal axis at right angles to the shortest distance between the two electrode-, and placed in a balh of copper sulphate. Its two halves become respectively electro-positive and electro-negative when a current is passed through the bath, and consequently metal is deposited on one half and dissolved from the other half. The rotation of the disc under the influence of gravity is caused to mark time. An electrolytic clock could therefore be made to answer roughly as an electric meter. Clock, Master The central or con- trolling clock in a system of electric time-dis- tribution, from which the time is transmitted to the secondary clocks in the circuit. (See Clock, Electric?) Clock, Secondary Any clock in a system of time telegraphy that is controlled by the master clock. (See Clock, Electric) Clock, Self-Winding A clock that at regular intervals is automatically wound by the action of a small electro-magnetic motor contained within it. This motor is usually run by one or more vol- taic cells, concealed in the case of the clock. Closed-Circnit (See Circuit, Closed) Closed-Circuit Battery. (See Battery, Closed-Circuit^ Closed-Circuit, Single-Current, Signal- ing (See Signaling, Single-Current, Closed-Circuit^ CIo.] 105 [Coe. Closed-Circuit Thermostat. (See Ther- mostat, Closed-Circuit) Closed-Circuit Voltaic Cell. (See Cell, Voltaic, Closed-Circuit) Closed-Circuit Voltmeter. (See Volt- meter, Closed-Circuit) Closed-Circuited. Placed in a closed or completed circuit. A voltaic battery, or other source, is closed cir- cuited when its poles or terminals are electrically connected with each other. Closed-Circuited Conductor. (See Con- ductor, Closed-Circuited) Closed-Circular Current. (See Current, Closed-Circular) Closed-Coil Disc Dynamo-Electric Ma- chine. (See Machine, Dynamo-Electric, Closed-Coil Disc.) Closed-Coil Drum Dynamo-Electric Ma- chine. (See Machine, Dynamo-Electric, Closed-Coil Drum.) Closed-Coil Dynamo-Electric Machine. (See Machine, Dynamo-Electric, Closed- Coil.) Closed-Coil Ring Dynamo-Electric Ma- chine. (See Machine, Dynamo- Electric, Closed-Coil Ring.) Closed-Iron-Circuit Transformer. (See Transformer, Closed-Iron-Circuit.) Closed-Loop Parallel-Circuit. (See Cir- cuit, Closed-Loop Parallel.) Closed-Magnetic Circuit. (See Circuit, Closed- Magnetic.) Closed-Magnetic Core. (See Core, Closed- Magnetic^ Closure. The completion of an electric circuit. Cloth Discs, Carbonized, for High Re- sistances Discs of cloth carbonized by heating to an exceedingly high temperature in a vacuum, or out of contact with air. After carbonization the discs retain their flex- ibility and elasticity and serve admirably for high resistances. When piled together and placed in glass tubes, they form excellent variable resist- ances when subjected to varying pressure. Club-Footed Magnet. (See Magnet, Club-Footed) Cluteh, Carbon, of Arc Lamp A clutch or clamp attached to the rod or other support of the carbon of an arc lamp, pro- vided for gripping or holding the carbon. (See Lamp, Electric Arc) Clutch Rod. (See Rod, Clutch) Coating, Metallic A covering or coating of metal, usually deposited from solutions of metallic salts by the action of an electric current . (See Plating, Electro) Coating of Condenser. A sheet of tin foil on one side of a Leyden jar or condenser, directly opposite a similar sheet on the other side for the purpose of receiving and collecting the opposite charges. (See Jar, Leyden. Condenser?) Coatings of Leyden Jar. The sheets of tin foil or other conductor on the opposite sides of a Leyden jar or condenser. (See Jar, Leyden. Condenser) Code, Cipher A code in which a number of words or phrases are represented by single words, or by arbitrary words or syl- lables. The message thus received requires the posses- sion of the key to render it intelligible. Code,Telegraphic The pre-arranged signals of any system of telegraphy. (See Alphabet, Telegraphic. Alphabet, Tele- graphic, Morse's. Alphabet, Telegraphic, International Code) Co-efficient, Algebraic A number prefixed to any quantity to indicate how many times that quantity is to be taken. The number 3, in the expression 3a, is a co- efficient and indicates that the a, is to be taken three times, as a -|- a -j- a = 3a. Co-efficient, Economic, of a Dynamo- Electric Machine The ratio between the electrical energy, or the electrical horse- power of the current produced by a dynamo, and the mechanical horse-power expended in driving the dynamo. The economic co-efficient is usually called the efficiency. Coe.] 106 [Coi, The efficiency may be the commercial effi- ciency, which is the useful or available energy in the external circuit divided by the total mechan- ical energy; or it may be the electrical efficiency, which is the available electrical energy divided by the total electrical energy. The efficiency of conversion is the total elec- trical energy developed, divided by the total mechanical energy applied. If M, equals the mechanical energy, W, the useful or available electrical energy, and w, the electrical energy absorbed by the machine, and m, the stray power, or the power lost in friction, eddy currents, air friction, etc. Then, since The Commercial Efficiency = = W M W + w + m' The Electrical Efficiency W ~ W + w' The Efficiency of Conversion _W-fw_ W + w ~M W + w + m' Co-efficient of Electro-Magnetic Inertia. (See Inertia, Electro-Magnetic, Co-effi- cient of) Co-efficient of Expansion. (See Expan- sion, Co-efficient of) Co-efficient of Expansion, Linear (See Expansion, Linear, Co-efficient of) Co-efficient of Magnetic Induction. (See Induction, Magnetic, Co-efficient of) Co-efficient of Magnetization. (See Magnetization, Co-efficient of.) Co-efficient of Mutual- Inductance. (See Inductance, Mutual, Co-efficient of) Co-efficient of Mutual-Induction. (See Induction, Mutual, Co-efficient of) Co-efficient of Self-induction. (See In- duction, Self, Co-efficient of) Coercitive Force. (See Force, Coerci- tive) Coercive Force. (See Force, Coercive) Coil, Choking A coil of wire so Fig> 14 * Ckoking- Coil - wound on a core of iron as to possess high self-induction. Choking -coils are used to obstruct or cut off an alternating current with a loss of power less than with the use of a mere ohmic resistance. Fig. 141 shows a choking-coil. It consists of a circular solenoid of insulated wire, wound on a core of soft iron wire. A thorough divis- ion of the core is obtained by forming it of coils of insulated iron wire. In this way, no eddy currents are produced in the coil. When a simple periodic electromotive force is applied to the terminals of such a coil, if the magnetic permeability of the coil is constant, a simple periodic current is produced, which lags be- hind the phase of the im- pressed electromotive force by a constant angle. If the impressed electromo- tive force is sufficiently great to more than satu- rate the core, the choking coil ceases to choke the current. The higher the periodicity the greater is the choking effect of a given coil, or the smaller the coil may be made to produce a given effect. Since an open-magnetic circuit requires a greater current to saturate it than a closed-mag- netic circuit, the complete throttling or choking power of such a coil is increased by forming its core of a closed magnetic circuit, i. e., of a circuit in which there is no air space or gap. (See Circuit^ Divided- Magnetic. Circuit, Closed- Magnetic.) Coil, Electric -- A convolution of in- sulated wire through which an electric current may be passed. (See Magnet, Electro) The term coil is usually applied to a number of turns or to a spool of wire. Coil, Impedance -- A term sometimes applied to a choking-coil. (See Coil, Chok- ing) Such a coil has a high self-induction. Its im- pedance is therefore high. (See Induction, Self* Impedance) Coil, Induction -- An apparatus con- sisting of two parallel coils of insulated wire employed for the production of currents by mutual induction. (See Induction, MutuaL Induction, Electro-Dynamic) Coi.] 107 [Coi, A rapidly interrupted battery current, sent through a coil of wire called the primary coil, induces alternating currents in a coil of wire called the secondary coil. As heretofore made, the primary coil consists of a few turns of a thick wire, and the secondary coil of many turns, often thousands, of fine wire. Such coils are generally called Ruhmkorff coils, from the name of a celebrated manufacturer of them. In the form of Ruhmkorff coil, shown in Fig. 142, the primary wire, wound on a core formed Fig. 142. Ruhmkorff Coil. of a bundle of soft iron wires, has its ends brought out as shown at f, f. The fine wire, forming the secondary coil, is wrapped around an insulated cylinder of vulcanite, or glass, surrounding the primary coil. This wire is very thin, and in some coils is over one hundred miles in length. If the core of an induction coil were made solid it would heat considerably and therefore cause a loss of energy. The core is therefore laminated, usually by forming it of a bundle of soft iron wire. Too great a division of the core, however, is inadvisable, since, although the eddy currents therein are thereby avoided, yet, too great a division of the core acts practically so to decrease the magnetic permeability that the greatest efficiency cannot be obtained. The ends of the secondary coil are connected to the insulated pillars A and B. The primary current is rapidly broken by means of a mercury break, shown at L and M. The commutator, shown to the right and front of the base, is provided for the purpose of cutting off the current through the primary, or for chang- ing its direction. When a battery which produces a comparatively large current of but a few volts electromotive force is connected with the pri- mary, and its current rapidly interrupted, a torrent of sparks will pass between A and B, having an electromotive force of many thousands of times the number of volts of the primary cur- rent, but of a correspondingly smaller current strength. In such cases, excepting losses during conver- sion, the energy in the primary current, or C E, is equal to the energy in the secondary current, or C' E'. As much therefore as E', the electro- motive force of the secondary current, exceeds E, the electromotive force of the primary current, the current strength C', of the secondary, will be less than the current strength C, of the primary. This is approximately true only, and only in in- duction coils possessing a closed magnetic circuit. (See Transformer.") Fig. 143 shows diagramatically the arrange- Fig. 143. Circuit Connections of Induction Coil. ment and connection of the different parts of an induction coil. The core II', consists of a bundle of soft iron wires, each of which is covered with a thin insu- lating layer of varnish or oxide. A primary wire P P, consisting of a few turns of comparatively thick wire, is wound around the core, and a greater length of thin wire S S, is wound upon the primary. This is called the secondary. So as not to confuse the details of the figure it is repre- sented as a few turns. The terminals of the battery B, are connected to the primary wire, through the automatic inter- rupter, in the manner shown. It will be seen that the attraction of the core II', for the vibrating armature H, will break contact at the point o, and cause a continued interruption of the battery current The condenser cc', is connected as shown. It acts to diminish the sparking at the contact points on breaking contact, and thus, by making the battery current more sudden, to make its in- ductive action greater. The reactions which take place when a simple CoL] 108 [Coi. periodic electromotive force is impressed on the primary of an induction coil are substantially thus stated by J. A. Fleming : (i.) The application of a simple periodic im- pressed electromotive force produces a simple periodic current, moving under an effective elec- tromotive force of self-induction, and brings into existence a counter- electromotive force of self- induction, which causes the primary current to lag behind, by an angle called the angle of lag. (2.) The field around the primary, and, there- fore, the induction through the secondary, is in consonance with the primary current, and the im- pressed electromotive force in the secondary is in quadrature with the primary current. (See Consonance. Quadrature, In.) (3.) The secondary-impressed electromotive force gives rise to a secondary current moving under an effective electromotive force and creat- ing a counter electromotive force of self-induc- tion. (4.) This secondary current reacts in its turn on the primary, and creates what is called the back -electromotive force, or the reacting-induc- tive-electromotive force of the primary circuit. (5.) There is then a phase-difference between the primary and secondary currents, and also be- tween the primary-impressed electromotive force and the primary current. If, as in Fig. 144, two electric circuits are Fig. 144. Electric and Magnetic Link. linked with a magnetic circuit, and a small periodic electromotive force be impressed on the primary, the following phenomena occur: (i.) A periodic primary current is set up in the primary circuit, which, though of the same periodic time as the impressed electromotive force, differs from it in phase. (2.) A wave of counter electromotive force is produced in the primary circuit by the inductive action, which does not coincide either with the impressed electromotive force, nor with the primary current. (3.) A wave of magnetization is produced in the iron core, which lags behind the primary current by somewhat less than 90 degrees of phase. (4.) A wave of impressed electromotive force is produced in the secondary circuit, due to and measured by the rate of change of magnetic in- duction in the core, and lagging 90 degrees, or more, behind the magnetization wave. (5.) A wave of secondary current, lagging be- hind the secondary electromotive force in phase, except where the circuit consists of a few turns of conductor, or is connected with an external cir- cuit of practically no inductance. {Fleming.') Coil, Induction, Inverted An induction coil in which the primary coil is made of a long, thin wire, and the secondary coil of a short, thick wire. By the use of an inverted coil, a current of high electromotive force and comparatively small cur- rent strength, i. e., but of few amperes, is con. verted or transformed into a current of compar- atively small electromotive force and large cur- rent strength. For advantages of this conversion see Electricity, Distribution of, by Alternating Currents. Inverted induction coils are called converters or transformers. (See Transformer.} Coil, Induction, Medical An induction coil used for medical purposes. A form of induction coil used for medical pur- poses is shown in Fig. 145. Fig. 145. Medical Induction Coil. Coil, Induction, Microphone An induction coil, in which the variations in the circuit of the primary are obtained by means of microphone contacts. (See Microphone?) The carbon -button telephone transmitter is a microphone in its action, its electric resistance varying with the varying pressure caused by the sound waves. The carbon-button is in the prim- ary circuit of an induction coil, variations in Coi.] primary of which, under the influence of the sound waves, produce corresponding variations in the currents induced in the secondary. Coil, Kicking" A term sometimes applied to a Choking-Coil. (See Coil, Chok- ing) The term kicking-coil has arisen from the fact that the impedance due to self-induction opposes the starting or stopping of the current somewhat in the manner of an opposing kick. Coil, Magnet A coil of insulated wire surrounding the core of an electro-mag- net, and through which the magnetizing cur- rent is passed. (See Magnet. Electro^) Coil, Primary That coil or con- ductor of an induction coil or transformer, through which the rapidly interrupted or alter- nate inducing currents are sent. In the Ruhmkorff induction coil the primary coil consists of a comparatively short length of thick wire, the secondary coil being formed of a comparatively great length of fine wire. In the transformer or converter, the primary ceil consists of wire that is longer and thinner than that in the secondary coil. In other words, the transformer or converter consists of an inverted induction coil. (See Coil, Induction. Trans- former.) Coil, Reaction A magnetizing coil, surrounded by a conducting covering or sheathing, which opposes the passage of rapidly alternating currents less when directly over the magnetizing coil than when a short distance from it. A term often used for choking-coil. (See Coil, Choking?) Coil, Reaction, Balanced A coil employed in a system of distri- bution by means of transformers for maintaining a constant cur- rent in the sec- ondary Circuit, Fi S- Z 4(>- Balanced- Reaction Coil. despite changes in the load placed therein. A balanced-reaction coil is shown in Fig. 146. [Coi. A reaction coil is placed in the circuit of lamps in series in a constant potential system. The sheath- ing of this coil is maintained in a balanced position by the counter weight P, and the spring S. If now a lamp is extinguished in the circuit, the increase of current, due to decreased resistance, causes the sheath to be deflected, and, thus increasing the self-induction of the coil, reduces the lamp current to its normal value. Coil, Resistance A coil of wire of known electrical resistance employed for measuring resistance. In order to avoid self-induction and the mag- netizing effects of the coils on the needles of the galvanometer used in electric measurements, as well as the disturbing effects of self-induction, the wire of the resistance coil is doubled on itseli before being wound, and its ends connected with the brass bars, E, E, Fig. 147. The inser- Fig. 14.1. Connections of Resistance CoiU. tion of the plug-key cuts the coil out of the cir- cuit by short-circuiting. (See Box, Resistance. Bridge* Electric. Coil, Resistance, Standard.) The coils are made of German silver, or plati- noid, the resistance of which is not much affected by heat. Coil, Resistance, Standard A coil the resistance of which is that of the stand- ard ohm or some multiple or sub-multiple thereof. The standard ohm, as issued by the Electric Standards Committee of England, has the form shown in Fig. 148. The coil of wire is formed of an alloy of platinum and silver, insulated by silk covering and melted paraffine. Its ends are sol- dered to thick copper rods, r, r', for ready con- nection with mercury cups. The coil is at B. The space above it, at A, is filled with paraffine. A hole, at t, runs through the coil for the readv Coi.] 110 [Coi.. insertion of a thermometer. The lower part of the coil, B, is immersed in water up to the shoul- der of A, and the water stirred from time to Fig. 148. Standard Ohm. time. Since the coil is heated by the current, sue- cessive observations should be at least ten minutes apart. Only mild currents should be passed through the coils. Coil, Resistance, Standardized - Resistance coils whose resistances have been carefully determined by comparison with a standard ohm or other standard coils. Coil, Ruhmkorff A term some- times applied to any induction coil, the secondary of which gives currents of higher electromotive force than the primary. (See Coil, Induction?) Coil, Secondary That coil or con- ductor of an induction coil or transformer, in which alternating currents are induced by the rapidly interrupted or alternating currents in the primary coil. (See Coil, Induction* Transformer^) Coil, Shunt - A coil placed in a de- rived or shunt circuit, (See Circuit, Shunt) Coil, Spark A coil of insulated wire connected with the main circuit m a system of electric gas-lighting, the extra spark pro- Fig. T4Q. Spark Coil. duced on breaking the circuit of which is em- ployed for electrically igniting gas jets. Spark coils are employed where the number of gas jets to be simultaneously lighted is not too' great. When this number exceeds certain limits, the spark from an induction coil is more advan- tageously used. A spark coil is shown in Fig. 149. Coils, Armature, of Dynamo-Electric Machine The coils, strips or bars that are wound or placed on the armature core. To avoid needless resistance the wire, or other conductor, of the armature coils, should be as short and thick as will enable the desired electro- motive force to be obtained without excessive speed of rotation. The armature coils should enclose as many lines of force as possible (i. 5- Resolution of Firces. of the arrows, along A B, and A C, with intensi- ties proportioned to the lengths of the lines A B, and A C, respectively, will move it in the direc- tion A D, obtained by drawing B D, and D C, parallel to A C, and A B, respectively, and then drawing A D, through the point of intersection, D. This is called the Composition of Forces. A D, is the resultant force, and A B and A C, are its components. Conversely, a single force, acting in the direc- tion of D B, Fig. 165, against a surface, B C, may be regarded as the resultant of the two sep- arate forces, D E, and D C, one parallel to C B, and one perpendicular to it. D E, being parallel to C B, produces no pressure, and the absolute effect of the force will, therefore, be represented by CD. This separation of a single force into two or more separate forces is called the resolution of forces, the force, D B, being resolved into the components, D E and D C. Component Currents. (See Currents, Component) Component, Horizontal, of Earth's Mag- netism That portion of the earth's directive force which acts in a horizontal di- rection. That portion of the earth's magnetic force which acts to produce motion in a com- pass needle free to move in a horizontal plane only. Let A B, Fig. 166, represent the direction and magnitude of the earth's magnetic field on a mag- netic needle. The magnetic force will lie in the plane of the magnetic merid- ian, which will be assumed to be the plane of the paper C A D. The earth's field, A B, can be resolved into two compo- nents, A D, the horizontal com- ponent, and A C, the vertical component. In the case of a magnetic needle, like the ordinary com- pass needle, which is free to move in a horizontal plane only, the horizontal component alone directs the needle. A weight is applied to balance the vertical component. When the needle is free to move in a vertical plane, and this plane corresponds with that of the magnetic meridian, the entire magnetic force, A B, acts to place the needle, supposed to be properly balanced, in the direction of the lines oi force of the earth's magnetic field at that point. Magnetism. Com.] 117 [Con. Component, Vertical, of Earth's Magnet- ism - That portion of the earth's directive force which acts in a vertical direc- tion. In the vertical plane at right angles to the plane of the magnetic meridian, the vertical component alone acts, and the needle points vertically down- wards, in no matter what part of the earth it may be. In Fig. 1 66, A C, is the vertical com- ponent of the earth's directive force. Composite Balance. (See Balance, Com- posite) Composite-Field Dynamo. (See Dynamo, Composite-Field) Composition ot Forces. (See Forces, Composition of) Compound Arc. (See Arc, Compound) Compound, Binary In chemistry, a compound formed by the union of two different elements. Water is a binary compound, being formed by the union of two atoms of hydrogen with one atom of oxygen. Its composition is expressed in chemical symbols, H 8 O, which indicates that two atoms of hydrogen are combined, or chemically united, with one atom of oxygen. Water is therefore a binary compound, because it is formed of two different elementary substances. Compound, Chatterton's A com- pound for cementing together the alternate coatings of gutta-percha employed on a cable conductor, or for filling up the space between the strand conductors. The composition of Chatterton's compound is as follows: Stockholm tar I part by weight. Resin I " " Gutta-percha 3 " " (Clark &> Sabine.) Compound Circuit. (See Circuit, Com- pound.) Compound, Clark's A compound for the outer casing of the sheathing of sub- marine cables. The composition of Clark's compound is as fol- lows: Mineral pitch 65 parts by weight. Silica 30 " Tar 5 (Clark & Sabine.) Compound - Horseshoe Magnet. (See Magnet, Compound-Horseshoe.) Compound Magnet. (See Magnet, Com- pound) Compound Radical. (See Radical, Com- pound) Compound-Winding of Dynamo-Electric Machines. (See Winding, Compound, of Dynamo-Electric Machine) Compound- Wound Dynamo-Electric Ma- chine. (See Machine, Dynamo-Electric, Compound- Wound) Compound- Wound Motor. (See Motor, Compound- Wound) Concentration of Lines of Force. (See Force, Lines of, Concentration of) Concentric Carbon Electrodes. (See Electrodes, Concentric Carbon) Concentric Cylindrical Carbons. (See Carbons, Concentric Cylindrical) Condenser. A device for increasing the capacity of an insulated conductor by bring- ing it near another insulated earth-connected conductor, but separated therefrom by any medium that will readily permit induction to- take place through its mass. A variety of electrostatic accumulator. If the conductor A, Fig. 167, standing alone Fig. 167. /Epinus Air Condenser. and separated from other conductors, be con- nected with an electric machine, it will receive only a very small charge. on.] 118 [Con. If, however, it be placed near C, but separated from it by a dielectric, such as a plate of glass B, and C, be connected with the ground, A, will receive a much greater charge. (See Dielectric.') Suppose, for example, that A, be connected with the positive conductor of a frictional electric machine, it will by induction establish a negative charge on the surface C, nearest it, and repel a positive charge to the earth. The presence of these two opposite charges on the opposed sur- faces of A and C, permits A, to receive a fresh charge from the machine. (See Induction, Electrostatic.) The charge in a condenser in reality resides on the opposite surfaces of the glass, or other dielectric separating the metallic coatings, as can be shown by removing the coatings after charg- ing. The condenser resulted from the discovery of the Leyden jar. (See Jar, Ley den.) The capacity of a condenser is measured in microfarads. (See farad.) In practice condensers are made of sheets of tin foil, connected to A and B, respectively, and separated from one another by sheets of oiled silk, paraffined paper, or thin plates of mica, as shown in Fig. 168. Fig. r68. Condenser. A Leyden jar or condenser does not store elec- tricity any more than a storage battery does. The same quantity of electricity passes out of the opposite coating of the jar that is passed into the other coating. The jar, therefore, possesses no store of electricity. What it really possesses is a store of electrical energy. According to Ayrton, if the capacity of a con- -denser, in farads, be F, and the difference of po- tential, with which it is charged, be V, volts, the store of electric energy it possesses, or the work it can do when discharged, is, F x V s Work = - foot-pounds. Condenser, Adjustable A con- denser, the plates of which can be readily adjusted so as to obtain the same capacity as that of the conductor to be measured. In order to obtain a comparatively wide range of adjustability, a condenser is composed of say four separate sections: consisting of one of 2 microfarads, one of I microfarad and two of microfarad, thus making in all 4 microfarads. Condenser, JEpinns A name given to an early form of condenser. (See Con- denser.) Condenser, Air A condenser in which layers of air act as the dielectric. A form of air condenser is shown in Fig. 169. Fig. rbq. Air Condenser. It consists essentially of one set of thin plates of glass partially coated on both sides with sheets of tin foil, so as to leave uncoated a space of about one inch around the edge of the glass. The glass plates do not act as dielectrics, but merely as sup- ports for the tin foil, hence the foil on both sides of the plates is connected electrically. Another set of plates alternating with the above have the tin foil placed over the whole surface of the glass. These plates are placed, alternately, over one another on a stand between guide rods of vulcan- ite E, E, E, E, in the manner shown, and are separated from one another by fragments of glass of the same thickness. The plates with the foil over their entire surface are all connected to- gether and to the terminal B, to form the outer coating, and the plates with the foil over nearly all their surfaces are all connected together and to the terminal A, to form the inner coating of the condenser. There is thus formed a condenser in which practically two extended conducting surfaces are Con.] 119 [Con. separated from each other by a thin layer of air, which acts as the dielectric. Condenser, Alternating-Current A condenser suitable for use in connection with a system for the distribution of electric energy by means of alternating currents. Alternating-current condensers must have a very thin dielectric in order to avoid too great bulk. This, of course, introduces a difficulty as regards liability of failure of insulation, which must be carefully avoided. Condenser, Armature of ^(See Arm- ature of a Condenser} Condenser, Capacity of The quan- tity of electricity in coulombs a condenser is capable of holding before its potential in volts is raised a given amount. The ratio between the quantity of electric- ity in coulombs on one coating and the poten- tial difference in volts between the two coat- ings. (Ayrton} The capacity is directly proportional to the charge Q : and inversely proportional to the po- tential V, or, TT $ K ' or, since Q = K V, the quantity of electricity re- quired to charge a condenser to a given potential is equal to the capacity of the condenser multi- plied by the potential through which it is carried. The capacity of a condenser increases in direct proportion to the increase in the area of its coat- ings. When the coatings are plane and parallel to ach other, the capacity of the condenser is in the inverse ratio to the distance between the coatings. Condenser, Coating of (See Coat- * n g of Condenser} Condenser, Plate -A condenser, the metallic coatings of which are placed on suitably supported plates. Condenser, Poles of (See Poles of Condenser.) Condenser, Time-Constant of The time in which the charge of a condenser falls to the 1-2.71828 part of its original value. Condensers, Distribution of Electricity l>y Means of -(See Electricity, Distri- bution of by Alternating Currents, by means of Condensers Electricity, Distribution of, by Continuous Currents, by means of Con- densers} Conduct To pass electricity through con- ducting substances. To determine the general direction in which electricity shall pass through the ether or dielectric surrounding the so-called conduct- ing substance. (See Conduction, Electric!) Conductance. A word sometimes used in place of conducting power. Conductivity. Conductance, Magnetic A word sometimes used instead of magnetic permea- bility. (See Permeability Magnetic} The magnetic conductance is equal to the total induction through the circuit divided by the magnetizing force. Conducting Cord. (See Cord, Conduct- ing} Conducting, Electrical Possessing the power of passing electricity through any conducting substance. Possessing the power of determining the direction in which electricity shall pass through the ether surrounding a substance. (See Conductor} Conducting Power. (See Power Con- ducting} Conducting Power for Electricity. (See Power, Conducting, for Electricity.) Conducting Power for Lines of Mag- netic Force. (See Force, Magnetic, Lines of, Conducting Power of.) Conducting Power, Tables of (See Power, Conducting, Tables of.) Conduction Current. (See Current, Con- duction} Conduction, Disruptire A species of conduction in which the resistance of the conductor is suddenly overcome. Disruptive conduction is seen in the disruptive discharge of a condenser, or Leyden jar. Conduction, Electric The so- Con.] 120 [Con. called flow or passage of electricity through a metallic or other similarly acting substance. The ability of a substance to determine the direction in which electric energy shall be transmitted through the ether surrounding it. The ability of a substance to determine the direction in which a current of electricity passes from one point to another. When a conducting wire has its ends connected with an electric source, a current of electricity is, in common language, said to flow through the wire, and this was formerly believed to be a correct statement. According to modern views, however, the electric energy is believed to pass through the ether or other dielectric surrounding the con- ductor, the so-called conductor forming merely a sink, where the electrical energy dissipates itself. The conductor simply acts to direct the current. Since, however the energy practically passes by means of, and in the general direction of the conductor, there is no objection in speaking of the electricity as flowing through the conductor. Conduction, Electric, Disruptive A conduction of electric energy which ac- companies a disruptive discharge. (See Discharge, Disruptive^ Conduction, Electric, Metallic A conducting of electric energy of the same char- acter as that which occurs in metallic sub- stances. Conduction, Electrolytic A term sometimes employed to indicate the passage of electricity through an electrolyte. There is no passage of electricity through an electrolyte in the same sense as through an ordi- nary conductor. When, through electrolysis, an electromotive force is brought to bear on a molecule of say HC1, it is assumed by some that the liberated hydrogen atoms travel on the whole in one di- rection, and the liberated chlorine atoms in the opposite direction. The atoms thus moving through the liquid may by their electric charges be assumed to convey electricity, and this fact has given rise to the term electrolytic conduc tion. In electrolytic conduction the charges are necessarily equal, but the speeds of their motion are unequal. In a given liquid, each atom has its own rate of motion, no matter with what it has been combined. Hydrogen travels faster than any other kind of atom. The conductivity of a liquid depends on the sum of the speeds with which the two opposed atoms travel. This assumed double stream of oppositely mov ing atoms is denied by most physicists. (See Hypothesis, Grot thus.'] Cond ucti ve-Discharge. (See Discharge, Conductive?) Conductivity, Electric The recip- rocal of electric resistance. Since the conductivity is greater the less the re- sistance, the conductivity will be equal to the recip- rocal of the resistance, and may be so denned. The conductivity is therefore equal to - -_ R ' Conductivity, Equivalent A con- ductivity equal to the sum of several conduc- tivities. Conductivity per Unit of Mass. The re- ciprocal of the resistance of a substance per unit of mass. Conductivity per Unit of Volume. The. reciprocal of the resistance of a substance per cubic centimetre or per cubic inch. The resistance is mea=ured from one face of the cube to the opposite fa>.e. Conductivity Resistance. (See Resist- ance, Conductivity?) Conductivity, Specific The par- ticular conductivity of a substance for elec- tricity. The specific or particular resistance of a given length and unit of cross-section of a substance as compared with the same length and area of cross-section of some standard substance. Conductivity, Specific Magnetic : The specific or particular permeability of a substance to lines of magnetic force. The specific magnetic conductivity is measured by the ratio of the magnetization produced to the magnetizing force which produces it. The specific magnetic conductivity is the an- alogue of specific inductive capacity, or conduc- tivity for lines of electrostatic force. It is also the analogue for specific conducting power for heat. Con.] 1 Conductor. A substance which will per- mit the so-called passage of an electric current. A substance which possesses the ability of determining the direction in which electricity shall pass through the ether or other dielec- tric surrounding it. Some electrolytes, such, for example, as vari- ous mixtures of sulphuric acid and water, possess a true power of conducting electricity, and there- fore have a specific resistance. Generally, how- ever, the passage of the electrolyzing current is regarded as different from that of a current which merely heats the conductor. The space or region around a conductor through which an electric current is passing has a magnetic field produced in it. The term conductor is opposed to non-conductor, or a substance which will not permit the passage of an electric current through it alter tne manner of a conductor. The terms conductors and non-conductors are only relative. There sue no such things as either perfect conductors or perfect non con- ductors. Conductors in general, are distinguished from electrolytes, in that the latter do not allow ihe electricity to pass save by undergoing a chemical decomposition. Conductor, Anisotropic A con- ductor which, though homogeneous in struc- ture like crystalline bodies, has different physical properties in different directions, just as crystals have different properties in the direction of their different crystalline axes. Anisotropic conductors possess different powers of electric conduction in different d.rectiuns. But in opposite directions along in-' same axis their conductivity is .equal. They differ in this respect from isotropic conductors. (See Conductor, Jso- tropic.) Conductor, Anti-Induction A con- ductor so constructed as to avoid injurious inductive effects from neighboring telegraphic or electric light and power circuits. Such anti-induction conductors sometimes con- sist of a conductor for constant currents and a metallic shield surrounding the conductor, and designed to prevent induction from taking place in the wire itself. The anti-induction conductor generally con- [Con. sists of twin conductors surrounded by ordinary insulation and sometimes enclosed by some form of metallic shield, in order to prevent the action of electrostatic induction. When a periodic current is to be transmitted through a conductor, the most effective way of annulling its inductive effects on neighboring cir- cuits is to place the lead of the conductor in the axis of another conductor, used as a return. In other words, to employ concentric cylinders, in- sulated from one another and from the earth. Under these conditions, calling the current in one direction positive, and in the other direction negative, the shielding action will be perfect when the algebraic sum of the currents in the core and sheath are zero. The same effect is obtained in metallic circuits, by placing the leads parallel to the return, and crossing and recros?ing the wires repeatedly. (See Connection, Telephonic Crots.) Elihu Thomson renders ordinary telephone conductors, arranged as single lines with earth returns, free from induction by means of the counter-electromotive force produced in a coil of wire by the disturbing cause. In applying this system to the case of an elec- tric arc or power line passing alongside a tele- phone line, a wire coil, whose turns are pro- portioned in number to the induction to be bal- anced, is introduced into the electric light line and placed near another coil of finer wire inserted as a loop in the telephone circuit. The second coil is placed parallel to or inclined at an angle to the first coil. In practice, the second coil is inclined until the counter-induction set up in the tele- phone wire is equal to that produced in the main line, and silence is thus produced, so far as in- duction is concerned, in the telephone. Conductor, Armored A conduc- tor provided with a covering or sheathing of metal placed over the insulating covering for protection from abrasion or external wear. Armored conductors are used in situations where the conductor is exposed to abrasion or other external wear. Conductor, Branch A conductor placed in a shunt circuit. (See Circuit, Skunt.) Conductor, Closed-Circuited - A conductor connected as a closed or com- pleted circuit. Con.] 122 [Coii. Conductor, Conjugate In a system of linear conductors, any pair of conductors that are so placed as regards each other that a variation of the resistance or the electro- motive force in the one causes no variation in the current of the other. Conductor, Earth-Circuited - -A conductor connected to the ground, or to an earth-connected circuit. Conductor, House-Service A term employed in a system of multiple incan- descent lamp distribution for that portion of the circuit which is included between the ser- vice cut-out and the centre or centres of dis- tribution, or between this cut-out and one or more points on house mains. Conductor, Isotropic A conduc- tor which possesses the same powers of elec- tric conduction in all directions. An electrically homogeneous conducting medium. Conductor. Leakage A conductor placed on a telegraph circuit for the purpose of preventing the disturbing effects of leakage into a neighboring line by providing a direct path for such leakage to the earth, The leakage conductor, as devised by Varley consists of a thick wire attached to the telegraph pole. The lower end of the conductor is grounded, and its upper end projects above the top of the pole. There exists some doubt in the minds of expe- rienced telegraph engineers whether it is well to apply leakage conductors to telegraphic or tele- phonic lines of over 12 or 15 miles in length, since such conductors greatly increase the electro- static capacity of the line, and thus cause serious retardation. Conductor, Lightning A term sometimes used for a lightning rod. (See Rod, Lightning?) Conductor, Open-Circuited A con- ductor arranged as an open or broken circuit. Conductor, Potential of The rela- tion existing between the quantity of elec- tricity in a conductor and its capacity. A given quantity of electricity will raise the potential of a conductor higher in proportion as the capacity of the conductor becomes less. Conductor, Potential of, Methods of Yarying The potential of a conductor may be varied in the following ways : (i.) By varying its electric charge. (2.) By varying its size or shape without alter- ing its charge. (3.) By varying its position as regards neigh- boring bodies. This resembles the case of a gas whose tension or pressure may be varied as follows, viz. : (I.) By varying the quantity of gas. (z.) By varying the size of the gas holder in which it is kept, and (3.) By varying the temperature. Difference of potential, therefore, corresponds (I.) With difference of level in liquids. (2.) With difference of pressure in gases. (3.) With difference of temperature in heat. (Ayr ton,) Conductor, Prince The positive conductor of a frictional electric or electro- static machine. (See Machine, Frictional Electric^ Conductor, To Short-Circuit a To shunt a conductor with a circuit of com- paratively small resistance, Conductor, Underground An elec- tric conductor placed underground by actual burial or by passing it through underground conduits or subways. Underground conductors, though less unsightly than the ordinary aerial conductors, require to be laid with unusual care to render them equally safe, since, when contacts do occur, all the wires in the same conduit are apt to be simultaneously affected, thus spreading the danger in many dif- ferent directions. They are, however, less liable to dangers arising from occasional accidental crosses or contacts. Conductors, Service Conductors employed in systems of incandescent lighting connected to the street mains and to the electric apparatus placed in the separate buildings or areas to be lighted. Conduit, Cement-Lined A cable conduit, the separate ducts of which are sur- rounded by any suitable cement. Con.] 123 [Con. Conduit, Handhole of (See Hand- hole of Conduit) Conduit, Manhole of (See Man- hole of Conduit?) Conduit, Multiple A conduit formed of concrete or other insulating mate- rial, and furnished with a number of separate ducts. Conduit, Open-Box A conduit consisting of an open box of wood placed in a trench and closed with a wooden cover after the introduction of the cable. Cables or wires may be drawn through such conduits in the usual manner. Conduit, Rodding a Introducing a wire or rope into the duct of a closed conduit preparatory to drawing the cable through. Various methods are in use for rodding a con- duit. One much followed consists in using sec- tions of gas pipe, the ends of which are furnished with screw threads. The sections are about four feet in length. One section is pusVied into the duct at one manhole and the successive sections are introduced into the duct and screwed onto the section in the duct and pushed through until a sufficient length is obtained to reach the next manhole, a rope or cable is then pulled through from one manhole to the next. Conduit, Underground Electric An underground passageway or space for the reception of electric wires or cables. (See Subway, Electric?) Congelation. The act of freezing, or the change of a liquid into a solid on loss of heat, or change of pressure. Conjugate Coils. (See Coils, Conjugate?) Connect. To place or bring into electric contact. Connecting. Placing or bringing into elec- tric contact. Connection for Intensity. Connection in series. (See Connection, Series.) This term is now nearly obsolete. Connection for Quantity. Connection in multiple. (See Connection, Multiple?) This term is now nearly obsolete. Connection, Mercurial A form of readily adjustable connection obtained by providing the poles of one piece of electric apparatus with cups or cavities filled with mercury, into which the terminals of another piece of apparatus are dipped in order to place the two in circuit with each other. This form of connection is used particularly when a very perfect contact or one iree from friction is desired. Connection, Multiple Such a con- nection of a number of separate electric sources, or electro-receptive devices, or circuits, that all the positive terminals are connected to one main or positive conductor, and all the negative terminals are connected to one main or negative conductor. In the multiple connection of a number of electro-receptive devices, when the devices are connected as above described to positive and negative leads that are maintained at a constant difference of potential, the current passes through the devices from one lead to the other by branch- ing and flowing through as many separate cir- cuits as there are separate receptive devices, and the opening or closing of one of these cir- cuits does not affect the others. (See Circuits, Varieties of. ) Connection, Multiple-Series Such a connection of a number of separate electric sources, or separate electro-receptive de- vices, or circuits, that the sources or devices are connected in a number of separate groups in series, and each of these groups connected to main positive and negative conductors or leads in multiple arc. (See Circuits, Varie- ties of?) Connection of Battery for Quantity. (See Battery, Connection of, for Quantity?) Connection of Electric Sources in Cas- cade. (See Cascade, Connection of Electric Sources in?) Connection of Voltaic Cells for Inten- sity. (See Intensity, Connection of Voltaic Cells for?) Connection, Series The connec- tion of a number of separate electric sources, or electro-receptive devices, or cir- Con.] 124 [Coil. cuits, so that the current passes successively from the' first to the last in the circuit. (See Circuits, Varieties of.) Connection, Series-Multiple Such a connection of a number of separate electro- receptive devices, that the devices are placed in multiple groups or circuits, and these separate groups connected with one another in series. Connection, Telephonic Cross A device employed in systems of telephonic communication for the purpose of lessening the bad effects of induction, in which equal lengths of adjacent parallel wires are alter- nately crossed so as to alternately occupy the opposite sides of the circuit. Connector. A device for readily con- necting or joining the ends of two or more wires. (See Post, Binding?) Connector, Double A form of bind- ing screw suitable for readily connecting two wires together. A form of double con- nector is shown in Fig. 170. Conning* Tower. (See Tower, Conning?) Consequent Points. (See Points, Conse- quent?) Consequent Poles. (See Poles, Conse- quent?) Conservation of Energy. (See Energy, Conservation of?) Consonance, " In Consonance." A term employed to express the fact that one simple periodic quantity, i. e., a wave or vibration, agrees in phase with another. Constant. That which remains invariable. Constant-Current. (See Current, Con- stant?) Constant-Current Circuit. (See Circuit, Constant Current?) Constant-Current, Distribution of Elec- tricity by (See Electricity, Distri- bution of, by Constant Currents?) Fig. i -jo. Double Connector, Constant, Dielectric A term some- times employed in place of specific inductive capacity. (See Capacity, Specific Inductive?) Constant, Galvanometer The numerical factor connecting the current pass- ing through a galvanometer with the deflec- tion produced by such current. Sometimes a distinction is made between the galvanometer constant and the reduction factor, the former being used to indicate the relation between the current and the geometrical constant of the galvanometer, while the latter is used in the sense just defined of galvanometer constant. Constant Inductance. (See Inductance, Constant?) Constant Potential. (See Potential, Constant?) Constant-Potential Circuit. (See Cir- cuit, Constant-Potential^ Constant, Time, of Electro-Magnet The time required for the magnetizing current to rise to the 5Z1 of its final value, e Contact-Breaker, Automatic A device for causing an electric current to rapidly make and break its own circuit. The spring c, Fig. 171, carries an armature of soft iron, B, and is placed in a circuit in such a manner that the circuit is closed when platinum con- tacts placed on the ends of D and B, touch each other. In this case the arma- ture, B, is attracted to the core A, of the electro- magnet, thus breaking the circuit and causing the magnet to lose its magnetism. The elasticity of the spring C, causes it to fly back and again close the contacts, thus again energiz- ing the electro-magnet and again attracting B, and breaking the circuit. The makes and breaks usually follow each other so rapidly as to produce a musical note. (See Alarm, Electric.} Contact, Dotting An electric con- Fig. 17 T. Automatic Contact Breaker. Con.] 125 [Con. tact obtained by the approach of one con- tact point towards another. The term dotting contact is used in contradis- tinction to a rubbing contact. The rubbing contact is generally to be preferred, since it tends automatically to remove dust and keep the con- tact surfaces polished and free from oxides. Contact Dynamo. (See Dynamo, Con- tact^ Contact Electricity. (See Electricity, Contact?) Contact, Fire- Alarm A contact so arranged that an alarm is given when any predetermined temperature is reached. Fire-alarm contacts are generally operated by the expansion of a metal or of a conducting fluid, such as mercury. (See Thermostat.} Contact Force. (See Force, Contact?) Contact, Full-Metallic A contact, which from its small resistance establishes a good or complete connection. (See Contact, Metallic^ Contact, Intermittent The occa- sional contact of a telegraphic or other line with other wires or conductors by swing- ing, or by alternate contraction or expansion under changes of temperature. Contact, Metallic A contact of a metallic conductor produced by its coming into firm connection with another metallic conductor. Contact, Partial A contact of a telegraphic, or other line, arising from defect- ive insulation, bad earths, or connection with an imperfect conductor. Contact, Rolling A contact con- nected with one part of an electric circuit, that completes the circuit by being rolled over a conductor connected with and forming another part of the circuit. Rolling contacts are employed on electric rail- roads. (See Railroad, Electric.} Contact, Rubbing A contact effected by means of a rubbing motion. Contact Series. (See Series, Contact^ Contact, Sliding A contact con- nected with one part of a circuit that closes or completes an electric circuit by being slid over a conductor connected with another part of the circuit. Sliding contacts are employed in electric rail- roads, in rheostats, switches, and a variety of other apparatus. (See Railroad, Electric. Rheostat. &y, Discharge.} Contact, Spring A spring-sup- ported contact connected with one part of a circuit that completes said circuit by being moved so as to touch another contact con- nected with the other part of the circuit. The movement required to bring the two con- tacts together may be non-automatic, as in the case of a push-button, or automatic, as in the case of a thermostat. (See Button, Push. Thermostat.} Contact Theory of Toltaic Cell. (See Cell, Voltaic, Contact Theory of.) Contact, Vibrating A spring con- tact, connected with one part of a circuit and so supported as to be able to vibrate towards and from another contact connected with another part of the circuit, thus automatically closing and opening said circuit. A vibrating contact is used in the automatic contact-breaker in which the movement of an armature towards an electro-magnet is caused to break the circuit of the coils of the electro-magnet, and, on its movement away from the magnet, to close another contact which again completes the circuit of the electro-magnet. (See Contact Breaker, Automatic.) Contact, Wiping A contact ob- tained by a wiping movement of one con- ductor against another. The spark for electrically igniting a gas jet is obtained by means of a wiping contact of a spring moved by the motion of the pendant. (See Burner, Plain-Pendant Electric. ) Contacts. A variety of faults occasioned by the accidental contact of a circuit with any conducting body. The word contacts as employed above is in the sense of accidental contacts as distinguished from predetermined contacts. Contacts of an accidental character are of the following varieties, viz. : (I.) Full, or metallic, as when the circuit is Con.] 126 [Con, accidentally placed in firm connection with an. other metallic circuit. (2.) Partial, as by imperfect conductors being placed across wires, or bad earths, or defective insulation. (3.) Intermittent, as by occasional contacts of swinging wires, etc. Contacts, Burglar Alarm Con- tacts fitted to windows, doors, tills, steps, floors, etc., so that a movement of the parts from their natural position gives an alarm by sounding a conveniently located bell. Contacts, Lamp Metallic plates or rings connected with the terminals of an incan- descent lamp tor ready connection with the line. Contacts, Mercurial Electric con- tacts that are opened or closed by the ex- pansion or contraction of a mercury column. In the commonest forms of mercurial con. tacts, on the expansion of the mercury by heat it reaches a contact point placed in the tube, and thus completes the circuit through it own mass. Or, on contraction it breaks a contact, and thus disturbing an electric balance, sounds an alarm. Continental Code Telegraphic Alphabet. (Set Alphabet, Telegraphic, International Code) Continuity of Current. (See Current, Continuous) Continuous Current. (See Current, Con- tinuous) Continuous Current, Distribution of Electricity by (See Electricity, Dis- tribution of, by Constant Currents) Continuous Current, Dynamo-Electric Machine (See Machine, Dynamo- Electric, Continuous Current) Continuous-Sounding Electric Bell. (See Bell, Continuous-Sounding Electric) Continuous Wires or Conductors. (See Wires or Conductors, Continuous) Contraction, Anodic Closure The muscular contraction observed on the closing of a voltaic circuit, the anode of which is placed over a nerve, and the kathode at some other part of the body. This term is generally written A. C. C. Contraction, Anodic Duration The length of time the muscle continues in contraction on the opening or closing of a circuit, the anode of which is placed over the part contracted. This term is generally written A. D. C. Contraction, Anodic Opening The muscular contraction observed on the opening of a voltaic circuit, the anode of which is placed over a nerve, and the kathode at some other part of the body. This term is generally written A. O. C. When the anode is placed over a nerve and a weak current is employed, if the circuit be kept closed ior a few minutes, it will be noticed that, on opening the circuit the contraction will be much greater than if it had been opened after being closed for only a few seconds. The effect of the A. O. C. therefore depends not only on the current strength, but also on the time during which the current has passed through the nerve. Contraction of Lines of Magnetic Force. (See Force, Magnetic, Contraction of Lines of) Contractures. In electro-therapeutics, prolonged muscular spasms, or tetanus, caused by the passage of electric currents. Contraplex Telegraphy. (See Telegra- phy, Contraplex) Controlled Clock.-(See Clock, Electric) Controller. A magnet, in the Thomson- Houston system of automatic regulation, whose coils are traversed by the main cur- rent, and by means of which the regulator magnet is automatically thrown into or out of" the mam circuit on changes in the strength of the current passing. (See Regulation, Automatic) Controlling Clock. (See Clock, Electric) Controlling Magnet. (See Magnet, Con- trolling) Convection Currents. (See Currents.Con- vection) Convection, Electric The air par- ticles, or air streams, which are thrown off from the pointed ends of a charged, insulated- conductor. Con.] 127 [Cop. Convection streams, like currents flowing through conductors, act magnetically, and are themselves acted on by magnets. The same thing is true of the brush discharge, of the voltaic arc, and of convective discharges in vacuum tubes. Convection, Electrolytic A term proposed by Helmholtz to explain the appa- rent conduction of electricity by an electro- lyte, without consequent decomposition. Helmholtz assumes that the atoms of oxygen or hydrogen, adhering to the electrodes during elec- trolysis, are mechanically dislodged and diffused through the liquid, thus carrying off the elec- tricity by the charges received while in contact with the electrodes. Convection of Heat, Electric (See Heat, Electric Convection of.) Convection Streams. (See Streams, Con- vection^ Convective Discharge. (See Discharge, Convective?) Conversion, Efficiency of, of Dynamo The total electric energy developed by a dynamo, divided by the total mechanical energy required to drive the dynamo. (See Co-efficient, Economic, of a Dynamo-Electric Machine?) The efficiency of conversion \V + w W -f w W + w -f m, where W, equals the useful or available electrical energy, M, the total mechanical energy, w, the electrical energy absorbed by the machine, and m, the stray power, or the power lost in friction, eddy currents, air friction, etc. Converted Currents. (See Currents, Converted?) Converter. The inverted induction coil employed in systems of distribution by means of alternating currents. A term sometimes used instead of trans- former. (See Transformer?) Converter, Closed-Iron Circuit A closed-iron circuit transformer. (See Transformer, Closed-Iron Circuit?) Converter, Constant-Current A constant : current transformer. (See Trans- former, Constant-Current.} Converter, Efficiency of The effi- ciency of a transformer. (See Transformer, Efficiency of.} Converter Fuse. (See Fuse, Converter} Converter, Hedgehog A form of transformer. (See Transformer, Hedgehog.} Converter, Multiple A multiple transformer. (See Transformer, Multiple.} Converter, Open-Iron-Circuit An open-iron-circuit transformer. (See Trans- former, Open-Iron-Circuit?) Converter, Series A series trans- former. (See Transformer, Series.} Converter, Step-down A step-down transformer. (See Transformer, Step-down.} Converter, Step-up A step-up transformer. (See Transformer, Step-up.} Converter, Welding A welding transformer. (See Transformer, Welding.} Converting Currents. (See Currents, Converting.} Cooling Box of Hydro-Electric Machine. (See Box, Cooling, of Hydro-Electric Machine?) Co-ordinates, Axes of The axes of abscissas and ordinates. The two straight lines, usually perpendicular to each other, to which distances representing values are referred for the graphic represen- tation of such values. (See Abscissas, Axes of.} Copper Bath. (See Bath, Copper?) Copper Plating. (See Plating, Copper?] Copper Ribbon. A variety of strap cop- per. (See Copper, Strap.} Copper, Strap Copper conductors in the form of straps or flat bars. Strap copper is used on the armatures of some dynamos. Heavy copper conductors for such purposes are divided into strap copper so as to avoid eddy currents. The straps are placed alongside one another and insulated by a coating of varnish. Copper Wire, Hard-Drawn (See Wire, Copper, Hard-Drawn.} Copper Wire, Soft-Drawn (See Wire, Copper, Soft-Drawn.} Cop.] 128 [Cor. Copper Voltameter (See Voltameter, Copper.} Coppered Plumbago. (See Plumbago, Coppered} Coppering, Electro Electro-plating with copper. (See Plating, Electro} Cord-Adjuster. (See Adjuster, Cord} Cord, Conducting A small flexible cable, usually containing several conductors separated from one another by insulating ma- terial. Cord, Electric A flexible, insulated electric conductor, generally containing at least two parallel wires. Electric cords are named from the purposes for which they are employed, battery cords, dental cords, lamp cords, motor cords, switch cords, etc. Fig. 172. Flexible Cord. A two-conductor flexible cord, in which each cord is composed of a number of bare copper wires placed parallel to and in contact with one another, is shown in Fig. 172. The several separate wires give flexibility to the cord. Cord, Pendant A flexible conductor provided for conveying the current to a hang- ing electric lamp supported by it. Cords, Telephone Flexible con- ductors for use in connection with a tele- phone. Fig. 173. Telephone Cords. Telephone cords, attached to an articulating telephone, are shown in Fig. 173. Core, Armature, Filamentous An armature core, the iron of which consists of wire. Core, Armature, H An armature core in the shape of the letter H, generally known as the shuttle armature, and some- times as the girder armature. This form is also called an I armature. The H armature core was the form originally given to the Siemens armature. In this form a single coil of wire was secured on the cross-bar of the H armature core, so as to fill up the entire space inside the letter, and the ends of the wire connected to a two-part commutator. Core, Armature, Lamination of The subdivision of the core of the armature of a dynamo-electric machine into separate insulated plates or strips for the purpose of avoiding eddy or Foucault currents. This lamination must always be perpendicular to the direction of the eddy currents that would otherwise be produced. (See Currents, Eddy.) Core, Armature, of Dynamo-Electric Machine The iron core, on, or around which, the armature coils of a dynamo-electric machine are wound or placed. The armature core is laminated for the pur- pose of avoiding the formation of eddy or Fou- cault currents. In drum, and in ring-armatures, the laminas should be in the form of thin insulated discs or plates of soft iron ; in pole-armatures they should be in the form of bundles of insulated wires. The iron in the cores should be of such an area of cross-section, as not to be readily oversaturated. Core, Armature, Radially-Laminated An armature core, the iron of which consists of thin iron washers. Core, Armature, Ribbed A cylin- drical armature core provided with longi- tudinal projections or ribs that serve as spaced channels or grooves for the reception of the armature coils. Core, Armature, Tangentially-Laminated An armature core, the iron of which consists of a coiled ribbon. Core, Armature, Ventilation of Means for passing air through the armature Cor.J 129 [Cou. cores of dynamo-electric machines in order to prevent undue accumulation of heat. A properly proportioned dynamo-armature may need no ventilation, since in such the amount of heat generated is small as compared with the extent of the radiating surface. Since, however, in practice all armatures tend to heat at full load, especially in certain installa- tions in heated situations, ventilation of the ar- mature is desirable. Core, Closed-Magnetic A mag- netic core so shaped as to provide a complete iron path or circuit for the lines of magnetic force of its field. Core, Laminated A core of iron which has been divided or laminated, in order to avoid the injurious production of Foucault or eddy currents. Core, Lamination of Structural subdivisions of the cores of magnets, arma- tures, and pole-pieces of dynamo-electric machines, electric motors, or similar appa- ratus, in order to prevent heating and subse- quent loss of energy from the production of local, eddy or Foucault currents. These laminations are obtained by forming the cores of sheets, rods, plates, or wires of iron in- sulated from one another. The cores of dynamo-electric machine arma- tures should be subdivided in planes at right angles to the armature coils; or in planes parallel to the direction of the lines of force and to the motion of the armature; or, in general, in planes perpendicular to the currents that would otherwise be generated in them. Pole -pieces should be divided in planes per- pendicular to the direction of the currents in the armature wires. Magnet cores should be divided in planes at right angles to the magnetizing current. Core of Cable. The conducting wires of an electric cable. (See Cable, Electric) Core, Open-Magnetic Any mag- netic core so shaped that the lines of magnetic force of its field complete their circuit partly through iron and partly through air. Core Ratio of Cable. (See Cable, Core Ratio of) Core, Ring A hollow, cylindrical core of short length. Core, Ring, Elongated A hollow, cylindrical core of comparatively great length. Core, Solenoid A core so arranged as to be drawn into a solenoid on the passage of the current through its coils, and to be withdrawn therefrom, on the stopping of the current by the action of a spring or weight. (See Solenoid) Core, Stranded, of Cable The conducting wire or core of a cable formed of a number of separate conductors or wires in- stead of a single conductor of the same weight per foot as the combined conductors. Core Transformer. (See Transformer, Core.) Cored Carbons. (See Carbons, Cored) Cored Electrodes. (See Electrodes, Cored) Coronae, Auroral A crown-shaped appearance, sometimes assumed by the auro- ral light. (See Aurora Borealis) Corposant. A name sometimes given by sailors to a St. Elmo's Fire. (See Fire, St. Elmo's) Correlation of Energy. (See Energy, " Correlation of) Corresponding Points. (See Points, Cor- responding) Cosine. One of the trigonometrical func- tions. (See Trigonometry) Cotangent. One of the trigonometrical functions. (See Trigonometry) Coulomb. The unit of electrical quantity. A definite quantity or amount of the thing or effect called electricity. Such a quantity of electricity as would pass in one second in a circuit whose resistance is one ohm, under an electromotive force of one volt. The quantity of electricity contained in a condenser of one farad capacity, when sub- jected to an electromotive force of one volt. The quantity of electricity that flows per second past a cross-section of a conductor Con.] 130 [Cou. conveying an ampere. (Ayrton.) (See Am- pere. Farad. Volt.) Coulomb's Torsion Balance. (See Bal- ance, Coulomb's Torsion?) Coulomb-Volt A Joule, or .7373 foot- pound. The term is generally written volt-coulomb. (See Volt-Coulomb.) Counter, Electric A device for counting and registering such quantities as the number of fares collected, gallons of water pumped, sheets of paper printed, revolutions of an engine per second, votes polled, etc. Various electric devices are employed for this purpose. They are generally electro-magnetic in character. Counter-Electromotive Force. (See Force, Electromotive, Counter.) Counter Electromotive Force Lightning Arrester. (See Arrester, Lightning, Coun- ter-Electromotive Force?) Counter-Electromotive Force of Convec- tive Discharge. (See Force, Electromotive, Counter, of Connective Discharged) Counter-Electromotive Force of Mutual Induction. (See Force, Electromotive, Counter, of Mutual Induction?) Counter-Electromotive Force of Self-In- duction. (See Force, Electromotive, Coun- ter, of Self-Induction?) Counter-Electromotive Force of Self-In- duction of the Primary. (See Force, Electromotive, Counter, of Self-Induction of the Primary?) Counter-Electromotive Force of Self-In- duction of the Secondary. (See Force, Electromotive, Counter, of Self-Induction of the Secondary?) Counter-Electromotive Force of the Primary. (See Force, Electromotive , Counter, of the Primary?) Counter Inductive Effect (See Effect, Counter Inductive?) Couple. In mechanics, two equal parallel forces acting in opposite directions but not in the same line, and tending to cause rotation. The moment, or effective power of a couple, is equal to the intensity of one of the forces multiplied by the perpendicular distance between the direc- tions of the two forces. Couple, Astatic Two magnets of exactly equal strength so placed one over the other m the same vertical plane as to com- pletely neutralize each other. An astatic couple has no directive tendency. A pair of magnets combined as an astatic couple is called an astatic needle. (See Needle, Astatic.) Couple, Magnetic The couple which tends to turn a magnetic needle, placed in the earth's field, into the plane of the magnetic meridian. If a magnetic needle is in any other position than in the magnetic meridian, there will be two parallel and equal forces acting at A and B, Fig. 174, in the directions shown by the arrows. Their effect will be to ro- tate the needle until it comes to rest in the mag- netic meridian N S. The total force acting w , on either pole of a needle free to move in any direc- tion, is equal to the strength of that pole mul- tiplied by the total inten- sity of the earth's field at that place ; or, if free to move in a horizontal direction only, is equal to the intensity of the earth's horizontal component of magnetism at that place, multiplied by the strength of that pole. The effective power or moment of a magnetic couple is equal to the force exerted on one of the poles multiplied by the perpendicular distance, P Q, between their directions. Couple, Moment of The effective power or force of a couple. The moment of a couple is equal to the inten- sity of one of the forces multiplied by the perpen- dicular distance between the direction of the forces. Couple, Thermo-Electric Two dis- similar metals which, when connected at their ends only, so as to form a completed electric circuit, will produce a difference of potential, and hence an electric current, when one of the ends is heated more than the other. Thus if a bar of bismuth be soldered to a bar Fig. 174. Magnetic Couple. Cou.] 131 [Cre. of antimony the combination will form a thermo- electric couple, and the circuit so formed will have a current passing through it when one junc- tion is hotter or colder than the other. There is, according to Lodge, a true contact force, at a thermo-electric junction, as is shown by the reversible heat effects produced when an electric current is passed across such junction; for, in one direction more heat is produced, and in the opposite direction less heat. This, as is well known, differs from the irreversible heat produced by a current through a homogeneous metallic conductor. The reversible heat effects, or as they are called the Peltier effects, may overpower and conceal the heating effects. But, in addition to these effects, since a difference of potential, calU-d a Thomson effect, exists in a substance unequally heated, currents are so produced, and these are also influential in causing the difference of poten- tial of a thermo-electric couple. " There are then," says Lodge, "in a simple circuit of two metals with their junctions at differ- ent temperatures, altogether four E. M. Fs., one in each metal, from hot to cold, or vice versa, and one at each junction, and the current which flows around such a circuit is propelled by the resultant of these four." * * * "These four forces, two Thomson forces in the metals, and two Peltier forces at their junctions, may some of them help and some hinder the current." * * * "When- ever they help, the locality is to that extent cooled; whenever they hinder, it is to that extent warmed." The action of a thermo-electric couple in pro- ducing a difference of potential is therefore a complicated one, and depends on Peltier and Thomson effects, as well as on the thermo-electric effect. (See Effect, Peltier. Effect, Thomson. Effect, Thermo-Electric.) Couple, Voltaic Two materials, usually two dissimilar metals, capable of acting as an electric source when dipped in an electrolyte, or capable of producing a difference of electric potential by mere con- tact. Liquids and gases are capable of acting as voltaic couples. All voltaic cells have two metals, or a metal and a metalloid, or two gaseous or liquid substances which are of such a character that, when dipped into the exciting fluid one only is chemically acted on. Each one of these two substances is called an element of the cell, and the two taken collectively form a voltaic couple. The elements of a voltaic couple may consist of two gases or two liquids. (See Battery, Gas.) Coupled Cells. (See Cells, Coupled) Coupler, Voltaic Any device by means of which voltaic cells may be readily coupled or connected in different forms of circuits. (See Circuits, Varieties of.) Coupling of Voltaic Cells or Other Electric Sources. A term indicating the manner in which a number of separate electric sources may be connected so as to form a single source. (See Circuits, Varie- ties of) Cramp, Telegrapher's An affec- tion of the hand of a telegrapher due to im- moderate and excessive use of the same muscles, somewhat similar to the disease known as writer's cramp. Telegrapher's cramp, like writer's cramp, may be defined as a professional neurosis of co-ordina- tion. It appears not only in certain groups of muscles, but is limited to such groups, only w hen they are performing certain complicated opera- tions. For example, telegrapher's cramp is practically a paralysis of certain muscles of the hand and wrist of the operator. These muscles, when called on to perform the somewhat delicate movements required in sending a telegraphic dis- patch, are incapable of performing their proper functions, but when calle 1 on to perform in part other similar actions, provided all these actions are not required to be used, appear to be un- affected. * The ability of the operator to send with either hand would lessen the liability to this disease. Crater in Positive Carbon. A depression at the end of the positive carbon of an arc lamp which appears when a voltaic arc is formed. (See Arc, Voltaic) Creep, Diffusion The flow of an electric current in portions of a conducting substance, outside the parts that lie in the direct lines between the points where the terminals of the same are applied to the con- ducting: substance. Cre.] 132 [Cro. Creeping, Electric A term some- times applied to the creeping of a current. (See Current, Creeping of.) Creeping in Voltaic Cell. (See Cell, Vol- taic, Creeping in.) Creeping of Current (See Current, Creeping of, Electric?) Creeping, Saline The formation of salts by efflorescence on the walls of a solid immersed in a solution of a salt. Creosoting. A process employed for the preservation of wood, as, for example, tele- graph poles, by injecting creosote into the pores of the wood. (See Pole, Telegraphic) Crith. A term proposed by A. W. Hoff- man, as a unit of weight, or the weight of one litre, or cubic decimetre, of hydrogen at O C. and 760 mm. barometric pressure. Critical Current. (See Current, Crit- ical) Critical Current of a Dynamo. (See Current, Critical, of a Dynamo) Critical Distance of Lateral Discharge through Alternative Path. (See Distance, Critical, of Lateral Discharge through an Alternative Path) Critical Speed of Compound-Wound Dy- namo. (See Speed, Critical, of Compound- \Vound Dynamo) Crookes' Dark. Space. (See Space, Dark, Crookes') Crookes' Electric Radiometer. (See Ra- diometer, Electric, Crookes'.) Cross Arm. (See Arm, Cross) Cross-Connecting Board. (See Board, Cross-Connecting) Cross, Electric A connection, gen- erally metallic, accidentally established be- tween two conducting lines. A defect in a telegraph, telephone or other circuit caused by two wires coming into contact by crossing each other. A swinging or intermittent cross is caused by wires, which are too slack, being occasionaly blown into contact by the wind. A weather cross arises from defective action oi the insulators in wet weather. Cross, Swinging or Intermittent An accidental contact, generally metallic, caused by wires being brought into occasional contact with one another, or with some other conductor, by the intermittent action of the. wind. Cross, Weather A contact or leak occurring in a telegraphic or other line dur- ing wet weather, from the defective action of the insulators. Crossing Cleat. (See Cleat, Crossing) Crossing, Live-Trolley A device: whereby a trolley moving over a line that crosses a second line at an angle is enabled to maintain its electrical connection with the line while crossing. A live-trolley crossing is necessitated where one line of electric railway crosses another. The- upper line must, of course, provide a space or opening for crossing the lower line at the points; of intersection. This is effected in the Bagnall: live-trolley crossing, shown in Fig. 1 75, by attach- Fig. 173. Live-Trolley Crossing. ing to the upper trolley wire a bridge piece of light lathe casting, provided at its centre with a gap through which the trolley wire passes. This- bridge piece is insulated from the trolley wire by- means of a disc of insulating material at the cen- tre of the bridge, which is provided with a hinged curved lever, that in its normal position rests un- der the influence of gravity in the position shown, in the figure. The passage of the trolley wheel along the wire carries the line under it and thus bridges the gap, as shown by the position of the dotted lines. Crossing Wires. (See Wires, Crossing.} Cross-Over Block. (See Block, Cross- Over) Cross-Over, Trolley A device by means of which a trolley is enabled to pass over the points where different lines cross one another without serious interruption. Cro.] 133 [Cur. A trolley cross-over, for trolley lines, is shown in Fig. 176. Fig. ijb. Trolley Cross Over. Crow-foot Zinc. (See Zinc. Crow-foot. .) Crucible, Electric A crucible in which the heat of the voltaic arc, or of elec trie incandescence, is employed either to per- form difficult fusions, or for the purpose of effecting the reduction of metals from their ores or the formation of alloys. (See Fur- nace, Electric) Crystal, A solid body bounded by sym- metrically disposed plane surfaces. A definite form or shape is as characteristic of an inorganic crystalline substance as it is of an animal or plant. Each substance has a form in which it generally occurs. There are, however, certain modifications of the typical forms which cause plane surfaces to appear curved, and the Symmetrical arrangement of the faces to disap pear, These modifications often render it ex tremely difficult to recognize the true typical form For the different fundamental crystalline forms. or systems of crystals, see any standard work on chemistry. Crystal, Hemihedral A crystal whose shape or form has been modified by the replacement of half its edges or solid angles, A hemihedral crystal possesses different forms at the ends or extn_mities of its axes. Hemi hedral crystals, when unequally heated, develop electrical charges. Electricity produced in this way was formerly called pyro-electricity. (See Electricity, Pyro.) Crystal, Holohedral A crystal whose shape or form has been modified by the replacement of all its edges or solid angles. Crystalline Electro-Metallurgical De- posit, (See Deposit. Crystalline, Electro- Metallurgical.) Crystallization. Solidification from a state of solution or fusion in a definite crystalline form. The crystallization of a dissolved solid is fa- vored by any cause that gives increased freedom of movement to its molecules, such for example as solution, fusion, sublimation, or precipitation Crystallization by Electrolytical Decom- position. The crystalline deposition of vari- ous metals by the passage of an electric cur- rent through solutions of their salts under certain conditions. A strip of zinc immersed in a solution of sugar of lead (acetate of lead) soon becomes covered with bright metallic plates of lead, that are elec- trolytically deposited by the weak currents due to minute voltaic couples formed with the zinc by particles of iron, carbon, or other impurities in the zinc. The deposit assumes at times a tree- like growth, and is therefore called a lead tree. (See Couple, Voltaic.') Crystallization, Electro Crystalli- zation effected during elect rolytic deposition. Crystallize. To separate from a liquid or vapor, in the form of a crystalline solid. Crystalloid. Those portions of a mixed substance subjected to dialysis, that are capa- ble of crystallization. (See Dialysis.) Cube, Faraday's An insulated room cubic in shape, covered on the inside with tin foil, which, when charged on the outside gives no indications to an observer on the inside, though furnished with delicate in- struments. Faraday's cube illustrates the fact that an elec- trostatic charge resides on the outside of an insu- lated conductor. (See Net, Faraday's.) Cnp, Mercury A cup or cavity filled with mercury and connected with the pole of an electric apparatus for the ready placing of the same in circuit with other elec- tric apparatus. To connect apparatus it is only necessary ta insert the free terminal of one apparatus in the mercury cup of the other. Cup, Porous A porous cell. (See Cell, Porous) Curl), Double A device for in- creasing the speed of signaling, by means of which the line is rid of its charge before the next signal is sent, by sending an opposite charge, then another in the same direction. ur.] 134 [Cur. then finally another in the same direction before connecting with the ground. The effect of the third charge is to reduce the potential of the line more nearly to zero at the end of the signal. Curb, Single A device for in- creasing the speed of signaling telegraphic- ally by ridding the line of its previous charge by sending a reversed current through it be- fore connecting with the ground. In single-curb signaling the operator in dis- charging the line before sending another signal through it, before putting the line to earth, re- verses the battery, and then connects to earth. Current, Absolute Unit of A cur- rent of 10 amperes. (See Ampere. Units, Practical!) A current of such a strength that when passed through a circuit of a centimetre in length bent in the form of an arc of a circle one centimetre in radius, will act with the force of .a dyne on a magnetic pole of unit strength, placed at the centre of the arc. The ampere, the practical unit of current, is but ^ the value of the absolute unit of current. Current, Action of, on a Magnetic Pole An attraction or repulsion depend- ent on the name of the pole and the direction of the current. Two currents of electricity attract or repel each other according to the direction in which they are flowing, and the mutual positions of their circuits. A current and a magnetic pole exert an action on each other which, strictly speaking, is neither attraction nor repulsion, but which is ro- tation, that may, however, be regarded as being produced by the combined action of attraction and repulsion. Current, Alternating A current which flows alternately in opposite directions. A current whose direction is rapidly re- versed. The non-commuted currents generated by the differences of potential in the armature of a dynamo-electric machine are alternating or simple-periodic-currents. In a characteristic curve of the electromotive forces of alternating currents, positive electro- motive forces, or those that would produce cur- rents in a certain direction, are indicated by values above a horizontal line, and negative elec tromotive forces, by values below the line. The curves A B C, and C D E, Fig. 177, are B Fig, 177. Curve of Electromotive Forces of Alternating Currents. often called phases, and represent the alternate phases of the current. Current, Alternative A voltaic alternative. (See Alternatives, Voltaic) Current, Assumed Direction of Flow of The direction the current is as- sumed to take, z. e., from the positive pole of the source through the circuit to the negative pole of the source. The electricity is assumed to come out of the source at its positive pole, and to return or flow back into the source at its negative pole. This convention as to the direction of the electric cur- rent is in accordance with the assumption of the direction of flow of lines of magnetic forces. The oldidea'of a dual or double current flowing in opposite directions is still maintained by some, (See Force, Lines of, Direction of.) Current, Axial In electro-thera- peutics a current flowing in a nerve in the opposite direction to the normal impulse in the nerve. Current. Break-Induced The cur- rent induced by a current in its own, or in another circuit, on breaking or opening the same. The current induced in the secondary on the breaking of the primary circuit. The break -induced current set up by a current in its own circuit is sometimes called the direct- induced current. Lord Rayleigh has shown that within certain limits the break-induced current has a greater effect in magnetizing steel needles, the smaller the number of turns of wire in the secondary. In Cur.] 135 [Cur. the case of a galvanometer, it is well known that the opposite is true. The deflection of the gal- vanometer needle depends on the strength of the whole current. The magnetizing power depends, for the greater part, on the strength of the cur- rent at the beginning of its formation Current, Closed-Circular A cur- rent flowing in a circular circuit. A small closed-circular current may be replaced magnetically by a thin disc of steel, magnetized in a direction perpendicular to its lace, and the edge of which corresponds to the edge of the circular conductor. Current-Commuter. (See Commuter, Current?) Current Conduction The current that passes through a metallic or other con- ducting substance, as contradistinguished from a current produced m a non-conductor 01 dielectric. (See Current, Displacement?) Current, Constant A current that continues to flow in the same dnection for some time without varying in strength, This term is sometimes used to mean a con tinuous or direct current in contradistinction to an alternating current, but it ought to be applied only to unvarying currents, such, for example as a constant current of 10 amperes. Current, Continuous An electric current which flows in one and the same direction Although the term continuous current is used as synonymous with constant current, it is not entirely so; a continuous current flows constantly in the same direction A constant current not only flows continuously in the same direction, but maintains an approximately constant current strength This term continuous current is used in the opposite sense to alternating current, and in the same sense as a direct current. Current, Creeping of Electric A change in the direction of path of a current from the direct line between the points of connection with the source. When the terminals of any electric source are placed in contact with any two p jints of a metallic sheet of conducting material, the flow of the cur- rent ib not confined to the direct line between the points of contact, but creeps or diffuses into por- tions of the conducting plate surrounding this direct line. (See Current ', Diffusion of.) In a somewhat similar manner, the current is said to creep, or to establish a partial short- circuit around the poles of a poorly insulated voltaic battery, or other electric source. Current, Critical The current at which a certain result is reached. Current, Critical, of a Dynamo That value of the current at which the characteristic curve begins to depart from a nearly straight line. {Silvanus Fig 178 Critical P. Thomson.} Curve of Dynamo Current In Fig. 178 the critical current is shown in three different cases, as oc- curring where the dotted vertical line cuts the characteristic curves. The speed at which a series dynamo excites itself is often called the critical speed. Current, Demarcation A term sometimes applied to an electric current ob- tained from an injured muscle. " Every injury of a muscle or nerve causes at the point of injury a dying surface, which behaves negatively to the positive intact substance." (Landois 6- Stirling.) Current Density The current of elec- tricity which passes in any part of a circuit as compared with the area of cross-section of that part of the circuit. In a dynamo electric machine the current den- sity in the armature wire should not, according to Silvanus P. Thompson, exceed 2,500 amperes per square inch of area of transverse section of conductor. The current density in a dynamo wire, of necessity depends on the sectional area of the coils , If, for example, a current of 50 amperes be safe in an armature section of eight turns it may be safely increased to 100 amperes if the conductors are cross sectioned so as to make but four turns. (Urquhart.) In electro plating, for every definite current strength that passes through the bath, or in other words, for a definite number of coulombs, a definite weight of metal is deposited, the charac- Car.] 136 [Cur.' ter of which depends on the current density. The character of an electrolytic deposit will therefore depend on the current density at that part of the circuit where the deposit occurs. The following table from Urquhart gives the practical working value for the current density for electro-metallurgical deposits : CURRENT DENSITY (OR AMPERES ON CATHODE). Amperes Solution of per square foot. Copper, acid bath 5.0 to 10.0 Copper, cyanide bath 3.0 " 5.0 Silver, double cyanide 2.0 " 5.0 Gold, chloride in cyanide i.o " 2.0 Nickel, double sulphate 6.0 " 8.0 Brass, cyanide 2.0 " 3.0 Tin Current, Diacritical Such a strength of the magnetizing current as pro- duces a magnetization of an iron core equal to half-saturation. The diacritical current is the current which, flowing through the diacritical number of ampere- turns, will bring up the magnetism produced to half -saturation. The diacritical number of ampere-turns is such a number of ampere-turns as would reduce the magnetic permeability to half its iull value. Current, Diffusion of A term em- ployed to designate the difference in the density of current in different portions of a conductor. (See Current. Creeping of, Elec- tric) Current, Diffusion of Electro-Therapeu- tic The difference in the density of current in different portions of the human body between the electro-therapeutic elec- trodes. When the electrodes are placed at any two given points of the human body, the current branches through various paths, extending in a general direction from one electrode to the other, according to the law of branched or derived cir- cuits, and flowing in greater amount, or with greater density of current, through the relatively better conducting paths. (See Current Density.') This is sometimes called the creeping of the current. (See Current, Creeping of .} Current, Direct A current con- stant in direction, as distinguished from an alternating current. A continuous current. Current, Direct-Induced The cur- rent induced in a circuit by induction on it- self, or self-induction, on breaking or opening the circuit. (See Currents, Extra.} This is called the direct-induced current because its direction is in the same direction as the induc- ing current. Current, Direction of The direc- tion an electric current is assumed to take out from one pole of any source through the circuit and its translating devices back to the source through its other pole. Conventionally, the current is assumed to come out from the positive pole cf the source and to go> back to the source at the negative pole. Current, Displacement The rate of change of electric displacement. A brief conduction current produced in a dielectric by an electric displacement. (See Displacement, Electric?) This is called a displacement current in order to distinguish it from a conduction current in any conductor. The displacement current continues while the displacement of electricity is going on. Dis- placement currents have all the properties of con- duction currents, and, like the latter, produce a- magnetic field; in fact, they resemble extremely brief conduction currents. The difference between conducting substances and dielectrics, lies in the fact that the conducting substances do not possess an elastic force, en- abling them to resist electric displacement. In other words, conducting substances possess no- electric elasticity, and can have no true displace- ment current established in them. (See Elasti- city, Electric.} A displacement current, like a conduction cur- rent, possesses a magnetic field, or is encircled by lines of magnetic force. (See Field, Magnetic, of an Electric Current.) Current, Electric The quantity of electricity which passes per second through any conductor or circuit. The rate at which a definite quantity of elec- tricity passes or flows through a conductor or circuit. ur.] 137 [Cur. The ratio existing between the electro- motive force, causing the current, and the resistance which may, for convenience, be regarded as opposing it, expressed in terms of quantity of electricity per second. The unit of current, or the ampere, is equal to one coulomb per second. (See Ampere. Coulomb.) The word current must not be confounded with the mere act of flowing; electric current signifies rate of flow, and always supposes an electromotive force to produce the current, and a resistance to oppose it. The electric current is assumed to flow out from the positive terminal of a source, through the circuit and back into the source at the nega- tive terminal. It is assumed to flow into the positive terminal of an electro-receptive device such as a lamp, motor, or storage battery, and out of its negative terminal ; or, in other words, the positive pole of the source is always con- nected to the positive terminal of the electro-re- ceptive device. Professor Lodge draws the following com- parison between the motions of ordinary mat- ter, heat and electricity: "Consider the modes in which water may be made to move from place to place; there are only two. It may be pumped along pipes, or it may be carried about in jugs. In other words, it may travel through matter, or, it may travel with matter. Just so it is with heat, also. Heat can travel in two ways: it can flow through matter, by what is called ' conduction, ' or, it can travel with matter, by what is called 'convection.' There is no other mode of con- veyance of heat." * * * "For electricity the same is true. Electricity can travel with matter, or it can travel through matter, by con- vection, or by conduction, and by no other way." In the above, the radiation of heat is apparently lost sight of. In the opinion of some, an electric current con- sists of two distinct currents, one of positive and the other of negative electricity, flowing in oppo- site directions. Each of these currents is supposed to be equal in amount to the other. The electric currentis now regarded as passing through the dielectric surrounding the conductor, rather than through the conductor itself. (See Current, Electric, Method of Propagation of, Through a Circuit.') The current that flows or passes in any circuit is, in the case of a constant current, equal to the electromotive force, or difference of potential, divided by the resistance, as (SeeLawo/O/tm.) Current, Electric, Method of Propagation of, Through a Circuit -- When an electric current is propagated through a wire or other conductor, it is not sent or pushed through the conductor, like a fluid through a pipe or other conductor, but is, so to speak, rained down on the surface of the conductor from the medium or dielectric surrounding it. Poynting, who has carefully studied this mat- ter, remarks as follows, viz.: "A space contain- ing electrical currents may be regarded as the field where energy is transformed at certain points into the electric or magnetic kind, by means of batteries, dynamos, thermopiles, etc., and in other parts of the field this energy is being again transformed into heat, work done by the electro- magnetic forces, or any other form yielded by currents. "Formerly the current was regarded as some- thing traveling in the conductor, and the energy which appeared at any part of the circuit was supposed to be conveyed thither through the conductor by the current. But the existence of in- duced currents and electro-magnetic actions have led us to look on the medium surrounding the conductor as playing a very important part in the development of the phenomena. If we believe in the continuity of the motion of energy, we are forced to conclude that the surrounding medium is capable of containing energy, and that it is capable of being transferred from point to point. We are thus led to consider the problem, how does the energy about an electric current pass from point to point; by what paths does it travel, and according to what laws ? Let us take a spe- cific case. Suppose a dynamo at one spot gen- erates an electric current, which is made to operate an electric motor at a distant place. We have here, in the first place, an absorption of energy from the prime motor into the dynamo. We find the whole space between and around the conduct- ing wires magnetized and the seat of electro- magnetic energy. We have further a retrans- formation of energy in the motor. The question which presents itself for solution is to decide how the energy taken up by the dynamo is trans- mitted to the motor, by what path it travels Cur.] 138 [tuiv and according to what laws ? Briefly stated, the tendency of recent views is that this energy is conveyed through the electro-magnetic medium or ether, and that the function cf the wire is to localize the direction or to concentrate the flow in a particular path, and thus provide a sink or place in which the energy can be dissipated. * * *" Taking again, for instance, the case of the dis- charge of a condenser by a conductor. He says: "Before the discharge we know that the enegy resides in the dielectric, between the conducting plates. If these plates are connected by a wire, according to these views, the energy is transferred outwards along the electrostatic, equipotential sur- faces, and moves on to the wire and is there con- verted into heat. According to this view we must suppose the lines of electrostatic induction, running from plate to plate, to move outwards, as the dielectric strain lessens, and while still keep- ing their ends on the plates, to finally converge in on the wire and be there broken up and their energy dissipated as heat." In other words, some of the energy of the ex- panding lines of induction is changed into mag- netic energy; this energy is contained in ring- shaped tubes of force, which expand outwards from between the plates and then contract on some other part of the conductor. The time of the discharge, then, consists of the following steps, viz. : (I.) The time during which the energy of the charge is nearly all electrostatic and is repre- sented by the energy contained in the lines or tubes of electrostatic induction, running from plate to plate of the condenser. (2.) The time during which the discharge is at its maximum and the energy consists of two parts, viz.: energy associated with the outward ex- panding lines of electrostatic induction, and energy associated with the closed lines or tubes of mag- netic force, which at first are expanding and after- wards contracting. (3.) The time when the energy has been ab- sorbed, or the period in which the energy in the wire or the conductor has either been dissipated in the form of non- luminous radiation or obscure heat. (4.) The time during which this non-luminous heat gives up its energy again to the surrounding medium in the shape of heat waves. Current, Electro-Therapeutic Polarizing The current which produces the phenomena of electrotonus. (See Electro- tonus.) Current, Element of A term employed in mathematical discussions to in- dicate a very small part of a current for ease in considering its action on a magnetic needle or other similar body. Current, Faradic In electro- therapeutics, the current produced by an in- duction coil, or by a magneto-electric machine. A rapidly alternating current, as distin- guished from a uniform voltaic current. A voltaic current that is rapidly alternated by means of any suitable key or switch is sometimes called a voltaic alternative. The discharge from a Holtz machine is sometimes called a Franklinic Current. (See Alternatives , Voltaic. Current t Franklinic.') Current - Filaments. (See Filament, Current) Current, Franklinic A term some- times used in electro-therapeutics for a cur- rent produced by the action of a frictional electric machine. The term, Franklinic current, is used in con- tradistinction to Faradic current, or that produced by induction coils, or, in contradistinction to a galvanic or voltaic current, or that produced by a voltaic battery. Current, Generation of, by Dynamo-Elec- tric Machine The difference of potential developed in the armature coils by the cutting of the lines of magnetic force of the field by the coils, during the rota- tion of the armature. If a loop of wire whose ends are connected to the two-part commutator, shown in Fig. 179, be A Fig, IJQ. Induction in Armature Loop. rotated in the magnetic field between the magnet poles N and S, in the direction of the large arrow, differences of potential will be generated which Car,] 139 [Cur. will cause currents to flow in the direction indi- cated by the small arrows during its motion past the north pole from the top to the bottom, but in the opposite direction during its motion past the south pole from the bottom to the top. If, now, col- lecting brushes rest on the commutator in the positions shown in the Fig. 180. the vertical line A8P_ Fig. 180, Action of (Commutator. of the gap between the poles corresponding with the vertical gap between the commutator seg'- ments, the currents generated in the loop will be caused to flow in one and the same direction, and B , will become the positive brush, since the end of the loop is connected with it only so long as it is positive. As soon as it becomes negative, from the current in the loop flowing in the opposite direction, the other end, which is then positive, is connected with the positive brush. A similar series of changes occur at the nega- tive brush B. Theoretically, the neutral points, where the brushes rest, woull be in the vertical line coincid- ing with that of the gap between the poles. An inspection of the figure shows that the neutral line, or the diameter of commutation, is dis- placed in the direction of rotation. (See Commu- tation, Diameter of.) The displacement of the brushes, so necessitated, is called the lead. The cause of the lead is the reaction that occurs between the magnetic poles of the field magnets Fig i8r Cause of Lead of Brushes. and those of the armature, the result of which is to displace the field magnet poles, and to cause a change in the density in the field. This is shown in Fig, 181, where the density of the lines of force indicates the position of the diameter of commu- tation as being near, or at right angles to the di- ameter of greatest average magnetic density. (See Lead, Angle of. Lag, Angle of.) Current-Governor. (See Governor, Cur- rent) Current, Homogeneous Distribution of Such a distribution of a current through any conductor in which there is an equal density of current at all portions of any cross-section of the conductor. When the flow of a constant current is estab- lished in a solid conducting wire, there is a homogeneous distribution of current in that con- ductor. Current, Induced The current produced in a conductor by cutting lines of force. The induced current results from differences of potential produced by electro-dynamic induction. (See Induction, Electro- Dynamic.') Current - Induction. (See Induction^ Current.} Current, Intensity of An old term sometimes employed to indicate the current which resulted from a considerable difference of potential, or a great electromotive force. This term was also formerly used as synony- mous with strength of current. This use of the term is now abandoned. Voltaic batteries, connected in series so as ta give a considerable difference of potential, were spoken of as being connected for intensity. This term has also been used for the quantity of electricity conveyed per second across a unit area of cross -section. Intensity of current is more properly called density of current. (See Current Density.) Current, Intermittent A current that does not flow continually, but which flows and ceases to flow at intervals, so that elec- tricity is practically alternately present and absent from the circuit. Current, Inverse-Secondary The make-induced current. (See Current, Make- Induced) Current. Jacobi's Unit of Such a current that when passed through a volta- meter will liberate a cubic centimetre of Cur.J 140 [Cur. oxygen and hydrogen at O degrees C. and 760 mm. barometric pressure. One Tacobi's unit of current equals 10.32 ampere. (Obsolete.) Current, Make-Induced The current induced by a current in its own circuit on making or closing the same. The current produced in the secondary of an induction coil on the making or com- pletion of the circuit of the primary. The make-induced current is also called the inverse-secondary current, because its direction is opposite to that of the inducing current. Current, Make or Break Induced, Dura- tion of The time during which the induced inverse or direct-secondary currents continue. Blaserna made a number of experiments, which he claims shows : (I.) The greater the distance apart of the pri- mary and the secondary, that is, the less their mutual-induction, the less the maximum value of the secondary current, and the greater the delay in establishing that maximum. (2.) The delay in establishing the maximum of the break or direct-secondary current is not as great as in the case of the make, or inverse-sec- ondary current. (3.) When the coils are near together, the in- duced currents at starting are established by a series of electric oscillations. (4.) The primary current establishes itself by a series of electrical oscillations. (5.) That the interposition of dielectric sub- stances, such as glass between 'he coils, Deduces the time between tht making or breaking of the primary current and the beginning of the sec- ondary current. This last conclusion was nega- tived by some experiments of Bernstein. Blaserna determined in the ca<=e <>f certain ex- periments the following value for the durations of the secondary currents : In verse -secondary current lasts 000485 second, Direct -secondary current lasts .000275 second, Helmholtz contradicts the results of Blaserna, and asserts : (i.) That no perceptible difference in the zero points of the currents is produced by varying the distance between the primary and secondary , (2 ) That the sparks produced by the breaking of the primary last for an appreciable time, some- thing like Tjn ^ ff to ^hrs of a second. (3.) The duration of the break-spark is never constant, but depends in great part on the amount of platinum given off from the contacts at each spark. Current-Meter. A form of galvanometer. (See Galvanometer,) Current, Momentary A current that continues to flow but for a short time. Current, Multi-Phase A rotating current. (See Current, Rotating.) Current, Muscle In electro-thera- peutics, the current flowing through a muscle. Muscle currents are produced either by stimu- lation, or during activity of a muscle. According to L. Hermann, uninjured muscles, or perfectly dead muscles, yield no currents, but such cur- rents result only from an injury, (See Current, Demarcation , ) Current, Non-Homogeneous Distribution of Such a distribution of current pass- ing through a conductor m which there is an unequal density of current at all portions of any cross-section of the conductor. When a rapidly alternating current is passed through any solid conductor, the current density is greater at the surface and less towards the centre. The current distribution in such, a con ductor is non -homogeneous, and the want of uni formity of current density is greater as the rapid, ity of alternation or periodicity is greater. Current, Outgoing The current sent out over the line from a station provided with a duple* or quadruples transmission, as distinguished from the received current. (See Current, Received?) Current, Periodic A simple periodic current. (See Currents, Simple Periodic?) Current, Periodic, Power of An amount of work, per second, equal to the product of the electromotive force taken at successive moments of time during a com- plete cycle, multiplied by the current strength taken at the corresponding moments during the cycle. Since the electromotive force and current in Car.] 141 [Cur. a periodic circuit may be represented by two simple harmonic functions, the mean value of the two, when of different amplitude and phase, is equal to the product of their maximum value by the cosine of their difference of phase divided by two. Current, Polarization In electro- therapeutics, the constant current which when passed through a nerve produces in it the electrotonic state. (See Electrotonus.) Current. Pulsating A pulsatory current. (See Current, Pulsatory!) Current, Pulsatory A current, the strength of which changes suddenly. The pulsatory current usually consists of sudden and distinct impulses, or rushes of current, in contradistinction to an undulatory or harmonically varying current. Current, Received The current received from the distant end of the line at a station provided with a duplex or quadruplex transmission as distinguished from the out- going current. A term sometimes used in telegraphy to distinguish between currents that come in over the line from a distant station, and those that are sent out to a distant station. Current. Rectilinear A current flowing through straight or rectilinear por- tions of a circuit. In studying the effects of the attractions or repul- sions produced by electric currents the name ex- pressing the peculiarity of shape of any part of the circuit is often applied to the current flowing through that part of the circuit. Thus we speak of a rectilinear current, a sinuous current. Current, Reverse-Induced The current induced by a current in its own cir- cuit at the moment of making or closing the circuit. The current induced in the secondary on closing or making the circuit of the primary. This is called the reverse-induced current, be- cause its direction is opposite to that of the current in the inducing circuit. Current, Reversed A current whose direction is changed at intervals. (See Cur- rent, Alternating.} Current Reverser. (See Reverser, Cur- rent.) Current, Reversing a Changing the direction of an electric current. Current, Rotating A term applied to the current which results by combin- ing a number of alternating currents, whose phases are displaced with respect to one an- other. A rotating current is sometimes called a poly- phase or multiple-phase current, particularly if there are three or more currents combined. The rotating current is employed by Tesla, Dobrowolsky and others in a system of distribu- tion by transformers in place of the ordinary alternating current. In practice, three alternating current are combined. The currents and their combination are obtained by means of a specially constructed alternator. When three currents are combined the displacement between each set of phases is 1 20 degrees. A rotating current, unlike an alternating current, possesses, in a certain sense, a definite direction of flow. Its effect on a magnetic needle is to cause rotation. Hence motors constructed on the principle of rotating currents will start with a load. Current, Rotatory Phase Alternating A term sometimes employed for a rotating electric current, (See Current, Ro- tating.) Current, Secretion In electro- therapeutics, a current following stimulation of the secretory nerves. Current, Simple-Harmonic A term sometimes used instead of simple-periodic current. (See Currents, Simple Periodic.) Current, Sinuous A term some- times applied to currents flowing through a sinuous conductor. Sinuous currents exert the same effects of attrac- tion or repulsion on magnets, or on neighboring circuits, as would a rectilinear current whose length is that of the axis of such sinuous current. This can be shown by approaching the circuit A' B', Fig. 182, consisting of the sinuous con- ductor A', and rectilinear conductor B', to the movable conductor A B C, on which it produces no effect. The current A', therefore, neutral- Cur.] 142 [Cuiv izes the effects of the current B' ; or, it is equal to it in effect. Fig. z82. Rectilinear Equivalent of Sinuous Current. In calculating the effects of sinuous currents it is convenient to consider them as consisting of a Fig. 183. Sinuous Currents. succession of short, straight portions at right an- gles to one another, as shown in Fig. 183. Current, Steady A current whose strength does not vary from time to time. In a steady current the quantity of electricity flowing through each unit of area of the equi- potential surface of the conductor is the same for each succeeding interval of time. Such a current is sometimes called a uniformly distributed cur- rent. Current Streamlets. (See Streamlets, Current.} Current Strength. The product obtained by dividing the electromotive force by the resistance. The current strength for a constant current according to Ohm's law is c =l- Current strength is proportional to the amount of the magnetic or chemical (electrolytic) effects it is capable of producing. For a simple-periodic current, the current strength necessarily varies from time to time. The average current strength of a simple- periodic current is equal to the average impressed electromotive force divided by the impedance. (See Impedance. ) The maximum current strength is equal to the maximum impressed electromotive force divided by the impedance. Current, to Transform a To change the electromotive force of a current by its passage through a converter or trans- former. To convert a current. Current, Transforming a Chang- ing the electromotive force of a current by its passage through a converter or transformer. Current, Undulating An undu- latory current. (See Currents, Undulatory^) Current, Uniformly-Distributed A term sometimes employed in the same sense as steady current. (See Current, Steady?) Current, Unit Strength of Such a strength of current that when passed through a circuit one centimetre in length, arranged in an arc one centimetre in radius, will exert a force of one dyne on a unit mag- net pole placed at the centre. This absolute unit is equal to ten amperes or practical units of current. (See Ampere.) Current, Variable Period of The period which exists while an electric current is being increased or decreased in strength, or while it is being reversed. Currents, Action Physiological cur- rents obtained during the activity of a muscle or nerve. Currents, After In electro-thera- peutics, currents produced in nervous or muscular tissue when a constant current, which has been flowing through the same, has been stopped. After currents are due to internal polarization. Currents, Alternating-Primary The currents employed in the primary of a Cur.] 143 [Cur. transformer to induce alternating currents in the secondary. (See Transformer) Currents, Alternating-Secondary The currents induced in the secondary of a transformer by the alternating currents in the primary. (See Transformer?) Currents, Alternating, Shifting of Phase of (See Phase, Shifting of, of Alter- nating Currents,) Currents, Amperiaii The electric currents that are assumed in the amperian theory of magnetism to flow around the mole- cules of a magnet. (See Magnetism, Amperes Theory of.) The amperian currents are to be distinguished from the eddy, fotuanlt, or parasitical currents,. since, unlike them, they are directed so as to pro duce useful effects. (See Currents, Lddy ) It is not believed that the amperian currents are produced in magnetizable substances by the act of magnetization. The atoms or molecules were magnetic originally. All the magnetizing force does is to arrange the molecules or atoms, or to set them in one and the same direction. Currents. Angular Currents flow- ing through circuits that cross or are inclined to one another at any angle- (See Dynamics, Electro) Currents. Atomic A term some- times used instead of molecular or amperian currents. (See Currents, Amperian) Currents, Attractions and Repulsions of The mutual attractions or repul- sions exerted by currents on .one another through the interaction of their magnetic fields. (See Dynamics, Electro) Currents, Commuted Electric cur- rents that have been caused to flow in one and the same direction. (See Commutator) Currents, Commuting 1 Causing several currents to flow in one and the same direction. Currents, Conrw.ient The two or more currents into which it may be conceived that a single current can be divided, so as to produce the same effects of attraction or repulsion that the single current would do. The idea of component currents is based on the similar idea of the components of any single force. Currents Continuity of The freedom fro.n variation in current strength or current direction. Currents, Convection Currents produced by the bodily carrying forward of static charges in convection streams. (See Streams, Convection) In a convection current, the static charge is bodily carried forward. Rowland has shown experimentally that a moving electric charge is the equivalent of an electric current. He rotated a gilded ebonite disc between two gilt glass discs, near which were placed a number of delicate magnetic needles. When certain rapidity of rotation was obtained, the discs were found to affect the mag- netic needles the same as would a current of elec- tricity flowing in a circular conductor, whose form coincided with the periphery of the disc. Currents, Converted Electric cur- rents changed either in their electromotive force or in their strength, by passage through a converter or transformer. (See Trans- former) Currents, Converting Changing the electromotive force of currents by their passage through a converter or transformer. (See Transformer) Currents. Diaphragm Electric cur- rents produced by forcing a liquid through the capillary pores of a diaphragm. (See Osmose, Electric) Currents, Earth Electric currents flowing through the earth, caused by a differ- ence of potential at different parts. The causes of these diffe-ences of potential are various and are not well understood. Currents, Elly Useless currents produced in the pole pieces, armatures, field- magnet cores of dynamo-electric machines or motors, or other metallic masses, either by their motion through magnetic fields, or by variations in the strength of electric currents flowing near them. Sensible eddy currents are producd in the mass Cur.] [Cur. of the conducting wire on the armature of a dynamo-electric machine when the wire is com- paratively heavy. Such currents are called eddy currents, local currents, Foucault currents, or parasitical' cw- i ents. They form closed -circuits of comparatively low resistance, and tend to cause undue heating of armatures or pole pieces. They not only cause a Fig. 184. Foucault Currents in Pole Pieces. useless expenditure of energy, but interfere with the proper operation of the device. To reduce them as far as practicable, the pole pieces, armature cores or armature wires, are laminated. (See Core, Lamination of.) These local currents are perhaps preferably called Foucault currents when they take place in magnetic cores, pole pieces or armature cores, and eddy currents when they occur in the armature wire or conductor. When the armature conductor is made up of copper bars, for exam- ple, the eddy currents in the latter are usually considerable Since Foucault currents in dynamo-electric ma- chine cores are due to variations in the magnetic Fig. 183. Foucault Currents in Pole Pieces. strength of the field magnets, or of the arma- ture, they will be of greatest intensity when the changes in the magnetic strength are the greatest and most sudden. These changes are most marked, and conse- quently the Foucault currents are strongest at those corners of the pole pieces of a dynamo from which the armature is moved in its rotation, as will be seen from an inspection of Fig. 184. Fig. 185, shows Foucault currents generated in pole pieces. Currents, Eddy-Conduction A term employed for ordinary eddy currents in conductors, in order to distinguish them from eddy-disp'acement currents. (See Currents, Eddy-Displacement.) Currents, Eddy Deep Seated Eddy currents set up in the mass of a conductor sub- jected to electro-dynamic induction in con- tradistinction to superficially seated eddy cur- rents. (See Currents, Eddy, Superficial.) Currents, Eddy-Displacement Eddy currents produced in the mass of a dielectric or insulator, when lines of magnetic or electrostatic force pass through the di- electric or insulator. Eddy -displacement currents are produced in a dielectric or non-conductor, when it is moved across a magnetic field, so as to cut the lines of magnetic force. Eddy displacement currents would also occur if a dielectric is subjected to varying electrostatic induction. Currents, Eddy, Superficial Eddy currents produced in conducting substances that are limited to the outer layers thereof. The eddy currents produced by alternating currents are superficial if the alternating currents are sufficiently rapid. The oscillatory currents pro- duced during the discharge of a Leyden jar are more superficial in proportion as the discharge takes ' place rapidly. When currents are pro- duced in a magnetizable body by the discharge of a Leyden jar, they are more and mo: e super- ficial, as the discharge of the jar is more and more rapid. The reason a slow discharge of a jar or condenser produces a greater magnetizing eflect is, because of the checking or screening action the superficial eddy currents exert on the interior of the mass of the magnetizable substance when the discharge is very rapid. Currents, Electrotonic In electro- therapeutics, currents due to internal polariza- tion, in the nerve fibre between the conduct- ing core of the nerves and the enclosing sheaths. Currents, Extra Currents pro- duced in a circuit by the induction of the current on itself on the opening or closing of Car.] 145 LCur. the circuit (See Currents, Extra. Induc- tion, Self.} The extra current induced on breaking, flows in the same direction as the original current and acts to strengthen and prolong it. The extra current induced on making or com- pleting a circuit flows in the opposite direction to the original current and tends to oppose or re- tard the current. Both ot these currents are called induced or extra currents. The former is called the direct- induced current, and the latter the reversed-in- duced current. (See Current, Direct-Induced. Current, Reversed- Induced.} In order to distinguish this induction from that produced in a neighboring conductor by the pas- sage of the electric current, it is called selj -induc- tion. (See Induction, Self. Induction, Mutual.) The effect on a telegraphic line of the self-in- duced or extra currents is to decrease the speed ot signaling by retarding the beginning of a signal, and prolonging its cessation , The greater the number of turns of wire in a circuit, or magnet, and the greater the mass of iron in its core, the greater the strength of the extra currents. Currents, Foucault A name some- times applied to eddy currents, especially in armature cores. (See Currents. Eddy} Currents, Heating Effects of- The heat produced by the passage of an electric current through any circuit. (See Heat, Elec- tric^ Currents, Imbibition Currents produced in tissues by the imbibition or ab- sorption of a fluid. Imbibition currents are a species of diaphragm currents. The absorption of a fluid at the demarcation surface of an injured nerve or muscle, or at the contracted portion of muscles, produces imbibition currents. Such currents are also produced in plants by the movement of fluids produced by bending the stalk or leaves, or by active movements of certain sensitive plants. Currents, Induced-Molecular or Atomic Currents induced in the atoms or molecules of a magnetizable substance on its being brought into a magnetic field. These currents are called induced -molecular, or induced -atomic currents in order to distin- em from the molecular, atomic or amperian currents, or the currents which are assumed to be always present. It is by the presence of these assumed induced-molecular currents that the phenomena of diamagnetisra are explained by Weber. (See Diamagnetism, Weber's Theory of.) Currents, Local A name sometimes applied to eddy currents. (See Currents, Eddy.) Currents, Molecular or Atomic A term sometimes employed for amperian currents. (See Currents, Amperian?) Currents, Natural A term some- times applied to earth currents. (See Cur- rents Earth^) Currents, Negative A term em- ployed in single-needle telegraphy for cur- rents sent over a line in a negative direction by depressing a key that connects the line with the negative pole of a battery and so deflects the needle to the left. (See Teleg- raphy, Single-Needled) Currents, Network of A term sometimes applied to a number of shunt or derived circuits. (See Circuit, Shunt, Cir- cuit, Derived. Laws, Kirchhoff"s?) Currents of Motion. A term sometimes employed in electro-therapeutics for the cur- rents of electricity that traverse healthy muscle or nerve tissue during the sudden con- traction or relaxation thereof. The existence of these currents is denied by some. Currents of Rest. A term sometimes em- ployed in electro-therapeutics for the cur- rents of electricity that traverse healthy muscle or nerve tissue while the muscles are passive. The existence of these currents is denied by some. Currents, Orders of Induced elec- tric currents named from the order in which they are induced, as currents of the first, second, third, fourth, etc., orders. An induced current can be caused to induce an- other current in a neighborinir circuit, and this a third current, and so on. Such currents are dis- Cur.] 146 [Cur. tinguiahed by the term, currents of the second, third, fourth, etc., order. (See Coils, Henry's.) Currents, Parasitical A name sometimes applied to eddy currents. (See Currents, Eddy.} Currents, Positive A term em- ployed in single-needle telegraphy for currents sent over the line in a positive direction by de- pressing a key that connects the line with the positive pole of a battery and so deflects the needle to the right. (See Telegraphy, Single-Needle} Currents, Reversed A name some- times applied to alternating currents. (See Current, Alternating} Currents, Secondary The currents produced by secondary batteries in contra- distinction to the currents produced by primary batteries. The currents produced by the secondary conductor of an induction coil, as distinguished from the currents sent into the primaries. This second use of the term secondary current is more usual. Currents, Self-Induced A current produced by self-induction. An extra current. (See Induction, Self. Currents, Extra.} Currents, Simple Periodic Cur- rents, the flow of which is variable, both in strength and duration, and in which the flow of electricity, passing any section of the con- ductor, may be represented by a simple peri- odic curve. A current of such a nature that the con- tinuous variation of the flow of electricity past any area of cross-section of the con- ductor, or the variations in the electromotive force of which can be expressed by a simple- periodic or harmonic curve. (See Curve, Simple-Harmonic} Alternate currents are simple-periodic currents. The average current strength of simple-periodic currents is equal to the average impressed electro- motive force divided by the impedance. The transmission of rapidly varying or sim- ple-periodic currents through conductors differs very greitly from the transmission of steady cur- rents. With a steady current, the current density is the same for all areas of cross-section of the conductor. For a rapidly intermittent current, the current density is greater near the surface, and when the rate of intermission is sufficiently great, the current is entirely absent at the centre of the conductor. Lord Rayleigh has shown that when the rate of intermission is 1,050 per second, the effective re- sistance of a wire i6omm. in length, and 30 mm. in diameter, is 1 .84 times its resistance to steady currents. He found that the increase of resist- ance is greater in the case of conductors of great diameter than in those of small diameter, As regards the character of conductor best suited for transmitting rapidly alternating cur- rents, it can be shown : (i.) That for transmitting alternate currents of moderate frequency, say of about I, coo per sec- ond, copper conductors should be used in prefer- ence to rods of iron. (2.) That the conductor should be in the form of thin strips, or if tubular, of thin walls. (3.) That the mere stranding of the conductor, *. <., forming it of separate insulated conductors connected in parallel, will be of no effect in pre- venting the current from acting on the outside of the conductor, unless the conductor be arranged in the form of a cable, in which one part forms a lead, and another part the return. Stephan draws the following analogy between the flow of alternating currents in a conductor and the flow of heat in a hot wire : ' ' Suppose a wire or conductor, uniformly heated from centre to circumference, be suddenly taken into a space where the temperature i* high, the outer portions of the wire first rise in temperature, and afterwards the inner portions. In the case of a conductor of circular cross-section, the heat penetrates successive concentric layers. The same phenomena occur when an electromotive force is suddenly set up between the ends of a cylindrical conductor. The current gradually penetrates the conductor from the outside to the centre. " Now suppose the heated wire is carried into a cooler space, the heat waves pass out radially from the centre towards the circumference. The cooling wire corresponds to the case of a con- ductor in which the external electromotive force is suddenly removed." According to this conception, the heat conduct- ing power of any substance corresponds to its electrical conducting power. Cur.] 147 [Cur. According to Stephan, in the case of a con- ductor of iron of 4 mm. in diameter, traversed by an alternating current of 250 alternations per second, the current density on the surface is about tweuty-five times as great as that at its axis. Where the conductor is of non magnetic mate- rial, the difference in the current density is not so marked. Rapidly intermittent currents produce a real increase in the resistance of the conductor, which must not be confused with the fact that the impe- dance is greater than the ohmic resistance, but rather as an actual increase in the rate at which energy is dissipated per unit of current. Since current density is greatest at the outside portions of a conductor, and the central portions are nearly, if not entirely, deserted by the cur- rent, we may regard the conductor as having the ohmic resistance of a hollow cylinder of the same diameter as the conductor, with a cor- respondingly smaller area of cross-section, and therefore, of greater ohmic resistance per unic of length. The condition of affairs in the case of a con- ductor in which a current of electricity is begin- ning to flow, is now very generally regarded somewhat as follows, viz.: The current begins at the surface of the con- ductor, and more or less slowly soaks through towards the centre. If the current is constant, the current soon reaches the deepest layers; but, if it is rapidly intermittent, before it can soak very far into the conductor towards its axis, it is turned back towards the surface, and so becomes con- fined to layers which will be more and more super- ficial, as the rapidity of reversal increases. Therefore, for convenience, we may regard a solid conductor, through which a rapidly inter mittent current of electricity is flowing, as being practically converted into a hollow cylinder of the same diameter as the solid conductor, the area of cross -section of which hollow cylinder becomes smaller and smaller, as the rapidity of alternation is increased. Another, and perhaps the more correct concep tion of the condition of affairs in a solid conductor traversed by a rapidly alternating current of elec- tricity, has been pointed out by Maxwell, and after- wards by Heavyside, Rayleigh and Hughes. This conception is to regard the central portions of the conductor as possessing a counter electromotive force greater than the outer portions. The entire current flowing across any section of a conductor miy be regarded as made up of little current streamlets, parallel to one another. The central streamlets, or filaments, from their mutual induction on one another, experience a greater resistance in reaching their full strength than the surface filaments do. Taken in this sense, we may state generally that the transmis- sion of rapidly alternating currents through con- ductors depends on the inductance, rather than on the resistance; but for steady currents, it de- pends more on the resistance than on the induct- ance. In periodic or oscillatory currents, as those produced by. the discharge of a Leyden jar, or condenser, the surface streamlets have a current density far greater than the central streamlets. The true or ohmic resistance of the circuit is a minimum when the current is uniformly distrib- uted through all parts of the cross-section of the conductor, and the dissipation of energy through the generation of heat is less than for any other distribution. The conception of a periodic current flowing through a conductor, starting from the surface and gradually soaking in towaids the centre, regards the energy of an electric current not as being pushed through the conductor, as water through a pipe, but as actually being absorbed at its surface, from the surrounding dielectric, or as being, so to speak, rained down on the conductor from the space outside of it. Currents, Swelling In electro- therapeutics, currents that begin weak and are gradually made stronger and then weaker. Currents, Swelling-Faradic A term employed in electro-therapeutics for f ara- dic currents that are caused to gradually in- crease in strength and then to gradually de- crease to zero strength. Currents, Transient Currents that are but of momentary duration. Currents, Undnlatory Currents the strength and direction of whose flow gradually change. The term undulatory currents is used in con- tradistinction to pulsatory currents, in which the strength changes suddenly. In actual practice, such currents differ from undulatory currents more in degree than in kind, since, when sent into a line, the effects of retardation tend to obliterate, to a greater or less extent, the sudden Cur.] 148 [Cur. differences in intensity on which their pulsatory character depends. The currents produced in the coils of the Sie- mens magneto- electric key, in which the me- chanical to-and-fro motion of the key sends elec- trical impulses into the line, are, in point of fact, undulatory in character, when they follow one an- other rapidly. The currents in most dynamo-electric machines, the number of whose armature coils is compara- tively great, are, so far as the variations in their intensity or strength are concerned, undulatory in character even when non-commuted. The currents on all telephone lines that trans- mit articulate speech are undulatory. This is true, whether the transmitter employed merely varies the resistance by variations of pressure, or actually employs makes-and-breaks that rapidly follow one another. (See Current, Pulsatory. Current, Intermittent.) Curtain, Auroral A sheet of auroral light having the shape of a curtain. (See Atirora Borealis^) Curve, Asymptote of A straight line which continually approaches a curved line, but meets or becomes tangent to such curved line only at an infinite distance. In Fig. 186, the curve C D, continually ap- proacli~j t'.i,? asymptote y z, but never meets it. It is at first difficult to un- derstand how one line can continually approach an- other and yet never meet it. But it will be readily under- stood if it is remembered & ~"* that in all cases of asymp- F 'S- rS6. Asymptote totic approach each advance "/ Curve - becomes smaller and smaller. This mathematical conception is like a value which, although constantly reduced to one-half of its former value, is nevertheless never 1 reduced to zero or no value. Curve, Ballistic The curve ac- tually described by a projectile thrown in any other than a vertical direction through the air. The path of a projectile in a vacuum is a para- bola that is, the path A E B, Fig. 187. In air, the effects of fluid resistances cause the projectile to take the path A C D, called a ballistic curve. The ballistic curve has a smaller vertical height than the parabola. The projectile also has a. Dl|F Fig. 187. Ballistic Curve. smaller vertical range. Instead of reaching the- point B, it continually approaches the perpen- dicular E F. Curve, Characteristic A diagram in which a curve is employed to represent the ratio of certain varying values. The electromotive force generated in the arma- ture coils of a dynamo-electric machine, when the- magnetic field is of a constant intensity, is theo- retically proportional to the speed of rotation. In practice this is modified by a number of circum- stances. The relation existing between the speed and electromotive force may be graphically rep- resented by referring the values to two straight lines, one horizontal and the other vertical, called respectively the axes of abscissas and ordinates. (See Abscissas, Axis of.) If, in a. given case, the number of revolutions is marked off along 90<> ~ the horizontal line from the point o, Fig. 188, in distances from o, proportional to the number of revolu- tions, and the corre- sponding electromo- tive forces are marked off along the vertical line in distances from o, proportional to the electromotive forces, the points where these lines intersect will form the characteristic curve as shown in Fig. 188. Curve, Characteristic, of Parallel Trans- former A curve so drawn that its ordinate and abscissa at any point represent the secondary electromotive force and the sec- ondary current of a multiple connected trans- former, when the resistance of the secondary circuit has a certain definite value. With a constant electromotive force in the pri- Fig. JS8. Characteristic Curve. Car.] 149 [Cur. mary circuit, i. ., with the transformers in parallel, the characteristic curve is a straight line parallel to the axis of the current. This curve, as shown in Fig. 189, is practically a straight line. The par- allel transformer will be practically self- regulating under a constant primary electromotive force. According to Forbes, if a transformer has its lamp f,-^. jgg. Character- load in parallel with the istic of Parallel Trans- secondary circuit, the ex- former. tinction of its lamps will decrease the efficiency of the transformer. The efficiency is therefore less for light loads than for heavy loads of parallel lamps up to a certain point. Curre, Characteristic, of Series Trans- former A curve so drawn that its ordinate and abscissa at any point represent the secondary electromotive force and second- ary current of a series-connected transformer, when the resistance of the secondary current has a certain definite value. Fig. 190 shows characteristic curve of a series I? Fig. 19 o. Characteristic of Series Transformer. transformer. O a, is drawn perpendicular to the line representing the secondary current, and a b, perpendicular to O a, represents the correspond- ing secondary electromotive force. The various positions of b, as different values are given to O a, produce the elliptic curve which is the character- istic curve of the series transformer. " A series transformer, " says Fleming, "with a core sufficiently large to avoid saturation, can never be self-regulating if so used. It can only be made self- regulating with a non -saturated core, when working near the extremities of its charac- teristic, either with a small secondary current or a low electromotive force. Both of these con- ditions are uncommercial." Curve, Life, of Incandescent Lamp A curve in which the life of an electric lamp is represented by means of abscissas and ordinates proportional to the life in hours and the candle-power or the volts respectively. Carre, Logarithmic A curve in which the rate of increase or decrease of the ordinate is proportional to the ordinate itself. On the line O X, Fig. 191, mark off the time Y- 191. Logarithmic Curve. in lengths, reckoned from O. Represent the current strength by lines drawn vertically to the time-line. Let O Y, equal C = |- Applying the electromotive force, the current grows in the wire as represented by the graphic curve. According to Fleming, the growth of this cur- rent takes place according to the following law, viz.: "The current strength at any instant, added to the rate of growth of the current strength at that instant multiplied by the time-constant, is equal to the current which would exist if induc- tion were zero. ' ' Carre, Permeability -- A curve repre- senting the magnetic permeability of a mag- netic substance. There is a certain temperature for every para- magnetic substance, at which its permeability is no greater than that of air. This temperature for iron is reached at about 750 degrees C.; for nickel, at about 400 degrees C. Carre, Simple-Harmonic - The curve which results when a simple-harmonic motion in one line is compounded with a uni- form motion in a straight line, at right angles thereto. A harmonic curve is sometimes called a curve of sines, because the abscissas of the curve are proportional to the times, while the ordinates are proportional to the sines of the angles, which are themselves proportional to the times. Car.] 150 [Cut. Carves, Isochasmen Curves drawn on the earth's surface between zones having equal frequency of auroral discharges. The isochasmen curves are nearly at right angles to the magnetic meridian. Curves, Magnetic Curved lines showing the direction of the lines of mag- netic force in any field, formed by sprinkling iron filings on a sheet of paper or glass held in the field of a magnet, and gently tapping the support so as to permit the filing* to prop- erly arrange themselves. (See Fzgttres, Magnetic?) Cut-In, To To introduce an electro- receptive device into the circuit of an electric source by completing or making the circuit through it. Cut-Off, Automatic Gas A device for automatically cutting out the battery from an electric gas-lighting circuit on the accidental grounding of the circuit. Unless the battery is disconnected from the cir- cuit on the establishing of a ground, the battery will polarize and soon become useless. Cut-Out, A A device by means of which an electro-receptive device or loop may be thrown out of the circuit of an electric source. In any system of light or power distribution, a cut out is generally placed outside a building into which a loop or branch of the main circuit runs, so as to permit that loop or branch to be readily disconnected therefrom. In the same way cut-out keys or switches are generally placed in the circuit of the loop and each electro-receptive device. Cut-Out, Air-Space A modified form of paper cut-out, in which the disc of paper or mica is replaced by the resistance of an air-space. Although the resistance of an air-space is so high as to be practically immeasurable, yet it is overcome or broken by a much lower differ- ence of potential than an equal thickness of paper or mica. (See Path, Alternative. Cut- Out, Film.) Cut-Out, Automatic Any device that will automatically cut-out, or remove, a translating device, or an electric source, from an electric circuit, whenever any predeter- mined effect is produced. Cut-Out, Automatic, for Multiple-Con- nected Electro-Receptive Devices A device for automatically cutting an electro- receptive device, such as a lamp, out of the circuit of the leads. Automatic cut-outs for incandescent lamps, when connected to the leads in multiple-arc, con- sist of strips of readily melted metal called safety fuses, which on the passage of an excessive cur- rent fuse, and thus automatically break the cir- Fig. zqz. Ceiling Cut-Out. cuit in that particular branch. (See Catch, Safety.) A form of ceiling cut-out, made of porcelain, is shown in Fig. 192, with the two halves separated Fig. 193. Ceiling Cut-Out. to show interior details, and in Fig. 193, with the two halves placed together. Cut.] 151 [Cyc. Cut-Out, Automatic, for Series-Connected Electro-Receptive Devices A device whereby an electro-receptive device, such as an electric arc lamp, is, to all intents and purposes, automatically cut out, or removed from the circuit, by means of a shunt of low resistance, which permits the greater part of the current to flow past the lamp. It will be observed that the lamp, though still in the circuit, is to all practical intents cut out from the same, since the proportion of the current that now passes through it is too small to oper- ate it. In most series arc lamps, cut-outs are oper- ated by means of an electro-magnet placed in a shunt circuit of high resistance around the car- bons. If the carbons fail to properly feed, the arc increases in length and consequently in resist- ance. More current passes through the shunt magnet, until finally, when a certain predeter- mined limit is reached, the armature of the elec- tro magnet is attracted to the magnet pole and mechanically completes the short circuit past the lamp. In some automatic cut-outs the fusion of a readily fused wire, placed in a shunt circuit around the carbons, permits a spring to complete the short circuit. The automatic cut-out prevents the accidental extinguishing of any single lamp in a series cir- cuit from extinguishing the remaining lamps on that circuit. Cut-Out, Automatic Time A device arranged so as to automatically cut out a translating device, or an electric source, from a circuit, at the end of a certain predetermined time. Cut-Out, Duplex A cut-out so arranged that when one bar or strip is fused or melted by an abnormal current another can be immediately substituted for it. Cut-Out, Film A cut-out in which a film, or sheet of paper or mica, is interposed between a line plate and an earth plate, which, when punctured by a spark, short circuits the instruments on the line. Cut-Out, Main-Line - - An auto- matic cut-out placed on the main line. (See Cut-Out, Automatic) A form of main-line cut-out is shown in Fig. Fig 194. Main-Line Cut-Out. 194. The fuses are shown as attached to the fuse- block. Cut-Out, Paper A term sometimes employed instead of film cut-out. (See Cut- Out, Film.} Cut-Out, Rosette A rosette for an electrolier, containing a cut-out. (See Ro- sette} Cut-Out, Spring-Jack A device similar in general construction to a spring- jack, but employed to cut out a circuit An insulated plug is thrust between spring contacts, thus breaking the circuit by forcing them apart. Cut Out, To To remove an elec- tro-receptive device from the circuit of an electric source by disconnecting or diverting the circuit from it. Cutting Lines of Force. (See Force, Lines of Cutting.) Cycle. A period of time within which a certain series of phenomena regularly recur, in the same order. Cycle, Magnetic A single round of magnetic changes to which a magnetizable Cyc.] 152. [Danu substance, such as a piece of iron, is subjected when it is magnetized from zero to a cer- tain maximum magnetization, then decreased to zero, reversed and carried to a negative maximum, and then decreased again to zero. Cyclical Magnetic Variation. (See Va- riation, Cyclical Magnetic?) Cyclotrope. A name proposed in place of transformer or converter. (See Trans- former?) Cylinder, Yortex A number of vortex stream-lines grouped parallel to one another about a straight line which forms the axis or core of the vortex. Cylindrical Armature. (See Armature, Cylindrical?) Cylindrical Carbon Electrodes. (See Electrodes, Cylindrical Carbon?) Cylindrical Electro-Magnet. (See Mag- net, Electro, Cylindrical?) Cylindrical Magnet. (See Magnet, Cyl- indrical?) Cylindrical Ring Armature. (See Arm- ature, Cylindrical Ring?) Cymogene. An extremely volatile liquid which is given off from crude coal oil during the early parts of its distillation. The two liquids which are obtained from the condensation of the vapors given off during the first parts of the distillation of coal oil are called cymogene^ and rhigolene. These liquids are em- ployed on account of their extreme volatility for the artificial production of cold. Rhigolene is employed by some for the treat- ment or flashing of the carbons used in incan- descent lamps. (See Car&ons, Flashing Process for.) Cystoscopy, Electric A name given to Hitze's method of ocular examination of the human bladder by electric illumina- tion. Damped Magnetic Needle. (See Needle, Magnetic, Damped?) Damper. A metallic cylinder provided in an induction coil so as to partially or com- pletely surround the iron core, for the purpose of varying the intensity of the currents induced in the secondary. The metallic cylinder acts as a screen or shield foi the rapidly alternating currents traversing the field of the primary. (See Screening, Magnetic.') As the damper is pulled out, a greater length of the core is exposed to the induction. Damper. A term sometimes applied to a dash-pot or other similar apparatus provided for the purpose of preventing the too sudden movement of a lever or other part of a device. (See Dash-Pot) Some form of damper or dash-pot is used on most electric arc lamps, the upper carbon of which is fed by a direct fall. The double use of this word is unfortunate. Damping. The act of stopping vibratory motion such as bringing a swinging mag- netic needle quickly to rest, so as to deter- mine the amount of its deflection, without waiting until it comes to rest after repeated swingings to and fro. Damping devices are such as offer resistance to quick motion, or high velocities. 1 hose gen- erally employed in electrical apparatus are either air or fluid friction, obtained by placing vane* on the axis of rotation, or by checking the move- ments of the needle by means of the currents it sets up, during its motion, in the mass of any con- ducting metal placed near it. These currents, as Lenz has shown, always tend to produce motion in a direction opposed to that of the motion caus- ing them. Bell-shaped magnets are especially suitable for this kind of damping. (See Magnet^ Bell Shaped.) The needle of a galvanometer is dead-beat when its moment of inertia is so small that its oscillations in an intense field are very quick, and the mirror, acting as a vane, causes the movements to die out very rapidly, and the needle therefore moves sharply over the scale from point to point and comes quickly to a dead stop. When the needle or swinging coil is heavy and moves in an intense Dam.] 153 [Dea. field, as in the Deprez-d' Arson val galvanometer, the movements are dead-beat. Damping by means of pieces of india rubber is often applied to telephone diaphragms to prevent their excessive or continued vibration. Damping 1 , Electric A term some- times employed to express a decrease in the intensity of the electric oscillations pro- duced in a conductor by electric resonance, under circumstances where higher overtones are set up in the conductor. Daniell's Yoltaic Cell. (See Cell, Vol- taic, Daniell's.} Dark-Space, Crookes' (See Space, Dark, Crookes'.} Dark-Space, Faraday's (See Space, Dark, Faraday's.} Dash-Pot. A mechanical device to prevent too sudden motion in a movable part of any apparatus. The dash-pot of an automatic regulator, or of an arc -lamp, is provided to prevent too sudden movements of the collecting brushes on the com- mutator cylinder, or the too sudden fall of the upper carbon. Such devices consist essentially of a loose fitting piston that moves through air or glycerine. Dash-pots are species of damping devices, and, like the damping arrangements on galvanometers or magnet needles, prevent a too free movement of the parts with which they are connected. (See Damper. Damping. ) Day, Normal Magnetic A day dur- ing which the value of the earth's magnetic elements does not vary greatly from their mean value. (See Elements, Magnetic, of a Place^ Day of Disturbance, Magnetic A day during which the mean departure of the readings of a declinometer at any place, from the normal monthly value at that place, is once and a half the average. (Lloyd.} Dead-Beat. Such a motion of a galvanom- eter needle in which the needle moves sharply over the scale from point to point and comes quickly to rest. (See Damping:} Dead-Beat Discharge. (See Discharge, Dead-Seat.} Dead-Beat Galvanometer. (See Galva- nometer, Dead-Beat. ) Dead Dipping. (See Dipping, Dead.} Dead Earth. (See Earth, Dead or Total.) Dead Turns of Armature Wire, or Dead Wire. (See Turns, Dead, of Armature Wire.} Death, Electric Death resulting from the passage of an electric current through the human body. The exact manner in which an electric current .causes death is not known. When the current is sufficiently powerful, as in a lightning flash, or a powerful dynamo current, insensibility is prac- tically instantaneous. Death may be occasioned: (I.) As the direct result of physiological shock. (2.) From the action of the current on the res- piratory centres. (3.) From the actual inability of the nerves or muscles, or both, to perform their functions. (4.) From an actual electrolytic decomposition of the blood or tissues of the body. (5.) From the polarization of those parts of the body through which the current passes. (6.) From an actual rupture of parts by a dis- ruptive discharge, The current required to cause death will de- pend on a variety of circumstances, among which are: (i.) The particular path the current takes through the body, with reference to the vital organs that may lie in this path. (2.) The freedom or absence of sudden varia- tions of electromotive force. (3. ) The time the current continues to pass through the body. In some fatal cases, it is probably the extra- current, or the induced-direct current on break- ing, that causes death, since, as is well known, its electromotive force may be many times greater than that ot the original current. A comparatively low-potential continuous-cur- rent, cannot, therefore, be properly regarded as entirely harmless, simply because its electro- motive force is necessarily small. In the case of alternating currents the danger increases after a certain point with the number of alternations per second. When, however, the number of alter- nations per second reaches a given number, the danger decreases as the frequency of alternations Dec.] 154 LDeg. increases. This was conclusively shown by the independent investigations of Tatum and Tesla. Decalescence. A term proposed by Prof. Elihu Thomson for an absorption of sensible heat, which occurs at a certain time during the heating of a bar of steel. Decalescence will thus be observed to be the reverse of recalescence, which is the phenome- non of the emission of sensible heat at a certain time during the cooling of a heated bar of steel. (See Recalescence.) Deci (as a prefix). The one-tenth. Deci-Ampere. One-tenth of an ampere. Deci-AmpSre Balance. (See Balance, Deci-Ampere) Dsci-Lux. The one-tenth of a lux. (See Lux.} Declination. The variation of a mag- netic needle from the true geographical north. The magnetic declination is eat or west. (See Needle, Magnetic, Declination of.) Declination, Angle of The angle which measures the deviation of the mag- netic needle to the east or west of the true geo- graphical north. The angle of variation of a magnetic needle. In Fig. 195, if N S, rep- resents the true north and south line, the angle of de- clination is N O A, and Fig ipf. Declination the sign of the variation is f Needle, east, because the deviation of the needle is to- ward the east. (See Needle, Magnetic, Declina- tion of.) Declinometer. A magnetic needle suit- ably arranged for the measurement of the value of the magnetic declination or varia- tion at any place. Decomposition. In chemistry the separa- tion of a molecule into its constituent atoms or groups of atoms. (See Molecule. Atom.) Decomposition, Electric Chem- ical decomposition by means of an electric dis- charge or current. This decomposition may result from an increase of temperature produced by the electric discharge, or from the passage of the current. In the latter case it is more properly called electrolytic decom- position. Decomposition, Electric, Crystallization by (See Crystallization by Electro- lytical Decomposition.) Decomposition, Electrolytic The separation of a molecule into its constituent atoms or groups of atoms by the action of the electric current. These atoms or groups of atoms are either electro-positive or electro-negative in character. (See Electrolysis. Anion. Kathion.) De-energize. To deprive an electro-recep- tive device of its operating current. De-energizing. Depriving an electro- receptive device of its operating current. Deep-Seated Eddy Currents. (See Cur- rents, Eddy, Deep-Seated) Deep-Water Submarine Cable. (See Cable, Submarine, Deep-Sea^ Deflagration, Electrical The fusion and volatilization of metallic substances by the electric current. Deflagrator. The name given to a voltaic battery, of small internal resistance, employed by Hare in the electric deflagration of metal- lic substances. Deflection Method. (See Method, Deflec- tion^ Deflection of Magnetic Needle. (See Needle, Magnetic, Deflection of.) Degeneration. Such a degeneration of the muscular or cellular structure of any cell or organ that incapacitates it from performing its functions. Degeneration of Energy. (See Energy, Degeneration of) Degeneration, Partial, Reaction of That form of alteration to electric stimula- tion, in which the nerves show no abnormal reaction to electric stimulation, while the muscles, when directly stimulated by the con- stant current, exhibit the reaction of degen- eration. (See Degeneration, Reaction of?) Deg.] 155 [Dep. Degeneration, Reaction of A qualitative and quantitative alteration of nerves and muscles to electric stimulation. According to Landois and Stirling the following conditions characterize essentially the reaction of degeneration: "The excitability of the muscles is diminished or abolished for the faradic cur- rent, while it is increased for the galvanic current from the third to the fifty -eighth day ; it again diminishes, however, with variations, from the seventy -second to eightieth day ; the anodic clos- ing contraction is stronger than the kathodic closing contraction." * * * " The Siminu- tion of the excitability of the nerves is similar for the galvanic and faradic currents. ' ' Deka (as a prefix). Ten times. Dekar-Ampre. Ten amperes. Deka-Ampere Balance. (See Balance, Deka- A mpere.) De la Rue's Standard Voltaic Cell. (See Cell, Voltaic, Standard, De la Rue's.} Deliquescence. The solution of a crystal- line solid arising from its absorption of vapor of water from the atmosphere. Demagnetizable. Capable of being de- prived of magnetism. Demagnetization. A process, generally di- rectly opposite to that for producing a magnet, by means of which the magnet may be de- prived of its magnetism. A magnet may be deprived of its magnetism, or be demagnetized (i.) By heating it to redness. (2. ) By touching to its poles magnet poles of the same name as its own. (3.) By reversing the directions of the motions by which its magnetism was originally imparted, if magnetized by touch, by stroking it with a magnet in the opposite direction from that which would have to be given in order to produce the magnetization which is to be removed from it. (4.) By exposing it in a helix to the influence of currents which will impart magnetism opposite to that which it originally possessed. Avria claims th*t a smaller magnetizing force is required to demagnetize a needle than is required to magnetize it. Demagnetization of Watches. (See Watches, Demagnetization of.) Demagnetize. To deprive of magnetism. Demagnetizing. Depriving of magnetiza- tion. Demarcation Current (See Current, De- marcation?) Demarcation Surface. (See Surface, De- marcation?] Density, Electric The quantity of free electricity on any unit of area of surface. The density is said to be positive or negative according as to whether the charge is positive or negative. (See Charge^ Density of. Plane, Magnetic Proof '.) Density, Magnetic The strength of magnetism as measured by the number of lines of magnetic force that pass through a unit area of cross-section of the magnet, /. e., a section taken at right angles to the lines of force. (See Field, Magnetic} Density of Charge. (See Charge, Den- sity of.) Density of Current. (See Current Density?) Density of Field. (See Field, Density of.) Density, Surface A phrase used by Coulomb to mean the quantity of eiec- tricity per unit of area at any point on a sur- face. (See Charge Density. Density, Electric:) Dental-Mallet, Electro-Magnetic A mallet for filling teeth, the blows of which are struck by means of electrically-driven mechanism. Electro-magnetism was first employed for this purpose by Bonwill, of Philadelphia. Dentiphone. An audiphone. (See Audi- phone?) Depolarization. The act of reducing or removing the polarization of a voltaic cell or battery. (See Cell, Voltaic, Polarization of.) Depolarize. To deprive of polarization. Depolarizing. Depriving of polarization. Depolarizing Fluid. (See Fluid. De- polarizing.) 156 [Dev. Deposit, Black, Electro-Metallurgical A crystalline variety of electro - metallurgical deposit. (See Deposit, Electro- Metallurgical^ Deposit, Crystalline, Electro-Metallurgi- cal A non-adherent, non-coherent film of electrolytically deposited metal. (See Deposit, Electro-Metallurgical) Deposit, Electro-Metallurgical The deposit of metal obtained by any electro- metallurgical process. To obtain a good metallic deposit the density of the current must be regulated according to the strength of the metallic solution employed. Electro-metallurgical deposits are either (I.) Reguline, or flexible, adherent and strongly coherent metallic films, deposited when neither the current nor the solution is too strong; or, (2.) Crystalline; or non-adherent and non-co- herent deposits. The crystalline deposit may either be of a loose, sandy character, which is thrown down when too feeble a current is used with too strong a metallic solution, or it may consist of a blick deposit, which is thrown down when the current is too strong as compared with the strength of the solution. This latter character of deposit is sometimes technically called burning, and takes place most frequently at sharp corners and edges, where the current density is greatest. (See Current Density.) Deposit, Electro-Metallurgical Nodular A coherent, irregular electro-metal- lurgical deposit which occurs whenever the current density falls below its normal value. Deposit, Electro-Metallurgical, Reguline A flexible, adherent and strongly coherent film of metal electrolytically de- posited. (See Deposit, Electro-Metallur- gical^) Deposit, Electro-Metallurgical, Sandy A non-coherent electro-metallurgical deposit which occurs whenever the current density exceeds its normal value. Depositing Cell. (See Cell, Depositing) Depositing Tat. (See Vat, Depositing) Deposition, Electric The deposit- ing of a substance, generally a metal, by the action of electrolysis. (See Electrolysis) The electric deposition of a metal on any con- ducting surface is sometimes called an electro- metallurgical deposition. (See Metallurgy, Electro.} Deprez-d'Arsonval Galvanometer. (See Galvanometer, Deprez-d'Arsonval) Derivative Circuit (See Circuit, De- rivative) Derived Circuit (See Circuit, Derived) Derived Units. (See Units, Derived) Destructive Distillation. (See Distilla- tion, Destructive) Detector Galvanometer. (See Galva- nometer, Detector) Detector, Ground In a system of incandescent lamp distnbution, a device placed in the central station, for showing by the candle-power of a lamp the approximate location of a ground on the system. Fig. 196, shows a form of ground -detector, in Fig. igb. Ground-Detector, which a small transformer is placed on a board in connection with a lamp and a two-way switch. One terminal of the primary of the transformer is put to ground, while the other can be connected by means of the switch to one or the other of the two primary mains of the distribution circuit. Should an earth exist on either main, then when the testing transformer has its pole connected to the other main, the lamp in its secondary circuit will light up, providing the leak is of sufficient magnitude to permit a sufficiently great current to pass through the primary circuit. Detorsion Bar. (See Bar, Detorsion) Device, Electro-Receptive Various DeT.J 157 devices placed in an electric circuit, and energized by the passage through them of the electric current. A translating device. The following are among the more important electro-receptive devices, viz. : (i.) Electro magnets. (2.) Electric motors. (3.) Electro-magnetic signal apparatus. (4.) Telegraphic or telephonic apparatus. (5.) An arc or incandescent lamp. {6.) An electric heater. 47.) A plating bath or voltameter. (8.) An uncharged storage cell. .(9.) A converter or transformer. ELECTRO-RECEPTIVE DEVICES. Motion Reproduced. (I.) Electric motor. {2.) Telpherage system. (3.) Telephone receiver. {4.) Telegraphic apparatus. (5.) Telephote receiver. Radiant Energy Produced. (6.) Arc or incandescent electric lamp. (7.) Electric heater. (8.) Electric welder. (9.) Leyden jar or battery. Chemical Decomposition Effected. (10.) Electrolytic bath. (n.) Uncharged storage battery. Electro-Magnetism Produced. (12.) Electro-magnet. Device, Feeding, of an Arc Lamp A device for maintaining the carbon electrodes of an arc lamp at a constant distance apart during their consumption. (See Lamp, Electric Arc.) Device, Magneto-Receptive Any device that is capable of being energized when placed in a magnetic field. The term magneto-receptive device is used in contradistinction to electro-receptive device. (See Device, Electro-Receptive. ) Device or Arrangement, Electromotive A term sometimes employed instead of an electric source. (See Source, Electric. Arrangement or Device, Electromotive^ [DCY. Derice, Safety, for Arc Lamps, or Series Circuits Any mechanism which auto- matically provides a path for the current around a lamp, or other faulty electro-recep- tive device in a series circuit, and thus pre- vents the opening of the entire circuit on the failure of such device to operate. (See Lamp, Electric Arc.) Device, Safety, for Multiple Circuits A wire, bar, plate or strip of readily fusible metal, capable of conducting, without fusing, the current ordinarily employed on the circuit, but which fuses and thus breaks the circuit on the passage of an abnormally great current. The terms safety-catch, safety.plug, safety- strip and safety -fuse are also used for this safety device. (See Fuse, Safety.) Device, Translating A term em- bracing electro-receptive and magneto-recep- tive devices. (See Device, Electro-Recep- tive^ Translating devices are placed in an electric circuit, and when traversed by the current effect a change, or translation in the form of the electric energy whereby useful work is accomplished. Translating devices depend for their operation on the luminous, heating, magnetic, or chemical effects of the current. Devices, Electro-Receptire, Multiple- Connected A connection of electro- receptive devices, in which the positive poles of a number of separate devices are all con- nected with a single positive lead or conduc- tor, and the negative poles all connected with a single negative lead or conductor. The multiple-arc-connection of electro-receptive devices is suitable for constant potential circuits, or those m which the electromotive force is main- tained approximately constant In such circuits the energy absorbed by each device will increase as its resistance decreases, since the energy ab- sorbed is proportional to the current passing. (See Circuits, Varieties of.) Multiple-arc-connected electro-receptive devices are employed in incandescent lamp distribution. Each device added reduces the resistance of the entire circuit. Dey.] 158 [Dia. DeTices,Electro-Receptiye,]ttultiple- Arc- Connected A term used in place of multiple-connected electro-receptive devices. (See Devices, Electro-Receptive, Multiple- Connected^) Devices, Electro-Receptive, Multiple- Series-Connected A connection of electro-receptive devices in which a number of separate electro-receptive devices are con- nected in groups in series, and each of these separata groups afterwards connected in mul- tiple-arc. The multiple-series connection permits electro- receptive devices to be placed on mains whose electromotive force would be too high to permit a single service to be connected directly to them. It is of great value in the distribution of incandes- cent lamps by constant currents, since by per- mitting a higher electromotive force to be em- ployed on the main conductors, it reduces the dimsnsions of the conductors required for the economical distribution of the current. (See Circuits, Varieties of.} Devices, Electro-Receptive, Series-Con- nected The connection of electro- receptive devices in which the devices are placed consecutively in the circuit, so that the current passes successively through all of them from the first to the last. The series-connection of electro-receptive de. vices is suited to constant -current circuits. The work dons in tha device is developed by the fall of potential in each device. This kind of con- nection is used in most systems of arc light and telegraphic lines. (See Circuits, Varieties of.) Devices, Electro-Receptive, Series-Mul- tiple-Connected A connection of electro-receptive devices in which a number of separate electro-receptive devices are joined in separate multiple groups, and each of these groups subsequently connected with one an- other in series. The effect of series-multiple connections is to split up the current into a number of separa:e currents of smaller strength, but of the sanii electromotive force. It is applicable to such cases as the combination of arc and incandescent lamps in the same circuit. (S?e Circuits, Varieties of.) Devices, Translating, Multiple-Con- nected A term sometimes used for multiple-connected electro-receptive devices. (See Devices, Electro-Receptive, Multiple- Connected?) Devices, Translating, Multiple-Arc-Con- nected A term used in place of multiple-connected electro-receptive devices. (See Devices, Electro-Receptive, Multiple- Connected?) Devices, Translating, Multiple-Series- Connected A term sometimes used instead of multiple-series-connected electro- receptive devices. (See Devices, Electro- Receptive, Multiple-Series-Connected?) Devices, Translating, Series-Connected A term sometimes used for series- connected electro-receptive devices. (See Devices, Electro - Receptive, Series Con- nected?) Devices, Translating, Series-Multiple- Connected A term sometimes used for series-multiple-connected electro-recep- tive devices. (See Devices, Electro-Recep- tive, Series-Multiple-Connected?) Dextrorsal Helix. (See Helix, Dex- trorsal?) Dextrorsal Solenoid. (See Solenoid, Dex- trorsal.} Diacritical Current. (See Current, Dia- critical} Diacritical Number. (See Number, Dia- critical?) Diacritical Point of Magnetic Satura- tion. (See Saturation, Magnetic, Diacrit- ical Point of?) Diagnosis, Electro. Diagnosis by means of the exaggeration or diminution of the re- action of the excitable tissues of the body when subjected to the varying influences of electric currents. The electric current has also been applied in order to distinguish between forms of paralysis, and as a final test of death. Diagnostic, Electro Pertaining to electro-diagnosis. (See Diagnosis, Electro) Diagometer, Rousseau's An ap- paratus m which an attempt is made to Dia.] 150 [Dia. determine the chemical composition and con- sequent purity of certain substances by their electrical conducting powers. The arrangement of the apparatus is shown in Fig 197. A dry pile. A, has its negative, or Fig, 1 97- Rousseau's Diagometer. terminal, m', grounded. Its positive, or -(- ter- minal is connected to a delicately supported, and slightly magnetized needle, M, terminated by a conducting plate, L. Opposite L, and at the same height, is a fixed plate of slightly larger size. The needle M, when at rest in the plane of the magnetic meridian, is in contact at L, with the fixed plate. If, therefore, the upper plate of the pile is con- nected with the needle M, both plates arr. similarly charged and repulsion takes place, the needle coming to rest at a certain distance from the fixed plate. The substance whose purity is to be determined is placed in the cup G, which is connected, through L, with the fixed plate, A branch wire from the -f- terminal of the pile is then dipped into the substance in G, and its purity determined from the length of time required for the two plates at L, to be discharged through the material in G. It is claimed that the instrument will detect the difference between pure coffee and chicory. Its practical application, however, is very doubtful. Diagram, Thermo Electric A diagram in which the thermo-electric power between different metals is designated for different temperatures. The differences of potential, produced by the mere contact of two metals, varies, not only with the kind of metals, and the physical state of each metal, but also with their temperature. This difference of potential, maintained in conse- quence of the difference of temperature between the junctions of a thermo*electric couple, is ap- proximately proportional to the differences of temperature of these junctions, if these differences are not great, and is equal to the product of such differencesof temperature and anumber dependent on the metals in the couple. This number is called the thermo-electric power. (See Couple, Thermo-Electric. Thermo-Electric Power.) In Fig. 198 (after Tait), the thermo-electric 360o 400a 460" Fig. zcj8. Thermo-Electric Diagram. power is shown between lead and iron, and lead and copper. The numbers at the top of the table represent degrees of the centigrade thermometer. Those at the sides represent the differences of potential in micro -volts. The thermo-electric power of the copper-iron couple decreases from the freezing point of water, O degrees C., to a temperature of 274.5 degrees C., when it becomes zero. Beyond that temper- ature the thermo-electric power increases, but in the opposite direction. The point at which this occurs is called the neutral point. Dial Telegraph. (See Telegraphy, Dial.) Dialysis. The act of separating a mixture of crystalloids and colloids by diffusion through a membrane. If, for example, the contents of a stomach, in a case of suspected poisoning, be placed in a vessel, the bottom of which is formed of a sheet of parchment paper and floated in water, the crystalloid or substances capable of crystalliz- ing, will pass into the water and the colloid, an uncrystallized jelly-like substance, will remain in the vessel. This process has been used to detect the presence of poison in the stomach in post- mortem cases. Diamagnetic. The property possessed by substances like bismuth, phosphorus, anti- mony, zinc and numerous others, of being apparently repelled when placed between the poles of powerful magnets When diamagnetic substances in the form of rods or bars are placed, as in Fig. 199, between the poles of a powerful electro-magnet, they place themselves at right angles to the poles, or are apparently repelled. Paramagnetic substances like iron or steel, on the contrary, come to rest under similar circum- Dia.] 160 [Dia. Fig, 799 Effect of Para- magnetism, stances in a straight line joining the poles, at right angles to the position shown in Fig. 199. Paramagnetic substances are sometimes called ferro-magnetic, or substances magnetic after the manner of iron. This word is unnecessary and ill-advised. The term sidero-magnetic, which has also been proposed in place of paramagnetic, is also unnecessary. Paramagnetic substances appear to concentrate the lines of magnetic force on them ; that is, their magnetic resistance is smaller than that of the air or other medium in which the magnet is placed. They, there- fore, come to rest with their greatest dimen - sions in the direction of the lines of magnetic force. Diamagnetic sub- stances appear to have a greater magnetic re- sistance than that of the air around them. They, therefore, come to rest with their least dimensions in the direction of the lines of mag- netic force. The difference between paramagnetic and dia- magnetic substances is generally believed to be due to the varying resistance these substances thus offer to lines of magnetic force as compared with that offered by air or by a vacuum. Tyndall comes to the conclusion as the result of extended experimentation: "That the diamag netic force is a polar force, the polarity of dia- magnetic bodies being opposed to that of para- magnetic ones under the same conditions of excitement." This view, however, is not generally accepted by scientists. Diamagnetism is also possessed by certain liquid and gaseous substances. Diamagnetic Polarity. (See Polarity. Diamagnett'c.} Diamagnetically. In a diamagnetic man- ner. Diamagnetism. A term applied to the magnetism of diamagnetic bodies. (See Dza- magnetic^) Diamagnetism, Weber's Theory of A theory to account for the phenomena of diamagnetism. Weber's theory of diamagnetism, like Ampere's theory of magnetism, supposes that magnetic substances consist of originally magnetized mole- cules or atoms, and that the act of magnetization consists of polarizing these atoms or molecules, or turning them in one and the same direction. That the original condition of the molecules or atoms is probably due to the passage of electricity, which continually circulates through their mass, the atoms being supposed to possess perfect con- ductivity. Suppose the substance through whose mole- cules or atoms these currents are flowing be immersed in a magnetic field. All of the mole- cules or atoms which can turn so as to look along lines of force in the right direction will have the current flowing in them thereby weakened so long as they remain in the field. When drawn out of it, however, these currents will regain their nor- mal strength. Suppose now the case of a substance, in which the currents are normal but weak, immersed in a strong magnetic field. There may thereby be effected a complete reversal of the direction of these currents, and others may be produced which flow in the opposite direction, and which will continue so to flow as long as the substance remains in the field. Such currents would then be sufficient to explain the phenomena of diamag netic action. An electric current produced in a circuit near which a momentary current of electricity is sud - denly brought has now the opposite direction to that which produces it, and this momentary cur- rent would tend to produce repulsion. When, Fig 200 Weber's Theory of Diamagnetism, too, the circuit is drawn out of the neighborhood in which another current is flowing, another mo- Dia.j 161 [Die. mentary current is produced in the same direc- tion. This produces attraction. Now, regarding the same phenomena from the standpoint of lines of magnetic force, when a conductor through which a current is passing is placed in a magnetic field, any increase in the number of lines of magnetic force passing through it tends to move the conductor out of the magnetic field, while any decrease in the number of lines of force tends to move the conductor into the field. To experimentally show the attractions and repulsions produced by magnetization or demagnetization, the following apparatus may be employed: A stout disc of copper, Fig. 200, is supported on a horizontal arm in the position shown in front of the pole of a powerful electro- magnet. When the curre it is sent through the electro- magnet the disc of copper is repelled from the magnetic pole. When the magnetism is being destroyed by the opening of the circuit and by the weakening of the current, the copper disc is attracted. Diamagnetometer. An apparatus de- signed for studying diamagnetism. (See Dta- magnetism. ) The apparatus for the study of paramagnetism generally receives simply the name of magnet- ometer. Diamagnets. Diamagnetic substances subjected to magnetic induction and formerly called diamagnets in contradistinction to or- dinary magnets. Diamagnets are supposed by some to possess a polarity the same as that of the inducing pole, instead of the opposite polarity, as in paramagnetic substances. (See Diamagnetism.) Diaphragm. A sheet of some solid sub- stance, generally elastic in character and cir- cular in shape, securely fixed at its edges and capable of being set into vibration. The receiving diaphragm of a telephone is generally a thin plate or disc of ii on, fixed at its edges, placed near a magnet pole and set into vibration by variations in the magnetic strength of the pole, due to variations in the current that is passed over the line. The transmitting diaphragm of the telephone or of a phonograph, consists of a plate fixed at its edges and set into vibration by the sound waves striking it. Diaphragm. A term sometimes employed for a plate form of porous cell. Diaphragm Currents. (See Currents, Diaphragm. Cell, Porous") Diaphragm of Voltaic Cell. A term sometimes used for the porous cell of a double fluid voltaic cell when m the form of a plate. Dice-Box Insulator. (See Insulator. Dice-Sox.) Dielectric. A substance which permits induction to take place through its mass. This word is sometimes, but improperly, writ- ten Di-Electric. The substance which separates the opposite coatings of a condenser is called the dielectric. All dielectrics are non-conductors. All non-conductors or insulators are dielectrics, but their dielectric power is not exactly propor- tional to their non-conducting power. Substances differ greatly in the degree or ex- tent to which they permit induction to take place through or across them. Thus, a certain amount of inductive action takes place between the insu- lated metal plates of a condenser across the layer of air between them. A dielectric may be regarded as pervious to rapidly reversed periodic currents, but opaque to continuous currents. There is, however, some conduction of continuous currents. According to Swinburne, there are three species of conduction that may take place in < iclectrics, all of which produce a heating of the dielectric, viz.: (I.) Metallic Conduction, i. e., such a conduc- tion as takes place in a metal. This kind of con- duction arises from the presence of metallic par- ticles embedded in the dielectric. (2.) Disruptive Conduction, or a momentary current accompanying a disruptive discharge. (3.) Electrolytic Conduction, or that kind of conduction which ac:ompanies the elec'rolysis of a conductor. This kind of conduction may take place in some kinds of glass. Faraday regarded the dielectric as the true seat of electric phenomena. Conducting substances he considered as mere breaks in the continuity of the dielectric. This is the view now generally held. Dielectric Capacity. (See Capacity, Di- electric.) Die. 162 [Dim. Dielectric Constant (See Constant, Dielectric!) Dielectric Density of a Gas. (See Gas, Dielectric Density of.) Dielectric, Polarization of A molecular strain produced in the dielectric of a Leyden jar or other condenser, by the attrac- tion of the electric charges on its opposite faces, or by the electrostatic stress. (See Strain, Dielectric!) A term formerly employed in place of electric displacement. Faraday, in his study of the action of induction, in denying the possibility of action at a distance, thought that the dielectric through which induc- tion takes place was polarized, and that in this way the induction was transmitted across the intervening space between the inducing and the induced body, by the action of the contiguous particles of the dielectric. The polarization of the glass of a Leyden jar, and the accompanying strain, are seen by the frequent piercing of the glass, and by the residual charge of the jar. (See Charge, Resid- ual.-) Dielectric Resistance. (See Resistance \ Dielectric) Dielectric Strain. (See Strain, Dielec- tric) Dielectric Strength of a Gas. (See Gas, Dielectric Strength of.} Dielectric Stress. (See Stress, Dielec- tric^ Difference of Potential. (See Potential, Difference of!) Differential Electric BelL (See Bell, Differential Electric) Differential Galvanometer. (See Gal- vanometer, Differential!) Differential Inductometer. (See Induc- tometer, Differential!) Differential Method of Duplex Tele?- raphy. (See Telegraphy, Duplex, Differ- ential Method of !) Differential Relay. (See Relay, Differ- ential!) Differential Thermo-Pile. (See Pile, Thermo, Differential!) Differential Voltameter. (See Voltam- eter. Siemens' Differential) Differentially Wound Motor. (See Motor Differentially Wound.} Diffusion, Anodal A term applied to the introduction of any drug into the human body by electricity. The cataphoretic introduction of drugs into the body. (See Cataphoresis) A sponge or other similar electrode, saturated with a solution of the drug, is connected with the anode of a source and placed over the part to be treated and its kathode connected to another part of the body in a nearly direct line with the anode and the current passed, Diffusion Creep. (See Creep Diffusion!) Diffusion of Electric Current -(See Current, Diffusion of) Diffusion of Lines of Force. (See Force. Lines of Diffusion of!) Dimensions of Acceleration. (See Ac* celeration. Dimensions of!) Dimensions of Units (See Units. Dimen- sions of!) Diminished Electric Irritability. (See Irritability, Electric, Diminished) Dimmer A choking coil, employed in a system of distribution by converters or transformers, for regulating the potential of the feeders. The dimmer consists essentially of a choking coil wound around a laminated ring of soft iron, fig. 201. Reaction Coil Dimmer. and provided with an envelope of heavy copper. The copper ring, by its position as regards the choking coil, adjusts or regulates the self-induc- tion of the coil, and consequently regulates the potential of the feeders. The dimmer is used in theatres or similar situations to turn the lights up Dio.] [Dip. The reaction coil or dimmer is shown in Fig. 201. The choking coil is wound on a ring of iron. The copper sheath is furnished with a handle to permit its position to be readily changed with respect to the coil of insuhted wire. A laminated iron drum is supported on bearings inside the ring. When the sheath is over the coil, the coil offers but a small resistance to the passage of the current. When away from it the self-induction of the coil is increased. Dioptre. A unit of refracting power. A lens of one dioptre has a focal length of one metre. One of two dioptres has a focal length of 50 centimetres; one of four dioptres 25 centimetres. This is also spelled dioptry. Dioptric. Relating to dioptrics. Dioptrics. The science which treats of the refraction of light. Dioptry. A word sometimes used for di- optre. (See Dioptre?) Dip, Magnetic The deviation of a magnetic needle from a true horizontal posi- tion. The inclination of the magnetic needle to- wards the earth. The magnetic needle shown in Fig. 202, though Fig. SO 2. Angle of Dif. supported at its centre of gravity, will not retain a horizontal position in all places on the earth's .surface. In the northern hemisphere its north-seeking end will dip or incline at an angle B O C, called the angle of dip. In the southern hemisphere its south seeking end will dip. The cause of the dip is the unequal distance of the magnetic poles of the earth from the poles of the needle. The magnetic equator is a circle passing around the earth midway (in intensity) between the earth's magnetic poles. There is no dip at the magnetic equator. At either magnetic pole the angle of dip is 90 degrees. Dip, or Inclination, Angle of The angle which a magnetic needle, free to move in both a vertical and a horizontal plane, makes with a horizontal line passing through its point of support. The angle of dip of a magnetic needle. (See Inclination, Angle of.} Diplex Telegraphy. (See Telegraphy, Diplex) Dipping. An electro-metallurgical process whereby a deposit or thin coating of metal is obtained on the surface of another metal by dipping it in a readily decomposable metallic salt. Cleansing surfaces for electro-plating pro- cesses by immersing them in various acid liquors. Dipping, Bright Dipping in acid liquors for the purpose of obtaining a bright electro-metallurgical coating. Dipping Circle. (See Circle, Dipping) Dipping, Dead Dipping in acid liquors for the purpose of obtaining a dead or unpolished surface on an electro-metallurgical coating. Dipping, Electro-Metallurgical A process for obtaining an electro-metallur- gical deposit on a metallic surface by dipping it in a solution of a readily decomposable metallic salt. A bright, polished iron surface, when simply dipped into a solution of copper-sulphate, re- ceives a coating of metallic copper from the elec- trolytic action thus set up. This process is known technically as dipping. The term dipping is also used in electro metal- lurgy to indicate the process of cleaning the Din] 164 [Dis, articles, that are to be electro-plated, by dipping them in various acid or alkaline baths. Direct Current (See Current, Direct^ Direct-Current Electric Motor. (See Motor, Electric, Direct-Current) Direct Electromotive Force. (See Force, Electromotive, Direct?) Direct Excitation. (See Excitation, Direct?) Direct-Induced Current. (See Current, Direct-Induced) Direct, or Break-Induced Current (See Current, Direct, Current, Break- Induced^) Direct Working. (See Working, Direct) Direction, Negative, of Electrical Con- vection of Heat A direction in which heat is transmitted through an unequally heated conductor by electric convection, during the passage of electricity through the conductor, opposite that of the current. (See Heat, Electric Convection of.) Direction of Lines of Force. (See Force, Lines of, Direction of) Direction, Positive, of Electrical Con- vection of Heat A direction in which heat is transmitted through an un- equally heated conductor by electric convec- tion, during the passage of electricity through the conductor, the same as that of the cur- rent. (See Heat, Electric Convection of) Direction, Positive, Bound a Circuit In a plane circuit looked at from one side, a direction opposite to that of the hands of a clock. This is a convention which has been made in order to conveniently c innect the direction of the electromotive force produced by induction, with the directio.i of the induction. Direction, Positive, Through a Circuit In a plane circuit, looked at from one side, a direction through the circuit away from the observer. Directive Tendency of Magnetic Needle. (See Needle, Magnetic, Directive Ten- dency of.) Disc, Arago's A disc of copper or other non-magnetic metallic substance, which, when rapidly rotated under a mag- netic needle, supported independently of the disc, causes the needle to be deflected in the direction of rotation, and, when the velocity of the disc is sufficiently great, to rotate with it. Such disc is shown in Fig. 203 at b. The move- Fig. 203. Arago's Disc. ment of the needle is due to electric currents, in- duced by the disc moving through the field of the needle so as to cut its lines of magnetic for.e. To obtain the best results the disc must move very rapidly, and should be near the needle. More- over, the needle should be powerful. This effect was discovered by Arago, in 1824. Since a magnetic needle moving over a metallic plate produces electric currents in a direction which tends to stop the motion of the needle, a damping of the motion of a magnetic needle is sometimes effected by causing it to move near a metal plate. The induced currents, which the needle produces in the plate by its motion over it, tend to retard the motion of the needle. (See Damping. Law, Lenz* s.) Disc Armature. (See Armature, Disc) Disc, Faraday's A metallic disc movable in a magnetic field on an axis- parallel to the direction of the field. Such a disc is shown in Fig. 204, and moves r Fig. 204. Faraday's Disc. as will be seen, so as to cut the lines of magnetic force at right angles. The difference of potential generated by the motion of such a disc may be caused to produce a current, by providing a circuit which is com- pleted through the portion of the disc that at any Dis.] 165 [Dis. moment of its rotation is situated between spring contacts resting on the axis of rotation and the circumference of the disc, respectively. In Barlow ' s or Sturgeon's wheel, Fig. 205, the Fig. 20S- Barlov/s Wheel. wheel itself rotates in the direction shown, when a current is sent through it in a direction indicated by the arrows. Discharge. The equalization of the dif- ference of potential between the terminals of a condenser or source, on their connection by a conductor. The removal of a charge from the surface of any charged conductor by connecting it with the earth, or another conductor. The removal of a charge by means of a stream of electrified air particles. The discharge of an insulated conductor, a cloud, a condenser, or a Leyden battery, is oscil- latory. The oscillatory currents continue but for a short time. The discharge is therefore often spoken of as producing momentary currents. The discharge of a voltaic battery, or a stor- age battery, is nearly continuous, and furnishes a current which is practically continuous, as dis- tinguished from the momentary currents produced by the discharge of a condenser. A discharge may be alternating, brush, brush and spray, conductive, convective, dead-beat, disruptive, flaming, glow, lateral, oscillatory, periodic, stratified, streaming, impulsive and periodic. Discharge, Alternating An elec- tric discharge which changes its direction at regular intervals of time. A periodic discharge. Discharge, Brush A faintly lu- minous discharge that occurs from a pointed positive conductor. The brush discharge is a species of convective discharge. In it, the streams of electrified air particles assume the characteristic brush shape. (See Discharge, Convective. ) Discharge, Brush-and-Spray A form of streaming discharge obtained by in- creasing the frequency of the alternations of a high potential current which assumes the appearance of a spray of silver-white sparks, or a bunch of thin silvery threads around a powerful brush. Some idea of the brush-and-spray discharge may be obtained from Fig. 206, taken from Fig. 206. Brush-and-Spray Discharge ( Tesla). Tesla, who has carefully studied these phenom- ena. The brush-and-spray discharge is best obtained, according to Tesla, by bringing the terminals of a source of rapidly alternating electrostatic currents of high potential somewhat nearer to- gether, when the s'.reaming discharge l;as been obtained, and preferably increasing the frequency of the alternations. The brush-and-spray discharge, when power- ful, closely resembles a gas flame from gas escap- ing under great pressure. Says Tesla: "But they do not only resemble, they are verita' le flames, for they are hot. Certainly they are not as hot as a gas burner, but they would be so if the frequency and the potential would be sufficiently high." The brush-and-spray discharge, at higher fre- quencies, passes into a form of discharge for which Tesla has proposed no particular name. He de- scribes this form, in a publication of a lecture before the American Institute of Electrical Engi- neers, as follows, viz.: "If the frequency is still more increased, then the coil refuses to give any spark unless at com- paratively s.nall distances, and the fifth typical form of discharge may be observed (Fig. 207). The tendency to stream out and dissipate is then so great that when the brush is produced at one terminal no sparking occurs, even if, as I have re- peatedly tried, the hand, or any conducting ob- ject, is held within the stream ; and, what is more Dis.] singular, the luminous stream is not at all easily deflected by the approach of a conducting body. "At this stage the streams seemingly pass with the greatest freedom through considerable thick- nesses of insulators, and it is particularly interest- ing to study their behavior. For this purpose it is convenient to connect to the terminals of the coil two metallic spheres, which may be placed at any desired distance (Fig. 208). Spheres are pref- 166 [Dis. Fig. 207. Fifth. Typical Form of DiscJiarge ( Tesla). erable to plates, as the discharge can be better observed. By inserting dielectric bodies between the spheres, beautiful discharge phenomena may be observed. If the spheres be quite close and a spark be playing between them, by interposing a thin plate of ebonite between the spheres the spark instantly ceases and the discharge spreads into an intensely luminous circle several inches in diameter, provided the spheres are sufficiently large. The passage of the stream heats, and, after a while, softens the rubber so much that two Fig. 208. Lu-ninous Discharge with Interposed Insulators. plates may be made to stick together in this man- ner. If the spheres are so far apart that no spark occurs, even if they are far beyond the striking distance, by inserting a thick plate of glass the discharge is instantly induced to pass from the spheres to the glass in the form of luminous streams. It appears almost as though these streams pass through the dielectric. In reality this is not the case, as the streams are due to the molecules of the air which are violently agitated in the space between the oppositely charged sur- faces of the spheres. " When no dielectric other than air is present, the bombardment goes on, but is too weak to be visible ; by inserting a dielectric the indue- tive effect is much increased, and besides, the projected air molecules find an obstacle and the bombardment becomes so i.itense that the streams become luminous. If by any mechanical means we could effect such a violent agitation of the molecules we could produce the same phenom- enon. A jet of air escaping through a small hole under enormous pressure and striking against an insulating substance, such as glass, may be luminous in the dark, and it might be possible to produce phosphorescence of the glass or other insulators in this manner. ' ' The greater the specific inductive capacity of the interposed dielectric, the more powerful the effect pi oduced. Owing to this the streams show themselves with excessively high potentials even if the glass be as much as one and one-half to two inches thick. But besides the heating due to bom- bardment, some heating goes on undoubtedly in the dielectric, being apparently greater in glass than in ebonite. I attribute this to the greater specific inductive capacity of the glass in conse- quence of which, with the same potential differ- ence, a greater amount of energy is taken up in it than in rubber. It is like connecting to a battery a copper and a brass wine of the same dimen- sions. The copper wire, though a more perfect conductor, would heat more by reason of its tak- ing more current. Thus what is otherwise con- sidered a virtue of the glass is here a defect. Glass usually gives way much quicker than ebo- nite ; when it is heated to a certain degree the discharge suddenly breaks through at one point, assuming then the ordinary form of an arc." Discharge, Conductive A dis- charge effected by leading the charge off through a conductor placed in contact with the charged body. Discharge, Conrective A dis- charge which occurs from the points on the surface of a highly charged conductor, through the repulsion by the conductor of air particles that in this manner carry off minute charges. Dis.] 167 [Dis. A convective discharge, though often attended by a feeble sound, is sometimes called a silent discharge, in order to distinguish it from the noisy, disruptive discharge, which is attended by a sharp snap, or when considerable, by a loud report. A convective discharge is also called aglow or brush discharge. The latter is best seen at the small button at the end of the prime or positive conductor of a frictional electric machine. T\& positive discharge from a point or small rounded conductor is always brush-shaped; the negative discharge is always star -shaped. In rarefied gases, the discharge is convective in character and- produces various luminous effects of great beauty, the color of which depends on the kind of gas, and the size, shape and material of the electrodes, and on the degree of the vacuum. Thus in the rarefied space of the vessel shown in Fig. 209, the discharge ] becomes an ovoidal mass | of light, sometimes called the Philosopher's Egg. When the discharges] in rarefied gases follow one another very rapid- ly, alternations of light and darkness, or stratifi- cations, or stria are pro- duced. The breadth of the dark bands increases as I the vacuum becomes | higher. The light por- tions start at the positive I electrode, and are hotter | than the dark portions. The effects of luminous &e**og. Discharge in. convective discharges are Rarefied Ai, best seen in exhausted g'ass tubes, called Geissler tubes, containing residual atmospheres of various gases. (See Tubes, Geissler.) Discharge, Dead-Beat A non- oscillatory discharge. (See Discharge, Oscillatory^) Discharge, Disruptive A sudden, and more or less complete, discharge that takes place across an intervening non-con- ductor or dielectric. A mechanical strain of the dielectric occurs, which suddenly breaks down as it were and per- mits the discharge to pass as a spark, or rapid succession of sparks. In air, the spark, when long, generally takes the zigzag path, as shown in Fig. 210. The sparks produced by disruptive discharges consist of heated gases, together with portions of the conductor that are volatilized by the heat. The discharge of a Ley- denjar or condenser may be disruptive, as when the discharging rod is held with one knob con- nected with one coating, and the other near the other coating. It may be gradual, as when the two coatings are alter- nately connected with the ground. The discharge of a Leyden jar as, in- deed, the disruptive dis- charge in general, is os- cillatory. The stress is often suf- ficient to pierce the glass. Discharge, Dura- tion of The time required to effect a complete disruptive discharge. The disruptive discharge is not instantaneous; some time is required to effect it Estimates of the duration of a flash of lightning based on the duration of a Leyden jar discharge, are mislead- ing from the enormous difference in the quantity and the potential in the two cases. The fact that the disruptive discharge is oscillatory and consists of a number of discharges taking place in alter- nately opposite directions shows that the discharge is not instantaneous. Leyden jar discharges, are, however, accom- plished in very small periods of time. Discharge, Flaming The white and naming arc-like discharge that occurs between the terminals of the secondary of an induction coil, when, with a great number of alternations per second, the current through the primary is increased beyond that required for the sensitive-thread discharge. (See Dis- charge, Sensitive-Thread) Fig- 210. Disruptive Discharge. Dis.] 168 [Dis. According to Tesla the flaming discharge is best produced when the number of alternations is not too great and certain re ations between ca- pacity, self-induction and frequency are observed. These relations must be such as will permit the flow through the circuit of the maximum current, and thus may be obtained with wide variations in the frequency. The flaming discharge develops considerable heat, and is characterized by the absence of the shrill note accompanying less pow- erful discharges. This is probably due to the enormous frequency. Some idea of the flaming discharge may be had Fig, 211. Flaming Discharge (Tesla). from an inspection of Fig. 211, taken from Tesla. Discharge, Glow A form of con- vective discharge. (See Discharge, Con- vectivel) Discharge, Impulsive A dis- charge produced in conductors by suddenly created differences of potential. Impulsive discharges are influenced more by the inductan e of a conductor than by its true ohmic resistance. (See Inductance. Resistance, Ohmic. ) A mass of guncott m simply ignit.'d in the open air, produces but little effect on any resisting object placed below it. If, however, itbe rapidly ignited by meai.s of a detonator, and is thus fired with much greater rapidity, it may shatter any- thing placed beneath it. In a si nilar manner, a rapidly discharged cur- rent, or impulsive discharge, produces, through the inductance of the conductor, a series of effects somewhat similar to the above, in which a great impedance is produced by a sudden change of direction. Discharge, Induced Currents, Effects Produced by Varying classes of effects produced by the discharges of induced currents. The effects produced by discharges of induced currents are classified by Fleming as follows: (i.) Effects depending on the entire quantity of the discharge. a. Galvanometric effects. If the need'.e of the galvanometer has a period or time of oscillation that is long, as compared with the time of duration of the discharge, the sine of one-half the angle of deflection is proportional to the whole quantity of the discharge. i>. Electro-chemical effects. The quantity of an electrolyte broken up is- proportional to the quantity of electricity which passes through it. (2.) Effects depending on the average of the square of the current strength at any instant dur- ing the discharge. a. Heating effects. The rate of dis. ipation as heat, according to Joule's law, is proportional to the square of the current strength passing. b. Electro-dynamic effects. When a discharge passes through a circuit, part of which is fixed and part movable, the forces of attraction and repulsion which take place be- tween t'.iem at any instant are proportional ta the square of the current strength. (3.) Effects depending on rate of change of the current. a. Physiological effects. The effect of the discharge in producing physi- ological shock increases with the suddenness of the discharge. Of two discharges which reached the same maxima that which reached it first would produce the greatest physiological effect. Recent investigations by Tesla and others would appear ta partly disprove the above statement b. Telephonic effects. The telephone, like the body ef an animal, is affected more by the rate of change than by the current strength at any instant. c. Magnetic effects. Rayleigh has shown that the magnetic effects of the discharge depend upon the maximum current strength during the discharge, or upon the initial current strength, in cases where the current dies away gradually. Since the time required for the permanent magnetizing of a steel wire is small co npared with the duration of the induced cur- rent, the am Hint of magnetism acquired depends essentially on the initial or maximum current strength during the discharge, irrespective of the time during which said discharge lasts. Bis.] 169 [Dis. d. Luminous effects. These are also dependent in the case of induced discharges on the rate of change of the current. Discharge-Key. (See Key, Discharge^ Discharge, Lateral A discharge, taking place on the discharge of a Leyden jar, or other disruptive discharge, between parts of the jar or conductors, not in the circuit of the main discharge. If a charged Leyden jar is placed on an insulat- ing stool, anJ is then discharged by the discharg- ing rod, the lateral discharge is seen as a small spark that passes between the outside coating of the jar and a body connected with the earth at the moment of the discharge through the rod. A lateral discharge is also seen in the sparks that can be taken from a conductor in good con- nection with the earth, by holding the hand near the conductor, while it is receiving large sparks from a powerful machine in operation. These discharges are due to induction. If a Leyden jar be discharged by means of a con- ducting wire bent as shown in Fig. 212, in which Fig. 212, two parts of the circuit are closely approached as at A, whenever a spark occurs at B, another spark produced by a lateral discharge occurs at A. Although the resistance of the metallic circuit is enormously less than the resistance of the air space through which the lateral discharge occurs, yet the counter electromotive force produced in the metallic circuit by the impulsive discharge, renders its resistance far greater than that of the air space. The path of a lateral discharge is called the alternative path. (See Path, Al- ternative. ) Discharge, Luminous Effects of The luminous phenomena attending and pro- duced by an electric discharge. The luminous effects vary as to color, intensity, shape and accompanying acoustic phenomena according to a variety of circumstances, the prin- cipal of which are as follows, viz. : (I.) With the kind of gaseous medium through which the discharge passes. Thus, a spark passed through hydrogen has a crimson or reddish color; through carbonic acid or chlorine, a greenish color. (2.) With the density of the medium. In a partial vacuum, the discharge from an induction coil becomes an ovoidal mass of light. As the vacuum increases, the light at first grows brighter, but as a higher vacuum is reached, striae of al- ternate dark and light bands appear. Finally, with very high vacua the discharge fails to pass. (See Discharge, Convective.) (3.) With the nature of the substances forming the points from which the discharge is taken. This is due to the partial volatilization of the ma- terial of the electrodes. (4.) With the kind of electricity, i. e., whether positive or negative. A positive charge assumes the shape of a fan; a negative discharge, that of a star. (5.) On the density of the discharge. The in- troduction of a Leyden jar or condenser in the circuit of a Holtz machine, for example, causes the spark to change from the faint bluish to the silvery white. (6.) The disruptive discharge through air is at- tended by snapping or crackling sound, which, in the case of lightning, reaches the intensity of thun- der. When the disruptive discharge takes place through a vacuum a faint hissing sound is heard, or all sound may entirely disappear. (7.) Luminous effects resulting from molecular bombardment occurring in co nparatively high vacua. These luminous effects may result : (a.) From actual incandescence of some refrac- tory material produced by the blows of the mole- cules; or, (b.) As a result of phosphorescence or fluores- cence due to such blows. Canary glass, or glass stained by uranium oxide, fluoresces and emits a yellowish green light; solu- tion of sulphate of quinine emits a bluish light. Discharge, Non-Oscillatory A dead-beat discharge. (See Discharge, Dead- Beat.] Discharge, Oscillating A number of successive discharges and recharges which occur on the disruptive discharge of a Leyden jar, or condenser. A discharge which periodically decreases by a series of oscillations. A discharge which produces a dying-away- backwards and forwards current. Dis.] 170 [Dis. The disruptive discharge of a Leyden jar, or condenser, is not effected by a single rush of elec- tricity. When discharged through a compara- tively small resistance, a number of alternate partial discharges and recharges occur, which produce true oscillations or undulatory discharges. These oscillations are caused by the induction, of the discharge on itself, and are similar to the self-induction of a current. The existence of the oscillating discharge in the case of a Leyden jar or condenser, proves, in the opinion of some, that electricity, taken along with matter, possesses a property similar to inertia. Discharge, Oscillatory A term sometimes used for an oscillating discharge. (See Discharge, Oscillating^ Discharge, Periodic An electric discharge which changes its direction at reg- ular intervals or periods. An alternating discharge. Discharge, Periodically-Decreasing An oscillating discharge whose decrease is periodic. (See Discharge, Oscillating^) Discharge, Sensitive-Thread The thin, thread-like discharge that occurs be- tween the terminals of the secondary of an in- duction coil of high frequency. The sensitive-thread discharge occurs, accord- ing to Tesla, when the number of alternations per Fig. 2 13- Sensitive- Thread Discharge (Tesla). second is high and the current through the primary small. This discharge has the form of a thin, feebly -colored thread. Though very sensi- tive, being deflected by a mere breath, it is never- theless quite persistent, if the terminals be at one-third of the striking distance apart. Tesla ascribes its extreme sensitiveness, when long, to the motion of suspended dust particles in the air. The general appearance of the sensitive-thread discharge is shown in Fig. 213, taken from Tesla. Discharge, Silent A name given to a convective discharge in order to distin- guish it from the more noisy disruptive dis- charge. The convective discharge in reality is attended by a feeble sound, which, however, is quiet when compared with the more pronounced sound of the disruptive discharge. (See Discharge, Connec- tive.) Discharge, Stratified The form of alternate light and dark spaces assumed by the discharges of an induction coil through a partially exhausted gas. (See Tube, Strati- fication^ The strise are explained by Curtis as follows: "Under the influence of the electric rhythm of the rapidly following discharges the molecules of the residual gas collect in alternately dense and rarefied spaces. The light bands correspond to the spaces where the molecules ar comparatively crowded together, and their concomitant friction produces the luminous disturbance. The dark spaces are where the molecules are further apart, and where their collisions are consequently less frequent. ' ' Discharge, Streaming A form as- sumed by the flaming discharge between the terminals of the secondary of an induction coil when the frequency of the alternations increases beyond a certain limit, and the potential has consequently increased. The streaming discharge partakes of the general characteristics of the flaming discharge. Lumi- nous streams pass in abundance, not only between the terminals of the secondary, but, according to Tesla, who has carefully studied these phe- nomena, between the primary and the secondary, through the insulating dielectric separating. Fig. 214. Streaming Discharge (Tesla). them. The streams not only pass between the terminals, but also issue from all points and pro- Dis.] 171 [Dis. jections, as will be seen from Fig. 214, taken from Tesla. When the streaming discharge reaches a cer- tain higher limit it becomes a br us h-and spray discharge. (See Discharge, Brush- and- Spray.) The streaming discharge obtained from an in- duction coil with high frequencies differs from that of an electrostatic machine in that it neither pos- sesses the violet color of the positive static dis- charge nor the brightness of the negative, but is inlenneJiate in color. Discharge, Surging -- A term some- times applied to an oscillatory discharge. (See Discharge, Oscillatory^) Discharge, to Electrically -- To equalize differences of potential by connecting them by means of a conductor. Discharge, Undulatory -- A dis- charge, the strength and direction of which gradually change. (See Currents, Undu- Discharge, Unidirectional - An electric discharge which takes place from the beginning to the end, in one and the same di- rection. Discharge, Velocity of -- The time required for the passage of a discharge through a given length of conductor. According to modern views it is the ether sur- rounding the wire or conductor which conveys the electric pulses. All the c nergy which gets into the conductor is dissipated as heat. The velocity of propagation of discharge of the pulses produced by the oscillating discharge of a Leyden jar through the inter-atomic or inter- molecular ether, i.e. , through the fixed ether within different substances, varies with the substance. Through free ether the velocity is that of light, or 185,000 miles a second. The velocity of discharge through long con- ductors or- cables is much lessened by incapacity of the cable, and the effects of induction, and will therefore vary in different cases. (See Retard- ation.) Discharger, Universal An appa- ratus for sending the discharge of a powerful Leyden battery or condenser in any desired direction. The universal discharger consists essentially of metallic rods, supported on insulated pillars and capable of ready motion, both toward sand from, one another, as well as in vertical and horizon- tal p'anes. The object which is to receive the discharge is placed on an insulated table between the rods, and the latter connected with the opposite coatings of the battery or condenser, when the discharge passes through it. The term universal discharger is sometimes ap- plied to the discharging tongs. Discharging, Electrically The act of equalizing differences of potential by connection with a conductor. Discharging Rod. (See Rod, Discharg- ing) Discharging Tongs. (See Tongs, Dis- charging^] Disconnect. To break or open an electric circuit. Disconnecter. A key or other device for opening or breaking a circuit. Disconnecting. The act of opening or breaking an electric circuit. Disconnection. A term employed to des- ignate one of the varieties of faults caused by the accidental breaking or disconnection of a circuit. Disconnections of this kind may be : (i.) Total ; as by a switch inadvertently left open; or by the accidental breaking of a part of the circuit. (2.) Partial; as by a dirty contact; a loose, or badly soldered joint; a poorly clamped binding screw ; a loose terminal, or a bad earth. (3.) Intermittent; as by swinging joints, alter- nate expansions or contractions on changes of temperature; the collection of dustand dirt in dry weather, and then- washing out in wet weather. Disconnection, Intermittent - Any fault in a line which occurs at intervals or intermittently. Disconnection, Partial A partial fault in a line caused by any imperfect con- tact. Disconnection, Total A fault in a line occasioned by a complete break in the circuit. Disguised Electricity.- (See Electricity, Disguised.) Dis.] 172 [Dis. Disjunctor. A device employed in a sys- tem for the distribution of electric energy by means of continuous currents by condensers, for the purpose of periodically reversing the constant current sent over the line. (See Electricity, Distribution of, by Continuous Current by Means of Condensers?) Dispersion Photometer. (See Photome- ter, Dispersion?) Displacement Current (See Current, Displacement?) Displacement, Electric A displace- ment of electricity in a uniform and non- crystalline dielectric when lines of electro- static or magnetic force pass through it. The quantity of electricity displaced in any homogeneous, non-crystallizable dielectric, by the action of an electric force through the unit area of cross-section, taken perpen- dicular to the direction of the electric force. Electric displacement is produced under an elastic strain, which continues only while the elec- tric force is acting. Displacement, Electric, Lines of Lines of electric induction along which elec- tric displacement takes place. Displacement, Electric, Oscillatory A displacement of electricity in a di- electric or non-conductor of an oscillatory character. Displacement, Electric, Theory of A theory which regards the electricity produced on an insulated conductor, by in- duction through a dielectric, as displaced out of the dielectric on to the conductor, or into the dielectric from the conductor, by the in- fluence of the electric force. This conception was introduced into science by Maxwell, after a careful study of Faraday's denial of action at a distance. Suppose a small insulated sphere to receive a charge of electricity -|- Q- It will, by induction, produce an equal and opposite charge Q, on the inner surface, and a similar charge on the outer surface of the small hollow sphere, placed near it, but separated by the dielectric. There has, therefore, been a displacement of electricity through the dielectric. The medium of the dielectric has connected the two bodies, and the phenomena have appeared by the action of the electric force on the substance of the dielectric; or, in other words, there has been no action at a distance. According to this conception, an electric cur- rent, called a displacement current, exists in the dielectric, while displacement is taking place. Displacement Waves. (See Waves, Dis- placement.] Disruptive Electric Conduction. (See Conduction, Electric, Disruptive.} Dissimulated or Latent Electricity. (See Electricity, Dissimulated or Latent?) Dissipation of Charge. (See Charge, Dissipation of.) Dissipation of Energy. (See Energy, Dissipation of.) ' Dissipation of Energy, Hysteresial (See Energy, Hysteresial, Dissipation of. Hysteresis?) Dissipation, Specific Hysteresial The specific loss of energy by hysteresis in the case of a particular substance. (See Hysteresis?) Dissociate. To separate a compound sub- stance into its constituents. Dissociation. The separation of a chemi- cal compound into its constituent parts. Dissymmetrical Induction of Armature. (See Armature, Dissymmetrical Induc- tion of.) Dissymmetrical Magnetic Field. (See Field, Magnetic, Dissymmetrical) Dissymmetry of Commutation. (See Commutation, Dissymmetry of.) Distance, Critical, of Lateral Discharge Through an Alternative Path The distance at which a discharge will take place through an air space of given dimensions, in preference to passing through a metallic cir- cuit of comparatively small resistance. Distance, Explosive A term some- times employed for sparking distance. (See Distance, Sharking?) Distance, Sparking The distance Dis.J 173 [Dot. at which electrical sparks will pass through an intervening air space. (See Spark, Length of.) Distant Station. (See Station, Distant?) Distillation, Destructive - The action of heat on an organic substance, while out of contact with air, resulting in the decomposition of the substance into simpler and more stable compounds. The different products resulting from destruc- tive distillation may be successively collected by the ordinary processes of distillation. Distillation, Dry A species of de- structive distillation. (See Distillation, De- structive?) Distillation, Electric - The dis- tillation of a liquid in which the effects of heat are aided by an electrification of the liquid. Beccaria discovered that a liquid evaporates more rapidly when electrified than when unelectrified. Crookes has shown that evaporation is aided by negative electrification, or that evaporation takes place more rapidly at the negative terminal during a discharge than at the positive. (See Evaporation, Electric. ) Distributing Box of Conduit. (See Box, Distributing, of Conduit?) Distributing Station. (See Station, Dis- tributing.) Distributing Switch for Electric Light. (See Switch, Distributing, for Electric Lights.) Distribution-Box for Arc Light Circuits. (See Box, Distribution, for Arc Light Circuits?] Distribution, Centre of In a sys- tem of multiple-distribution, any place where branch cut-outs and switches are located in order to control communication therewith. The electrical centre of a system of distri- bution as regards the conducting network. Distribution of Charge. (See Charge, Distribution of.) Distribution of Electricity. (See Elec- tricity, Distribution of.) Distribution of Electricity by Alternat- ing Currents (See Electricity, Dis- tribution of, by Alternating Currents?) Distribution of Electricity by Alternat- ing Currents by Means of Condensers. (See Electricity, Distribution of, by Alter- nating Currents by Means of Condensers.) Distribution of Electricity by Cominu- tatiug Transformers. (See Electricity, Distribution of, by Commutating Trans- formers?) Distribution of Electricity by Constant Potential Circuit. (See Electricity, Multi- ple Distribution of, by Constant Potential Circuit.) Distribution of Electricity by Contin- uous Current by Means of Transformers. (See Electricity, Distribution of, by Contin- uous Current by Means of Transformers.) Distribution of Electricity by Motor- Generators. (See Electricity, Distribution of, by Motor-Generators?) Distribution, Series, of Electricity by Constant Current Circuit. (See Electricity, Series Distribution of, by Constant Current Circuit?) District Call-Box. (See Box, District Call.) Diurnal Inequality of Earth's Magnet- ism. (See Inequality, Diurnal, of Earth's Magnetism?) Divided Magnetic Circuit (See Circuit, Divided Magnetic.) Door-Opener, Electric A device for opening a door from a distance by elec- tricity. Various devices consisting of electro-magnets, acting against, or controlling springs or weights, are employed for this purpose. Dosage, Electro-Therapeutical The apportioning of the amount of the cur- rent and the duration of its application to the body for the treatment of disease. Dosage, Galvanic Electro-thera- peutical dosage. (See Dosage, Electro- Therapeutical) . Dotting Contact (See Contact, Dotting.) DOR,] 174 [Dro. Double-Break Knife Switch.-(See Switch, Double-Break Knifed) Double-Carbon Arc Lamp. (See Lamp, Electric Arc, 'Double-Carbon) Double-Cone Insulator. (See Insulator, Double-Cone) Double- Connector. (See Connector, Double) Double-Contact Key. (See Key, Double- Contact) Double-Cup Insulator. (See Insulator, Double-Cup) Double-Curb. (See Curb, Double) Double-Curb Signaling. (See Signaling, Curb, Double) Double-Current Signaling. (See Signal- ing, Double-Current) Double-Current Translator. (See Trans- lator, Double-Current) Double-Current Transmitter. (See Transmitter, Double-Current) Double-Current Working The employment, in systems of telegraphy, by means of suitable keys, of currents from voltaic batteries, in alternately opposite directions, thus increasing the speed of signaling. (See Working, Reverse-Current) Double-Fluid Electrical Hypothesis. (See Electricity, Double-Fluid Hypothesis of) Double-Fluid Voltaic Cell. (See Cell, Voltaic, Double-Fluid) Double-Magnet Dynamo-Electric Ma- chine. (See Machine, Dynamo-Electric, Double- Magnet) Double-Pen Telegraphic Register. (See Register, Double-Pen, Telegraphic) D o n b 1 e-Refraction. (See Refraction, Double) Double-Refraction, Electric. (See Re- fraction, Double, Electric) Double-Shackle Insulator. (See Insula- tor, Double-Shackle) Double-Shed Insulator. (See Insulator, Double-Shed) Double-Tapper Key. (See Key, Double- Tapper) Double-Touch, Magnetization by A method for producing magnetization by the simultaneous touch of two magnet poles. (See Magnetization, Methods of) Double-Transmission. (See Transmis- sion, Double) Double-Trolley. (See Trolley, Double) Doubler of Electricity. An early form of continuous electrophorus. (See Electro- phorus) Drifting Torpedo. (See Torpedo, Drift- ing) Drill, Electro-Magnetic A drill applied especially to blasting or mining opera- tions, operated by means of electricity. Drip Loop. (See Loop, Drip) Driven Pulley. (See Pulley, Driven) Driven Shaft. (See Shaft, Driven) Driving Pulley. (See Pulley, Driving) Driving Shaft. (See Shaft, Driving) Driving Spider. (See Spider, Driving) Drop, Annunciator A movable signal operated by an electro-magnet, and placed on an annunciator, the dropping of which indicates the closing or opening of the circuit with which the electro-magnet is con- nected. The falling of the drop may be attended by the sounding of a bell or other alarm, or, it may give a silent indication. Drop, Annunciator, Automatic -A drop for an annunciator, which on the closing of a circuit, falls and holds the circuit closed until the drop is raised. Drop, Annunciator, Gravity A drop for an annunciator, acted on by gravity when released by the movement of the arma- ture of an electro-magnet. Drop, Automatic A device for au- tomatically closing the circuit of a bell and holding it closed until stopped by resetting a drop. Dro.] 175 [Byn. The automatic drop is especially applicable to burglar alarms. On the opening of a door or shutter, the closing of the circuit moves the armature of an elec- tro-magnet, and, by the falling of a drop, closes the cir- cuit and holds it closed until me- chanically opened by the replacing of the drop. The general appearance of the automatic drop is shown in Fig. 215. Drop, Calling _ _ A n an- Fig ' 2 * 3 ' Automatic EroP- nunciator drop employed to indicate to the operator in a telegraphic or telephonic system that one subscriber wishes to be connected with another. Drop of Potential. (See Potential, Drop of-} Drops, Clearing- Out - Restoring the drops of annunciators to their normal position after they have been thrown out of the same by the closing of the circuits of their magnets. These clearing-out devices as placed on most forms of annunciators are general. y mechanical in operation. Drum Armature. (See Armature, Drum.} Drum, Electro-Magnetic -- A drum, used in feats of legerdemain, operated by .an automatic electro-magnetic make and break apparatus. Dry Distillation. (See Distillation, JDry.} Dry Electrode. (See Electrode, Dry) Dry Pile. (See Pile, Dry.} Dry Voltaic Cell. (See Cell, Voltaic, Dub's Laws. (See Laws, Dud's.} Duplex Cable. (See Cable, Duplex.} Duplex Cut-Out. (See Cut-out, Duplex.} Duplex Flat Cable. (See Cable, Flat Duplex.} Duplex Telegraphy. (See Telegraphy, Duplex) Duplex Wire. (See Wire, Duplex) Duration of Electric Discharge. (See Discharge, Duration of) Duration of Make-Induced Current. (See Current, Make or Break Induced, Du- ration of) Dust Figures, Lichtenberg's - (See Figures, Lichtenberg's Dust) Dyad. A chemical element which has two bonds by which it can unite or combine with another element. An element whose atomicity is bivalent. Dyeing, Electric The application of electricity either to the reduction or the oxidation of the salts used in dyeing. Goppelsroder, in his processes of electric dyeing, forms and fixes ani'.ine black on cloth as follows, viz. : the cloth, saturated with an aniline salt, is placed on an insulated metallic plate, inert to the aniline salt, and connected with one pole of a battery or other electric source. The other pole is connected with a metallic plate on which the required design is drawn. On the passage of the current, the design is traced in aniline black on the cloth. A minute or two suffices for the operation. A species of electrolytic writing is obtained on cloths arranged as above by substituting a carbon pencil for the metallic plate. On writing with this pencil, as with an ordinary pencil, the pas- sage of the current so directed is followed by the deposition of aniline black. By means of a somewhat similar process writ- ing in white on a colored ground is obtained. Dynamic Electricity. (See Electricity, Dynamic) Dynamics, Electro That branch of electric science which treats of the action of electric currents on one another and on themselves or on magnets. The principles of electro dynamics were dis- covered by Ampere in 1821. A convenient form of apparatus, for showing experimentally the action of one current on another, consists of two upright metallic columns 176 [Dyn. or pillars, which support horizontal metallic arms containing mercury cups, y, and c, Fig. 216. Fig. 2r6. Deflection of a Circuit by a Current. The circuit is bent in the form of a rectangle, circle or solenoid, and terminates in points that dip in the mercury cups. The current is led into and out of the apparatus at the points -j- and at the base of the upright supports. When a magnet, or another circuit, is ap- proached to the movable circuit thus provided, attractions or repulsions are produced according to th2 position of the magnet, or the direction of the currents in the two circuits. If a magnet A B, Fig. 217, be placed, as shown, Fig. 217. Deflection of Circuit by a Magnet. below the movable circuit C C, the circuit will tend to place itself at right angles to the axis of the magnet. This movement is the same as would occur if electric currents were circulating around the magnet in the direction cf the assumed Amperian currents. It also illustrates the prin- ciple of the electric motor. (See Magnetism, Am- pere's Theory of. ) Ampere has given the results of his investigations as to the mutual attractions and repulsions of cur- rents in the following statements, which are known as Ampere 's Laws: (I.) Parallel portions of a circuit attract one another if the currents in them are flowing in the same direction, and repel one another if the currents are flow- ng in opposite direc- tions. A current flowing through a spiral tends to shorten the spiral ***'* Action of Solenoid: from the attraction of the parallel currents in contiguous turns. Similar poles of two solenoids repel each other,, as at A, A', Fig. 218, because, when opposed to each other, the currents that produce these poles Fig. 219. Ampere's Stand. are flowing in opposite directions, as may be seen from an inspection of the drawing. Dissimilar solenoid poles, on the contrary, at- tract each other as at A, B, in Fig. 218, since C Fig. 220. Electro- Dynamic Attraction. the currents which produce them flow in thg same- direction. In Fig. 219, a form of Ampere's stand is shown, in which one of the circuits is in the form of the yn,] 177 coil M N ; its action on the movable circuit C B, is to repel it, since the currents, as shown, are flowing in an opposite direction in the adjacent portions of the fixed and movable circuits. (2.) Two portions of a circuit intersecting each other mutually attract each other when the cur- rents in both circuits flow .either towards or from the point of intersection, tut repel each other if they flow in opposite di- rections from this point. Thus, in Fig. 220, the currents in both circuits P 5 P Q and A B C D, flow ftf- 221- Continuous .towards and from the Rotation of Current. point of intersection Y, and attract one another and cause a motion until the two circuits are parallel. If the currents flow in opposite directions they repel each other, and, if free to move, will come to rest when parallel to each other ; therefore, two portions of a circuit crossing each other tend to move until they are parallel, and their currents are flowing in the same direction. (3.) Successive portions of the circuit of the same rectilinear current, that is, a current flowing in the same straight line, repel one another. A circuit O A, Fig. 221, movable on O, as a ftf. 222. Mutual Action of Magnetic Fields. centre, will be continuously rotated in the direc- tion of the curved arrow by the rectilinear cur- rent, P Q ; for, the directions of the currents being as shown by the arrows, there will be attraction in the positions (i) and (2), and repulsion in po- sition (4). The cause of the mutual attractions and repul- sions of electric circuits will readily appear from a. consideration of the mutual action of their magnetic fields. Thus an inspection of Fig. 222 shows : (l.) That parallel currents flowing in the same direction attract, because their lines of force have opposite directions in adjoining parts of the cir- cuit of these lines. , (2.) That parallel currents flowing in opposite directions repel, because their lines of force have the same directions in adjoining parts of the cir- cuit. These laws may therefore be generalized thus, viz. : Lines of magnetic force extending in oppo- site directions attract one another; lines of magnetic force extending in the same direction repel one another. Ampere proved that a circuit, doubled on itself so that the current flows in opposite directions in the two parts, exerts no force on external objects. This expedient is adopted in resistance coils to prevent any disturbance of the galvanometer needles. He also showed that a sinuous circuit, or one bent into zigzags, produces the same effects of attraction or repulsion as it would if it were straight. (See Coil, Resistance.) The term sinuous current is sometimes applied to the current in a sinuous circuit. (See Current, Sinuous.) This must be di.-tinguished from the term sinusoidal current, which applies to fluctua- tions in the current and not to peculiarities in the shape of the conductor. When two inclined magnets, free to move, are left to their mutual attractions and repulsions, they gradually come to rest with their axes parallel to each other. Two conductors through which electric cur- rents are flowing act on one another as two magnets would. A conductor conveying a current of electricity tends to rotate round a magnetic pole. A mag- netic pole tends to rotate continuously round an electric current. The motion of a magnet near a conductor produces an electromotive force in that conductor provided the conductor cuis the lines offeree. A magnetized substance becomes magnetized when placed in a magnetic field. A conductor through which a current of elec- tricity is passing tends to wrap itself around a neighboring magnetic pole. The following ex- periments illustrate this tendency: (I.) The experiment suggested by Lodge: A powerful current of electricity is passed through some eight feet in length of gold thread such as is employed for making lace. The thread is hung in a vertical position, near a vertical bar 178 magnet. As soon as the current passes, the thread will wrap itself around the bar magnet, one half of it twisting itself round the north pole, the other half round the south pole. (2.) The experiment suggested by Professor S. P. Thompson: An electric current is sent through a stream of mercury while it is flowing between two poles of a powerful electro-magnet; when the current is sent through the magnet, the stream is twisted in spiral directions which vary, either with the direction of the current, or with the direction of the magnetic polarity. (3.) Somewhat similar effects can be shown by the rotation of a stream cf gas round a magnetic pole placed in an exhausted glass receiver. Dynamo. The name frequently applied to a dynamo-electric machine used as a gener- ator. (See Machine, Dynamo-Electric?) Dynamo Balancing Rheostat. (See Rheostat, Dynamo Balancing?) Dynamo-Battery. (See Battery, Dy- namo?) Dynamo Brush Trimmer. (See Trim- mer, Dynamo Brush?) Dynamo, Composite-Field A dynamo whose field coils are series and separately excited. Additional separately excited coils placed on the field of a series wound dynamo render it self- regulating. A composite dynamo is a form of compounded dynamo. Dynamo, Compound-Wound. A com- pound-wound dynamo-electric machine. (See Machine, Dynamo-Electric, Compound- Wound?) Dynamo, Contact A form of dyna- mo in which the space between the arma- ture and field magnet poles is so reduced that they actually touch one another. In contact dynamos both field and armature revolve. This form of dynamo has. not been very successful in practice. Dynamo-Electric Machine. (See Ma- chine, Dynamo-Electric?) Dynamo-Electric Machine, Alternating Current (See Machine, Dynamo- Electric, Alternating' Current?) [Dyn, Dynamo-Electric Machine Armature. (See Armature, Dynamo-Electric Machine?) Dynamo-Electric Machine Armature Coils. (See Coils, Armature, of Dynamo- Electric Machine?) Dynamo-Electric Machine Armature Core. (See Core, Armature, of Dynamo- Electric Machine?) Dynamo-Electric Machine Battery. (See Battery, Dynamo-Electric Machine?) Dynamo-Electric Machine, Bi-Polar (See Machine, Dynamo-Electric, Bi- Polar?) Dynamo-Electric Machine, Collecting Brushes of (See Brushes, Collecting, of Dynamo-Electric Machine?) Dynamo-Electric Machine Commutator (See Commutator, Dynamo-Electric Machine?) Dynamo-Electric Machine, Compound- Wound (See Machine, Dynamo- Electric, Compound- Wound?) Dynamo-Electric Machine, Generation of Current by 'See Current, Genera- tion of, by Dynamo-Electric Machine?) Dynamo-Electric Machine, Field Mag- nets (See Magnets, Field, of Dynamo- Electric Machine?) Dynamo-Electric Machine, Methods ol Increasing the Electromotive Force Gene- rated by (See Force, Electromotive, Generated by Dynamo-Electric Machine, Method of Increasing?) Dynamo-Electric Machine, Mouse-Mill, Sir William Thomson's (See Ma- chine, Dynamo-Electric, Mouse-Mill, Sir William Thomson's?) Dynamo-Electric Machine, Mnltipolar (See Machine, Dynamo-Electric, Multipolar?) Dynamo-Electric Machine, Pole-Pieces of (See Pole-Pieces of Dynamo-Electric Machine?) Dynamo-Electric Machine, Reversibility of (See Machine, Dynamo-Electric, Reversibility of?) Dyn.J 179 [Dyn. Dynamo-Electric Machine, Varieties of (See Machine, Dynamo-Electric, Varieties of.} Dynamo, Inductor A dynamor electric machine for alternating currents in which the differences of potential causing the currents are obtained by magnetic changes in the cores cf the armature and field coils by the movement past them of laminated masses of iron inductors. The coils corresponding to the armature and fie'd magnets of the ordinary dynamo are sta- tionary. The laminated masses of iron, employed to cause magnetic changes in the cores of the field and armature coils, are fixed on an inductor wheel which is rapidly revolved in front of them. The magnets corresponding to the field magnets are called the primary poles, and are magnetized by an exciter. The magnets corresponding to the armature are called the secondary poles and are placed so as to alternate with the primary poles. The inductors are so shaped that they carry the magnetism of one pole of the primary magnet to the secondary poles when the inductor is in one position, and of the opposite pole when in a slightly different position. The inductor wheel therefore acts as a magnetic commutator and changes the position of the secondary magnet as it rotates, thus producing electromotive force. The number of alternations per revolution is equal to twice the number of inductors placed on the inductor wheel. Dynamo, Inverted A dynamo-elec- tric machine m which the armature bore or chamber is placed below the field magnet coils. The term inverted is used in contradistinction to the overtype dynamo. (See Dynamo, Over- type.} Dynamo, Mouse Mill A form of dynamo-electric machine designed by Sir William Thomson to act as the replenisher of one of his electrometers. (See Replenisher!) Dynamo, Multiphase A polyphase dynamo. (See Dynamo, Polyphase. Dyna- mo, Rotating Current) Dynamo, Overtype A dynamo- electric machine, the armature bore or cham- ber of which is placed above the field magnet coils instead of below them as in many forms. The overtype form of dynamo possesses the advantage oi better avoiding magnetic leakage. Dynamo, Polyphase A name some- times applied to a rotating current dynamo. (See Dynamo, Rotating Current!) Dynamo, Pyromagnetic A name sometimes applied to a pyromagnetic gen- erator. (See Generator, Pyromagnetic!) Dynamo, Rotary-Phase A term sometimes employed for a rotating current dynamo. (See Dynamo, Rotating Current!) Dynamo, Separately-Excited A separately-excited dynamo-electric machine. (See Machine, Dynamo-Electric, Separ- ately-Excited!) Dynamo, Series A series-wound dynamo- electric machine. chine, Dynamo- Electric, Series- Wound^ Dynamo, Shunt A shunt- wound dynamo- electric machine. (See Machine, Dynamo - Electric, Shunt- Wound!) Dynamograph. A term some- times applied to a type-writing tele- graph that records the message in type-written char- acters, both at the sending and the receiving ends. Dynamometer. (= A name given to a rariety of appar- F ig. 223. Parses Dyna- atus for measuring mometer. the power of an engine or motor. In all dynamometers the strain on the belt or other moving part is measured, say in pounds, and the speed of the moving part is also measured in feet per second. The product of the strain in. Dyn.] 180 pounds by the velocity in feet per second, di- vided by 550, will give the horse power. One of the many forms of dynamometers is shown in Fig. 223. It is known as Parsons' Dy- namometer. The driving pulley is shown at A, and the driven pulley at C. Weights hung at Q 15 are va- ried so as to maintain the axes of the suspended pulleys, D and B, as nearly as possible at the same height. Then the tension T 1 and.T 2 , on the sides O and O', of the belts, will be repre- sented by the following equation : Since the same current passes through both the fixed and movable coils, and they both act on each other, the deflecting force here is evidently proportional to the square of the strength of the from which, knowing the belt speed, the horse power may be deduced. There are several other forms of dynamometer, such as the cradle dynamometer, in which the machine is supported on knife edges and the torque or pull exerted on or by the machine is balanced by weights sliding on a lever. In these dynamometers the power is transmitted through them and they are therefore called transmission dynamometers. Dynamometer, Electro A form of galvanometer for the measurement of electric currents. In Siemens' Electro-Dynamometer, shown in Fig. 224, there are two coils ; a fixed coil, C, se- cured to an upright support, and a movable coil, L, consisting often of but a single turn of wire. The movable coil is suspended by means of a thread and a delicate spring, S, capable of being twisted by turning a milled screw-head through an angle of torsion measured on a scale by means of an index connected to the screw-head. The two ends of the movable coil dip into mercury cups so connected that the current to be measured passes through the fixed and movable coils in series. When ready for use the movable coil is at right angles to the fixed coil. The current to be meas- ured is then sent into the coils, and their mutual action tends to place the movable coil parallel to the fixed coil against the torsion of the spring, S. The amount of this force can be ascertained by determining the amount of torsion required to bring the movable coil back to its zero position. Fig. 224. Siemens' Electro- Dynamometer. current to be measured. The deflecting force, and consequently the current strength, is there- fore proportional to the square root of the angle of torsion, and not directly to the angle of tor- sion. Dyne. The unit of force. The force which in one second can impart a velocity of i centimetre per second to a mass of i gramme. The dyne is the unit of force, or a force capa- ble, after acting for one second on a mass of I gramme, of giving it a velocity of I centimetre per second. The weight of abody in dynes, or the force with which it gravitates, is equal to its mass in grammes, multiplied by the acceleration imparted to it in centimetres per second. For this latitude the acceleration is about 981 centi- metres per second. E.J 181 [Edd. E. A contraction sometimes used for earth. A contraction sometimes used for electro- motive force, or E. M. F., as in the well- known formula for Ohm's law, E. M. D. P. A contraction for electro- motive difference of potential. (See Poten- tial, Difference of, Electromotive?) E. M. F. A contraction generally used for electromotive force. (See Force, Electro- motived) Earth. A fault in a telegraphic or other line, caused by accidental contact of the line with the ground or earth, or with some con- ductor connected with the latter. This is more frequently called a ground. Earths are of three kinds, viz.: (I.) Dead or Total Earth. (2.) Partial Earth. ( 3 . ) Intermittent Earth . The term earth is also applied to a plate buried in the ground, and intended to make a good con- tact between the earth and a wire circuit, which is connected with the plate. Earth Circuit. (See Circuit, Earthy Earth-Circuited Conductor. (See Con- ductor, Earth-Circuited?) Earth Currents. Electric currents flow- ing through different parts of the earth caused by a difference of potential at different points. The causes of these differences of potential are various and are not well understood. Earth, Dead or Total --- A fault in a telegraphic or other line in which the line is thoroughly grounded or connected with the earth. Dead earth is sometimes called total earth. Earth-Grounded Wire. (See Wire, Earth-Grounded. ) Earth, Intermittent -- A swinging earth. (See Earth, Swinging or Intermit- tent?) Earth or Ground. That part of the earth or ground which forms part of an electric circuit. A circuit is put to earth or ground when the earth is used for a portion of the circuit. The resistance of an earth connection may vary in time from the following causes, viz.: (I.) The corrosion of the ground plate. This is especially apt to occur in the case of a copper plate. (2.) From polarizaiion, a counter-electro- motive force being produced, thus introducing a spurious resistance into the circuit. (See Resist- ance, Spurious.) Earth, Partial A fault in a tele- graphic or other line in which the line is in partial connection with the earth. The term partial earth is used in contradistinc- tion to dead or total earth. Earth, Return A circuit in which the return current passes back to the source through the earth. Earth, Swinging 1 or Intermittent A fault in a telegraphic or other line in which the action of the wind, or occasional expansion by heat, brings the line into inter- mittent contact with the earth. A term sometimes (See Earth, Dead or Earth, Total used for dead earth. Total.) Ebonite. A tough, hard, black substance, composed of india rubber and sulphur, which possesses high powers of insulation and of specific inductive capacity. Ebonite is often called vulcanite. Vulcanite rubbed with cat-skin acts as one of the best known substances for becoming electri- fied by friction. For this purpose both substances should be thoroughly dried. Economic Co-efficient of Dynamo-Elec- tric Machine (See Co-efficient, Economic, of a Dynamo-Electric Machine?) Eddy Currents. (See Currents, Eddy.) Eddy Currents, Deep-Seated (See Currents, Eddy, Deep-Seated?) Eddy Currents, Superficial (See Currents, Eddy, Superficial?) Edd.] 182 [Eff. Fig. 223. Electric Eel. Eddy-Displacement Currents. (See Cur- rents, Eddy-Displacement^ Eel, Electric An eel possessing the power of giving powerful electric shocks. The gymnotus electricus. The electricity is produced by an organ ex- tending the entire length of the body. According to Faraday, the shock given by a specimen of the animal examined by him was equal to that of 15 Leyden jars, having a total surface of 25 square feet. Fig. 225 shows the general appearance of the animal. Effect, Acheson The increase in the electro- motive force of the sec- ondary of a transformer by the action of the changes in temperature of its core. (See Electricity, Cal) Effect, Chemical - The effect occasioned by atomic combina- tion, which results in a loss of those properties or peculiarities by which the substances en- tering into combination are ordinarily recog- nized. Atomic combination, resulting in the for- mation of new molecules. The formation of new molecules necessitates the possession by the new substance of properties dis- tinct and separate from those of its constituents. Black carbon, and yellow sulphur, for example, both solids, unite chemically to form a trans- parent colorless liquid. Chemical changes differ from physical changes, which latter can occur in a substance without the formation of new molecules, and consequently without the loss by it of the properties it ordi- narily possesses. Thus a sheet of vulcanite, electrified by friction, still retains its characteristic density, shape, color, etc. Effect, Counter-Inductive The opposal of current or charge by means of a counter-electromotive force produced by in- duction. In the Thomson counter-electromotive force lightning arrester, a counter-electromotive force, produced by the inductive effects of the passage of the bolt to earth, protects the instrument by opposing the passage of the bolt. (See Arrester, Lightning Countcr-Electromotive Force.") Effect, Edison An electric dis- charge which occurs between one of the ter- minals of the incandescent filament of an electric lamp, and a metallic plate placed near the filament but disconnected therefrom, as soon as a certain difference of potential is reached between the lamp terminals. The effect of the discharge is to produce a cur- rent in a circuit connected to one pole of the lamp terminals and the metallic plate, as may be shown by means of a galvanometer. Effect, Electrotonic An altered condition of excitability of a nerve produced when in the electrotonic state. (See Elec- trotonus.) Effect, Faraday -The rotation of the plane of polarization of a beam of plane polarized light by its passage through a magnetic field. Lodge suggests the following explanation for the Faraday effect: As is well known, a strongly magnetized medium possesses a different magnetic susceptibility to additional magnetizing forces in the same direction than it does in the opposite direction. I- therefore follows that the vibra- tions are resolved into two opposed circular com- ponents, which travel through the medium with different rates of velocity, since one tends to mag- netize it and the other to demagnetize it. The plane of rotation will therefore be rotated. He also suggests th.3 following explanation for the Faraday effect, viz.: He assumes that the Amperian molecular currents in such substances as exhibit rotation in a magnetic field, do not consist of two eq jal and opposite electrical cur - rents, but thac or.3 cf the currents is slightly stronger than the other. Suppose, for example that in iron the positive Amperian current is weaker than the negative, and that the ether as a whole is rotating with the negative current. Any ethereal vibration entering such a medium will begin to screw itself in the direction opposed to that of the magnetizing current. In copper, or other similar substances, the rotation should take place in the opposite direction. Eff.J 183 [Eff, Effect, Ferranti An increase in the electromotive force, or difference of potential, of mains or conductors towards the end of the same farthest from the terminals that are con- nected with a source of constant potential. The Ferranti effect refers to the increase of the electromotive force on the mains employed in systems for the transmission of electrical energy by means of alternating currents. It was found, for example, in the currents used on the mains connected with one of Mr. Ferranti's alter- nating dynamos and leading to the town of Dept- ford, that instead of finding a drop of potential at the ends of the mains farthest from the dynamo, as was expected, a notable increase in the poten- tial occurred. These effects were observed dur- ing the laying of the mains. Testing the poten- tial by placing an incandescent lamp in the circuit across the mains, the increase of the potential with the increase of the length of the main was shown by the increased brilliancy of the light of the incandescent lamp. Various explanations have been given as the cause of the Ferranti effect. Effect, Hall A transverse elec- tromotive force, produced by a magnetic field in substances undergoing electric dis- placement. This transverse electromotive force is probably Fig. 226. Hall Effect. due to magnetic whirls, in a manner similar to the Faraday effect. The Hall effect is produced by placing a very thin metallic strip, conveying an electric current, in a strong magnetic field. The cross A B C D, Fig. 226, is cut out of a gold leaf or other very thin metallic sheet The ends A and B, are connected with the terminals of a battery S, and the ends C and D, with the galvanometer G. None of the battery current can therefore flow through the galvanometer. If, now, the metallic cross be placed in a power- ful magnetic field, the lines of force of which are perpendicular to the plane of the cross, the deflec- tion of the galvanometer needle will show the existence of a current, which, if the battery cur- rent flows in the direction of the arrow, or from A, to B, and the lines of magnetic force pass through the paper from the front to the back of the sheet, when the cross is formed of gold, silver, platinum or tin-foil, will flow through C D, from C to D, but in the opposite direction if formed of iron. These effects cease if the conductor is increased in thickness beyond a certain extent. As regards the production of the Hall effect by the influence of a magnetic field on conductors, Mr. Shelford Bidwell suggests that since magnet- ism affects the conductivity of metals in a- complicated manner, it is possible that metallic substances conveying an electric current in a magnetic field are more or less strained by the mechanical forces, and that, therefore, heat may be unequally developed, and that the resistance thus being modified in places, there may be pro- duced disturbances of the flow which may rapidly produce in part a transverse electromotive force. Effect, Hall, Real A transverse elec- tromotive force produced in conductors con- veying electric currents, by magnetic whirls, in a manner similar to that in which the Far- aday effect is produced. (See Effect, Fara- day^ Effect, Hall, Spurious An appa- rent transverse electromotive force produced in conductors conveying electric currents in magnetic fields, by changes, produced by mag- netism, in the conductivity of the metals, and the consequent production of local distur- bances in the electrical flow, thus resulting- in an apparent transverse electromotive force. Effect, Impulsion The restoration or loss of sensitiveness of a photo-voltaic cell to the action of light, produced by means of an impulse such as that of a tap or blow, or electro-magnetic impulse. Eff.] 184 [Eff. Effect, Joule The heating effect produced by the passage of an electric cur- rent through a conductor, arising merely from the resistance of the conductor. The rate at which this occurs is proportional to the resistance of the conductor through which the current is passing multiplied by the square of the current. (S^e Heat, Electric. ) Effect, Kerr A term applied to the electrostatic optical effect discovered by Dr. Kerr, viz., that a beam of plane polarized light is elliptically polarized when transmitted across an electrostatic field. The Kerr effect does not take place in free space, but occurs in different senses or directions in dif- ferent media. Like the Faraday effect, the Kerr effect de- pends on the presence of a dense medium, and the direction of the effect depends on the character of the medium. Effect, Mordey A term some- times applied to a decrease in the value of hysteresis in the iron of a dynamo armature at full load. Effect, Peltier The heating ef- fect produced by the passage of an electric current across a thermo-electric junction or surface of contact between two different met- als. (See Junction, Ther mo-Electric.) The passage of the current across a thermo- electric junction produces either heat or cold. If heat is produced by its passage in one direction, cold is produced by its passage in the opposite direction. The Peltier effect may, therefore, mask the Joule effect. The Peltier effect is the converse of the thermo- electric effect, where the unequal heating of metal- lic junctions results in an electric current. (See Effect, Joule. Effect, Thomson.) The quantity of heat absorbed or em'tted by the Peltier effect is proportional to the current strength, and not, as in the Joule effect, to the square of the current. Effect, Photo-Yoltaic The change in the resistance of selenium or other substances effected by their exposure to light. The photo-voltaic effect is seen in the case of the selenium cell. (See Cell, Selenium?) Effect, Seebeck A term sometimes used instead of thermo-electric effect. (See Effect, Thermo-Electric^) This term has nearly passed out of use. Effect, Skin The tendency of alter- nating currents to avoid the central portions of solid conductors and to flow or pass mostly through the superficial portions. The so-called skin effect is more pronounced the more frequent the alternations. Effect, Thermo-Electric The pro- duction of an electromotive force at a thermo-electric junction by a difference of temperature between that junction and the other junction of the thermo-electric couple. (See Couple, Thermo-Electric. Junction, Ther mo-Electric.) Effect, Thomson The production of an electromotive force in unequally heated homogeneous conducting substances. A term also applied to the increase or de- crease in the differences of temperature in an unequally heated conductor, produced by the passage of an electrical current through the conductor. The Thomson effects vary according to whether the current passes from a colder to a I otter part of the conductor, or the reverse. The Thomson effects differ in direction in differ- ent metals, and are absent in lead. Thomson has pointed out the similarity between this species of thermo-electric phenomena, and convection by heat, or the phenomena of a liquid circulating in a closed rectangular tube, under the influence of differences of temperature, in which the heated fluid gives out heat in the cooler parts of the cir- cuit, and takes in heat in the warmer parts, This would presuppose that positive electricity carries heat in copper like a real fluid, but that in iron it acts as though its specific heat were a negative quantity, in which respect it is unlike a true fluid. We may express," says Maxwell, " both the Peltier and the Thomson effects by stating that when an electric current is flowing from places oi smaller to places of greater thermo-electric power, heat is absorbed, and when it is flowing in the reverse direction heat is generated, and this whether the difference of thermo-electric power in the two places arises from a difference in the Eff.J 185 [Ele. nature of the metals, or from a difference of tem- perature in the same metal." Effect, Yoltaic A difference of potential observed at the point of contact of two dissimilar metals. This difference of potential was formerly as- cribed to the mere contact of dissimilar metals, and is even yet believed by some to be due to such contact. It is, however, perhaps more ac- curately ascribed to the greater affinity of oxygen of the air for the positive metal than for the negative metal; that is, to a chemical action on the positive element of a voltaic couple. Effective Electromotive Force. (See Force, Electromotive, Effective?) Effective Secondary Electromotive Force. (See Force, Electromotive, Second- ary, Effective?) Effects of Capillarity on Voltaic Cells. (See Capillarity, Effects of, on Voltaic Cell?) Efficiency, Commercial The useful or available energy produced divided by the total energy absorbed by any machine or ap- paratus. The Commercial Efficiency = W _ W ~M~ ~~ W + w -f- m, when W = the useful or available energy; M = the total energy ; w, the energy absorbed by the machine, and m, the stray power, or power lost in friction of bearings, etc., air friction, eddy cur- rents, etc. Efficiency, Commercial, of Dynamo The useful or available electrical energy in the external circuit, divided by the total mechanical energy required to drive the dynamo that produced it. (See Co-efficient, Economic, of a Dynamo-Electric Machine?) Efficiency, Electric The useful or available electrical energy of any source, divided by the total electrical energy. The electric efficiency = W where W, equals the useful or available electrical energy, and w, the electrical energy absorbed by the machine. Efficiency of Conversion. The ratio be- tween the energy present in any result and the energy expended in producing that result. Efficiency of Conversion of Dynamo. (See Conversion, Efficiency of, of Dynamo?) Efficiency of Transformer. (See Trans- former, Efficiency of?) Efficiency, Quantity, of Storage Battery The ratio of the number of ampere- hours taken out of a storage or secondary battery, to the number of ampere-hours put in the battery in charging it. Efficiency, Real, of Storage Battery The ratio of the number of watt-hours taken out of a storage battery, to the number of watt-hours put into the battery in charg- ing it. Efflorescence. The drying of crystals by losing their water of crystallization and be- coming pulverulent or crumbling. The term is sometimes loosely applied to the deposition of solid matter by the crystal- lization of a salt, above the line of the liquid, on the surface of a vessel containing a vaporiz- able saline solution. The liquid, by capillarity in a porous vessel, or by adhesion to the walls of an impervious vessel, rises above the level of the main liquid line, and, evaporating, deposits crystals on the vessel. This process is technically called creeping, and is often the cause of much annoyance in voltaic cells. Egg, Philosopher's A name given to the ovoidal, or egg-shaped mass of light that appears when a convective discharge is taken between two electrodes in a partial vacuum. The philosopher's egg is but one of the shapes- assumed by the convective discharge. (See Dis- charge^ Convective. ) Elasticity, Electric The quotient arising from dividing the electric stress by the electric strain. It can be shown mathematically that the elec- tric elasticity is equal to 4, or 4 x 3. 1416, divided by the specific inductive capacity. Electrepeter. An instrument for chang- ing the direction of an electric current. The old term for switch, key, or pole changer. (Obsolete.) Electric. Pertaining to electricity. Ele.] 186 [Ele. Electric Absorption. (See Absorption, Electric?) Electric Acoutemeter. (See Acouteme- ter, Electric) Electric Actinometer. (See Actinomeier, Electric) Electric Adhesion. (See Adhesion, Elec- tric) Electric Aging of Alcohol. (See Alco- hol, Electric Aging of) Electric Alarm. (See Alarm, Electric) Electric Alarm Speaking-Tube Mouth- Piece. (See Speaking-Tube Mouth-Piece, Electric Alarm) Electric Amalgam. (See Amalgam, Electric) Electric Ammunition Hoist. (See Hoist, Ammunition, Electric) Electric Analysis. (See Analysis, Elec- tric) Electric Analyzer. (See Analyzer, Elec- tric) Electric Anemometer. (See Anemome- ter, Electric) Electric Annealing. (See Annealing, Electric) Electric Annunciator Clock. (See Clock, Electric Annunciator) Electric Arc. (See Arc, Electric) Electric Arc Blow-Pipe. (See Blow- Pipe, Electric Arc) Electric Argand Burner, Hand-Lighter (See Burner, Argand Electric, Hand- Lighter) Electric Argand Burner, Plain-Pendant (See Burner, Argand Electric, Plain-Pendant) Electric Argand Burner, Ratchet-Pend- ant (See Burner, Argand Electric, Ratchet-Pendant) Electric Balance. -(See Balance, Elec- tric) Electric Balloon. (See Balloon, Elec- tric) Electric Battery. (See Battery, Elec- tric) Electric Bell, Continuous-Sounding (See Bell, Continuous-Sounding Electric) Electric Bell, Differential. (See Bell, Differential Electric) Electric Bell, Mechanical. (See Bell, Electro-Mechanical) Electric Bell Pull. (See Pull, Bell, Elec- tric) Electric Bioscopy. (See Bioscopy, Elec- tric) Electric Bi-Polar Bath. (See Bath, Bi- Polar) Electric Blasting. (See Blasting, Elec- tric) Electric Bleaching. (See Bleaching, Electric) Electric Blow-Pipe. (See Blow-Pipe, Electric) Electric Boat. (See Boat, Electric) Electric Bobbin. (See Bobbin, Electric) Electric Body-Protector. (See Body-Pro- tector, Electric) Electric Boiler-Feed. (See Boiler-Feed, Electric) Electric Branding. (See Branding, Elec- tric) Electric Breeze. (See Breeze, Electric) Electric Bridge. (See Bridge, Electric) Electric Buoy. (See Buoy, Electric) Electric Burner. (See Burner, Auto- matic Electric) Electric Buzzer. (See Buzzer, Electric) Electric Cable. (See Cable, Electric) Electric Calamine. (See Calamine, Elec- tric) Electric Call-Bell. (See Bell, Call) Electric Calorimeter. (See Calorimeter, Electric) Electric Candle. (See Candle, Electric) Electric Case-Hardening. (See Case- Hardening, Electric) Electric Cauterization. (See Cauteriza- tion, Electric) Electric Cauterizer. (See Cauterizer, Electric) Ele.] 187 [Ele. Electric Cautery. (See Cautery, Elec- tric) Electric Charge.- (See Charge, Electric) Electric Chimes. (See Chimes, Electric) Electric Chronograph. (See Chrono- graph, Electric) Electric Chronoscope. (See Chronoscope, Electric) Electric Cigar-Lighter. (See Lighter, Cigar, Electric) Electric Circuit. (See Circuit, Electric) Electric Cleats. (See Cleats, Electric) Electric Clepsydra. (See Clepsydra, Elec- tric) Electric Clock.- (See Clock, Electric) Electric Coil.- (See Coil, Electric) Electric Column. (See Column, Elec- tric) Electric Communicator. (See Commu- nicator, Electric) Electric Conducting. (See Conducting, Electrical) Electric Conduction. (See Conduction, Electric) Electric Convection of Heat. (See Heat, Electric Convection of) Electric Cord. (See Cord, Electric) Electric Counter. (See Counter, Elec- tric) Electric Creeping. (See Creeping, Elec- tric) Electric Cross. (See Cross, Electric) Electric Crucible. (See Crucible, Elec- tric) Electric Current. (See Current, Elec- tric) Electric Cystoscopy. (See Cystoscopy t Electric) Electric Damping. (See Damping, Elec- tric) Electric Death. (See Death, Electric) Electric Decomposition. (See Decom- position, Electric) Electric Density. (See Density, Elec- tric) Electric Deposition. (See Deposition, Electric) Electric Determination of Longitude. (See Longitude, Electric Determination of) Electric Displacement. (See Displace- ment, Electric) Electric Distillation. (See Distillation, Electric) Electric Door-Bell Pull. (See Pull, Electric Door-Bell) Electric Double-Refraction. (See Double-Refraction, Electric) Electric Dyeing. (See Dyeing, Electric) Electric Dynamometer, Siemens'. (See Dynamometer, Electro) Electric Eel. (See Eel, Electric) Electric Efficiency. (See Efficiency, Elec- tric) Electric Elasticity. (See Elasticity, Elec- tric) Electric Elevator. (See Elevator, Elec- tric) Electric Endosmose. (See Endosmose, Electric) Electric Energy. (See Energy, Electric) Electric Entropy. (See Entropy, Elec- tric) Electric Escape. (See Escape, Electric) Electric Etching. (See Etching, Elec- tro) Electric Evaporation. (See Evapora- tion, Electric) Electric Excitability of Nerve or Mus- cular Fibre. (See Excitability, Electric, of Nerve or Muscular Fibre) Electric Exhaustion. (See Exhaustion, Electric) Electric Expansion. (See Expansion, Electric) Electric Exploder. (See Exploder, Elec- tric Mine) Ele.J 188 [Ele. Electric Explorer. (See Explorer, Elec- tric^ Electric Field. (See Field, Electric) Electric Figures, Breath (See Figures, Electric, Breath) Electric Figures, Lichtenberg's (See Figures, Electric, Lichtenberg's) Electric Fishes. (See Fishes, Electric) Electric Fly. (See Fly, Electric) Electric Flyer. (See Flyer, Electric) Electric Fog. (See Fog, Electric) Electric Force. (See Force, Electric) Electric Furnace. (See Furnace, Elec- tric) Electric Fuse. (See Fuse, Electric) Electric Gas-Lighting. (See Gas-Light- ing, Electric) Electric Gas-Lighting, Multiple (See Gas-Lighting, Multiple Electric) Electric Gas-Lighting Torch. (See Torch, Electric Gas-Lighting) Electric Gastroscope. (See Gastroscope, Electric) Electric Gilding. (See Gilding, Electric) Electric Governor. (See Governor, Elec- tric) Electric Hand-Lighter for Argand Burner. (See Burner, Argand Electric Hand-Lighter) Electric Head-Bath. (See Bath, Head, Electric) Electric Head-Light (See Head-Light, Locomotive, Electric) Electric Heat (See Heat, Electric) Electric Heater. (See Heater, Electric) Electric Horse Power. (See Power, Horse, Electric) Electric Hydrotasimeter. (See Hydro- tasimeter, Electric) Electric Ignition. (See Ignition, Elec- tric) Electric Images. (See Images, Electric) Electric Incandescence. (See Incandes- cence, Electric) Electric Indicator for Steamships. (See Indicator, Electric, for Steamships) Electric Indicators. (See Indicators* Electric) Electric Inertia. (See Inertia, Electric) Electric Insolation. (See Insolation, Electric) Electric Installation. (See Installation, Electric) Electric Insulation. (See Insulation* Electric) Electric Irritability. (See Irritability, Electric) Electric Jar. (See Jar, Electric) Electric Jewelry. (See Jewelry, Elec- tric) Electric Lamp, Arc (See Lamp, Electric, Arc) Electric Lamp-Bracket. (See Bracket* Lamp, Electric) Electric Lamp, Incandescent (See Lamp, Electric, Incandescent) Electric Lamp, Semi-Incandescent (See Lamp, Electric, Semi-Incandescent) Electric Lamp, Socket for. (See Socket, Electric Lamp) Electric Launch. (See Launch, Elec- tric) Electric Letter-Box. (See Letter-Sox* Electric) Electric Light (See Light, Electric) Electric Lighting, Central Station (See Station, Central) Electric Lighting, Isolated (See Lighting, Electric, Isolated) Electric Light or Power Cable. (See Cable, Electric Light or Power) Electric Lock. (See Lock, Electric) Electric Locomotive. (See Locomotive* Electric) Electric Log. (See Log, Electric) Electric Loom. (See Loom, Electric) Electric Loop. (See Loop, Electric) Electric Machine, Frictional (See Machine, Frictional Electric) Die.] ]89 [Ele. Electric Main. (See Main, Electric) Electric Masses. (See Masses, Electric) Electric Measurements. (See Measure- ments, Electric.) Electric Megaloscope. (See Megalo- scope, Electric) Electric Meter. (See Meter, Electric) Electric Mine-Exploder. (See Mine-Ex- ploder, Electro-Magnetic. Fuse, Electric) Electric Motor. (See Motor, Electric) Electric Motor, High-Speed (See Motor, Electric, High-Speed) Electric Motor, Low-Speed (See Motor, Electric, Low-Speed) Electric Multipolar Bath - (See Bath, Multipolar, Electric) Electric Musket (See Musket, Electric) Electric Organ. (See Organ, Electric) Electric Oscillations. (See Oscillations, Electric) Electric Osmose. (See Osmose, Electric) Electric Osteotome, (See Osteotome, Electric) Electric Overtones. (See Overtones, Electric) Electric Pen. (See Pen, Electric) Electric Pendant (See Pendant, Elec- tric) Electric Pendant-Lamps. (See Lamps, Electric Pendant) Electric Pendulum. (See Pendulum, Electric) Electric Permeancy. (See Permeancy, Electric) Electric Phosphorescence. (See Phos- phorescence, Electric) Electric Photometer. (See Photometer) Electric Piano. (See Piano, Electric) Electric Plow. (See Plow, Electric) Electric Position-Finder. (See Finder, Position, Electric) Electric Potential. (See Potential, Elec- tric) Electric Power. (See Power, Electric.) Electric Probe. (See Probe, Electric) Electric Prostration. (See Prostration, Electric) Electric Protection. (See Protection, Electric, of Houses, Ships and Buildings) Electric Protection of Metals. (See Metals, Electrical Protection of) Electric Pulse. (See Pulse, Electrical) Electric Pyrometer, Siemens'. (See Pyrometer, Siemens', Electric) Electric Radiometer, Crookes' (See Radiometer, Electric, Crookes ' ) Electric Range-Finder. (See Finder, Range, Electric) Electric Ratchet-Pendant for Argand Burner. (See Burner, Argand Electric, Ratchet-Pendant. ) Electric Ray. (See Ray, Electric) Electric Reaction Wheel. (See Wheel, Reaction, Electric) Electric Rectification of Alcohol. (See Alcohol, Electric Rectification of) Electric Refining of Metals. (See Metals, Electric Refining of) Electric Register, Watchman's (See Register, Watchman's Electric) Electric Registering Apparatus. (See Apparatus, Registering, Electric) Electric Relay-Bell. (See Bell. Relay, Electric) Electric Repulsion. (See Repulsion, Electric) Electric Resistance. (See Resistance, Electric) Electric Resonance. (See Resonance, Electric) Electric Retardation. (See Retardation, Electric.) Electric Rings. (See Rings, Electric) Electric Safety Lamps. (See Lamp, Electric Safety.) Electric Saw. (See Saw, Electric) Ele. 190 [Ele. Electric Seismograph. (See Seismo- graph, Electric.) Electric Shadow. (See Shadow, Elec- tric.) Electric Shock. (See Shock, Electric.) Electric Shower Bath. (See Bath, Shower Electric.) Electric Shunt Bell. (See Bell, Shunt, Electric.) Electric Single-Stroke Bell. (See Bell, Single-Stroke Electric?) Electric Siphon. (See Siphon, Electric.) Electric Soldering. (See Soldering, Electric?) Electric Sphygmograph. (See Sphygmo- graph, Electrical?) Electric Sterilization. (See Steriliza- tion, Electric?) Electric Storm. (See Storm, Electric?) Electric Striae. (See Stria, Electric?) Electric Submarine Boat. (See Boat, Submarine, Electric) Electric Sunstroke. (See Sunstroke, Electric?) Electric Surgings. (See Surgings, Elec- tric?) Electric Swaging. (See Swaging, Elec- tric?) Electric Tanning. (See Tanning, Elec- tric.) Electric Target. (See Target, Electric?) Electric Teazer. (See Teazer, Electric Current?) Electric Telehydrobarometer. (See 7V/- ehydrobarometer, Electric?) Electric Tell-Tale Signal. (See Signal, Electric Tell-Tale?) Electric Tempering. (See Tempering, Electric.) Electric Tension. (See Tension, Elec- tric?) Electric Thermo-Call. (See Thermo- Call, Electric?) Electric Thermometer. (See Thermom- eter, Electric?) Electric Throwback-Indicator. ( See Indicator, Electrical Throwback?) Electric Time-Ball. (See Ball, Electric Time?) Electric Time-Meter. (See Meter. Elec- tric Time?) Electric Torpedo. (See Torpedo, Elec- tric?) Electric Tower. (See Tower, Electric?) Electric Tramway. (See Tramway, Elec- tric?) Electric Transmitters. (See Transmit- ter, Electric?) Electric Trumpet. (See Trumpet, Elec- tric?) Electric Turn-Table. (See Turn-Table, Electric?) Electric Typewriter. (See Typewriter, Electric.) Electric Valve. (See Valve, Electric?) Electric Valve Burner, Argand (See Valve Burner, Argand Electric.) Electric Varnish. (See Varnish, Elec- tric?) Electric Vibrating Burner. (See Burner, Vibrating, Electric?) Electric Volatilization. (See Volatiliza- tion, Electric?) Electric Water or Liquid Level Alarm. (See Alarm, Water or Liquid Level?) Electric Welding. (See Welding, Elec- tric?) Electric Whirl. (See Whirl, Electric?) Electric Whistle, Automatic Steam (See Whistle, Steam, Automatic Elec- tric?) Electric Wood Mouldings. (See Mould- ings, Electric Wood.) Electric Work. (See Work, Electric.) Electrical Controlling Clock. (See Clock, Electrical Controlling.) Electrically. In an electrical manner. Electrically Controlled Clock. (See Clock, Electrically Controlled.) Ele.J 191 [Ele. Electrically Discharge, To (See Discharge, To Electrically^) Electrically Discharging. (See Dis- charging, Electrically?) Electrically Energizing. (See Energiz- ing, Electrically) Electrically Operated Alarm. (See Alarm, Electrically Operated.) Electrically Retarding. (See Retard- ing, Electrically) Electrician. One versed in the principles and applications of electrical science. Electrician, Electro-Therapeutical A medical electrician. Electrician, Medical One skilled in the application of electricity to the human body for diagnosis or curative purposes. A medical electrician should possess a full knowledge, not only of the principles and appli- cations of electric science, but also of physics and chemistry and of the medical sciences. Electricity. The name given to the un- known thing, matter or force, or both, which is the cause of electric phenomena. Electricity, no matter how produced, is be- lieved to be one and the same thing. The \.cnnafrittifftial-e?ectridty, pyro-electricity, magneto-electricity, 'voltaic or galvanic electricity, thermo-electricity, contact-electricity, animal or vegetable-electricity, etc., etc., though convenient for distinguishing their origin, have no longer the significance formerly attributed to them as representing different kinds of the electric force. (See Electricity, Single- Fluid Hypothesis of.) Electricity, Accumulated Elec- tricity collected in or by means of accumula- tors. Electricity, Accumulating Ob- taining successively increasing electrical charges. (See Electricity, Accumulation of) Electricity, Accumulation of A general term applied indifferently to (i.) The gradual collecting of electric energy in a Leyden jar or condenser. (2.) The increase of an electric charge by the action of various devices called accumu- lators. (3.) The production of a charge by the use of machines called influence machines. (4.) The collection of electric energy in the so-called storage batteries or accumulators. Electricity, Animal - Electricity produced during life in the bodies of animals. All animals produce electricity during life. In some, such as the electric eel or torpedo, the amount is comparatively large. In others, it is small. Some of these animals, when of full size, are able to give very severe shocks, and use this curious power as ;' means of defense against their enemies. If the spinal cord of a recently killed frog be brought into contact wiih the muscles of the thigh, a contraction will ensue. (Mattered.) The nerve and muscle of a frog, connected by a water contact with a sufficiently delicate galvanometer, show the presence of a current that may last several hours. Du Bois-Reymond showed that the ends of a section of muscular fibres are negative, and their sides positive, and has obtained a current by suitably connecting them. In the opinion of some electro-therapeutists no electric current exists in passive, normal nerve or muscular tissue. In an injured tissue a current, called a demarcation current, is produced. (Sej Current, Demarcation.) All muscular contractions, however, apparently produce electric currents. In electro-therapeutics, it is probable that greater success would accrue in practice if the human body were regarded as an electric source as well as an electro-receptive device. Electricity, Atmospheric The free electricity almost always present in the atmos- phere. The following facts have been discovered con- cerning atmospheric electricity, viz. : (i.) The free electricity of the atmosphere is generally positive, but often changes to negative on the approach of fogs and clouds. (2.) It exists in greater quantity in the higher regions of the air than near the earth's surface. (3.) It is stronger when the air is still than when the wind is blowing. (4.) It is subject to yearly and daily changes in its intensity, being stronger in winter than in summer, and at the middle of the day than either at the beginning or the close. Ele.] 192 [Ele. Electricity, Atmospheric, Origin of The exact cause of the free electricity of the atmosphere is unknown. Peltier ascribes the cause of the free electricity of the atmosphere to a negatively excited earth, which charges the atmosphere by induction. (See Induction, Electrostatic.) Free atmospheric elec- tricity has also been ascribed to the evaporation of water; to the condensation of vapor; to the friction of the wind; to the motion ol terrestrial objects through the earth's magnedc field; to in- duction from the sun and other heavenly bodies; to differences of temperature ; to combustion, and to gradual oxidation of plant and animal life. It is possible that all these causes may have some effect in producing the fiee electricity of the at- mosphere. Whatever is the cause of the free electricity of the atmosphere, there can be but little doul-t that it is to the condensation of aqueous vapor that the high difference of potential of the lightning flash is due. (See Potential, Difference of.) As the clouds move through the air they colkct the free electricity on the surlaces of the minute drops of water of which they are composed, ai.d when uiany thousands of these subsequently collect in b.rger drops the difference of potential is enor- irously increased in consequence of the equally enormous decrease in the surface of any single drop over the sum ot the surfaces of the drops that have coalesced to form it. Electricity, Atom of A quantity of electricity equal in amount to that pos- sessed by any chemical monad atom. Professor Lodge points out the fact that the charge of a monad atom of any element is the smallest charge a body can possess, and is possibly as indivisible as the atom itself. He points out the fact that chemical affinity or atomic attraction may bedue to the electrical attraction of atoms con tain- ing unlike charges; that although the difference of potential between the atoms is small, probably somewhere between i and 3 volts, the distances separating them are so very small that their mutual attractive force must be almost infinitely great. As D'Auria has pointed out, if the centres of at- traction of the at~>ms be the ce> tres of the atoms themselves, then the atoms, if approached to actual contact, would be separated from one another by a distance equal to half the sum of ' then- diameters. If, however, the centre of at- traction be situated at any point on the surface of the atoms the distance of separation would be- come equal to zero, calling d, the distance be- tween them, m and m 1 , their respective masses, and S, a co-effecient varying with the substance, and f, the force of mutual attraction, then : from which we see that the value of f^ becomes infinite when the atoms are in contact. Electricity, Cal - Electricity pro- duced by changes of temperature in the core of a transformer. The changes of temperature in the transformer core can produce a difference of potential in the secondary circuit which increases the electro- motive force induced in the secondary by the variations in the primary. This is sometimes called the Acheson effect. (See Effect, Acheson.) Electricity, Conservation of A term proposed by Lippman to express the fact that when a body receives an electric charge in the open air, the earth and heavenly bodies receive an equal and opposite charge, thus preserving the sum of the total positive and negative electricities in the universe. Electricity, Contact - Electricity produced by the mere contact of dissimilar metals. Th^ mere contact of two dissimilar metals re- sults i i the production of opposite electrical charges on their opposed surfaces, or in a differ- ence of electric potential between these surfaces. The cause of this difference of potential is now very generally ascribed to the voltaic couple being surrounded by the atmosphere, the oxygen of which acts more energetically on the positive element than it does on the negative element. The mere contact of dissimilar metals cannot produce a constant electric current. An electric current possesses kinetic energy. To produce a constant electric current, therefore, energy must be expended. The voltaic pile through the contact of dis- similar metals produces a difference of potential, yet the cause of the current is to be found in chemical action. (See Cell, Voltaic.') Electricity, Disguised - - Dissimu- lated electricity. (See Electricity, Dissimu- lated or Latent) Ele.J 193 [Ele. Electricity, Dissimulated or Latent The condition of an electric charge when placed near an opposite charge, as inaLeyden jar or condenser. In this case, merely touching one of the charged surfaces will not effect its complete dis- charge. Electricity in the condition of a bound charge was formerly called latent electricity. This term is now in disuse. Such a charge is now called a bound charge. (See Charge, Bound. Charge, Free.) Electricity, Distribution of Va- rious combinations of electric sources, circuits and electro-receptive devices whereby elec- tricity generated by the sources is carried or distributed to more or less distant electro- receptive devices by means of the various cir- cuits connected therewith. A number of different sys'ems for the distribu- tion of electricity exist. Among the most import- ant are the following, viz.: (i.) Direct or continuous-current distribution. (2.) Alternating-current distribution. (3.) Storage battery or secondary distribution. (4.) Distribution by means of condensers. (5.) Distribution by means of motor-gener- ators. Electricity, Distribution of, by Alterna- ting- Currents A system of electric distribution by the use of alternating currents. A system of electric distribution in which lamps, motors, or other electro-receptive de- vices are operated by means of alternating currents that are sent over the line, but which, before passing through said devices, are modi- fkd by apparatus called transformers or con- verters. Such a system embraces : (I.) An alternating-current dynamo- electric machine or battery of machines. (2.) A conductor or line wire arranged in a metallic circuit. (3.) A number of converters or transformers whose primary coils are placed in the circuit of the line wire. (4.) A number of electro-receptive devices placed in the circuit of the secondary coil of the converter. (See Transformer.) Electricity, Distribution of, by Alterna- ting Currents by Means of Condensers A system of alternate current distribution in which condensers are employed to trans- form current of high potential, received from an alternating current dynamo, to currents of low potential which are fed to the lamps or other electro-receptive devices. In the system of McElroy the conversion from high to low potential is obtained 1 y making the primary plates of the condensers charged by the dynamo smaller than the secondary plates, the ratio of the area of the primary plates to that of the secondary plates being made in accordance with the ratio of conversion desired. Electricity, Distribution of, by Commuta- ting Transformers A system of elec- trical distribution in which motor-generators are used, but neither the armature nor the field magnets are revolved, a special commu- tator being employed to change the polarity of the magnetic circuits. Electricity, Distribution of, by Constant Currents A system for the distribution of electricity by means of direct, /. e., con- tinuous, steady or non-alternating currents, as distinguished from alternating currents. Distribution by means of direct currents may be effected in a number of ways ; the most im- portant are: (l.) Distribution with constant current or series - distribution . (2.) Distribution with constant potential or multiple-distribution. Strictly speaking, these, as, indeed, all systems, are systems for the distribution of electric energy rather than the distribution of electricity. In a system of series-distribution, the electro- receptive'devices are placed in the main line in series, so that the electric current passes succes- sively through each of them. In such a sj stem each device added increases the total resistance of the circuit so that the total resistance is equal to the sum of the separate resistances on the line. In order, therefore, to maintain the current strength constant, independent of the number of devices added to or removed from the circuit, the electromotive force of the source must increase with each electro-receptive device added, and de- crease with each electro-receptive derice taken Ele.] 194 [Ele. out- If the number of electro-receptive devices be great, such a circuit is necessarily character- ized by a comparatively high electromotive force. Since the current passes successively through all the electro-receptive devices, an automatic safety device is necessary in order to automatically provide a short circuit of comparatively low resist- ance past a faulty device, and thus prevent a single faulty device from invalidating the action of all other devices in the circuit Arc lamps are usually connected to the line circuit in series. In a system of 'multiple -distribution, the electro- receptive devices are connected to the main line or leads in multiple-arc, or parallel, so that each device added decreases the resistance of the circuit. In order, therefore, to maintain a proper current through the electro-receptive devices, the mains must be kept at a nearly constant difference of potential. The electro-receptive devices employed in such a system of distribution are generally of high electric resistance, so that the introduction or removal of a few of the electro-receptive devices will not materially alter the resistance of the whole circuit, and will not, therefore, materially affect the remaining lights. In this system automatic safety devices, opera- ting by the fusion of a readily melted alloy or metal, are provided for the purpose of preventing too powerful currents from passing through any branch connected with the main conductors or leads. (See /%<, Fusible.) Incandescent lamps are generally connected with the main conductors or leads in parallel or multiple-arc, Distribution of incandescent lamps by series connections is sometimes employed. Such lamps arc usually of comparatively low resistance, and are provided each with an automatic cut-out, which establishes a short circuit past the lamp on its failure to properly operate. During the passage of an electric current through any series-distribution circuit, energy is expended in different portions of the circuit, in proportion to the resistance of these parts. In any system, economy of distribution necessitates that the energy expended in the electro-receptive devices must bear as large a proportion as prac- ticable to the energy expended in the source and leads. In series-distribution, this can readily be accomplished even if the resistance of the leads is comparatively high, since the total resistance of the circuit increases with every electro-receptive device added. Comparatively thin wires can therefore be employed for a very considerable extent of territory covered, without very great loss. In systems of multiple-distribution, however, this is impossible ; for, si.ice every electro-recep- tive device added decreases the total res.stance of the circuit, unless the resistance of the leads is correspondingly decreased the economy becomes smaller, unless the resistance of the leads was orig- inally so low as to be inappreciable when com- pared with the change of resistance. In systems of distribution by alternating cur- rents this is avoided by passing a current of but small strength and considerable difference of potential over a line connecting distant points, and converting this current into a current oflargc strength and small difference of potential at the places where it is required for use. Electricity, Distribution of, by Contin- uous Current, by Means of Condensers A system of distribution devised by Doubrava, in which a continuous current is conducted to certain points in the line where a device called a " disjunctor " is employed, to reverse it periodically, and the reversed cur- rents so obtained directly used to charge con- densers in the circuit of which induction coils are used. This method of distribution is a variety of dis- tribution by means of constant currents. The condensers are used to feed incandescent lamps or other electro-receptive devices. Electricity, Distribution of, by Continu- ous Current, by Means of Transformers A system for the transmission of elec- tric energy by means of continuous or direct currents that are sent over the line to suitably located stations where motor-dynamos are used for transformers. The dynamo armature is used with two sepa- rate circuits, one of a short and coarse wire, and one of a long fine wire. This construction will permit the conversion of a high to a low potential or vice versa; or two separate dynamos can be placed on the same shaft and one used as the motor. It is evident that a motor generator can be con- structed to convert continuous currents into alter- nate, or alternate currents into continuous cur- Die.] 195 [Ele. rents. In this last case the armature and fixed circuits must be kept separate. Another form of continuous current conversion is effected by means of the motion of a commutator which effects a rotation of magnetic polarity in a double- wound armature of fine and coarse wire. Electricity, Distribution of, by Motor Generators A system of electric dis- tribution in which a continuous current of high potential, distributed over a main line, is employed at the points where its electric en- erg)' is to be utilized for driving a motor, which in turn drives a dynamo, the current of which is used to energize the electro-recep- tive devices. This method of distribution is a variety of dis- tribution by means of continuous or direct cur- rents. In another system of distribution by means of motor generators, the motor and dynamo are combined in one with a double-wound anrature, the fine wire coils in which receive the high po- tential driving current and the coarse wire coils iurnish the low potential current used in the dis- tribution circuits. Electricity, Double Fluid Hypothesis of A hypothesis which endeavors to ex- plain the causes of electric phenomena by the assumption of the existence of two different electric fluids. The double fluid hypothesis assumes: (i.) That t',e phen> mena of electricity are due to two tenuous and imponderable fluids, the posi- tive and the negative. (2.) That the particles of the positive fluid repel one another, as do also the particles of the nega- tive fluid; but that the particles of positive fl .id attract the particles of the negative and vice versa. (3.) That the two fluids are stronely Attracted by matter, and when present in it produce elec- trification. (4.) That the two fluids attract one another and unite, thus masking the properties of < ach. (5.) That the act of friction separates these fluids, one going to the rubber and the other to the thing rubbed. Professor Lodge is disposed to favor the double rather than the single fluid hypothesis. He states an support of this belief the following facts, viz. : (I.) An electric wind or breeze is produced Ixjthat the positive and negative terminals of an electrical machine, and this whether the point be attached directly to these terminals, or whether it be he.ld in the hand of a person near them. (2.) The well known peculiarities connected with the spark discharge, seen in Wheatstone's experiments on the velocity of electricity. (3.) An electrostatic strain scarcely affects the volume of the dielectric, thus suggesting or show- ing a distorting stress, which alters the shape of the substance of the dielectric, but not its size. (4.) The effects of electrolysis in what he as- sumes the double procession of the atoms past each other in opposite directions. (5.) The phenomena of self-induction, or the behavior of a thick wire on an alternating current. (6.) The apparent absence of momentum in the electric current, or moment of inertia in an elec- tro-magnet so far as tested. Electricity, Dynamic A term some- times employed for current electricity in con- tradistinction to static electricity. Electricity, Franklinic A term sometimes employed in electro-therapeutics, for the electricity produced by a frictional or an electrostatic-induction machine. (See Current, Franklinic^) Electricity, Frictional Electricity produced by friction. This term as formerly employed to indicate static charges as distinguished from currents, is gradually falling into disuse, and the frictional electric machines are being generally replaced by continuous-induction machines, like those of Holtz, TOpler-Holtz, or Wimshurst. The character of the charge produced by fric- tion depends on the nature of the rubber as well as on that of the thing rubbed. In the following table the substances are so ar- ranged that any one in the li t becomes positively electrified when rubbed by any which follows it : Positive. Cat's fur. Polished glass. Wool. Cork at ordinary temperatures. Coarse brown paper. Cork heated. White silk. Black silk. Shellac. Rough glass. (Forbes.) Ele.] 196 [Ele, Negative. It will be seen that the character of the charge produced by friction depends on the character of the surfaces rubbed. This is seen from the fore- going table, where (i.) The roughness of the surface, as in the case of glass, produces a difference in the nature of the charge; thus, rough glass is at the bottom of the table, and smooth, polished glass near the top. (2.) The state of the surface as shown by the color. Black silk rubbed with white silk is nega- tive to it. (3.) The state of the surface, as varied by the temperature. Hot cork receives a negative charge when rubbed against a piece of cold cork. Forbes has pointed out that these differences are probably due to the change produced in the ability of the surface to radiate heat or light. A substance or body which radiates the most light or heat is negative. Thus, a hot body radiates more heat than a cold body, and is negative to it. A rough surface is negative to a smooth surface because it radiates more heat than a smooth sur- face. For the same reason a black surface is neg- ative to a white surface. In this latter case, how- ever, the black surface is t'.e worse radiator of light. The contact of dissimilar substances has long been considered by some as one of the requisites for the ready production of electricity by friction. In fact, the production of electricity by friction has been ascribed as an effect due to a true contact force at the points of junction of the rubber and the thing rubbed. Others, however, deny the existence of a true contact force of this nature. (See Force, Contact.) Electricity, Galvanic A term used by some in place of voltaic electricity. (See Electricity, Voltaic^ The use of the term galvanic electricity would appear to be less logical than the word voltaic, since Volta, and not Galvani, was the first to find out the true origin of the difference of potential produced in the voltaic pile. Electricity, Hertz's Theory of Electro- Magnetic Radiations or Waves A theory, now generally accepted, which regards light as one of the effects of electro-magnetic pulsations or waves. The recent brilliant researches of Dr. Hertz, of Carlsruhe, show that when an impulsive discharge is passing through a conductor, ether waves are- radiated or propagated in all directions in the space surrounding the conductor, and that these waves are in all respects similar to those of light, except that they are much longer. The electro-magnetic waves are set up in the- luminiferous ether, and move through it with the same velocity as that of light. Moreover, electro- magnetic waves possess the same powers of reflec- tion, refraction, interference, resonance, etc., etc., as are possessed by waves of light. (See Resona- tor, Electric.} When an alternating or simple faradic current or pulse of electricity is transmitted from one end to the other of a long metallic conductor, the pulses are believed to travel through the universal ether surrounding the conductor rather than through the conductor itself. The velocity of this propagation in free ether is the same as that of light, and, indeed, is identical with that of light itself. In the inter-atomic or inter -molecular ether, whether of conductors, or of dielectrics, the velocity of propagation varies with the nature of the medium. The waves produce 1 by electric pulses are of much greater length than those of light. According to Lodge a condenser of the capacity of a micro-farad, if discharged through a coil hav- ing the self-induction of I ohm, will give rise- to waves in the ether 1, 200 miles in length, and will possess a rate of oscillation equal to about 157 complete wave-lengths per second. A common pint Leyden jar discharged through an ordinary discharging rod, will produce a se- ries of waves about 15 to 20 metres in length, and will possess a rate of oscillation equal to about ten million per second. Lodge calculates that in order to obtain the short waves requisite to influence the retina of the eye, and thus produce light, the circuit in which the electrical oscillations take place must have at least atomic dimensions, and that the phenomena of light may therefore be due to local oscillations or surgings in circuits of atomic dimensions. (See Light, Maxwetfs Electro-Magnetic Theory of.} Electricity, Latent A term for- merly applied to bound electricity. Electricity, Magneto Electricity produced by the motion of magnets past con- ductors, or of conductors past magnets. Electricity produced by magneto-electric: Ele.] 197 [Ele. induction. (See Induction, Electro-Dyna- mic.} Electricity, Multiple-Distribution of, by Constant Potential Circuit Any system for the distribution of continuous cur- rents of electricity in which the electro- receptive devices are connected to the leads in multiple-arc or parallel. (See Electricity, Distribution of, by Constant Currents?) Electricity, Natural Unit of A term sometimes used in place of an atom of electricity. The natural unit of electricity is an amount equal to the charge possessed by any monad atom of . chemical element. The natural unit of electricity is equal to the hundred thousand millionth of the ordinary electrostatic unit, or less than a hundred tril- lionth of a coulomb. (See Electricity, A ton of.) Electricity, Negative One of the phases of electrical excitement. The kind of electric charge produced on resin when rubbed with cotton. Electricity, Photo Electrical dif- ferences of potential produced by the action of light. Electricity, Plant Electricity pro- duced in plants during their growth. Electricity, Positive One of the phases of electric excitement. The kind of electric charge produced on cotton when rubbed against resin. Electricity, Production of, by Light The production of electric differences of potential by the action of light. Hallwachs 'has noticed that a clean, metallic plate becomes electrified when light falls upon it. Differences of potential are produced in a selenium cell when its electrodes are unequally illumined. A thermo cell is an illustration of a difference of potential produced by non-luminous radiation. Electricity, Pyro Electricity de- veloped in certain crystalline bodies by un- equally heating or cooling them. Tourmaline, in the crystalline state, possesses this property in a marked degree. When a crystal of tourmaline is heated or cooled, it acquires opposite electrifications at opposite ends or poles. In the crystal of tourmaline shown in Fig. 227, the end A, called the analogous pole, acquires a. positive electrification, and the end B, called the antilogous pole, a nega- tive electrification, -while the temperature of the crystal is rising. While cooling, the opposite electrifications are pro- duced. A heated crystal of tourmaline, suspended by a fibre, is attracted or repelled by an electrified body or by a second heated tourmaline, in the & 2*7- Pyro-Ehctric same manner as an elec- Crystal. trified body. Many crystalline bodies possess similar prop- erties. Among these are the ore of zinc known as electric calamine or the silicate of zinc, bora- cite, quartz, tartrate of potash, sulphate of quinine, etc. Electricity, Radiation of - The radiation of electric energy by means of elec- tro-magnetic waves. (See Electricity, Hertz's Theory of Electro-Magnetic Radiations or Waves.) Electricity, Resinous A term formerly employed in place of negative elec- tricity. It was at one time believed that all resinous substances are negatively electrified by friction. This we now know to be untrue, the nature of electrification depending as much on the char- acter of the rubber as on the character of the thing rubbed. Thus resins rubbed with cotton, flannel or silk, become negatively excited, but when rubbed with sulphur or gun cotton, positively excited. The terms positive and negative are now exclusively employed. Electricity, Series Distribution of, by Constant Current Circuit Any sys- tem for the distribution of constant currents of electricity in which the electro-receptive devices are connected to the line-wire or circuit in series. (See Electricity, Distribu- tion of, by Constant Currents.) Ele.] 198 [Ele. Electricity, Single-Fluid Hypothesis of A hypothesis which endeavors to ex- plain the cause of electrical phenomena by the assumption of the existence of a single electric fluid. The single-fluid hypothesis assumes: (r.) That the phenomena of electricity are due to the presence of a single, tenuous, imponder- able fluid. (2 ) That the particles of this fluid mutually repel one another, but are attractjd by all matter. (3.) That every substance possesses a definite capacity for holding the assumed electric fluid, and, that when this capacity is just satisfied no effects of electrification are manifest. (4.) That when the body has less than this quantity present, it becomes negatively excited, and when it has more, positively excited. (5.) That the act of friction causes a redistribu- tion of the fluid, part of it going to one of the bodies, giving it a surplus, thus positively electrifying it, and leaving the other with a deficit, thus negatively electrifying it. The single-fluid hypothesis has been provis- ionally accepted by some with this modification, that a negatively excitad body is thought to be the one wtich contains the excess of the assumed fluid, and a positively excited body the one which contains the deficit. They make this change on account of the phenomena observed in Crookes' tube, where the molecules of the residual gas are observed to be thrown off from the negative and not from the positive terminal. (See Tube, Crookes'.) Another view considers electricity to be due to differences of ether pressure, electricity being the ether itself, and electromotive force, the differences of ether pressures. Positive electrification is as- sumed to result from a surplusage of energy, and negative electrification from a deficit of energy. At the present time the views of Hertz are generally accepted. (See Electricity, Hertz's Theory of Electro-Magnetic Radiations or Waves.) Electricity, Specific Heat of A term proposed by Sir William Thomson to indicate the analogies existing between the absorption and emission of heat in purely thermal phenomena, and the absorption and emission of heat in thermo-electric phe- nomena. (See Heat, Specific!) As we have already seen heat is either given out or absorbed, when an electric current passes from one metal to another across a junction be- tween them. (See Effect, Peltier.) So, too, when electricity passes through an un- equally heated wire, the current tends to increase or decrease the differences of temperature, ac- cording to the direction in which it flows, and according to the character of the metal. (See Effect, Thomson.') " If electricity were a fluid," says Maxwell, "running through the conductor as water does through a tube, and always giving out or ab- sorbing heat till its temperature is that of the conductor, then in passing from hot to cold it would give out heat, and in passing from cold to hot it would absorb heat, and the amount of this heat would depend on the specific heat of the fluid." Electricity, Static A term applied to electricity produced by friction. The term static electricity is properly em- ployed in the sense of a static charge but not as static electricity, since that would indicate a par- ticular kind of electricity, and, as is now gen- erally recognized, electricity, from no matter what source it is derived, is one and the same thing. Electricity, Storage of A term improperly employed to indicate such a storage of energy as will enable it to directly reproduce electric energy. A so-called storage battery does not store elec- tricity, any more than the spring of a clock can be said lo store time or sound. The spring stores muscular energy, i. e., renders the muscular kinetic energy potential, which, again becoming kinetic, causes the works of the clock to move or strike. In the same way in a so-called storage battery, the energy of an electric current is caused to produce electrolytic decompositions of such a nature as independently to produce a current on the removal of the electrolyzing current. (See Cell, Secondary. Cell, Storage.) Electricity, Thermo Electricity produced by differences of temperature at the junctions of dissimilar metals. If a bar of antimony is soldered to a bar of bis- muth, and the free ends of the two metals are connected by means of a galvanometer, an appli- cation of heat to the junction, so as to raise its Die.] 199 [Ele. temperature above the rest of the circuit, will pro- duce a difference of potential, which, if neutral- ized, will cause a current to flow across \hejttnc- tiort from the bismuth to the antimony (against the alphabet, or from B to A). If the junction be cooled below the rest of the circuit, a current is produced across the junction from the antimony to the bismuth (with the alphabet, or from A to B). These currents are called thermo-electric currents, and are proportional to the differences of tem- perature. Even the same metal, in different physical states or conditions, such as a wire, part of which is straight and the remainder bent into a spiral as at H C, Fig. 228, if heated at F by the flame of Fig 228. Th'-r mo- Electricity. a lamp will have a difference of potential devel- oped in it. The same thing may also be shown by placing a cylinder of bismuth J, Fig. 229, in a gap in a Fig. 229. Thermo-Electric Ci hollow rectangle of copper A B, inside of which a magnetic needle, M, is supported. The rectangle of copper being placed in the magnetic meridian, on heating the junction by the flame of a lamp F, the needle will be deflected by a current produced by the difference of tem- perature. Thermo-electricity is generally obtained by means of the combination of a thermo-electric couple, in a thermo-electric cell. (See Couple, Thermo-Electric. Cell, Thermo-Electric.} Since the difference of potential produced by a single thermo-electric couple is small, a number of such couples or cells are generally connected in series to produce a thermo-electric battery. (See Battery, Thermo-Electric.) Electricity, Unit Quantity of The quantity of electricity conveyed by unit current per second. The practical unit quantity of electricity is the coulomb, which is the quantity conveyed by a current of one ampere in one second. Electricity, Unit Quantity of, Natural The quantity of electricity pos- sessed as a charge by any elementary monad atom. (See Electricity, Atom of.) Electricity, Tarieties of A classi- fication of electricity according to its state of rest or motion, or to the peculiarities of its motion. Lodge classifies the different varieties of elec- tricity as follows, viz. : (i.) Electricity at Rest, or Static Electricity. This branch of electric science treats of phenom- ena belonging to stresses and strains in insulated media, when brought into the neighborhood of electric charges, together with the modes of ex- citing such electric charges, and the laws of their interactions. (2.) Electricity in Locomotion, or Current Elec- tricity. This branch of electric science treats of the phe- nomena produced in metallic conductors, chem- ical compounds and dielectric media, by the pas- sage of electricity through them, and the modes of exciting electricity into motion, together with the laws of its flow. (3.) Electricity in Rotation, or Magnetism. This branch of electric science treats of the phe- nomena produced in electricity in whirling or vortex motion, the manner in which such whirls may be produced, the strains and stresses which they produce, and the laws of their interactions. (4.) Electricity in Vibration, or Radiation. This branch of electric science treats of the study of the propagation of periodic or undulatory dis- turbances through various kinds of media, the laws regulating wave velocity, wave length, re- flection,' interference, dispersion, polarization and other similar phenomena generally studied under light. A misleading classification of electricity is sometimes made according to the sources which produce it. This is misleading, since electricity, no matter how produced, is one and the same. Ele.] 200 [Ele. The so-called varieties of electricity may be di- vided into different classes according to the nature of the source. The principles of these are as fol- lows : (I.) Frictional-Electricity, or that produced by the friction of one substance against another. (2.) Voltaic-Electricity, or that produced by the contact of dissimilar substances under the in- fluence of chemical action. (3.) Thermo-Electricity, or that produced by differences of temperature in a thermo couple. (4.) Pyro-Electricity, or that produced by dif- ferences of temperature in certain crystalline solids. (5.) Magneto-Electricity, or that produced by the motion of a conductor through the field of permanent magnets. This is a variety of (6.) Dynamo-Electricity, or that produced by moving conductors so as to cut lines of magnetic force. (7.) Vital-Electricity, or that produced under the influence of life or accompanying life. Electricity, Yitreous A term for- merly employed to indicate positive elec- tricity. It was formerly believed that the friction of glass with other bodies always produces the same kind of electricity. This, however, is now known not to be the case. . The term is now replaced by positive elec- tricity. (See Electricity, Resinous.') Electricity, Yoltaic Differences of potential produced by the agency of a vol- taic cell or battery. Electricity is the same thing or phase of energy by whatever source it is produced. Electrics. Substances capable of becom- ing electrified by friction. Substances like the metals, which, when held in the hand cou'.d not be electrified by friction were formerly called non-electrics. These terms were used by Gilbert in the early history of the science. This distinction is not now generally employed since conducting substances if insulated,, may be electrified by friction. Electriflable. Capable of being endowed with electric properties. Electrification. The act of becoming electrified. The production of an electric charge. Electrified Body. (See Body, Electri- fied^ Electrify. To endow with electrical prop- erties. Electrine. Relating to electrum, or am- ber. Electrization, Therapeutical Sub- jecting different parts of the human body to the action of electric currents for the cure of diseased conditions. Electro-Biology. (See Biology, Electro} Electro-Brassing. (See Brassing, Elec- tro} Electro-Bronzing. (See Bronzing, Elec- tro.} Electro - Capillary Phenomena. (See Phenomena, Electro-Capillary} Electrocesis. A word proposed for cur- ing by electricity. Electro-Chemical Equivalent. (See Equivalent, Electro-Chemical} Electro-Chemical Meter. (See Meter, Electro-Chemical} Electro-Chemical Telephone. (See Tele- phone, Electro-Chemical} Electro-Chemistry. (See Chemistry, Electro} Electro-Chromic Rings. (See Rings, Electro-Chromic} Electro-Contact Mine. (See Mine, Elec- tro-Contact} Electro-Coppering. (See Coppering, Electro} Electro-Crystallizal ion. (See Crystalli- zation, Electro} Electrocution. Capital punishment by means of electricity. Electrode. Either of the terminals of art electric source. The term was applied by Faraday to either of the conductors placed in an electrolytic bath and conveying the current into it, and this is its strict meaning. The terms pole or terminal apply to the ends of a break in any electric circuit. Electrode, Aural A therapeutic electrode, shaped for the treatment of the Ele.] [Ele. ear. (See Electrode, Electro-Thera- peutic?) Electrode, Brush A therapeutic electrode fashioned like a wire brush or other conducting brush. (See Electrode, Electro- Therapeutic.} Electrode, Cautery-Knife A knife- shaped electrode, that is rendered incan- descent by the passage of the electric cur- rent. Electrode, Clay A therapeutic elec- trode of clay shaped to fit the part of the body to be treated. (See Electrode, Electro- Therapeutic.} Electrode, Disc A disc-shaped elec- trode employed in electro-therapeutics. (See Electrode, Electro- Therapeutic?) Electrode, Dry A therapeutic elec- trode applied in a dry state. (See Electrode, Electro- Therapeutic?) Electrode, Electro-Therapeutic In electro-therapeutics the electrode mainly concerned in the treatment or diagnosis of the diseased parts. Either the positive or the negative electrode may be the therapeutic electrode, and one or the other is employed according to the particular character of the effect it is desired to obtain. The other electrode is placed at any convenient and suitable part of the body, and is called the indifferent electrode. The therapeutic electrode is generally placed nearer the organ or part to be treated than the indifferent electrode. Electrode-Handle, Pole-Changing and Interrupting' A handle provided for the ready insertion of electro-therapeutic electrodes, and provided with means for inter- rupting or changing the direction of the cur- rent. Electrode, Illumined That elec- trode of a selenium cell which is exposed to the light. (See Cell, Selenium?) Electrode, Indifferent In electro- therapeutics the electrode that is employed merely to complete the circuit through the organ or part subjected to the electric cur- rent, and is not directly concerned in the treatment or diagnosis of the diseased parts. Either the positive or the negative electrode may be the indifferent electrode. (See Electrode, Electro. Therapeutic.} Electrode, Moist A therapeutic- electrode applied in a moist condition. (See Electrode, Electro- Therapeutic?) Electrode, Needle A therapeutic electrode in the shape of a needle, and em- ployed for electrolytic treatment. (See Elec- trode, Electro- Therapeutic?) Electrode, Negative The electrode connected with the negative pole of an elec- tric source. Electrode, Non-Illumined That electrode of a selenium cell that is protected from the direct action of light. (See Cell, Sel- enium.} Electrode, Non-Wasting A term sometimes applied to the negative electrode of an arc-lamp when made of iridium or other similar material. Electrode, Positive The electrode connected with the positive pole of an electric source. Electrode, Rectal A therapeutic electrode, suitably shaped for the treatment of the rectum. (See Electrode, Electro- Thera- peutic.} Electrode, Sponge - A moistened sponge connected to one of the terminals of an electric source and acting as the electro- therapeutic electrode. Electrode, Urethral An electro- therapeutic electrode suitably shaped for the treatment of the urethra. (See Electrode, Electro- Therapeutic.} Electrode, Vaginal An electro- therapeutic electrode suitably shaped for the treatment of the vagina. (See Electrode, Electro- Therapeutic?) Electro-Deposits. (See Deposits, Elec- tro.} Electrodes. The terminals of an electric source. The positive electrode is sometimes called the Ele.] 202 [Ele. Anode, and the negative electrode the Kathode. No matter for what purposes employed, they are generally in electro-therapeutics termed electrodes. In precise use these terms should be restricted to the electrodes when used for electrolytic de- composition. The electrodes are made of different shapes and of different materials according to the character of the work the current is to perform. Electrodes, Carbon, for Arc-Lamps Rods of artificial carbon employed in arc lamps. These are more properly called simply arc- lamp carbons. Arc-lamp carbons are moulded into the shape of rods, from plastic mixtures of carbonaceous materials and carbonizable liquids. On the sub- sequent carbonization of these rods the ingredients are caused to cohere in one solid mass by the de- posit of carbon derived from the carbonizable materials. (See Carbons* Artificial.'] Carbons for arc-lamps are generally copper- coated, so as to somewhat decrease their resist- ance, and insure a more uniform consumption. Arc-lamp carbons are sometimes provided with a central core of softer carbon, which fixes the po- sition of the arc and thus insures a steadier light. (See Carbons, Cored.} Electrodes, Cored Carbon elec- trodes of a cylindrical shape provided with a central cylinder of softer carbon. The use of cored electrodes for arc lamps is for the purpose of steadying the light by maintain- ing the arc in a central position. This is effected by the greater vaporization of the softer carbon of the core. Electrodes, Cylindrical Carbon Carbon cylinders used for electrodes of arc- lamps, or for battery plates. Electrodes, Electro-Therapeutic ' Electrodes of various shapes employed in electro-therapeutics. The electro-therapeutic electrode, as distin- guished from the indifferent electrode, is especially shaped for the particular purpose for which it is designed. When the electricity is intended to affect the skin or superficial portions of the body only, it is applied dry, and is then generally metallic. To reach the deeper structures, such as the muscle or nerve trunks, moistened sponge electrodes are employed. Before their use the skin should be thoroughly moistened. Sponge-electrodes are generally made conducting by a solution of some saline substance, such as common salt. Electrodes, Erb's Standard Size of Standard sizes of electrodes generally adopted in electro-therapeutics. The following standard sizes have been pro- posed by Erb, viz. : (I.) Fine electrode ^ centimetre diameter^ (2.) Small " 2 " " (3.) Medium " 7.5 " " (4.) Large " ... .6x2 " < (5.) Very large do 8 x 16 " " Electrodes, Non-Polarizable Electrodes employed in electro-therapeutics, that are so constructed as to avoid the effects of polarization. Non-polarizable electrodes are obtained by employing two amalgamated zinc wires, dipped into saturated solution of zinc chloride placed in glass tubes, and closing the lower ends of the tubes by a piece of potter's clay. The contact of an electrode so prepared with the tissues of the body does not produce a polarization. Electro-Diagnosis. (See Diagnosis, Elec- /.) Electro-Diagnostic. (See Diagnostic^ Electro^ Electro-Dynamic Attraction. (See At- traction, Electro-Dynamic^) Electro-Dynamic Capacity. (See Ca- pacity, Electro-Dynamic^) Electro-Dynamic Induction. (See Induc- tion, Electro-Dynamic^) Electro-Dynamic Repulsion. (See Re- pulsion, Electro-Dynamic?) Electro-Dynamics. (See Dynamics, Electro.} Electro-Dynamometer. (See Dynamom- eter, Electro.} Electro-Etching. Electric etching. (See Etching, Electro?) Electrogenesis. Results following the application of electricity to the spinal cord or nerve after the withdrawal of the electrodes. Electro-Gilding. (See Gilding, Electro^ Ele.] 203 [Ele. Electro-Kinetics. (See Kinetics, Elec- tro) Electrolier. A chandelier for holding electric lamps, as distinguished from a chan- delier for holding gas-lights. Electrology. That branch of science which treats of electricity. (Obsolete.) Electrolysis. Chemical decomposition effected by means of an electric current. When an electric current is sent through an electrolyte, i. e. , a liquid which permits the cur- rent to pass only by means of the decomposition of the liquid, the decomposition that ensues is called electrolytic decomposition. The electrolyte is decomposed or broken up into atoms or groups of atoms or radicals, called ions. The ions are of two distinct kinds, viz. : The electro-positive ions, or kathions, and the electro* negative ions, or unions. Since the anode of the source is connected with the electro-positive terminal, it is clear that the anions, or the electro-negative ions, must appear at the anode, and the kathions, or electro-positive ions, must appear at the kathode. Hydrogen, and the metals generally, are kathions. Oxygen, chlorine, iodine, etc., are unions. The vessel containing the electrolyte, in which these decompositions take place, is sometimes called an electrolytic cell. An electrolytic cell is called a voltameter when it is arranged for measuring the current passing by means of the amount of decomposition it effects. (See Voltameter.} Electrolysis by Means of Alternating- Currents. Electrolytic decomposition ef- fected by means of alternating currents. When an alternating current is passed through dilute sulphuric acid, in a voltameter provided with large platinum electrodes, no visible decom- position occurs. If, however, the size of the electrodes be decreased below a certain point, then visible decomposition occurs. Verdet showed that when no other break ex- ists in the circuit of the alternating current within the voltameter, no indications of elec- trolysis are obtained, unless the alternating current is very powerful. If, however, a break is made in the secondary circuit, so that the dis- charge has to pass as a spark, then visible signs of electrolysis are produced by comparatively feeble alternating currents. When electrolysis occurs by means of alternat- ing currents (I.) The gases collected at both electrodes have the same composition. (2.) Where the quantities of electricity that al- ternately pass in opposite directions are unequal, the electrodes show manifest polarization, and, when connected by a conductor, yield a current like a secondary battery. (3.) The electrodes manifest no sensible polari- zation where the quantities of electricity that al- ternately pass in opposite directions are equal. Electrolysis, Faraday's Laws of The principal facts of electrolysis are given in the following laws: (i.) The amount of chemical action in any given time is equal in all parts of the circuit. (2.) The number of ions liberated in a given time is proportional to the strength of the cur- rent passing. Twice as great a current will liberate twice as many ions. The current may be regarded as being carried through the elec- trolyte by the ions: since an ion is capable of carrying a fixed charge only of -f- or electri- city, any increase in the current strength necessi- tates an increase in the number of ions. (3.) When the same current passes successively through several cells containing different elec- trolytes, the weights of the ions liberated at the different electrodes will be equal to the strength of the current multiplied by the electro-chemical equivalent of the ion. (See Equivalence, Elec- tro- Chemical, Law of. ) The chemical equivalent is proportional to the- atomic weight divided by the valency. (See Equivalent, Chemical. ) The electro-chemical equivalent of any element is equal to the weight in grammes of that element set free by one coulomb of electricity, and is found by multiplying the electro-chemical of hydrogen by the chemical equivalent of that element. (See Equivalent, Electro- Chemical. ) Electrolyte, Polarization of The formation of molecular groups or chains, in which the poles of all the molecules of any chain are turned in the same direction, viz.: with their positive poles facing the negative plate, and their negative poles facing the Ele.] 204 [Ele, positive plate. (See Cell, Voltaic. Hypoth- esis, Grotthus' '.) Electrolytic or Eleetrolytical. Pertain- ing to electrolysis. Electrolytic Analysis. (See Analysis, Electrolytic) Electrolytic Cell. (See Cell, Electro- lytic, Testa's.) Electrolytic Clock. (See Clock, Electro- lytic) Electrolytic Conduction. (See Conduc- tion, Electrolytic) Electrolytic Convection. (See Convec- tion, Electrolytic) Electrolytic Decomposition. (See De- composition, Electrolytic) Electrolytic Hydrogen. (See Hydrogen, Electrolytic) Electrolytic Writing. (See Writing, Electrolytic) Electrolytically. In an electrolytic man- ner. Electrolyzable. Capable of being elec- trolyzed, or decomposed by means of elec- tricity. Electrolyzed. Separated or decomposed by means of electricity. Electrolyzing. Causing or producing electrolysis. Electro-Magnet. (See Magnet, Electro) Electro-Magnetic Ammeter. (See Am- meter, Electro-Magnetic) Electro-Magnetic Annunciator. (See Annunciator, Electro-Magnetic) Electro-Magnetic Attraction. (See At- traction, Electro-Magnetic) Electro-Magnetic Bell-Call. (See Call. Bell, Magneto-Electric) Electro-Magnetic Bell, Siemens' Arma- ture (See Bell, Electro-Magnetic, Siemens' Armature Form) Electro-Magnetic Brake. (See Brake, Electro-Magnetic) Electro-Magnetic Cam. (See Cam, Electro-Magnetic) Electro-Magnetic Dental-Mallet. (See Dental-Mallet, Electro-Magnetic) Electro-Magnetic Drill. (See Drill, Electro-Magnetic) Electro-Magnetic Engine. (See Engine, Electro-Magnetic) Electro-Magnetic Exploder. (See Ex- ploder, Electro-Magnetic) Electro-Magnetic Eye. (See Eye, Elec- tro-Magnetic) Electro-Magnetic Impulse. (See Im- pulse, Electro-Magnetic) Electro-Magnetic Induction. (See In- duction, Electro-Magnetic) Electro-Magnetic Medium. (See Me- dium, Electro-Magnetic) Electro-Magnetic Meter. (See Meter, Electro-Magnetic) Electro-Magnetic Momentum of Sec- ondary Circuit. (See Momentum, Elec- tro-Magnetic, of Secondary Circuit) Electro-Magnetic Pop-Gun. (See Pop- Gun, Electro-Magnetic) Electro-Magnetic Radiation. (See Ra- diation, Electro-Magnetic) Electro-Magnetic Repulsion. (See Re- pulsion, Electro- Magnetic) Electro-Magnetic Resonator. (See Res- onator, Electro- Magnetic) Electro-Magnetic Shunt. (See Shunt, Electro-Magnetic) Electro-Magnetic Solenoid. (See Sole- noid, Electro-Magnetic) Electro-Magnetic Strain. (See Strain, Electro-Magnetic) Electro-Magnetic Stress. (See Stress, Electro-Magnetic) Electro-Magnetic Theory of Light, Max- well's (See Light, Maxwell's Elec- tro-Magnetic Theory of) Electro-Magnetic Vibrator. (See Vi- brator, Electro-Magnetic) Electro-Magnetic Voltmeter. (See Volt- meter, Electro-Magnetic) Hie.] 205 [Ele. Electro-Magnetic Units. (See Units. Electro-Magnetic?) Electro-Magnetics. (See Magnetics, Electro?) Electro-Massage. (See Massage, Elec- tro?) Electro-Mechanical Alarm. (See Alarm, Electro-Mechanical?) Electro-Mechanical Gong. (See Gong, Electro-Mechanical?) Electro-Metallurgical Crystalline De- posit. (See Deposit, Crystalline, Electro- Metallurgical?) Electro-Metallurgical Galvanization. (See Galvanization, Electro- Metallurgical?) Electro-Metallurgical Nodular Deposit. (See Deposit, Electro - Metallurgical Nodular?) Electro - Metallurgical Reguline De- posit. (See Deposit, Electro-Metallurgical Reguline?) Electro-Metallurgical Sandy Deposit (See Deposit, Electro-Metallurgical Sandy.) Electro-Metallurgy. (See Metallurgy, Electro?) Electrometer. An apparatus for measur- ing differences of potential. Electrometers operate, in general, by means of the attraction or repulsion of charged conduc- tors on a suitably suspended needle or disc. As no current is required to flow through the appa- ratus electrometers are especially adapted to many cases where voltmeters could not be so readily used. Electrometer, Absolute An elec- trometer the dimensions of which are such that the value of the electromotive force can be directly determined from the amount of the deflection of the needle. A form of attracted-disc electrometer. (See Electrometer, Attracted-Disc?) Electrometer, Attracted-Disc A form of electrometer devised by Sir William Thomson, in which the force is measured by the attraction between the two discs. Thomson's Attracted-Disc Electrometer is shown in Fig. 230. It consists of a plate C, sus- pended from the longer er.d of a lever 1, within the fixed guard plate, or guard ring B, immediately above a second plate A, supported on an insulated stand, and capable of a measurable approach Fig. 2 jo. A.tracted'Disc Electrometer. towards C, or a movement away from it. The plate, C, is placed in contact with B, by means of a thin wire. By means of this connection the distribution of the charge over the plate, C, is uniform. The electrostatic attraction is meas- ured by the attraction of the fixed disc, A, on the movable disc, C, connected respectively to the two bodies whose difference of potential is to be measured. One of these may be the earth. The fulcrum of the lever 1, is formed of an aluminium wire, the torsion of which is used to measure the force of the attraction; or, it may be measured directly by the counterpoise weight Q. This instrument is sometimes called an absolute electrometer, because, knowing the dimensions of the apparatus, the value of the difference of poten- tial can be directly determined from the amount of the motion observed. Electrometer, Capillary An elec- trometer in which a difference of potential is Fig. 231. Capillary Electrometer measured by the movement of a drop of sulphuric acid in a tube filled with mercury. Ele.J 206 [Ele. A form of capillary electrometer is shown in Fig. 231, in which a horizontal glass tube with a drop of acid at B, has its ends connected with two vessels M and N, filled with mercury. If a current be passed through the tube, a move- ment of the drop towards the negative pole will be observed. Where the electromotive force does not exceed one volt, the amouit of the movement is proportional to the electro- motive force. Electrometer, Quadrant An elec- trometer in which an electrostatic charge is measured by the attractive and repulsive force of four plates or quadrants, on a light needle of aluminium suspended within them. The sectors or quadrants are of brass, and are so shaped as to form a hollow cylindrical box when placed together. The four sectors, or quad- rants, are insulated from one another, but the opposite ones are connected by a conducting wire, as shown in Fig. 232. A light needle of aluminium, u, maintained at some constant potential, by connection with the inner coating of a Leyden jar, is suspended, gener- ally by two par- allel silk threads, so as to freely swing inside the hollow box. This needle, when at rest, is in the position shown by the dotted lines, with its axis of symmetry exactly under one of the slots or spaces between two opposite sectors. (See Suspension^ Bi- Filar.) The quadrant electrometer, shown in Fig. 233, has one of its quadrants removed so as to show the suspended aluminium needle. A similar form of instrument is shown in Fig. 234, with all the quadrants in place, and the whole instrument covered by a glass shade. To use the quadrant electrometer the pairs of sectors are connected with the two bodies whose difference of potential is to be measured, and the deflection of the needle observed, generally through a telescope, by means of a spot of light reflected from a mirror attached to the upper part of the needle. Sometimes the segments are made in the shape of a cylinder, and the needle in the shape of a suspended rectangle. Fig. 232. Quadrant Elec- trometer. Electrometer, Registering An elec- trometer, the deviations of the needle ot which are automatically registered. Fig- 233. Quadrant Electrometer, Showing Suspended; Needle. The registration of this class of electrometer is" obtained by means of photography. The spot ot Fig. 234. Quadrant Electrometer. light, reflected from the mirror of the electrometer, falls on a fillet of sensitized paper, moved by clockwork. Ele.) [Ele. Electromotive Arrangement or Device. (See Arrangement or Device, Electromo- tive) Electromotive Difference of Potential. (See Potential, Difference of Electromotive?) Electromotive Force. (See Force, Elec- tromotive?) Electromotive Force, A verage (See Force, Electromotive, Average or Mean?) Electromotive Force, Back or Counter (See Force, Electromotive. Back?) Electromotive Force, Direct (See Force, Electromotive, Direct?) Electromotive Force, Inductive (See Force, Electromotive, Inductive?) Electromotive Force, Secondary-Im- pressed (See Force. Electromotive, Secondary-Impressed?) Electromotive Force, Simple-Periodic (See Force, 'Electromotive, Simple- Periodic?) Electromotive Force, Transverse (See Force, Electromotive. Transverse?) Electromotive Impulse. (See Impulse, Electromotive?) Electro-Motograph. (See Motograph , Electro?) Electro-Muscular. (See Muscular, Elec- tro?) Electro-Muscular Excitation. (See Ex- citation. Electro-Muscular?) Electronecrosic. Pertaining to capital punishment by means of electricity. Electronecrosis. A word proposed for capital punishment by means of electricity. Electro-Negative Ions. (See Ions, Elec- tro-Negative?) Electronegatives. The atoms or radicals that appear at the anode or positive terminal during electrolysis. The anions. (See Electrolysis. Anton?) Electro-Nervous Excitability. (See Ex- citability, Electro-Nervous?) Electro- N ickeling. (See Nickeling, Electro) Electro-Optics. (See Optics, Electro?) Electrophanic. Pertaining to capital pun- ishment by means of electricity. Electrophanical Pertaining to capital punishment by means of electricity. Electrophanize. To inflict capital pun- ishment by means of electricity. Electrophany. Capital punishment by means of electricity. The word electrophany would appear to be far preferable to the word electrocution, since it is in accordance with etymological usage, while elec- trocution is not. Electrophila. A devotee of electricity. Electrophobia. A word proposed for fear of electricity. Electrophoric. Pertaining to an electro- phorus. (See Electrophorus?) Electrophorus. An apparatus for the production of electricity by electrostatic induc- tion. (See Induction, Electrostatic?) A disc of vulcanite, or hard rubber B, contained in a metallic form, is rub- bed briskly by a piece of cat's skin and the insu- lated metallic disc, A, is Fig. 233. Electrofihorus. placed on the centre of the Ch&rging. vulcanite disc, as shown in Fig. 235. The negative charge produced in B, by fric- tion, produces by induction a positive charge on the part of A, nearest it, and a negative charge on the part furthest from it. In this condition, if the disc be raised from the plate by means of its insulating handle, as shown in Fig. 236, no electrical effects will be noticed, since the two op- posite and equal charges unite and neutralize each Fi S- other. If, however, the disc A, be first touched by the finger, and then raised from the disc B, it will be found to be pos- itively charged. Elecirophorus, Discharging. Ele.] 208 [Ele. E 1 e c t r o-Physiology. (See Physiology, Electro) Electropic Medium. (See Medium, Elec- tropic) Electro-Plating. (See Plating, Electro) Electro-Plating Bath. (See Bath, Elec- tro-Plating) Electro-Pneumatic Signals. (See Sig- nals, Electro-Pneumatic) Electro-Pneumatic Thermostat. (See Thermostat, Electro-Pneumatic) Electropoion Liquid. (See Liquid, Elec- tropoion) Electro-Positive Ions. (See Ions, Elec- tro-Positive) Electropositives. The atoms or radicals that appear at the kathode or negative termi- nal of any source during electrolysis. Thekathions. (See Electrolysis. Kathion) E 1 e c t r o-Prognosis. (See Prognosis, Electric) Electro-Puncture. (See Puncture, Elec- tro) Electro-Receptive Devices. (See Device, Electro-Receptive) Electro-Receptive Devices, Multiple-Arc- Connected (See Devices, Electro- Receptive, Multiple-Arc-Connected) Electro-Receptive Devices, Multiple-Se- ries-Connected (See Devices, Elec- tro-Receptive, Multiple-Series-Connected) Electro-Receptive Devices, Series-Con- nected (See Devices, Electro-Recep- tive, Series-Connected) Electro-Receptive Devices, Series-Mul- tiple-Connected (See Devices, Elec- tro-Receptive, Series-Multiple-Connected) Electroscope. An apparatus for showing the presence of an electric charge, or for de- termining its sign, whether positive or nega- tive, but not for measuring its amount or value. In the gold-leaf electroscope, two gold leaves, n, n, Fig. 239, suspended near each other, show by their repulsion the presence of an electric charge. Two pith balls may be used for the same purpose. The pith balls B, B, shown in Fig. 237, form a simple electroscope. If repelled by a charge, when approached by a similar charge in S, they will at once be still further repelled, as shown by the dotted lines. To use an electroscope for determining the sign of Fig- 237' p ' th Bal1 Electroscope. an unknown charge, the gold leaves or pith balls are first slightly repelled by a charge of known name, as, for example, positive, applied to the knob C, Fig. 239. They are then charged by the electrified body whose charge is to be determined. If they are further repelled, its charge is positive. If they are first attracted and afterwar s repelled, its charge is negative. Two posts B, Fig. 239, connected with the earth, increase the amount of divergence by in- duction. Electroscope, Condensing, Yolta's An electroscope employed for the detection of feeble charges, the leaves of which are charged by means of a condenser. The condensing electroscope, Fig. 238, is formed of two metallic plates, placed at the top of the instrument, and separated by a suitable dielectric. The upper plate, P, is removable by means of the insulated han- dle, G. To employ the elec troscope, as for exam- ple, to detect the free | charge in an unequal- Figm 23 g_ Condensing Elec. ly heated crystal of troscope. tourmaline, the crystal is touched to the lower plate, while the upper plate is connected to the ground by the finger. On the subsequent re- moval of the upper plate an enormous decrease Ele.J 209 [Ele. Gold-Leaf Electroscope. ensues in the capacity of the condenser, and the charge now raises the potential of the lower plate, and causes a marked divergence of the leaves L, L. (See Electricity, Pyro.) Electroscope, Gold-Leaf An elec- troscope in which two leaves of gold are used to detect the presence of an electric charge, or to determine its character whether positive or negative. When a charge is imparted to the knob C, Fig. 239, the gold leaves n, n, diverge. This will oc- cur whether the charge be positive or negative. To determine the char- acter of an unknown charge, the leaves are first caused to diverge by means of a known positive or neg- ative charge. The un- known charge is then given Fig. 239. to the leaves, tf they di- verge still further, then the charge is of the same name as that originally possessed by the leaves. If, however, they first move to- gether and are afterwards re- pelled, the charge is of the opposite name. Electroscope, Pith - Ball An electroscope which shows the presence of a charge by the repulsion of two similarly charged pith balls. (See Electroscope) Any two pith balls, suspend- ed by conducting threads, but insulated from the earth, will serve as an electroscope. Electroscope, Quadrant, Henley's An electro- scope sometimes employed to indicate large charges of electricity. A pith ball placed on a light ||j||i] arm A, of straw or other simi- lar material, Fig. 240, is pivoted at the centre of a graduated circle B. The arm, C, is at- Fig. 240. Henley's tached by means of the screw Electroscope. to the prime conductor of an electric machine. The s : milar charge imparted to A, by contact with C, causes a repulsion which may be meas- ured on the graduated arc. This instrument approaches the electrometer in the character of its operation, since by its means, approximately correct measurements may be made of the value of the repulsion. It should not, how- ever, be confounded with the quadrant electrom- eter. (See Electrometer, Quadrant. ) Electroscopieally. By means of the elec- troscope. (See Electroscope) Electroscopy. The art of determining the kind of charge a body possesses, by means of an electroscope. Electro - Sensibility. (See Sensibility, Electro) Electro-Silvering. (See Silvering, Elec- tro) Electro-Smelting. (See Smelting, Elec- tro) Electrostatic Attraction. (See Attrac- tion, Electrostatic.) Electrostatic Capacity. (See Capacity, Electrostatic) Electrostatic Circuit. (See Circuit, Electrostatic) Electrostatic Field. (See Field, Electro- static) Electrostatic Induction. (See Induction, Electrostatic) Electrostatic Induction Machine. (See Machine, Electrostatic Induction) Electrostatic Leakage. (See Leakage, Electrostatic) Electrostatic Lines of Force. (See Force, Electrostatic, Lines of) Electrostatic Repulsion. (See Repulsion, Electrostatic) Electrostatic Screening. (See Screening, Electrostatic) Electrostatic Stress. (See Stress, Elec- trostatic) Electrostatic Units. (See Units, Electro- static) Electrostatics. That branch of electric science which treats of the phenomena and measurement of electric charges. Ele.] 210 [Ele. The principles of electrostatics are embraced in the following laws, viz.: (i.) Charges of like name, *'. e., either positive or negative, repel each other. Charges of unlike name attract each other. (2.) The forces of attraction or repulsion be- tween two charged bodies are directly propor- tional to the product of the quantities of elec- tricity possessed by the bodies and inversely proportional to the square of the distance be- tween them. These laws can be demonstrated by the use of Coulomb's torsion balance. (See Balance, Tor- sion.) Calling q, and q 1 , the quantities of electricity possessed by the two bodies, and r, the distance between them, then, if f, is the force exerted by their mutual action, Electro-Technics. (See Technics, Elec- tro) Electrothanasing. Producing death by electricity. Electrothanasis. A word proposed for death by electricity. The death referred to here is death other than that caused by capital punishment. Electrothanasise. To produce death by electricity. The death here referred to is other than that caused by capital punishment. Electrothanatose. To cause death by electricity. Electrothanatosic. Pertaining to capital punishment by means of electricity. Electrothanatosing. Causing death by electricity. Electrothanatosis. A word proposed for death by electricity. The death here referred to is death other than that caused by capital punishment Electro-Therapeutic Bath. (See Bath, Electro- Therapeutic) Electro-Therapeutic Breeze. (See Brteze, Electro- Therapeutic^ Electro-Therapeutic Diffusion of Cur- rent. (See Current, Diffusion of, Electro- Therapeutic) Electro-Therapeutic Dosage. (S e e Dosage, Electro- Therapeutical) Electro-Therapeutic Electrode. (See Electrode, Electro- Therapeutic) Electro-Therapeutic Electrodes. (See Electrode, Electro- Therapeutic) Electro-Therapeutic Galvanization. (See Galvanization, Electro- Therapeutical) Electro-Therapeutic Head-Breeze. (See Breeze, Head, Electro- Therapeutic) Electro-Therapeutics. (See Therapeu- tics, Electro) Electro-Therapeutist. (See Therapeu- tist, Electro) Electro-Therapy. (See Therapy, Elec- tro) Electro-Thermal Meter. (See Meter, Electro-Thermal) Electro-Tinning. (See Tinning, Elec- tro) Electrotisic. Pertaining to capital pun- ishment by means of electricity. Electrotising. Producing capital punish- ment by means of electricity. Electrotisis. A word proposed for capi- tal punishment by means of electricity. Electrotonic Current. (See Current, Electrotonic) Electrotonic Effect (See Effect, Electro- tonic) Electrotonic Excitability. (See Excita- bility, Electrotonic) ' Electrotonic State. (See State, Electro- tonic) Electrotonus. A condition of altered functional activity which occurs in a nerve when subjected to the action of an electric Ele.J 211 [Ele. The electrotonic state is produced by the passage through a nerve of a constant current .called the polarizing current. Electrotonus is attended by the modification of the nerve in the following respects, viz. : (r.) In its electromotive force. (2.) In its excitability. The passage of the constant current produces a change in the electromotive force of that part of the nerve traversed by the current. This alteration in muscular excitability may consist in either an increased or a decreased func- tional activity. The decreased functional activity occurs in the neighborhood of the anode, or the positive terminal, and is called the anelectrotonic state. The increased functional activity occurs in the neighborhood of the kathode, or the negative terminal, and is called the kathelectrotonic state. (See Anelectrotonus. Katheleclrotonus .) This altered functional activity affects not only the intra polar parts of the nerve, or that part between the electrodes, but also the extra-folar -portions, or, in other words, the remainder of the nerve. The electrotonic state is characterized by two varieties, viz.: those in which the electromotive force of the nerve is decreased, and those in which the electromotive force of the nerve is increased. These varieties of electrotonus are called respec- tively the negative and positive phase of electro- tonus. (See Electrotonus, Negative Phase of. Electrotonus, Positive Phase of.) Electrotonus, Negative Phase of A decrease in the electromotive force of a nerve effected by sending a current through the nerve in the opposite direction to the nerve current. (See Current, Nerved) Electrotonus, Positive Phase of An increase in the electromotive force of a nerve effected by sending a current through the nerve in the same direction as the nerve current. The increase in the electromotive force not only affects the portions of the nerve in the intra-polar regions, but in the extra polar regions as well. Electrotype. A type, cast, or impression of an object obtained by means of electro- metallurgy. (See Metallurgy, Electro. Elec- trotyping) Electrotyping, or the Electrotype Pro- cess Obtaining casts or copies of objects by depositing metals in molds by the agency of electric currents. The molds are made of wax, or other plastic substance, rendered conducting by coating it with powdered plumbago. The mold is connected with the negative battery terminal, and placed in a metallic solu- tion, generally of copper sulphate, opposite a plate of metallic copper, connected with the posi- tive battery terminal. As the current passes, the metal is deposited on the mold at the kathode, and dissolved from the metallic plate at the anode, thus producing an exact copy or cast and at the same time maintaining constant the strength of the bath. Electrozemia. A word proposed for capi- tal punishment by means of electricity. Electrum. A name given by the ancients to various substances that could be readily electrified by friction. The term electrum included a number of sub- stances, but was applied mainly either to amber or to an alloy of gold and silver. Element. Any kind of matter which can- not be decomposed into simpler matter. Matter that is formed or composed of but one kind of atoms. Oxygen and hydrogen are elements or varie- ties of elementary matter. They cannot be de- composed into anything but oxygen or hydrogen. Water, on the contrary, is compound matter, since it can be decomposed into its constituent parts, oxygen and hydrogen. There are about seventy well-known elements, some of which are very rare, occurring in ex- tremely small quantities. The evidence of the true elementary condition of many of the elements is based, to a great ex- tent, on the fact that so far they have resisted all efforts made to decompose them into simpler sub- stances. We should bear in mind, however, that until Divy's use of the voltaic battery, potash, soda, and many other similar compounds were re- gaidcd as true elements. It is not improbable that many of the now so-called elements, may hereafter be decomposed into simpler constitu- ents. The following table gives the names, chemical Ele.] [Ele, symbols, approximate atomic weights and equiva- lents of the principal elements : Names ot Elements. t/5 Approximate Atomic Weight. Chemical Equivalent.* Aluminium Antimony Arsenic Karium Al. bb. As. Ba. 27. 120. 9 [compounds 40 in aus, 24 in ic 24. gin ous, 15 in ic 68 4 Beryllium Bismuth Boron Be Bi. B. 207.5 6 4-6 Bromine Cadmium Caesium Calcium'..".".!!!' Br. Cd. Ca'. 79.8 79-8 II' 9 66.3 Carbon Cerium Chlorine Cobalt C. Ce. Cl. Cr. Co 12. 140.4 35-4 p: 9 6 26 inous, 17.3 inic Cu. 63.2 31.6 D Erbium E. Fluorine Gallium Germanium Glucinum Goid F. Ga. Ge. G. Au 72.3 19. H. Inoium Iodine Iridium Iron Lanthanum Lead In. Fe. L, llli 192.7 55-9 .38-5 il 96.4, 64.2, 48.2 2,i in aus, 18.6 in ic L-thium L-. Magnesium Manganese Mercury Ml: Hg 84. 53-9 12 Molybdenum Nickel ... Mo. Ni 95-5 28 Nb 93.8 N. Os 198 '-5 o 8 Palladium Phosphorus Pd. P. Pt. K. 105.7 194.4 52. gin aus, z6.4\nie 6 . 2 in phosphates 97 . 2 in aus , 48 . 6 in ic Rhodium Rubidium R. Rb. Ru 52 in ous, 34.7 in tc 8 5-3. . . Samarium Scandium Selenium Silicon Silver s... Sc. So. Ae 150.02 78 : 8 28.2 7. Sodium btrontium Sulphur Tantalum Tellurium Thallium Thorium Na-: Sr. S. Ta. Te Tl. Th. Sn. * . 128. 203.7 233-4 23 43-7 203 . 7 in aus, 67 . 9 inic 58 . 9 in aus. 29. 4 in ic Tungsten W. 4 91.8 invus Vanadium Ytterbium Va. Yb. 17.1 inous Yttrium Y. M Zirconium Zn. Zr. 64.9 89.4 3-5 ! Atomic weight divided by the valency. Element, Negative One of the substances forming a voltaic couple. (See Couple, Voltaic?) Element, Negative, of a Toltaic Cell That element or plate of a voltaic cell into- which the current passes from the exciting" fluid of the cell. The plate that is not acted on by the elec- trolyte during the generation of current by the cell The copper or carbon plate, respectively, in a zinc-copper or zinc-carbon couple. It must be carefully borne in mind that the conductor attached to the negative element of & voltaic pile is the positive conductor or electrode of the pile, since the current that flows into the plate from the liquid or electrolyte must flow out of the plate where it projects beyond the liquid. Element of Current. (See Current, Ele- ment of.} Element of Storage Battery. (See Bat- tery, Storage, Element of.) Element, Positive That element or plate of a voltaic cell from which the current passes into the exciting fluid of the cell. The element of a voltaic couple which is acted on by the exciting fluid of the celL (See Couple, Voltaic.) Element, Thermo-Electric One of the two metals or substances which form a thermo-electric couple. (See Couple, Ther- mo-Electric?) Element, Voltaic One of the two metals or substances which form a voltaia couple. (See Couple, Voltaic?) Elements, Electrical Classification of A classification of the chemical ele- ments into two groups or classes according to whether they appear at the anode or kathode when electrolyzed. The chemical elements may be arranged into electro-positive and electro-negative according to whether, during electrolysis, they appear at the negative or positive terminal of the source respec-- tively. The electro-positive elements or radicals are called kathions, and appear at the kathode or electro-negative terminal. The' electro-negative; Ele.J 213 [Ene, elements are called onions, and appear at the anode, or the electro- positive terminal. (See Ions.) The metals generally are electro-positive; oxy- gen, chlorine, iodine, fluorine, etc., are electro- negative. Elements, Magnetic, of a Place The values of the magnetic intensity, the mag- netic decimation or variation, and the mag- netic inclination or dip at any place. Elevator Annunciator. (See Annuncia- tor, Elevator?) Elevator, Electric An elevator operated by electric power. Elongated Ring Core. (See Core, Ring, Elongated?) Elongation, Magnetic An increase in the length of a bar of iron on its magnetiza- tion. This increase in length is thought "to greatly strengthen Hughes' theory of magnetism. (See Magnetism, Hughes' 1 Theory of.) Elongation of Needle. (See Needle, Elon- gation, of.) Embosser, Telegraphic An appa- ratus for recording a telegraphic message in raised or embossed characters. Emptied. A term sometimes applied to a completely discharged secondary or storage cell. It is difficult to determine exactly when a stor- age cell is completely emptied or "discharged." The cell is generally regarded as discharged when its voltage falls below a certain point. Endosmose. The unequal mixing of two liquids or gases through an interposed me- dium. The presence of an electric current affects the endosmose. (See Currents, Diaphragm.) Endosmose, Electric. Differences in the level of liquids capable of mixing through the pores of a diaphragm separating them, pro- duced by the flow of an electric current through the liquid. Wiedemann, who investigated these phenom- ena, employed a porous earthenware vessel closed at the bottom and terminated at its upper end by a glass bell provided with a glass tubulure, to which was attached a horizont.il arm for the es- cape of the liquid raised in the tubulure. The battery terminals were attached to platinum elec- trodes placed respectively inside the porous cell, and in a vessel of water outside of the porous cell, in which the porous cell was placed ; on the passage of the current from the outside of the cell to the inside the liquid rose in the glass tubulure and ran. over the'horizontal tube into a vessel placed ready to receive it. Energizing, Electrically Causing electricity to produce any effect in an electro- receptive device. An electro-magnet is energized by the passage of a current through its coils. Energy. The power of doing work. The amount of work done is measured by the product of the force, by the space through which the force moves. Thus one pound raised verti- cally through ten feet, ten pounds raised through one foot, or five pounds raised through two feet, all represent the same amount of work; viz., ten fool- pounds. If a weight of ten pounds be raised through a, vertical height of one foot, by means of a string passing over a pulley, there will have been ex- pended an amount of energy represented by the work often foot pounds. If the weight be pre- vented in any way from falling, as by securing the string to a fixed support, the weight will have stored in it an amount of energy equal to ten foot- pounds, and if permitted to fall, will be capable of doing an amount of work which, leaving out air resistance and friction, is exactly equal to that originally expended in raising it to the position from which it fell; viz., ten foot-pounds of work. Energy, Actnal Energy actually employed in doing work as distinguished from energy that only possesses the power of doing work, but not actually doing such work. This term is also used in the sense of kinetic energy or energy due to motion, but kinetic en- ergy is no more actual than potential energy. Energy, Atomic Chemical-potential energy. (See Energy, Chemical-Potential.) Energy, Chemical-Potential - The potential energy possessed by the elementary chemical atoms. (See Energy, Potential.) If a weight of one pound be raised vertically Ene.] 214 [Ene. against the earth's attraction, through a distance of say ten feet, and placed on a suitable support, an amount of energy, equal to the ten foot-pounds of work done on the weight, becomes potential. In the same manner if the elementary atoms of carbon and oxygen, when combined so as to form carbonic acid, are raised or separated fi om one another sufficiently to decompose the carbonic acid and separate the carbon from the oxygen, the amount of potential energy the carbon and oxygen possess, as a result of having been separated, is equal precisely to that originally required to sepa- rate them. In this manner each chemical element possesses a store of chemical -potential energy peculiar to it, and any element with which it may subsequently enter into combination. When ele- ments combine chemically this potential energy is expended in producing heat. Energy, Conservation of The in- destructibility of energy. The total quantity of energy in the universe is unalterable. The total energy of the universe is not, how- ever, available for the production of work useful for man. When energy disappears in one form it reap- pears in some other form. This is called the con- servalion or indestructibility of energy. The com - monest form in which energy reappears is as heat, and in this case some of the heat is lost to the earth by radiation. This degradation or dissipa- tion of energy causes some of the energy of the earth to bt come non-available to man. Energy is therefore available and non-available. {See Entropy.) Energy, Correlation of A term sometimes applied to the different phases un- der which energy may appear. Since energy is indestructible, when it disap- pears in one form or phase, it must reappear in another form or phase. The correlation of the different phases of energy, therefore, necessarily follows from the fact that all energy is indestruc- tible. Energy, Degradation of Such a dissipation of energy as to render it non- available to man. (See Energy, Conserva- tion of. Entropy.) Energy, Dissipation of The ex- penditure or loss of available energy. Energy, Electric The powei which electricity possesses of doing work. In the case of a liquid mass at different levels, the liquid at the higher level posses>es a certain amount of potential energy measured by the quantity of the liquid at the higher level, an 1 the excess of its height over that of the lower level; or, by the difference between the two levels. Any difference of level will produce a flow of the liquid from the higher to the lower level, and during the flow of this current of liquid, potential energy will be lost, and a certain amount of work will be done. In the case of electricity, the difference of elec- tric level, or potential, between any two points of a conductor, causes an electric current to flow between these points toward the lower electric level, during which electric potential energy is lost, and work is accomplished by the electric current. (See Potential, Electric.) The amount of this electric work is measured by the quantity of electricity that flows, multiplied by the difference of potential under which it flows. (See Joule. Volt-Coulomb.) Electric energy, however, is generally meas- ured in electric power, or rate of doing electric "work. Since an ampere is one coulomb-per-second, if we measure the difference of potential in volts, the product of the amperes by the volts will give the electrical power in volt-amperes, or watts, or units of electric power. C E = Watts. (See Ampere. Volt. Watt.) One horse power equals 550 foot-pounds per second. One watt or volt-ampere = , \ ff of a horse-power, or one horse-power equals 746 volt amperes or watts, therefore: The current in ampet es, multiplied by the dif- ference of potential in volts, divided by 746, equals the rate of doing work, in horse-powers. Thus, if .7 ampere is required to operate a 16 candle, no volt, incandescent lamp, it requires 4.8 watts per candle. One Wait = 44.2394 foot-pounds per minute. One Watt = .737324 foot-pound per second. The Heat Activity, or the heat-per-second produced by an electric current, is also propor- tional to the product C E, or the watts, for the heat is proportional to the square of the current in amperes multiplied by the resistance in ohms, or C* R = the watts. (See Calorimeter, Elec- tric.) Eiie.J By Ohm's Law (See Ohm's Law] C = f- (i), or C R = E (2), IX But the electric power, or the watts, = C E (3). If, now, we substitute the value of E, taken from equation (2) in equation (3) we have [Ene. therefore C R = Watts. To determine the heating power of a current in small calories, calling H, the amount of heat required to raise i gramme of water through i Cent., and C, the current in amperes H = C 1 R X -24. Or, for any number of seconds, /, H = C* R/ X .24. .(See Catorie.) But from O/n's Law, 1 nd the formula for electric power or the watts = C E. (2) By substituting in equation (2) and the value of C, in equation (i), E c E = EX R = Watts. That is to say, the electric power in any part of a circuit varies directly as the square of the . electromotive force. We, therefore, have three expressions for the value of the watt, or the unit of electric power, r -second, that passes, in amperes, and the difference of electric potential or level, through which it passes, in volts. (2.) C R = Watts; or the electric power varies directly as the resistance R, when the cur- rent is constant, or as the square of the current, if the resistance is constant. That is to say, if with a given resistance the power of a given current has a certain value, and the current flowing through this same resistance be doubled, the power is four times as great, or is as the square of the current. E (3.) j- = Watts, or the electric power is in- versely as the resistance R, when the electro- motive force is constant, and is directly propor tional to the square of the electromotive force if the resistance is constant. A circuit of one ohm resistance will have a power of one watt, when under an electromo- tive force of one volt, since it would then have a current of one ampere flowing through it, and C E = i. If, however, the resistance be halved or becomes .5 ohm, then two amperes pass, or the power equals 2 watts. The power varies as the square of the electro, motive force in any part of a circuit, when the resistance is constant in that part. Thus 2 am- peres, and 2 volts, in a circuit of one ohm resistance, give a power, C E=2X2=4 watts. If now, R, remaining the same, the electro- motive force be raised to 4 volts, then since E, is doubled, C, or the amperes, is doubled, and C XE: E 8 16 4 X 4 = 16 watts, or -^ = - = 16. Energy, Electric, Transmission of The transmission of mechanical energy be- tween two distant points connected by an electric conductor, by converting the me- chanical energy into electrical energy at one point, sending the current so produced through the conductor, and reconverting the electrical into mechanical energy at the other point. A system for the electric transmission of energy embraces: (I.) A conducting circuit between the two stations. (2.) An electric source or battery of electric sources or machines at one of the stations, gener- ally in the form f a dynamo-electric machine or machines, for converting mechanical energy into electric energy. (3.) Electro-receptive devices, generally electric motors, at the other station for reconverting the electric into mechanical energy. (See Motor, Electric. ) Energy, Flow of The flow or trans- mission of energy from the medium or die- lectric surrounding a conductor which is directing a current of electricity on to the conductor. (See Law, Poynting's.) Energy, Hysteresial, Dissipation of The dissipation of energy by means of Ene.] [Ent. hysteresis. (See Energy, Dissipation of. Hysteresis!) Energy, Kinetic Energy which is due to motion as distinguished from potential energy. (See Energy, Potential!) Energy-Meter. (See Meter, Energy!) Energy of Position. (See Position, En- ergy f) Energy of Stress. (See Stress, Energy of.) Energy, Potential Stored energy. Potency, or capability of doing work. Energy possessing the power or potency of doing work, but not actually performing such work. The capacity for doing work possessed by a body at rest, arising from its position as regards the earth, or from the position of its atoms as regards other atoms, with which it is capable of combining. A pound of coal, if raised vertically one foot, possesses, as a mere weight, an amount of energy capable of doing an amount of work equal to one foot-pound. The atoms of carbon, however, of which it is composed, have been raised or sepa- rated from those of oxygen, or some other elemen- tary substance, and when the coal is burned, or the carbon atoms fall towards the oxygen atoms (i. er-second, will liberate .0000105 gramme of hy- drogen per second. The number .0000105 is the electro-chemical equivalent of hydrogen. In the same manner the electro-chemical equiva- lent of the other elements are obtained by multi- plying the electro-chemical equivalent of hydrogen by the chemical equivalent of the substance. Thus, the chemical equivalent of potassium is 39.1, therefore its electro-chemical equivalent is 39.1 X .0000105 = .00041055. By multiplying the strength of the current that passes by the electro-chemical equivalent of any substance we obtain the weight of that substance liberated by electrolysis. (See Equivalence, Electro-Chemical, Law of.) To determine the electro-chemical equivalent of the other elements see table of chemical equiva- lents on page 212. Equivalent, Joule's The mechan- ical equivalent of heat. (See Heat, Mechan- ical Equivalent of.) Equivalent of Heat, Mechanical (See Heat, Mechanical Equivalent of.} Equivalent Resistance. (See Resistance, Equivalent!) Equivolt. A term proposed by J. T. Sprague for the unit of electrical energy, ap- plied especially to chemical decomposition. Sprague defines an equivolt as follows : ' ' The mechanical energy of one volt electromotive force exerted under unit conditions through one equiva- .cnt of chemical action in grains." This term has not been generally accepted. (See Volt. Coulomb. Joule.) Erb's Standard Size of Electrodes. (See Electrodes, Erb's Standard Size of.) Erg. The unit of work, or the work done when unit force is overcome through unit distance. The work accomplished when a body is moved through a distance of one centimetre with the force of one dyne. (See Dyne.) A dyne centimetre. The work done when a weight of one gramme is raised against gravity through a vertical height of one centimetre is equal to 981 ergs, because the weight of one gramme is I X 981 dynes, or 981 ergs. The following values for the erg, the unit of work, and the dyne, the unit of force, are taken from Hering: I erg = i dyne centimetre. I erg = o.ooooooi joule. 981 ergs = I gramme centimetre. 1,937.5 ergs = I foot grain. 13,562,609 ergs = I foot-pound. I dyne = 1.0194 milligrammes. I dyne = 0.015731 grain. I dyne = 0.0010194 grammes. I dyne = 0.00003596 ounce avoirdupois. 63.568 dynes = I grain. 981 dynes = I gramme. Ergmeter. An apparatus for measuring the work of an electric current in ergs. Erg-ten. A term proposed for ten million ergs or i X 10 10 = 10,000,000,000. In representing large numbers containing many ciphers the following plan is generally adopted for representing the number of ciphers that are to be added to a given number. Thus, suppose it is desired to represent the number 3,8co,ooo,ooo. When written 38 X IO 8 it indicates that 38 is to be multiplied by IO 8 or 100,000,000, or, in other words, that 38 is to be followed by 8 ciphers, thus 3,800,000,000. A negative exponent, as 3 X io~ 8 represents the corresponding decimal thus, .00000003. I erg X io 10 , or 10,000,000,000 is called an erg ten. I X IO 6 = an erg six. These terms are not in general use. Ten meg-ergs is a pref- erable phrase to an erg-ten. (See M the effects of negative electrifica- tion. He shows that under these circumstances the surface molecules of the platinum lose their power of cohering and fly off into the space around them, /'. e , suffer true evaporation. This action takes place under atmospheric pressures, but like ordinary evaporation, is greatly facili- tated by the presence of a high vacuum. True electric evaporation takes place with liquids as well as with solids. In an experiment with water, the influence of the kind of the elec infication was clearly shown. A vessel of water Fig. 242. Electrical Evaporation. exposed to the air was first positively electrified, but after an exposure of \\ hours only a trifling evaporation was noticeable. The water was then negatively electrified, and at the end of \\ hours had lost -j^ff part of its weight more than did the positively charged water. Professor Crookes experimented with cadmium, and, in order to show that electric evaporation is different from evaporation produced by the agency of heat, tried the following, viz. : A high vacuum U-tube, shaped as shown in Fig 242, was pro- A c Fig 243 al Evaporation. vided with platinum poles sealed in the glass at A and B. Two pieces of cadmium, C and D, were placed in the tube in the position shown, and the tube uniformly heated by means of a gas- burner and air bath, and maintained at a constant temperature. The current was then passed for about an hour, B, being made the negative pole. No metal was deposited in the neighborhood of the positive pole, the portions ot the tube sur- rounding the positive pole being quite clean, while the corresponding portions of the other limb of the tube were thickly coated, as shown by the shading in the drawing. In another experiment, in which the tempera- ture was kept lower than in the preceding, viz., just below the melting point of the cadmium, after the current had passed for an hour, the limb of the tube through which the current had passed had received a thick coating, while the other was nearly free from coating, as shown in Fig. 243. Here the increase in the amplitude of t' e mole- cular oscillation under the influence of the elec- tricity is manifest. Evaporation, Electrification by An increase in the difference of potential ex- isting in a mass of vapor attending its sudden condensation. The free electricity of the atmosphere is be- lieved by some to be due to the condensation of the vapor of the air that results in rain, hail, clouds, etc. It is probable, however, that the true effect of condensation is mainly limited to the increase of a feeble electrification already possessed by the air or its contained vapor. The small difference of potential of the exceedingly small drops of water in clouds is enormously in- creased by the union or coalescing of many thousands of such drops into a single rain drop. (See Electricity f , Atmospheric.} Exchange, Telephonic, System of A combination of circuits, switches and other devices, by means of which any one of a number of subscribers connected with a telephonic circuit, or a neighboring telephonic circuit or circuits, may be placed in electrical communication with any other subscriber connected with such circuit or circuits. A telephone exchange consists essentially of a multiple switchboard, or a number of multiple switchboards, furnished with spring-jacks, an- nunciator drops, and suitable connecting cords. A call bell, or bells, is also provided. The annun- ciator drops are often omitted. (See Board^ Multiple Switch.) Excitability. Electric, of Nerve or Mns- cular Fibre The effect produced by an electric current in stimulating the nerve of a Exc.J [Exh. living animal, or in producing an involuntary contraction of a muscle. Du Bois-Reymond has shown that these effects depend : (i.) On the strength of the current employed. The excitability occurs only when the current begins to flow, and when it ceases flowing; or, when the electrodes first touch the nerves, and when they are separated from it. Subsequent investigations have shown that this is true only for the frog's nerves, and is true for the human nerves only in the case of moderate currents, strong currents producing tetanus. (2.) On the rapidity with which the current used reaches its maximum value, that is, on the rapidity of change of current density. (See Current Density.) Excitability, Electro-Nervous In electro-therapeutics the electric excitation of a nerve. Excitability, Electrotonic The actual excitability of a nerve when in the electrotonic condition. (See Electrotonus. Anelectrotonus. Kathelectrotonus) Excitability, Faradic Muscular or nervous excitability following the employment of the rapidly intermittent currents produced by induction coils. (See Coil, Induction?) Faradic excitability is different from galvanic excitability, or that produced by means of a con- tinuous voltaic current. (See Excitability, Gal- vanic. ) Excitability, Galvanic A term sometimes employed for electric excitability of nerve or muscular fibre. (See Excitability, Electric, of Nerve or Muscular Fibred) Excitation, Compensated, of Alternator. (See Alternator, Compensated Excitation of.) Excitation, Direct The excitement of a muscle by placing an electrode on the muscle itself. Excitation, Electro-Muscular In electro-therapeutics the galvanic or faradic excitation of the muscle, or its excitation by the continuous currents of a voltaic battery, or the alternating currents of an induction coil. Excitation, Faradic Excitation of muscle or nerve fibre by means of rapidly alternating currents of electricity. (See- Excitability, Faradic?) Excitation, Indirect The excite- ment of a muscle from its nerve. Exciter of Field. (See Field, Exciter of.) Exciting Liquid of Voltaic Cell. (See Cell, Voltaic, Primary, Exciting Liquid of.) Execution, Electric Causing the death of a criminal, in cases of capital pun- ishment, by means of the electric current. Electric execution has been adopted by the State of New York, in accordance with the following law : "The Court shall sentence the prisoner to' death within a certain week, naming no day or hour, and not more than eight nor less than five weeks from the day of sentence. The execution must take place in the State prison to which con- victed felons are sent by the Court, and the execu- tioner must be the agent and warden of the prison. "No newspaper may print any details of the execution, which is to be inflicted by electricity. A current of electricity is to be caused to pass through the body of the condemned of sufficient intensity to kill him, and the application is to be- continued until he is dead." Exhaustion, Electric Physiological effects resembling those produced by sun- stroke, resulting from prolonged exposure to the radiation of unsually large voltaic arcs, (See Sun-Stroke, Electric.) Exhaustion of Primary Voltaic Cell. (See Cell, Voltaic, Primary, Exhaustion of.)> Exhaustion of Secondary Voltaic Cell. (See Cell, Voltaic, Secondary, Exhaustion of.) Exhaustion of Voltaic Cell. (See Cell, Voltaic, Exhaustion of.) Exhaustion, Reaction of A con- dition of nervous and muscular irritability to electric excitation when a certain reaction, produced by a given current strength, cannot be reproduced without an increase of current strength. The reaction of exhaustion may be regarded as a special variety of the reaction of degeneration. (See Degeneration, Reaction of.) The reaction of degeneration embraces the following modifications of irritability, viz. : Exp.J 223 [Eye. (i.) Disappearance or diminution of nervous irritability to both galvanic and farad ic currents. (2.) Disappearance of far die and increase of galvanic irritability of muscles, generally associ- ated with an increase of mechanical irritability. (3 ) Disappearance of faradic and increase of galvanic muscular irritability associated generally with increased mechanical irritability. (4.) Tardy, delayed contraction of muscles in- stead of quick reaction of normal muscle. (5.) Marked modifications of normal sequence of contraction. Liebig &> Rohe'. Expanding 1 Magnetic Whirl. (See Whirl, Expanding Magnetic?) Expansion, Co-efficient of -- The fractional increase in the dimensions of a bar or rod when heated from 32 degrees to 33 degrees F. or from o degree to i degree C. The fractional increase in the length of the bar is called the Co-efficient of Linear Expansion. The fractional increase in the surface is called the Co-efficient of Surface Expansion. The fractional increase in the volume is called the Co-efficient of Cubic Expansion. Expansion, Electric -- The increase in volume produced in a body on giving such body an electric charge. A Leyden jar increases in volume when a charge is imparted to it. This result is due to an expansion of the glass due to the electric charge. According to Quincke, some substances, such as resinous or oily bodies, manifest a contraction of volume on the reception of an electric charge. Expansion Joint. (See Joint, Expan- sion?] Expansion, Linear, Co-efficient of -- A number expressing the fractional increase in length of a bar for a given increment of heat. The co-efficients of expansion of a few sub- stances are given in the following table: Temp. 16 to 100 degrees C. .0.0000235 " ..0.0000188 " ..0.0000167 ' ..0.0000184 Aluminium Brass Copper German silver . Glass Iron Lead Platinum Silver ......... o Zinc ........... o 100 loo 100 ico 100 100 loo 100 loo ..0.0000071 ..0.0000123 ..0.0000280 . 0.0000089 .0.0000194 .0.0000230 (Anthony &> Brackett.) Exploder, Electric Mine A small magneto-electric machine used to produce the currents of high electromotive force employed in the direct firing of blasts. Exploder, Electro-Magnetic A small magneto-electric machine used to pro- duce the currents of high electromotive force employed in the direct firing of blasts. Explorer, Electric An apparatus operated by means of induced currents, and employed for the purpose of locating bullets or other foreign metallic substances in the human body. (See Balance, Induction, Hughes') Explorer, Magnetic A small, flat coil of insulated wire, used, in connection with the circuit of a telephone, to determine the position and extent of the magnetic leakage of a dynamo-electric machine or other similar apparatus. (See Magnetophone) Explosive Distance. (See Distance, Ex- plosive.) Extension Call-Bell. (See Bell, Exten- sion Call.) External Circuit (See Circuit, Exter- nal) External Secondary Resistance. (See Resistance, External Secondary ) Extra Currents. (See Currents, Extra.) Extraordinary Resistance. (See Resist- ance, Extraordinary) Extra-Polar Region. (See Region, Ex- tra-Polar) Eye, Electro-Magnetic A term pro- posed for a certain form of spark-micrometer employed by Hertz in his experiment on elec- tro-magnetic radiation. This apparatus has received the alx>ve name because it enables the observer to see or localize an electromagnetic disturbance. The particular spark -micrometer that has re- ceived the name of the electro-magnetic eye had the form of a circle 35 centimetres in radius, and was formed of a copper wire 2 millimetres in di- ameter. Like all spark-micrometer circuits, it had its terminals separated by a small air-space. Eye, Selenium An artificial eye in Fac.] 224 [Far. which a selenium resistance takes the place of the retina and two slides the place of the eyelids. The selenium resistance is placed in the circuit of a battery and a galvanometer. When the slides L, L, Fig, 244, are shut, the galvanometer deflection is less than when they are open. The opening of the aperture between the slides L, L, may be automatically accomplished by the action of the light itself, by moving them by an electro-magnet placed in the circuit of a local bat- tery, and a selenium resistance maybe so arranged that when light falls on it the slides L, L, are moved together, and when the amount of such aght is small they are moved apart, by the action of a spring. In this way there is obtained a device roughly resembling the dilatation or con- . Fig 244- Selenium Eye. traction of the pupil of the eye from the action of light on the iris. (See Photometer, Selenium.) Fac-Simile Telegraphy, or Panteleg- raphy. (See Telegraphy, Fac-Simile) Fahrenheit's Thermometer Scale. (See Scale, Thermometer, Fahrenheit's^) Fall of Potential. (See Potential, Fall of.) False Magnetic Pole (See Pole, Magnetic, False.) False Resistance. (See Resistance, False.) False Zero. (See Zero, False .) Fan Guard. (See Guard, Fan.) Farad. The practical unit of electric capacity. Such a capacity of a conductor or condenser that one coulomb of electricity is required to produce in the conductor or condenser a difference of potential of one volt. As in gases, a quart vessel will hold a quart of gas under unit pressure of one atmosphere, so, in electricity, a conductor or condenser, whose capa- city is one farad, will hold a quantity of electricity equal to one coulomb when under an electromotive force of one volt. It may cause some perplexity to the student to understand why there should be in electricity one unit of capacity to represent the size of the vessel or conductor, and another to represent the amount or quantity of electricity required to fill such vessel. But, like a gas, electricity acts, in effect, as if it were very compressible, so that the quantity required to fill any condenser will de- N P ' ' Fig 245- Elevation of Standardized Condenser. pend on the electromotive force under which it is put into the conductor or condenser. For purposes of measurement, capacities of conductors are compared with those of condensers Fig. 246. Plan of Standardized Condenser. whose capacities are known in microfarads, or fractions thereof. The microfarad, or the of a farad, is used because of the very 1,000,000 great size of a farad. JTar.J [Fan. Fig. 245 shows an elevation, and Fig. 246 a plan of the form often given to a standardized condenser or microfarad. The condenser is charged by connecting the terminals of the elec- tric source to the binding posts N and N. It is discharged by means of the plug key P', that connects the brass pieces A and B, when pushed firmly into the conical space between them. The condenser is made by placing sheets of tin foil between sheets of oiled silk or mica in the box and connecting the alternate sheets to one of the brass pieces B, and the other set to the brass piecs A, as will be better understood from an inspection of Fig. 247. Fig. 247 Method of Construction of a Condenser. Condensers are generally made of the capacity of the ^ of a microfarad. Sometimes, however, they are made so that either all or part of the condenser may be employed, by the insertion of the different plug keys. The form of condenser shown in Fig. 248 is Fig. 248. Standard Condenser capable of ready division into five separate val- ues, v;z.: .05, .05, .2, .2 an.l .5 microfarad. Farad, Micro The millionth part of a farad. (See Farad.) Faraday Effect. (See Effect, Faraday.) Faraday's Cube. (See Cube, Faraday >s) Faraday's Dark Space.- (See Space, Dark, Faraday ' s) Faraday's Net. (See Net. Faraday s.) Faradic Apparatus, Magneto-Electric (See Apparatus, Faradic. Mag- neto-Electric?) Faradic Brush. (See Brush. Faradic ) Faradic Current. (See Current Fara- dir) Faradic Excitation. (See Excitation. Faradic?) Faradic Induction Apparatus. (See Apparatus Faradic Induction) Faradic Irritability. (See Irritability, Faradic.) Faradic Machine. (See Machine, Fara- dic.) Faradization. In electro-therapeutics, the effects produced on the nerves or muscles by the use of a faradic current, in order to distinguish such effects from galvanization or those produced by a voltaic current. (See Galvanization?) Faradization, General A method of applying the faradic current similar to that employed in general galvanization. (See Galvanization, General.) Faradization, Local A method of applying the faradic current in general simi- lar to that employed in local galvanization. (See Galvanization, Local.) Fault. Any failure in the proper working of a circuit due to ground contacts, cross- contacts or disconnections. (See Contacts, Cross.) Faults are of three kinds, viz. : , (i.) Disconnections. (See Disconnection.) (2.) Earths. (See Earth.) (3.) Contacts. (See Contacts.) Various methods are employed for detecting and localizing faults, for the explanation of which reference should be had to standard elec- trical works on testing or measurements. Fault, Ironwork, of Dynamo A ground or connection between the current of a dynamo and any part of its ironwork. Fan.] [Fie. If the dynamo is in good connection with the ground, as is frequently the case in marine plants, this fault is the same as a ground. Faults, Localization of Determin- ing the position of a fault on a telegraph line or cable by calculations based on the fall in the potential of the line measured at different points, or by loss of charge, etc. For details, see standard works on electrical measurements. Feed, Clockwork, for Arc Lamps An arrangement of clockwork for obtaining a uniform feed motion of one or both elec- trodes of an arc lamp. The clockwork is automatically thrown into or out of action by an electro-magnet, usually placed in a shunt circuit around the carbons. Feed, To To supply with an electric current, as by a dynamo or other source. Feeder. One of the conducting wires or channels through which the current is dis- tributed to the main conductors. Feeder, Standard or Main The main feeder to which the standard pressure indicator is connected, and whose pressure controls the pressure at the ends of all the other feeders. The term pressure in the above definition is used in the sense of electromotive force or differ- ence of potential. Feeder-Wires. (See Wires, Feeder?) Feeders. In a system of distribution by constant potential, as in incandescent elec- tric lighting, the conducting wires extend- ing between the bus-wires or bars, and the junction boxes. A feeder differs from a main in that a main consist^ of a conductor that may be tapped at any point to supply a customer, while a feeder leads direct from the dynamo or other source to a main and is not tapped at any point. Feeders, Negative The feeders that are connected with the negative terminal of the dynamo. (See Feeders?) Feeders, Positive The feeders that are connected with the positive terminal of the dynamo. (See Feeders?) Feeding Device of Electric Arc Lamp. (See Device, Feeding, of an Arc Lamp. Feed, Clockwork, for Arc-Lamps?) Feeding-Wire. (See Wire, Feeding?) Feet, Ampe're The product of the current in amperes by the distance in feet through which that current passes. It has been suggested that the term ampere- feet should be employed in expressing the strength of electro-magnetism in the field magnets of dynamo-electro machines or other similar ap- paratus. Ferranti Effect. (See Effect, Ferranti?) Ferro-Magnetic Substance. (See Sub- stance, Ferro-Magnetic?) Fibre, Quartz A fibre suitable for suspending galvanometer needles, etc., made of quartz. The quartz fibre is obtained by fusing quartz and drawing out the fused material as a fine thread, in a manner similar to the production of glass fibres. Quartz fibres possess marked advantage over silk fibres, in that they are 5.4 times stronger for equal diameters, and especially, in that they return to the zero point, after very considerable deflections. Quartz fibres are readily obtained by fusing quartz pebbles together in the voltaic arc, and drawing them apart with a rapid, but steady, uni- form motion. Fibre Suspension. (See Suspension, Fibre?) Fibre, Vulcanized A variety of in- sulating material suitable for purposes not requiring the highest insulation. Vulcanized fibre is, however, seriously affected by long exposure to moisture. Fibrone. An insulating substance. Field, Air That portion of a mag- netic field in which the lines of force pass' through air only. Field, Alternating An electrostatic or magnetic field the positive direction of the lines of force in which is alternately reversed or changed in direction. Field, Alternating Electrostatic An electrostatic field, the potential of which is rapidly alternating. Fie.] 227 [Fie. An alternating electrostatic field is, according to Tesla's experiments, produced in the neighbor- hood of the terminals of the secondary of an in- duction coil, through whose primary, alternations of high frequency are passing. Field, Alternating Magnetic. A mag- netic field the direction of whose lines of force is alternately reversed. Field, Density of The number of lines of force that pass through any field, per unit of area of cross-section. Field, Electric A term sometimes used in place of an electrostatic field. (See Field, Electrostatic) Field, Electro-Magnetic The space traversed by the lines of magnetic force pro- duced by an electro-magnet. (See Field, Magnetic) Field, Electrostatic The region of electrostatic influence surrounding a charged body. Electrostatic attractions or repulsions take place along certain lines called lines of electro- static force. These lines of force produce a field called an electrostatic field. Electric level or potential is measured along these lines, just as gravitation levels are measured with a plumb line along the lines of gravitation force. (See Poten- tial, Elec'ric.) Work is done when a body is moved along the lines of electrostatic force in a direction from an oppositely charged body, or towards a similarly charged body, just as work is done against gravity when a body is moved along the lines of gravitation force, away from the earth's centre, or vertically upwards. Field, Exciter of In a separately excited dynamo-electric machine, the dyna- mo-electnc machine, voltaic battery, or other electric source employed to produce the field of the field magnets. (See Machine, Dyna- mo-Electric.} Field, Intensity of The strength ot a field as measured by the number of lines of force that pass through it per unit of area of cross-section. (See Field, Electrostatic. Field, Magnetic) Field, Magnetic The region of magnetic influence surrounding the poles of a magnet. A space or region traversed by lines of magnetic force. A place where a magnetic needle, if free to move, will take up a definite position, under the influence of the lines of magnetic force. Unit strength of magnetic field is the field which would be produced by a magnetic pole of unit strength at unit distance. Magnetic attractions and repulsions are assumed to take place along certain lines called lines of magnetic force. The directions of these lines in any plane of a magnetic field may be shown by sprinkling iron filings over a sheet of paper held in a horizontal position to a magnet pole inclined Ftf.249- Magnetic Field. to the paper in the desired plane and then gently tapping the paper. The groupings of iron filings so obtained are sometimes called magnetic figures. The directions of the lines of force thus shown will appear from an inspection of Fig. 249, taken in a plane joining the two poles of a straight bar magnet, and Fig. 250, taken in a plane at right angles to the north pole of a straight bar magnet. In Fig. 249, the repulsion of the lines of force at either pole is shown by the radiation of the chains ot magnetized iron particles. The mutual attraction of unlike polarit'es is shown by the curved lines. In Fig. 250, the repulsion of the similarly mag- netized chains is clearly shown. Lines of magnetic force are assumed to pass out from the north, pole and back again into the magnet at its south pole. This assumed direction Fie.] 228 [Fie, is called the direction of the lints of magnetic force. Faraday expressed his conception of lines of magnetic force as follows: ' ' Every line of force must therefore be consid- ered as a closed circuit, passing, in some part of its course, through a magnet and having an equal amount of force in every part of its course. There Fig. 250, Magnetic Field. exist lines of force within the magnet of the same nature as those without. What is more, they are exactly equal in amount to those without. They have a relation in direction to those without and are, in fact, continuations of them." When a conductor, such as a wire through which a powerful current of electricity is flowing, is dipped in a mass of iron filings, a chain of iron filings is formed, the north end of which is urged around the conductor in one direction and the south end in the opposite direction, so that the movable chain of filings surrounds or grips the conductor in concentric rings or circles. The density of a magnetic field \rce per unit of area of cross-section. A single line of fotce, or a unit line of force, is such an intensity of field as exists in each square centimetre of cross-section of a unit magnetic field. A magnetic field is uniform, or possesses uni- form intensity, when it possesses the same num- ber of lines of force per square centimetre of area of cross-section. Field, Magnetic, Alternating The magnetic field produced by means of an alternating current. Field, Magnetic, Dissymmetrical A field whose lines of force are not symmet- rically distributed in adjacent halves. Field, Magnetic, Expanding of An increase in the length of the lines of mag- netic force in any field, or an increase in the length of their magnetic circuit. Field, Magnetic, of an Electric Current The magnetic field surrounding a cir- Fig. 251. Field of Current. cuit through which an electric current is flow- ing. An electric current produces a magnetic field. This was discovered by Oersted ^ in 1819, and may be shown by \ sprinkling iron filings on a sheet of paper, placed on the wire conductor conveying the cur- rent, at right angles to the direc- tion in which the current is pass- ing. Here the lines of force appear as concentric circles, ex- tending around the conductor, as shown in Fig. 251. Their direction, as regards the length of the conductor, is shown in Fig. 252. The electric current sets up these magnetic whirls around the conductor on its passage through it. J The direction of the lines of -. __ magnetic force produced by an '^jonof Line'l/ electric current, and hence its Force, magnetic polarity, depends on the direction in which the electric current flows. This direction Fie.] 229 [Fie. may be remembered as follows: If the current flows towards the observer, the directions of the lines of magnetic force is opposite to that of the hands of a watch, as shown in Fig. 253. Fig 253. Direction of Lines of Force. It is from the direction of the lines of magnetic force that the polarity of a helix carrying a cur- rent is deduced. (See Solenoid, Magnetic, Mag. net, Electro. ) A magnetic field possesses the following prop- erties, viz.: (i.) All magnetizable bodies are magnetized when brought into a magnetic field. (See Induc- tion, Magnetic.} (2.) Conductors moved through a magnetic field so as to cut its lines of force have differences of potential generated in them at different points, and if these points be connected by a conductor, an electric current is produced. (See Induction, Electro-Magnetic. ) Field, Magnetic, Pulsatory A field, the strength of which pulsates in such manner as to produce oscillatory currents by induc- tion. Field, Magnetic, Reversing That portion of the field of a dynamo-electric ma- chine, produced by the field-magnet coils, in which the currents flowing in the armature coils are stopped or reversed after the coil has passed its theoretical position of neutrality. Sparkless commutation is obtained by placing the brushes on the commutator so as to corre- spond with the reversing field. Field, Magnetic, Shifting A term proposed by Professor Elihu Thomson to ex- press a field of magnetic lines of changing position with respect to the axis of the pole from which they emanate. A shifting magnetic field is especially a phe- nomenon of a rapidly alternating magnetic field occurring in a substance like hardened steel in which the coercive force is fairly nigh. It, for example, a single magnet pole of an electro- magnet, whose coils are traversed by a rapidly alternating current ot electricity, 15 placed near one end of a steel file, the changing polarity developed thereby moves or shifts trora the point directly over the pole towards the distant end. The presence of this shifting field can be shown by the rotation of discs of copper suitably inclined to the end of the file. In a similar manner a prismatic mass of steel, placed with one of its flat sides on the pole of a rapidly alternating magnetic field, will have a magnetic field developed in it, which will move or shift from the flat ba^-e towards the upper edge. Movable masses of good conducting metal, such as copper, will be set in rotation in a direction such as would be caused by an escape of gas therefrom. The shifting magnetic field travels from the upper portions of the prism just as a stream of escaping gaseous substance would. Field, Magnetic, Spreading-Out A term sometimes used to represent an expand- ing magnetic field. (See Field, Magnetic, Expanding of.) Field, Magnetic, Stray That por- tion of the field of a dynamo-electric machine which is not utilized for the development of differences of potential in the armature, be- cause its lines of force do not pass through the armature. Field, Magnetic, Strength of The dynamic force acting on a free magnetic pole, placed in a magnetic field. If a free magnetic pole could be placed in a magnetic field, it would begin to move towards the opposite pole of the field, under its magnetic attraction, just as an unsupported body, free to move, would begin to fall towards the earth. The strength of a magnetic field corresponds to the acceleration of the force of gravity in the case of a falling body. The strength of the mag. netic pole corresponds to the mass of the falling body. The force impressed in the case of the magnetic field is equal to the strength of the pole multiplied by the strength of the field. Field, Magnetic, Symmetrical A field whose lines of force are symmetrically distributed in adjacent halves. Pie.] 230 [Fil. Field, Magnetic, Uniform A field -traversed by the same number of lines of magnetic force in all unit portions of area of cross-section. (See Field, Magnetic?) Field, Magnetic, Waste A term sometimes employed for stray field. (See Field, Magnetic, Stray?) Field, Kotating-Current A mag- netic field produced by means of a rotating current. (See Current, Rotating?) Field, Uniform Density of A uni- form density in all equal areas of cross- section of field. Field, Yortex-Ring The field of influence possessed by a vortex-ring. Professor Dolbear points out the fact that the direction of the rotation of a fluid constituting a vortex-ring resembles the magnet flux in a mag- netic field, and shows, from the action of such rings on one another, that they possess a true field, or atmosphere of influence outside their actual bodies. He infers that such rings possess true polarity, since the motions producing them have different directions on opposite sides or ends. Figure of Merit of Galvanometer. (See Galvanometer, Figure of Merit of.) Figures, Breath Faint figures of condensed vapor produced by electrifying a coin, placing it momentarily on the surface of a sheet of clean, dry glass, and then breath- ing gently on the spot where the coin was placed. The moisture collects on the electrified portions of the plate and forms a iairly distinct image ot the coin. Figures, Electric Figures of various shapes produced on electrified surfaces by the arrangement of dust particles or vapor vesicles under the influence of electric charges. Electric figures are of two varieties, viz.: (I.) Dust figures. (2.) Breath figures. Figures, Lichtenberg's Dust Figures produced by writing on a sheet of shel- lac with the knob of a charged Leyden jar and then sprinkling over the sheet dried and powdered sulphur and red lead, which have been previously mixed together, and are so rendered, respectively negative and positive. The red lead collects on the negative parts of the shellac surface, and the sulphur on the posi- tive parts, in curious figures, known as Lichten- berg's Dust Figures, one of which is shown in Fig- 254. Fig. 254. Lichtenberg's Dust Figures. These figures show very clearly that an electric charge tends to creep irregularly over the surface of an insulating substance. Figures, Magnetic A name some- times applied to the groupings of iron filings on a sheet of paper so held in a magnetic field as to be grouped or arranged under the in- fluence of the lines of force of the same. (See Field, Magnetic?) Filament A slender thread or fibre. The term is applied generally to threads or fibres varying considerably in diameter. Filament, Current A term some- times employed in place of current streamlet. (See Streamlets, Current?) Filament, Magnetic A polarized line or chain of ultimate magnetic particles. This is sometimes called a uniform magnetic filament. A bar-magnet possesses but two free poles. When broken ai its neutral point or equator, the bar will develop free poles at the broken ends. This is explained by considering the magnet to be composed of a number of separate particles, separately magnetized. A single chain or fila- ment of such particles is called a magnetic filament. (See Magnet, Neutral Point of. Mag- netism, Hughes' Theory of. Magnetism, Swing's Theory of.) Filament of Incandescent Electric Lamp. 231 [Fir. (See Lamp, Incandescent Electric, Fila- ment of.) Filament, Uniform Magnetic A term sometimes applied to a magnetic fila- ment. (See Filament, Magnetic.} Filaments, Flashed Filaments for an incandescent lamp, that have been sub- jected to the flashing process. (See Carbons, Flashing Process for?) Filamentous Armature Core. (See Core, Armature, Filamentous!) Film Cut-Out. (See Cut-Out, Film.) Finder, Induction A term some- times employed for a magnetic explorer. Finder, Position, Electric A de- vice by means of which the exact position of an object can be obtained. By means of a position -finder a gunner can be telephoned or otherwise ordered to fire at ob- jects he cannot see, and yet obtain a fair degree of accuracy. Finder, Range, Electric A de- vice by means of which the exact distance of an enemy's ship or other target can be readily determined. The operation of an electric range-finder is based on a method somewhat similar to the solving of a triangle for the purpose of determining distances. If the base line of a triangle and the two angles at the base are known, the other two sides and the included angle can be determined. In the range-finder, the resistance of a German silver wire corresponds to the graduated arc of the theodolite used to measure the angles, and a rheostat, as a receiving instrument, measures the values of the angles. The base line is a constant, so that the receiving instrument is marked in yards instead of angles. To use the range-finder, two observers watch the target object continu- ously through a telescope. They do this and nothing else, while a third observer watches a galvanometer and so alters a resistance, by moving a contact or slide key along a resistance wire, as to keep the needle of the galvanometer constantly at zero. The exact distance being thus ascer- tained, the gunner can make the proper allowance in firing. Finder, Wire Any form of galva- nometer used to locate or . find the corre- sponding ends of different wires in a bunched cable. The different wires in a cable are usually tagged and numbered at the end of the cable and at the joints. The telephone has been successfully em- ployed as a wire finder. Fire Alarm Annunciator. (See Annun- ciator, Fire Alarm.) Fire Alarm, Automatic (See Alarm, Fire Automatic.) Fire Alarm Contact (See Contact, Fire Alarm.) Fire Alarm Signal Box. (See Box, Fire Alarm Signal!) Fire Alarm Telegraph Box. (See Box, Fire Alarm Telegraph.} Fire Ball. (See Ball, Fire.) Fire Cleansing. (See Cleansing, Fire.) Fire Extinguisher, Electric A thermostat or mercury contact, which auto- matically completes a circuit and turns on a water supply for extinguishing a fire, on a certain predetermined increase of tempera- ture. Fire, Hot, St. Elmo's A term pro- posed by Tesla for a form of powerful brush discharge between the secondary terminals of a high frequency induction coil. (See Dis- charge, Brush-and-Spray?) This form of St. Elmo's fire differs from the ordinary form in being hot. Its general appear- ance is shown in Fig. 255, taken from Tesla. Hot Fire. Describing its production he says : ' In many of these experiments, when powerful effects are wanted for a short time, it is advantageous to use Fir.] 232 [Flo. iron cores with the primaries. In such case a very large primary coil may be wound and placed side by side with the secondary, and, the nearest terminal of the latter being connected to the primary, a laminated iron core is introduced through the primary into the secondary as far as the streams will permit. Under these conditions an excessively powerful brush, several inches long, which may be appropriately called ' St. Elmo's hot fire, ' may be caused to appear at the other terminal of the secondary, producing strik- ing effects. It is a most powerful ozonizer ; so powerful indeed, that only a few minutes are suf- ficient to fill the whole room with the smell of ozone, and it undoubtedly possesses the quality of exciting chemical affinities." Fire, St. Elmo's Tongues of faintly luminous fire which sometimes appear on the pointed ends of bodies in connection with the earth, such as the tops of church steeples or the masts of ships. The appearance of the St. Elmo's fire is due to brush discharges of electricity. Fishes, Electric A term applied to various fishes, such as the eel and the ray, which possess the ability of protecting them- selves by giving electric shocks to objects touching them. (See Eel, Electric.} Fishing Box. (See Box, Fishing?, Fittings or Fixtures, Electric Light The sockets, holders, arms, etc., required for holding or supporting incandescent electric lamps. Fixed Secondary. (See Secondary, Fixed.} Fixtures, Telegraphic A term gen- erally limited to the variously shaped supports provided for the attachment of telegraphic wires. Fixtures, Telegraphic House-Top Telegraphic fixtures placed on the roofs of buildings for the support of the lines. Flaming Discharge. (See Discharge, Flaming?) Flash, Side A sparking or lateral discharge taking place from the sides of a conductor, when an impulsive rush of elec- tricity passes through it. The phenomeno.j of iiue flashing is due to a lateral discharge which takes the alternative path, instead of a path of much smaller ohmic resist- ance. The tendency to side flash result? from the fact that the metallic circuit possesses induct- ance. (See Path, Alternative. Discharge, Lat- eral. Inductance. ) Flashed Carbons. (See Cardans, Flashed.} Flashed Filaments. ( See Filaments t Flashed) Flashes, Auroral Sudden variations in the intensity of the auroral Hjht. Intermittent flashes of auroral light that occur during the prevalence of an aurora. (See Aurora Borealis.} Flashing of Carbons, Process for the (See Carbons, Flashing- Process for.} Flashing of Dynamo-Electric Machine. (See Machine, Dynamo-Electric, Flashing- of.} Flat Cable. (See Cable, Flat.} Flat Duplex Cable. (See Cable, Flat Duplex?) Flat Ring Armature. (See Armature, Flat Ring.} Flats. A name sometimes applied to those parts of commutator segments the surface of which, through wear, has become lower than the other portions. (See Commutator.} Fleming's Gauss. (See Gauss, Flem- ing's.} Fleming's Standard Voltaic Cell. (See Cell, Voltaic, Standard, Fleming's.} Flexible Electric Light Pendant. (See Pendant, Flexible Electric Light.} Flexible Lead. (See Lead, Flexible.} Floating Battery, De la Rive's. (See Battery. Floating, De la Rive's.} Flow. In hydraulics, the quantity of water or other fluid which escapes from an orifice in a containing vessel, or through a pipe, in a given time. Flow-Lines of Escaping Fluid. Lines \vithin the mass of a fluid in motion, drawn at Flo.] 233 [Fly. a number of points, so that the flow at any instant is tangential at such points to the curved path. Flow, Magnetic The magnetic flux. (See Flux, Magnetic!) Flow of Current, Assumed Direction of (See Current, Assumed Direction of Flow of.) Flow of Energy. (See Energy, Flow of) Flow of Lines of Electrostatic Force. (See Force, Electrostatic, Lines of, Assumed Flow of.) Flow of Magnetic Induction. (See In- duction, Magnetic, Flux or Flow of.) Fluid, Depolarizing An electro- lytic fluid in a voltaic cell that prevents polari- zation. (See Cell, Voltaic, Polarization of) Fluid Insulator. (See Insulator, Fluid) Fluoresce. To become self-luminous when exposed to light. A body is said to fluoresce when it shines, by means of the light it produces. In this respect it differs from an illumined body, which shines by reflected light. Fluorescence. A property possessed by certain solid or liquid substances of becoming self-luminous while exposed to light. In fluorescence the refrangibility of rays of light is changed. The invisible rays beyond the violet, the ultra violet, become visible, SD that the light is transformed, the particles absorbing one wave length and emitting another. (See Incan- descence) Canary glass, or glass colored yellow by oxide of uranium, or a solution of sulphate of quinine, possesses fluorescent properties. The path of a pencil of light brought to a focus in either of these substances, or a beam or cone of light passed through them, is rendered visible by the particles lying in this path becoming self-luminous. The path of a beam of light entering the dusty air of a darkened chamber is visible from the light being diffused or scattered in all directions by the float- ing dust particles. In a fluorescent substance, the path of the light is also rendered visible by the particles which lie in its path, throwing out light in all directions. There is, however, this difference, that in the case of the dust particles the light which comes directly from the beam is reflected ; while in the case of the fluorescent body the light comes from the particles themselves, which are set into vibra - tion by the light that is passing through, and has been absorbed by their mass. Fluorescence is, therefore, a variety of phos- phorescence. (See Phosphorescence.) Flnorescent. Possessing the capability of fluorescing. Fluorescing. Exhibiting the property of fluorescence. Flusi Box. (See Box, Flush) Fluviograph. An apparatus for electri- cally registering the varying height of water in a tidal stream or in the ocean ; or, in general, differences of water levels. Flux, Magnetic The number of lines of magnetic force that pass or flow through a magnetic circuit. The total number of lines of magnetic force in any magnetic field. The magnetic flux is also called the magnetic flow. A Committee of the American Institute of Electiical Engineers on " Units and Standards " propose 1 the following as the definition of mag- i.etic flux. " The magnetic flux through a surface bounded by a closed curve is the surface integral of mag- netic induction taken over the bounded surface, and when produced by a current is also equal to the line integral of the vector potential of the cur- rent taken round the boundary." " The uniform and unit time rate of change in flux through a closed electric circuit establishes unit electromotive force in the circuit." Fluxes range in present practical work from loo to 100,000,000 C. G. S. lines, and the working units would perhaps prefix milli- and micro-. Flux of Magnetic Induction. (See In- duction, Magnetic, Flux or Flow of) Flux or Flo'.v of Magnetism. (See Mag- netism, Flux or Flow of) Fly. Electric A wheel or other de- vice driven by the reaction of a convective discharge. (See Flyer, Electric. Convec- tion, Electric) Fly.] 234 [For. z Flyer, Electric A wheel arranged so as to be set into rotation by the escape of convection streams from its points when connected with a charged conductor. A wheel formed of light radial arms P, P, P, etc., shaped as shown in, Fig. 256, and capable of rotation on the vertical axis A, is set into rapid rotation when connected with the prime conduc- tor of a frictional or in- fluence machine, through the convection streams of air particles, which are Fig. 2j6. Electric Flyer. shot off from the points or extremities of the radial arms. The wheel is driven by the reac- tion of these streams in a direction opposite to that of their escape. (See Discharge, Connective. ) Focus. A point in front or back of a lens or mirror, where all the rays of light meet or seem to meet. (See Lens, Achromatic.} Fogr, Electric A dense fog which occurs on rare occasions when there is an unusual quantity of free electricity in the atmosphere. During these electric fogs the free electricity of the atmosphere changes its polarity at frequent intervals. Following Horn of Pole Pieces of Dynamo-Electric Machine. (See Horns, Following, of Pole Pieces of a Dynamo- Electric Machined) Foot-Candle. (See Candle, Foot.} Foot-Pound. A unit of work. (See Work.} The amount of work required to raise I pound vertically through a distance of I foot. The same amount of work, viz., 3 foot-pounds, is done by raising I pound through a vertical distance of 3 feet, or 3 pounds through a verti- cal distance of I foot. Apart from air friction, the amount of work done in raising I pound through I foot, viz., I foot-pound, is the same whether this work be done in one second or in one day. The power, or the rate of doing work, is, however, very dif- ferent in the two cases. (See Power.} Force. Any cause which changes or tends to change the condition of rest or moti the passage of convjc.ive dis- charges, therefore, is due to the following causes: (i.) True ohmic resistance. (2.) Counter electromotive force. Force, Electromotive, Counter, of Mutual Induction The counter electromotive force produced by the mutual induction of the primary and secondary circuits on each other. Force, Electromotive, Counter, of Self- induction That part of the impressed electromotive force which is producing, or which tends to produce, at any instant a change in the current strength. Force, Electromotive, Counter, of Self- induction of the Primary A counter electromotive force produced in the primary circuit of an induction coil by the action thereon of a simple periodic electromotive force. The counter electromotive force produced in the primary circuit of an induction coil by the application of a simple periodic impressed electromotive force to the primary circuit. Force, Electromotive, Counter, of Self- induction of the Secondary A counter electromotive force produced in the secondary by the periodic variations in the effective electromotive force in the secondary. For.] 237 [For. Force, Electromotive, Direct An electromotive force acting in the same direc- tion as another electromotive force already existing. The term d'rect electromotive force is em- ployed in contradistinction to counter electromo- tive force. (See force, Electromotive, Counter. ) Force, Electromotive, Effective The difference between the direct and the counter electromotive force. Force, Electromotive, Effective, of Sec- ondary The difference between the direct and the counter electromotive force in the secondary of an induction coil. Force, Electromotive, Generated by Dy- namo-Electric Machine, Method of Increas- ing The electromotive force of a dy- namo-electric machine may be increased in the following ways, viz : (I.) By increasing its speed of rotation. (2.) By increasing the strength of the magnetic field in which the armature rotates. (3.) By increasing the size of the field through which the armature passes in unit time, the in- tensity remaining the same. (4.) By increasing the number of armature windings, i. e., by making successive parts ot the same wire pass simultaneously through the field. Force, Electromotive, Impressed The electromotive force acting on any cir- cuit to produce a current therein. The impressed electromotive force may be re- garded as producing two parts, viz. : The effective electromotive force and the counter electromotive force. Force, Electromotive, Inductive A term sometimes used in place of counter electromotive force of self-induction. Force, Electromotive, Inverse An electromotive force which acts in the oppo- site direction to another electromotive force already existing. (See Force, Electromotive, Counter.} Force, Electromotive, Motor A term proposed by F. J. Sprague for the coun- ter electromotive force of an electric motor. (See Force, Electromotive, Counter!) This term was propose 1 by Sprague as express- ing the necessity for the existence of a counter electromotive force in an electric motor, in order to permit it to utilize the energy of the electric current which drives it. Force, Electromotive, of Induction The electromotive force developed by any inductive action. In a coil of wire undergoing induction, the value of the induced electromotive force does not depend in any manner on the nature of the ma- terial of which the coil is composed. It has been shown: (I.) That the electromotive force of induction is independent ot the width, thickness or material of the wire windings. (Faraday.) (2.) That it is depende.it on the form of the conductor, and the character of the change it ex- periences as regards the magnetic induction which takes place through it. Since any increase in the strength of a current flowing through a coiled circuii, piuduces a coun- ter electromotive force, which opposes the electro- motive force producing the current, it is clear that the impressed electromotive force must do work against this counter e.ectromotive force all the time the current strength is increasing. The movement of a circuit of a given length through a given field with a given velocity pro- duces the same electromotive force whether the circuit be formed of conducting material or non- conducting material, or consists of an electrolyte. Force, Electromotive, of Secondary or Storage Cell, Time-Fall of A gradual decrease in the potential difference of a stor- age battery observed during the discharge of the same. When a sec mdary or storage battery is first discharged, a slight decrease of its potential dif- ference takes place and a po'ential difference of a slightly decreased valu is m iintained nearly con- stant during a protracted period of dis harge. Force, Electromotive, of Secondary or Storage Cell, Time-Rise of A gradual increase in the potential difference of a secondary or storage cell observed on begin- ning the discharge after a prolonged rest. When a secondary or storage cell is discharged and then given a prolonged rest by opening its circuit, a gradual but decided rise in its potential difference is observed on ajain be^inninj is His- char.'*'. For. 233 [For. Force, Electromotive, Photo An electromotive force produced by the action of light on selenium. (See Cell, Selenium!) Force, Electromotive, Reacting Induc- tive, of the Primary Circuit The back or counter electromotive force produced in the primary circuit by the current set up by in- duction in the secondary. Force, Electromotive, Secondary Im- pressed An electromotive force pro- duced in the secondary coil or circuit by a periodic electromotive force impressed on the primary. Force, Electromotive, Simple-Periodic An electromotive force which varies in such manner as to produce a simple periodic current, or an electromotive force the variations of which can be correctly repre- sented by a simple-periodic curve. Force, Electromotive, Thermo An electromotive force, or difference of potential, produced by differences of temperature acting at thermo-electric junctions. Force, Electromotive, Transverse An electromotive force excited by a mag- netic ield in a substance in which electric displacement is occurring. It is to a transverse electromotive force that the Hall effect is due. (See Effect t Hall.) Force, Electromotive, Zig-zag An electromotive force, the curve of which would have the general form of a zigzag. Force, Electrostatic The force pro- ducing the attractions or repulsions of charged bodies. Force, Electrostatic, Lines of Lines of force produced in the neighborhood of a charged body by the presence of the charge. Lines extending in the direction in which the force of electrostatic attraction or repul- sion acts. An insulated charged conductor produces around it an electrostatic field, in a manner some- what similar to the magnetic field produced by a magnet or an electric current. (See Field, Electrostatic. ) Lines of electrostatic force pass through dielec- trics. Whether the force acts to produce electro- static induction, by means of a polarization of the dielectric, or by means of a tension set up in the substance of the dielectric, is not known. Force, Electrostatic, Lines of, Assumed Flow of A mathematical conception in which the phenomena of electricity are com- pared with the similar phenomena of heat. In heat no flow of heat occurs over isothermal surfaces, or surfaces at the same temperature. Between different isothermal surfaces, the flow will vary with the power of heat conduction. In electricity, no flow occurs over equipotential sur- faces. Specific inductive capacity corresponds to heat conductivity, and the lines of force to the lines of heat conduction. (See Capacity, Specific Inductive.) Force, Lines of, Contraction of A decrease that occurs in the length of the circular lines of force that surround a circuit through which an electric current is passing, while the current is decreasing in intensity or strength. The contraction or decrease in the average diameter of the circular lines of force of an elec- tric circuit is similar to the expansion or growth of lines of force, excepting that the movement is one of decrease in diameter, and takes place in the opposite direction, *. e., towards the circuit, instead of away from it. (See Force, Lines of, Growth or Expansion of. ) Force, Lines of, Cutting Passing a conductor through lines of magnetic force, so as to cut or intersect them. The cutting of lines of magnetic force produces differences of potential. This is true whether the conductor moves through a stationary field or whether the field itself moves through the stationary conductor, so that the lines of force and the conductor cut one another. This cut. ing is mutual. Each line of force cuts and is cut by the circuit Since all lines of force form closed-cir- cuits or paths, the cutting of the circuit by the lines of force, or the reverse, forms a link or chain, and the cutting takes place at the moment of linking or unlinking, *. e., of cutting. Force, Lines of, Diffusion of The deflection of the lines of magnetic force from For.] 239 [For. their ordinary position, between the poles that produce them. Force, Lines of, Direction of The direction in which it is assumed that the lines of magnetic force pass. It is generally agreed to consider the lines of magnetic force as coming out of the north pole of a magnet and passing into its south pole, as shown in Fig. 257. Fig-. 257. Direction of Lines of Force. This is sometimes called the positive direction of the lines of force and agrees in general with the direction in which the electric current is assumed to flow, which is from the positive to the nega- tive. That is to say, the lines of magnetic force are assumed to flow or pass out of the north pole and into the south pole of a magnet. Of course there is no direct evidence of any flow, or of any particular direction characterizing the lines of force. (See /? the number of lamps they guard. Fig. 263. Safety Fuse. Since incandescent lamps are generally placed in the circuit in multiple- arc, or in multiple-series, one or more of the circuits can be opened by the fusion of the plug without interfering with the continuity of the rest of the circuits. In series circuits, however, such as arc-light circuits, when a lamp is cut out, a short circuit or path around it must be provided in order to avoid the extin- guishing of the rest of the lights. Fuse Wire. (See Wire, Fuse.) Fusible Plug. A term commonly applied to a safety plug. (See Fuse, Safety G Gains. The spaces cut in the faces of telegraph poles for the support or placing of the cross arms. Galvanic Battery. (See Battery, Gal- vanic?) Galvanic Cell. (See Cell, Voltaic:) Galvanic Circle. (See Circle, Galvanic.) Galvanic Circuit (See Circuit, Gal- vanic?) Galvanic Dosage. (See Dosage, Gal- vanic?) Galvanic Electricity. (See Electricity r Galvanic?) Galvanic Excitability of Nerve or Mus- cular Fibre. (See Excitability, Electric, of Nerve or Muscular Fibre?) Galvanic Irritability. (See Irritability y Galvanic?) Gal.] 245 [Gal. Galvanic Multiplier. (See Multiplier, Galvanic?) Galvanic Polarization. (See Polariza- tion, Galvanic.} Galvanic Taste. (See Taste, Galvanic^ Galvanism. A term sometimes employed to express the effects produced by voltaic electricity. Galvanization, Central A variety of general galvanization in which the kathode is placed on the epigastrium and the anode moved over the body. Galvanization, Electro-Metallurgical The process of covering any conduc- tive surface with a metallic coating by elec- trolytic deposition, such, for example, as the thin copper coating deposited on the carbon pencils or electrodes used in systems of arc lighting. The term is borrowed from the French, in which it has the above signification. It is prefer- ably replaced by the term electro-plating. (See Plating, Electro.} The term galvanization is never correctly ap- plied to the process for covering iron with zinc or other metal by dipping the same in a bath of molten metal. Galvanization, Electro-Therapeutical In electro-therapeutics, the effects produced on nervous or muscular tissue by the passage of a voltaic current. Galvanization, General A method of applying a current therapeutically by the use of electrodes of sufficient size to direct the current through practically the entire body. Galvanization, Labile A term employed in electro-therapeutics, in contradis- tinction to stabile galvanization, to designate the method of applying the current by keep- ing one electrode at rest in firm contact with one part of the body, and connecting the other electrode to a sponge which is moved over the parts of the body that are to be treated. Galvanization, Local The applica- tion of galvanization to parts or organs of the body in contradistinction to general galvani- zation. Galvanization, Stabile A term employed in electro-therapeutics in which the current is caused to pass continuously and steadily through the portions of the body un- dergoing galvanization. In stabile galvanization, the current is applied to and removed from the body gradually, in order to avoid shocks at the beginning and end of the application. Galvanized Iron. (See Iron, Galvan- ized.} Galvano. A word sometimes used in France in place of the word electro, to signify an article reproduced in copper by electro- metallurgy, especially an electrotype or wood- cut. Galvano-Causty. (See Causty, Galvano.} Galvano-Cautery. (See Cautery, Gal- vano.} Galvano-Cautery, Chemical A term sometimes applied to electro puncture or the application of electrolysis to the treat- ment of diseased growths. (See Cautery, Electric. Puncture, Electro.} The term chemical galvano-cautery would ap- pear to be poorly chosen, as it would imply the existence of a cautery action, which in point of fact does not exist Galvano-Faradization. In electro-thera- peutics, the simultaneous excitation of a nerve or muscle by both a voltaic and a faradic cur- rent. Galvano-Magnet. A term sometimes used for electro-magnetic. Electro magnetic is by far the preferable term, and is almost universally employed in the United States. Galvanometer. An apparatus for meas- uring the strength of an electric current by the deflection of a magnetic needle. The galvanometer depends for its operation on the fact that a conductor, through which an elec- tric current is flowing, will deflect a magnetic needle placed near it. This deflection is due to the magnetic field caused by the current. (See Field, Magnetic, of an Electric Current.) This action of the current was first discovered by Oersted. A wire conveying a current in the Gal.] 246 [Gal. direction shown by the straight arrow, Fig. 264, or from + to , will deflect a magnetic needle in the direction shown by the curved arrows. The following rules show the direction of the Fig. 264. Oersted's Experiment. deflection of a magnetic pole by an electrical cur- rent : (i.) Place the right hand on the conductor through which the current is flowing, with the palm facing the north pole, and with the fingers pointing in the direction of the current. The thumb will indicate the direction in which the north pole tends to move. (2.) Suppose an ordinary corkscrew so placed along the conductor, through which a current of electricity is passing, that when twisted, it will move in the direction of the current. The han- dle will then turn in the direction in which the north pole of the magnet tends to move. (3.) Imagine one swimming along the con- ductor in the direction of the current and facing the magnet. The north pole will tend to move towards the left hand of the swimmer. Prof. Forbes has shown that the direction of the deflection of a magnet by a current is such A 8 C Fig. 26j. Amp'kre's Apparatus. that if the magnet were flexible, it would wrap itself round the current. If the wire be bent in the form of a hollow rec- tangle F, D, E, G, Fig. 265, and the needle, M, be placed inside the circuit, the upper and lower branches of the current will deflect the needle in the same direction, and the effect of the current will thus be multiplied. Mercury cups are pro- vided at A, B and C, for a ready change in the direction of the current. (See Needle, Astatic.') This principle of the multiplication of the de- flecting power of a current was first applied to gal- vanometers by Schweigger, who used a number of turns of insulated wire for the purpose of obtain- ing a greater deflection of the needle. He called such a device a multiplier. In extremely sensi- tive galvanometers, very many turns of wire are employed, in some cases amounting to many thousands. Such galvanometers are of high re- sistance. Others, of low resistance, often con- sist of a single turn of wire and are used in the direct measurement of large currents. A Schweigger's multiplier or coil C, C, of many turns of insulated wire, is shown in Fig. 266. The action of such a coil on the needle M, is com- paratively great, even when the current is small. Fig. at) 6. Schweigger's Multiplier. In the case of any galvanometer, when no cur- rent is passing, the needle, when at rest, should in general occupy a position parallel to the plane of the coil. On the passage of the current, the needle tends to place itself in a position at right angles to the direction of the current, or to the length of the conducting wire in the coil. The strength of the current passing is determined by observing the amount of this deflection as meas- ured in degrees on a graduated circle over which the needle moves. The needle is deflected by the current from a position of rest, either in the earth's magnetic field or in a field obtained from a permanent or an electro magnet In the first case, when in use to measure a current, the plane of the galvanom- eter coils must coincide with the planes of the magnetic meridian. In the other case, the instru- Gal.] 247 [Gal. merit may be used in any position in which the needle is free to move. Galvanometers assume a variety of forms ac- cording either to the purposes for which they are employed, or to the manner in which their deflec- tions are valued. Galvanometer, Absolute A galva- nometer whose constant can. be calculated with an absolute calibration. (See Calibra- tion, Absolute?) Such a galvanometer is called absolute because if the dimensions of its coil and needle are known, the current can be determined directly from the observed deflection of the needle. Galvanometer, Aperiodic A gal- vanometer the needle of which comes to its position without any oscillation. A dead-beat galvanometer. (See Galva- nometer, Dead-Beat.) Galvanometer, Astatic A galva- nometer, the needle of which is astatic. (See Needle, Astatic.) Nobili's astatic galvanometer is shown in Fig. 267. The astatic needle, suspended by a fibre b, has its lower needle placed inside a coil, a, con- sisting of many turns of insulated wire, its upper needle moving over the graduated dial. The cur- rent to be measured is led into and from the coil at the binding posts, x and y. Fig. 267. Astatic Galvanometer. In this instrument, if small deflections only are employed, the deflections are sensibly propor- tional to the strength of the deflecting currents. Galvanometer, Ballistic A galva- nometer designed to measure the strength of currents that last but for a moment, such, for example, as the current caused by the dis- charge of a condenser. The quantity of electricity passing in any cir- cuit is equal to the current multiplied by the time. Since the current caused by the discharge of a condenser lasts but for a small time, during which it passes from zero to a maximum and back again to zero, the magnetic needle in a ballistic galva- nometer takes the form of a ballistic pendulum, *". *., it is given such a mass, and acquires such a slow motion, that its change of position does not Fig. 268. Ballistic Galvanometer. practically begin until the impulses have ceased to act. In the ballistic galvanometer of Siemens and Halske, the coils R, R, Fig. 268, have a bell- shaped magnet, M, suspended inside them by means cf an aluminium wire. The magnet is pro- vided with a mirror S, for measuring the deflec- tions. The bell-shaped magnet is shown in ele- vation at M, and in plane at n, s. In using the ballistic galvanometer, it is neces- sary to see that the needle is absolutely at rest be- fore the charge is sent through the coils. A form of ballistic galvanometer by Nalder is shown in Fig. 269. The ordinary form of compensating magnet is, in this galvanometer, replaced by the small mag- net A, capable of rotation in a horizontal plane, but incapable of being raised or lowered, as is usual in such magnets. This form of compensating mag- net possesses the advantage of being able to alter the direction of the field on the needle system, Gal.] 248 [Gal. without considerably altering its intensity. When the galvanometer is for ready use the magnet A, is turned until the needle is brought to zero. The Fig. 269. Nalder's combined field of earth and magnet A, are then brought to the degree of sensitiveness required Fig. 270. Nalder s Galvanometer. by rotating magnet B, on its shaft, or altering its distance from the needle. In order to insure ease in replacing the fibre, the front coil is hinged as shown. The fibre D, is supported on E, one end of which it is free to turn, so as to permit of the removal of torsion; D, being twisted can be raised or lowered at E. The needle system with heavy bell-shaped magnet is shown in Fig. 270. Galvanometer, Combined Tangent and Sine A galvanometer furnished with two magnetic needles of different lengths. The small needle is used for tangent measure- ments, and the long needle for sine measure- ments. Galvanometer Constant. (See Constant, Galvanometer.) Galvanometer, Dead-Beat A gal- vanometer, the needle of which comes quickly to rest, instead of swinging repeatedly to-and- fro. (See Damping?) Galvanometer, Deprez-D'Arsonval A form of dead-beat galvanometer. The movable part of the Deprez-D'Arsonval galvanometer consists of a light rectangular coil C, Fig. 271, of many turns of wire, supported by two silver wires H J and D E, between the poles of a strong permanent horseshoe magnet A A. The position of the coil may be altered as to height by screws at H and E. The sup- porting wires, prevent by their torsion the swinging of the coil, as does also the cylinder of soft iron B, placed inside the coil, and sup - ported independently of it. The movements if of the coil are observed by means of a spot of light reflected from a mirror J, attached to & 271- Deprez-D" Arson- the Wire H J. l Galvanometer. Galvanometer, Detector A form of galvanometer employed for rough testing work. A form of detector galvanometer is shown in Fig. 272. Fig. 27 3. Detector Galvanometer. Galvanometer, Differential A gal- vanometer containing two coils so wound as to tend to deflect the needle in opposite directions. The needle of a differential galvanometer shows no deflection when two equal currents are sent through the coils in opposite directions, since, under these conditions, each coil neutralizes the other's effects. Such instruments may be used in comparing resistances. The Wheatstone Bridge, however, in most cases, affords a prefer- able method for such purposes. (See Bridge, Electric.') Gal.] 249 [Gal. A form of differential galvanometer is shown in Fig. 273. Sometimes the current is so sent through the two coils, that each coil deflects the nee- dle in the same di- rection. In this case the instrument is no longer differential in action. , : If the magnetic needle, in such cases, is suspended at the exact centre of the line which joins the centres of the coils, the advantage is gained by obtaining a field of more nearly uniform intensity Fig.2 73 . DtferentialGalva- around the needle. Galvanometer, Figure of Merit of The reciprocal of the current required to pro- duce a deflection of the galvanometer needle through one degree of the scale. The smaller the current required to produce a deflection of one degree, the greater the figure of merit, or the greater the sensitiveness of the galvanometer. Galvanometer, Marine A galva- nometer devised by Sir William Thomson for use on steamships where the motion of mag- netized masses of iron would seriously disturb the needles of ordinary instruments. An unscreened needle would be so much af- fected by the motion of the engines, the shaft and the screw, as to be useless for galvanometric measurement. The needle of the marine galvanometer is shielded or cut off from the extraneous fields so produced, by the use of a magnetic screen or shield, consisting of an iron box with thick sides, inside of which the instrument is placed. The needle is suspended by means of a silk fibre attached both above and below, in line with the centre of gravity of the needle. In this man- ner, the oscillations of the ship do not affect the needle. Galvanometer, Mirror A galva- nometer in which, instead of reading the de- flections of the needle directly by its move- ments over a graduated circle, they are read by the movements of a spot of light reflected from a mirror attached to the needle. This spot of light moves over a graduated scale, or its movements are observed by means oi a telescope. fr'ig. 274. Mirror Galvanometer. A form of mirror galvanometer designed by Sir William Thomson is shown in Fig. 274. The needle is attached directly to the back of a light, silvered glass mirror, and consists of several small magnets made of pieces of a watch spring. The needle and mirror are suspended by a single silk fibre and are placed inside the coil. A compen- sating magnet N S, movable on a vertical axis, is used to vary the sensitiveness of the instrument. The lamp L, placed back of a slot in a wide screen, throws a pencil of light on the mirror Q, from which it is reflected to the scale K. A form of lamp and scale with slot for light is shown in Fig. 275. Fig. 273. Galvanometer Lamp and Scale. Galvanometer, Potential A term sometimes applied to a voltmeter. (See Voltmeter.) Galvanometer, Reflecting A term sometimes applied to a mirror galvanometer. (See Galvanometer, Mirror.) Gal.] 250 [Gal. Galvanometer, Sensibility of The readiness and extent to which the needle of a galvanometer responds to the passage of an electric current through its coils. (See Gal- vanometer.} Galranometer-Shnnt. (See Shunt, Gal- vanometer?) Galvanometer, Sine A galva- nometer in which a vertical coil is movable around a vertical axis, so that it can be made to follow the magnetic needle in its deflections. In the sine galvanometer, the coil is moved so as to follow the needle until it is parallel with the coil. Under these circumstances, the strength of the deflecting currents in any two different cases is proportional to the sines of the angles of deflection. A form of sine galvanometer is shown in Fig. 276. The vertical wire coil is seen at M. A needle of any length less than the diameter of the coil M, moves over the graduated circle N. The coil M, is movable over the graduated horizontal circle H, by which the amount of the movement Fig. 276. Sine Galvanometer. necessary to bring the needle to zero is measured. The current strength is proportional to the sine of the angle measured on this circle, through which it is necessary to move the coil M, from its position when the needle is at rest in the plane of the earth's magnetic meridian, until the needle is not further deflected by the current, although parallel to the coil M. Galvanometer, Tangent An instru- ment in which the deflecting coil consists of a coil of wire within which is placed a needle very short in proportion to the diameter of the coil, and supported at the centre of the coil. Fig. 277. Tangent Galvanometer. A galvanometer acts as a tangent galvanometer only when the needle is very small as compared with the diameter of the coil. The length of the needle should be less than one-twelfth the diameter of the coil. A form of tangent galvanometer is shown in Fig. 277. The needle is supported at the exact centre of the coil C. Under these circumstances, the strengths of two different deflecting currents are proportional to the tangents of the angles of deflection. Tan- gent galvanometers are sometimes made with coils of wire containing many separate turns. Galvanometer, Tangent, Obach's A form of galvanometer in which the deflect- ing coil, instead of being in a fixed vertical position, is movable about a horizontal axis, so as to decrease the delicacy of the instru- ment, and thus increase its range of work. Galvanometer, Torsion A galva- nometer in which the strength of the deflecting current is measured by the torsion exerted on the suspension system. A ball-shaped magnet, shown at the right of Fig. 278, is suspended by a thread and spiral Gal.] 251 [Gal. spring between two coils of high resistance, placed parallel to each other in the positions shown. On the deflection of the magnet, by the current to be measured, the strength of the current is determined by the amount of the torsion re- quired to bring the magnet back to its zero point. Pig. 278. 'lorsion The angle of torsion is measured on the horizontal scale at the top of the instrument. In the torsion galvanometer, unlike the electro- dynamometer, the action between the coils and the movable magnet is as the current strength causing the deflection. In the electro-dynamometer, since an increase of current in the deflecting coils also takes place in the deflected coil, the mutual action of the two is as the square of the current strength causing the deflection. Galvanometer, Upright A gal- vanometer, the needle of which moves in a vertical plane. (See Galvanometer, Ver- tical. Galvanometer, Vertical A gal- vanometer the needle of which is capable of motion in a vertical plane only. In the vertical galvanometer, the north pole of the needle is weighted so that the needle as- sumes a vertical position when no current is pass- ing. In the form shown in Fig. 279, two needles Fig. 219. are sometimes employed, one of which is placed inside the coils C, C. The vertical galvanometer is not as sensitive as the ordinary forms. It is employed, however^ in various forms for an electric current indica- tor, or even for a rough current meas- urer. Galvanometer Voltmeter. An in- strument devised by Sir William Thom- son, for the meas- urement of differ- ences of electric potential. This instrument is so arranged that by a single correction for the varying strength of the earth's field in any place, the results are read at once in volts. A coil of insulated wire shown at A, Fig. 280, has a resistance of over 5,000 ohms. A magnetic needle, formed of short parallel needles placed above one another, and called a magnetometer needle, is attached to a long but light aluminium index, moving over a graduated scale. A mova- ble, semi-circular magnet B, called the restoring magnet, is placed over the needle, and is used for varying the effect of the earth's field at any point. The sensitiveness of the instrument may be varied either by the restoring magnet or by sliding the magnetometer box nearer to or further away from the coil. The voltmeter galvanometer depends for its operation on the fact that when a galvanometer of sufficiently high resistance is introduced be- Fig. 280. Galv.inometer Voltmeter. tween any two points in a circuit, the current that passes through it, and hence the deflection of its needle, is directly proportional to the difference of potential between such two points. UaL] 252 [Gas. Galvanometers for the commercial measure- ments of currents assume a variety of forms. They are generally so constructed as to read off the amperes, volts, ohms, watts, etc., directly. They are called amperemeters or ammeters, volt- meters, ohmmeters, wattmeters, etc. For their fuller description reference should be had to standard works on electrical measurement. Galvanometric. Of or pertaining to the galvanometer. (See Galvanometer!) Galvanometrical. Of or pertaining to the galvanometer. (See Galvanometer.} GalYanoinetrically. In a galvanometric manner. Galvano-Plastics. (See Plastics, Gal- vano) Galranoplasty. The art of galvano- plastics. (See Plastics, Galvano) Galyano-Puncture. (See Puncture, Gal- vano) Galyauoscope. A term sometimes im- properly employed in place of galvanometer. A galvanoscope, strictly speaking, is an instru- ment intended rather to show the exis ence of an electric current than to measure it in degrees. It may, however, be roughly calibrated, and then it differs from a galvanometer only in delicacy and accuracy. GalYano-Therapeutics. A term some- times used for electro-therapeutics. Electro- therapeutics is by far the preferable term and is almost universally employed in the United States. Gap, Air A gap, or opening in a magnetic circuit containing air only. (See Gap, Air, Magnetic!) The air gap between two magnetic poles may be regarded as the space in which an armature acting as a magneto receptive device is placed, which by the action upon it of the lines of mag- netic force passing through the gap has differ- ences of potential generated in its coils of insulated wire. Gap, Air, Magnetic A gap filled with air which exists in the opening at any part of a core of iron or other medium of high permeability. The space between the pole pieces and arma- ture core is called the air gap in dynamos or motors even though partly filled with copper con- ductors. It is also called the interference space. The gap or air space of an electro-magnet de- creases the strength of its magnetization be- cause The increased reluctance of the air gap causes a decrease in the number of lines of magnetic force which pass through the magnetic circuit. Gap, Spark A gap forming part of a circuit between two opposing conductors, separated by air, or other similar dielectric which is closed by the formation of a spark only when a certain difference of potential is attained. Gap, Wire-Gauge - (See Gauge, Wire, Gap.) Gas-Battery. (See Battery, Gas.) Gas Burner, Argand, Plain-Pendant, Electric (See Burner, Argand Electric, Plain- Pendant) Gas Burner, Argand, Ratchet-Pendant, Electric (See Burner, Argand Elec- tric, Ratchet-Pendant) Gas Burner, Automatic Electric (See. -Burner, Automatic Electric) Gas Burner, Plain-Pendant, Electric (See Burner, Plain-Pendant Elec- tric) Gas Burner, Ratchet-Pendant, Electric (See Burner, Ratchet-Pendant Elec- tric) Gas, Carbonic Acid A gaseous sub- stance formed by the union of one atom of carbon with two atoms of oxygen. Carbonic acid gas is formed during the com- bustion of carbon by a sufficient supply of air. Gas, Dielectric Density of A term sometimes emploved instead of dielectric strength of gas. (See Gas, Dielectric Strength of) Gas, Dielectric Strength of The strain a gas is capable of bearing without suffering disruption, or without permitting a disruptive discharge to nass through it. The dielectric strength of a gas depends (I.) On the nature of the gas. (2.) On its pressure. 253 l.uu. It has been calculated roughly that it requires 40,000 volts per centimetre to pas? a disruptive discharge through dry air at ordinary pressures. Gas-Jet, Carcel Standard (See Car eel Standard Gas- yet.) Gas-Jet Photometer. (See Photometer.) Gas-Lighting, Electric The electric ignition of a gas-jet from a distance. Gas-Lighting, Multiple Electric A system of electric gas-lighting in which a number of gas-jets are lighted by means of a discharge of high electromotive force, derived from a Ruhmkorff coil or a static induction machine. Such devices are operated by means of minute electric sparks which are .caused to pass through the escaping gas-jets. The spark for this pur- pose is obtained either by means of the extra current from a spark coil, by means of an induction coil or by static discharges. (See Currents, Extra. Coil, Spark Coil, Induction.) A gas tip for use in multiple gas-lighting ap- paratus is shown in Fig. 281. The spark is formed immediately over the slot in the burner, and therefore ignites the escaping gas. Gas, Occlusion of The absorption or shutting up of a gas in the pores, or on the surfaces of various substances. Carbon possesses in a marked degree the prop- erty of occluding or absorbing gases in its pores. These occluded gases must be driven out from the carbon conductor employed in an incandescent lamp, since otherwise their expulsion , on the in- candesence of the carbon, consequent on the light- ing of the lamp, will destroy the high vacuum of the lamp chamber and thus lead to the ultimate destruction of the filament (See Lamp, Electric, Incandescent. ) Gassing. The evolution of gas from the plates of a storage or secondary cell. Gastroscope. An electric apparatus for the illumination and inspection of the human stomach. Fig. 281. Midtiple Gas- jet. The light is obtained by means of a platinum spiral in a glass tube surrounded by a layer of water to prevent undue heating. The platinum spiral is placed at the extremities of a tube, pro- vided with prisms, and passed into the stomach of the patient. A separate tube for the supply of air for the extension of the stomach is also provided. Gastroscopy. The examination of the stomach by the gastroscope. (See Gastro- scope^) Gauge, Battery. A form of portable gal- vanometer, suitable for ordinary testing work. A form of battery gauge is shown in Fig. 282. Fig. 282. Battery Gauge. Gauge, Electrometer A device em- ployed in connection with some of Sir Wil- liam Thomson's electrometers to ascertain whether the needle, connected with the layer of acid that acts as the inner coating of the Leyden jar used in connection therewith, is at its normal potential. Gauge, Wire, American A name sometimes applied to the Brown & Sharpe Wire Gauge. (See Gauges, Wire, Varieties of.) Gauge, Wire, Birmingham A term sometimes applied to one of the English wire gauges. Gauge, Wire, Gap A wire gauge in which gaps are left for the introduction of the wire to be measured. Gau.] 254 [Gau. Gauge, Wire, Micrometer A gauge employed for accurately measuring the di- ameter of a wire in thousandths of an inch, based on the principle of the vernier or mi- crometer. (See Fig. 283.) The wire to be measured is placed between a fixed support B, and the end C, of a long mova- ble screw, which accurately fits a threaded tube a. A thimble D, provided with a milled head, fits over the screw C, and is attached to the upper part. The lower circumference of D, is divided into a sca'e of twenty equal parts. The tube A,is graduated into divisions equal to the pitch of the screw. Every fifth of these divisions is marked as a larger division. The principle of the operation of the gauge is as follows: Suppose the screw has fifty threads to the inch, the pitch of the screw, or the distance between two contiguous threads, is therefore ^ or .02 of an inch. One complete turn of the screw will, .therefore, advance the sleeve D, over the scale a, the .02 of an inch. If the screw is only moved through one of the twenty parts marked on the end of the thimble or sleeve parts, or the -^ of a com- plete turn, the end C, advances towards B, the *V f *V> * *> Trnnr or 01 incn - Suppose now a wire is placed between B and C, and the screw advanced until it fairly fills the: Fig. 283. Vernier Wire Gauge. space between them, and the reading shows two of the larger divisions on the scale a, three of the smaller ones and three on the end of the sleeve D, then Two large divisions of scale a = .2 inch- Three smaller divisions of scale a.. = .06 " Three divisions on circular scale onD = .003 " Diameter of wire .263 Serious inconvenience has arisen in practice* NEW LEGAL STANDARD WIRE GAUGE (ENGLISH). Tables of Sizes, Weights, Lengths and Breaking Strains of Iron Wire. Size 01 Wire Gaugt Diameter. i Sectional area in sq. inches. Weight of Length of Cwt. Breaking Strains. Size on Wire Gauge. > Inch. Millimetres. too yards. Mile. Annealed. Bright. Lbs. Lbs. Yards. Lbs. Lbs. $:::: .500 .464 ii^ !i69? 8: 3404 2930 67 9017 15700 13525 VS. 432 .400 n. 10.2 .1257 44. 23- 2541 2179 9 1 78,4 6702 11725 10052 $ 3/0. 2/0. 37 .348 ti .1087 .0951 07. 93- 1885 1649 5796 5072 8694 7608 3/o 2/0 I/O. 324 8.2 .0824 81 . 1429 38 4397 6595 I/O I. .300 7.6 .0707 69. 1225 01 3770 S^SS I 2. .276 7- .0598 58. 1037 90 3190 4785 2 3- .252 6.4 .0499 49- 864 228 260 2660 3 5- .212 5-4 0353 34- 732 612 209 322 1883 4 5 6. .192 4-9 .0290 28. 502 393 1544 - 6 7- .176 4-5 .0243 4- 422 47 1298 1946 7 8. .160 4.1 9 3*8 566 1072 1608 8 9- .144 3-7 .'0163 6. 282 700 869 1303 9 10. .128 3-3 .0129 2. 223 882 687 1030 10 n. .116 3- .0106 O. '83 1077 845 i 12. .104 2.6 .0085 8. 148 1333 454 680 2 13. .002 2-3 .0066 6. 114 1723 355 532 3 14. .080 2. .0050 5- 88 2240 268 402 4 15. .072 1.8 .0041 4- 7 2800 218 326 5 16. .064 1.6 .0032 3- 56 3500 172 257 6- '7- .056 1.4 .0025 42 4667 '3 1 197 7 18. .048 1.2 .0018 i .8 3 2 6222 97 H5 8 19. OfO I. .0013 I .2 9333 67 100 9 20. . .036 d .0010 I. 18 II200 55 82 20- (Issued by the Iron and Steel Wire Manufacturers' Association.) Gau.] 255 from the numerous arbitrary numbers of sizes of wires employed by different manufacturers. These differences are gradually leading to the abandonment of arbitrary sizes for wires and em- ploying in place thereof the diameters directly in inches or thousandths of an inch. Gauge, Wire, Round A device for accurately measuring the diameter of a wire. The round wire gauge shown in Fig. 284 is very generally used for telegraph lines. Notches Fig. 284.. Round Wire Gauge. for varying widths, cut in the edges of a circular plate of tempered steel, serve to approximately measure the diameter of a wire, the sides of the wire being passed through the slots. Numbers, indicating the different sizes of the wire, are affixed to each of the openings. Gauge, Wire, Self- Registering A wire gauge arranged to give the exact di- ameter of the wire to be measured directly without calculation. A form of self, register- ing wire gauge is shown in Fig. 285. The wire or plate is inserted in the gap between a fixed and Fig 285. Wire and a movable plate. The Flat* Gauge. numbers corresponding to the diameter of the wire or plate are shown on one side of the gauge and the gauge numbers on the other side. Gauge, Wire, Standard A wire gauge adopted by the National Telephone Exchange Association at Providence, R. I., and by the National Electric Light As- sociation, at Baltimore, Md., in February, 1886. The value of the standard as compared with the other gauges will be seen from an inspection of the table in this column: Gauges, Wire, Tarieties of The following table gives a comparison of the principal wire gauges in use. COMPARISON OF THE DIFFERENT WIRE GAUGES. ii American or Brown & Sharpe. Birmingham, j or Stubs. Washburn & II Moen Mfg. Co.. Worces- t*r, Mass. Trenton Iron Co., Trenton, N.J. |j Old English || from Brass Mfrs.' List. |l 000000 .46 00000 43 45 oooo .46 454 4 .400 000 .40964 425 .362 36 372 00 .3648 38 33' 33 .348 32495 34 307 35 .324 .2893 .3 .283 .285 .300 .25763 .58 4 .263 .265 .276 .22942 259 .244 245 .252 .20431 .238 .225 .225 .232 .,8,94 .22 .207 .205 .16202 .203 .192 .19 .,92 .14428 ..8 .,77 75 .176 . 12849 .165 .162 . 6 .160 "443 ,, 4 8 .148 45 '44 .,0,89 134 '35 .128 .090742 .,2 '75 .1,6 .080808 109 . ,05 .,04 07,961 .09 .092 0925 .002 .064084 .08 .08 08 .080 .083 .057068 .07 .072 .07 .072 .072 .05082 .06 .063 .061 .064 .065 .04525- .05 .052 0525 .056 .040303 .04 .047 .045 .048 049 .035390 .04 .041 039 .040 .04 .03,961 .03 035 034 036 03S .028462 3 .032 0315 025-347 .02 .028 .27 !28 .0295 0225;, .02 < 2 5 .024 .024 .027 O2OI .02 .023 .02,5 .022 .025 o 79 01594 .02 .02 .0 8 ;. .020 .023 27 0,4,95 .01 .0 7 017 .0 64 .01875 28 0,2641 .O, 48 .0165 29 0,1257 .0, o 5 o 5 .036 0,55 30 .0,0025 .01 .0 4 o 4 .0 24 "375 31 .008928 .01 .0 35 o 3 .0 16 .0,225 3 2 00705 .009 .0 3 2 .0,08 .0,125 33 .00708 .008 .0 I .Oil .0100 34 .006304 .007 .0 .01 .0092 .0095 35 .005614 .005 .0095 .009 .0084 .009 36 .005 .004 .009 .col .0076 .0075 37 .004453 .0085 .00725 .0068 .0065 38 .003965 .008 .0065 .006 00575 39 003531 .0075 .00575 .005"* .005 40 003144 .007 .005 .0048 .0045 256 [Gau. NUMBER, DIAMETER, WEIGHT, LENGTH AND RESISTANCE OF PURE COPPER WIRE. American Gauge. No. Diameter. Inches. Weight, sp. gr. = 8.889. Length. Resistance of Pure Copper at 70 Fahrenheit. Grs. per it. Lbs.per 1.000 Ft. per Ib. Ohms per 1,000 ft. Feet per ohm. Ohms per Ib. 0000... .46000 4475-33 640.40 1.56 .051 19605.69 .0000798 000. . 496| 3549-07 107.01 1.97 .064 I5547.87 .000127 00. . .36480 2814.62 4.2.09 2.49 .081 12330.36 .000202 0. . .32486 2-03.28 319.04 3-'3 .102 9783.63 .000320 I. . 2. . .28930 25763 1770.13 1403.79 252.88 200.54 3-95 4-99 :35 7754.66 6.49.78 .0005. .ojoSi. 3- .22942 1113.20 i59- 3 6.29 .205 4876.73 .001289 4- .20431 882.85 1,6.12 7 93 259 3867.62 .00205 5. .18.94 700. 10 JOO.OI 10.00 .326 3067.06 .00326 6. . . 16202 555- o '79-32 12. 6l .411 2432.22 .00518 t: :3C 440.27 349.18 62.90 49.88 15.90 20.05 519 654 .928.75 .529.69 .00824 .0.311 9. . .11443 270.94 39-56 25.28 .824 1213.22 .02083 10. . .10190 2'9-57 31-37 31.88 1.040 961.91 03314 I. . .09074 J74-'5 24.88 40.20 i .311 762.93 .05269 .'. . . .08081 138-11 19-73 50.69 1.653 605.03 .08377 3... .07x96 109.52 15.65 63.91 2.084 479.80 .13321 4... .06408 86.86 12.41 80.59 2.628 380.5. .21.8 I::: .05707 .05082 68.88 54-63 9.84 7.8, 10.. 63 128.14 3-3*4 4.179 301-75 239-32 .3368 5355 7... .04525 43-3* 6., 9 161 59 5.269 189.78 .8515 8 .. .04030 34-35 4.91 203.76 6-645 150.50 *-3539 9... .03589 26 49 3-78 264.26 8.617 116.05 2.2772 o .. .'3196 21. 6l 3.09 324.00 io.;66 94-65 3-423 i . . .0-846 17-13 2.45 408.56 '3-323 75.06 5,443 2 .. 025347 13-59 1.94 S'S-'S 16.799 59-53 8.654 3 .022572 10.77 1.54 649.66 21.185 47-20 13-763 4 8. 54 819.21 26.713 37-43 2.. 88 S 5 .0179 6.78 97 1032.96 3368 4 29.69 34-795 6 .. .01594 5-37 77 13 2.61 42.477 23-54 55-331 7... .014195 4.26 .61 1042.55 53-563 .8.68 87-979 8... .012641 3-38 .48 2071.22 67-542 14.81 139.893 9... .011258 2.68 38 2'.. I. 82 8 S . 17 o 11.74 222.449 0... .010025 2.13 30 3293-97 107.391 9 . 3 t 353-742 ; . . . . .008928 1.69 .24 4152.22 '35-402 7-39 562.221 2.. . 33- .00795 .0070^ :$ .19 !5 5236.66 660.271 170.765 215.312 5-86 4.64 894.242 1421.646 34... .0063 .84 .12 8328.30 271-583 3.68 2261.82 35- . .00561 67 .id 10501.35 342-4'3 2.92 3596.104 36... 37- .00445 S3 42 .08 .06 132*8.83 16691.06 43 I -7 544.287 IX 57I5-36 9084.71 3 8... 003965 34 .05 * 20854.65 686.511 1.46 14320.26 39- .003531 27 .04 26302.23 865.046 1.16 22752.6 40... 003144 .21 03 33'75-94 .091.865 92 36223.59 Gauss. The unit of intensity of magnetic field. The term gauss for unit of intensity of mag- netic field was proposed by S. P. Thompson as being that of a field whose intensity is equal to 108 C. G. S. units, that is, io lines of force per square centimetre. J. A. Fleming proposes, for the value of the gauss, such strength of field as would develop an electromotive force of one volt in a wire one million centimetres in length, moving through such a field with unit velocity. Fleming's value for the gauss was assumed on account of the small value of the gauss proposed by S. P. Thompson. It is one hundred times greater in value than Thompson's gauss. Sir William Thomson proposes, for the value oi the gauss, such an intensity of magnetic field as is produced by a current of one weber (ampere) at the distance of one centimetre. Gauss, Fleming's Such a strength of magnetic field as is able to develop an electromotive force of one volt in a wire one million centimetres in length moved through the field with unit velocity. (See Gauss.) Gauss, S. P. Thompsou's Such a strength of magnetic field that its intensity is equal to io s C. G. S. units. (See Gauss.) Gau.] 257 Gauss, Sir William Thomson's Such an intensity of magnetic field as would be produced by a current of one ampere at the distance of one centimetre. (See Gauss.) Geissler Mercurial Pump. (See Pump, Air, Geissler, Mercurial?} Geissler Tubes. (See Tubes, Geissler!) General Faradization. (See Faradiza- tion, General?) General Galvanization. (See Galvaniza- tion, General?) Generation of Current by Dynamo-Elec- tric Machine. (See Current, Generation of, by Dynamo-Electric Machine?) Generator, Dynamo-Electric An apparatus in which electricity is produced by the mechanical movement of conductors through a magnetic field so as to cut the lines of force. A dynamo-electric machine. (See Machine, Dynamo-Electric?) A dynamo electric machine operates on the general principles <~>f electro-dynamic induction. Strictly speaking, however, in a dynamo-electric generator the conductors are actually moved through the lines of force. In this respect, there fore, a dynamo-electric generator differs from a transformer, in which the lines of force are moved through the conductor. (See Induction, Electro- Dynamic. Transformer. Induction, Mutual.) Generator, Motor A dynamo-elec- tric generator in which the power required to drive the dynamo is obtained from an elec- tric current. Motor generators are used in systems of elec- trical distribution for the purpose of changing the potential of the current. They consi 5 t of dynamos, the armatures of which are furnished with two separate windings, of fine and coarse wire respectively. One of these, generally the fine wire, receives the driving or motor cur- rent, usually of high potential, and the other, the coarse wire, furnishes the current used, usu- ally of low potential. The advantage of having the windings, which receive the driving current, of fine wire, is to enable a current of high potential to be dis- tributed ever the line from distant stations to [Gen. places where it is desired to use the energy of the current at a much lower potential. Motor generators often consist simp'y of two distinct machines mechanically connected, one acting as a motor and the other as a dynamo. Motor generators are sometimes called dynamo- motors or dynamotors. Aldr ch draws the following distinction between a dynamo-motor and a dynamotor : (I.) A dynamo motor is an energy transformer with the dynamo and motor in the same electric circuit. (2.) A dynamotor is an energy transformer with the dynamo and motor in the same magnetic cir- cuit. Fig. 2S6. Edison's Fyr.-.Va ne!ic Generator. Generator, Pyro-Magnetic An ap- paratus for producing electricity directly from heat derived from the burning of fuel. Gen.] 258 [Gil. The operation of the pyro-magnetic generator is dependent upon the fact that any variation in the number of lines of magnetic force that pass through a conductor will develop differences of electric potential therein. Such variations may be effected either by varying the position of the conductor as regards the magnetic field, or by varying the magnetic field itself. The latter method of generating differences of potential is utilized in the pyro-magnetic generator, and is effected in it by varying the magnetization of rolls of thin iron or nickel by the action of heat. A form of pyro-magnetic generator devised by Edison is shown in Figs. 286 and 287. Fig. 287. Edis - Magnet i This apparatus is sometimes called a pyro- magnetic dynamo. Eight electro-magnets are provided, each with an armature consisting of a roll of corrugated iron. Each of these armatures is provided with a coil of insulated wire wound on it and pro- tected by asbestos paper. The armatures pass through two iron discs as shown. The armature coils are connected in series in a closed -circuit, the wires from the coils being connected with metallic brushes that rest on a commutator sup- ported on a vertical axis. A pair of metallic rings is provided above the commutator to carry off the current generated. The vertical axis is provided below with a semi- circular screen called a guard plate which rotates with the axis and cuts off or screens one-half the iron armatures from the heated air. When the axis is rotated, the difference in the magnetization of the armatures, when hot and cold, develops electromotive forces which result in the production of an electric current. Generator, Secondary A term fre- quently employed for a converter or trans- former. The word transformer is now almost univer- sally employed. (See Transformer.} Generator, Watt A term sometimes employed for stating the power in watts that any electric source is capable of producing. Estimating the power of a dynamo-electric machine by the number of watts it is capable of producing is very convenient in practice, and is now very generally adopted. A dynamo capable of furnishing a difference of potential of 1,000 volts, and a current of 10 amperes, would be said to be a 10,000 watt-generator. The term watt-generator, though applicable to the case of any electric source, is in practice generally limited to the case of dynamo-electric machines or secondary batteries. Generators, Motor, Distribution of Elec- tricity by (See Electricity, Distribu- tion of, by Motor Generators) Geographical Distribution of Thunder Storms. (See Storms, Thunder, Geograph- ical Distribution of.) Geographical Equator. (See Equator, Geographical.) Geographical Meridian. (See Meridian, Geographical.) German Silver Alloy. (See Alloy, Ger- man Silver.) Gilding, Electric The electrolytic deposition of gold on any object. Electro-plating with gold. (See Plating, Electro.) The surfaces of the object to be gilded are made electrically conducting, if not already MD, and are then connected to the negative terminal of a voltaic cell or other source, and immersed in a plating bath containing a solution of a salt of gold, directly opposite a plate of gold, connected with the positive terminal of the source. The objects to be plated thusbeco.ne the kathode, and the plate of gold the anode of the plating bath. On the passage of a suitable current, the gold is dissolved from the plate at the anode and deposited 259 [Gov. on the object at the kathode. (See Bath, Gold. Kathode. Anode.} Gilt Plumbago. (See Plumbago, Gilt.) Gimbals. Concentric rings of brass, sus- pended on pivots in a compass box, and on which the compass card is supported so as to enable it to remain horizontal notwithstand- ing the movements of the ship. (See Com- pass, Azimuth.) Each ring is suspended on two pivots placed directly opposite each other, that is, at the ends of a diameter, which in one ring is at right angles to that in the other. Girder Armature. (See Armature, Gir- der^ Globe, Vapor, of Incandescent Lamp A glass globe surrounding the cham- ber of an incandescent electric lamp, for the purpose of enabling the lamp to be safely used in an explosive atmosphere, or to permit the lamp to be exposed in places where water is liable to fall on it. Such a vapor globe is shown in Fig. 288. In the event of accidental breakage of the outside globe, the lamp chamber proper prevents the igni- tion of the explosive gases. In such cases, however, the outer pro- tecting chamber should be promptly replaced. In some forms of vapor globes, a valve is pro- vided, opening outwards, in order to permit the ex- panded air to escape when a given pressure is reached, and yet, at the same time, to prevent the entrance of gas or vapor from without. Glow Discharge. (See Discharge, Glow.) Glow Lamp. (See Lamp, Electric Glow.) Gold Bath. (See Bath. Gold.) Gold-Leaf Electroscope. (See Electro- scope, Gold-Leaf) Gold-Plating. -(See Plating, Gold.) Gong, Electro-Mechanical A gong Fig 2SS i afor Gtubs. struck or operated by mechanical force at times which are dependent on the passage of an electric current. The motive power is the mechanical force de- veloped by a bent spring, the fall of a weight, etc., and, by suitable mechanism, is permitted to act only on the passage of an electric current. Governor, Centrifugal A device for maintaining constant the speed of a steam engine or other prime mover, despite sudden changes in the load or work. In a ball governor, any increase in speed causes the balls to fly out from the centre of rota- tion by centrifugal force. This motion is utilized to control a valve or other regulating device. If the speed of the engine falls, the balls move towards the centre, shifting the valve or regulat- ing device in the opposite direction. Governor, Current A current regu- lator. A device for maintaining constant the cur- rent strength in any circuit. Current governors are either automatic or non- automatic. (See Regulation, Automatic.} Governor, Electric A device for electrically controlling the speed of a steam engine, the direction of current in a plating bath, the speed of an electric motor, the re- sistance of an electric circuit, the flow of water or gas into or from a containing vessel, or for other similar purposes. The particular form assumed by the apparatus varies with the character of the work it is intended to accomplish. In some cases an ordinary ball or centrifugal governor is employed to open or close a circuit; or, a mass of mercury in a rotat- ing vessel is caused, at a certain speed, to open or close a circuit; or, the resistance of a bundle of carbon discs i's caused to vary, either by pressure produced by centrifugal force, or by the move- ment of an armature. Governor, Periodic A name ap- plied by Ayrton & Perry to a form of gover- nor for an electric motor, in which the cur- rent is automatically cut out for a certain portion of each revolution. Governor, Spasmodic A name given by Ayrton & Perry to a form of gover- nor for an electric motor, in which the cur- Gov.J 260 [Gra- rent is automatically cut off in proportion as the work is cut off. The spasmodic governor consists essentially of a cone dipping into the surface of mercury in a rotat- ing vessel. As the speed of the governor increases on a lightening of the load, the surface of the mer- cury is curved by the increased centrifugal force, until finally the mercury leaves the contact point and thus cuts off the current. Governor, Steam, Electric A de- vice used in connection with a valve to so electrically regulate the supply of steam to an engine, that the engine shall be driven at such a speed as will maintain either a con- stant current or a constant potential. In the electric governor, the steam valve is operated by an electro-magnet, whose coils, in the case of a constant current machine, are of thick wire placed in the main circuit, and, in that of a constant potential machine, are of thin wire placed in a shunt around the mains. Graduators. Devices, generally electro- magnetic, employed in systems of simultane- ous telegraphic and telephonic transmission over the same wire, so inserted in the line cir- cuit as to obtain the makes and breaks re- quired in a system of telegraphic communi- cation so gradually that they fail to sensibly influence tie diaphragm of a telephone placed in the same circuit. Gramme. A unit of weight equal to 1543235 grains. The gramme is equal to the weight of one cubic centimetre of pure water at the temperature of its maximum density. It has various multiples and decimal divisions of the former, the kilogramme or one thousand grammes is the most frequently used; of the lattxr, the centigramme or the one- hundredth of a gramme, and the milligramme or the one -thousandth of a gramme. (See Weights and Measures, Metric System of. ) Gramme Atom. (See Atom, Gramme?) Gramme Molecule. (See Molecule, Gramme?) Gramophone. An apparatus for record- ing and reproducing articulate speech. (See Phonograph?) Gramophone Record. (See Record, Gramophone?) Graphite. A soft variety of carbon suit- able for writing on paper or similar surfaces. Graphite is the material that is employed for the so-called black lead of lead pencils. It is sometimes called plumbago. Strictly speaking, the term graphite is only applicable to the variety of plumbago suitable for use in lead pencils. Graphite is used for rendering surfaces to be electro-plated, electrically conducting, and also for the brushes of dynamos and motors. For the latter purpose it pos>esses the additional advantage of decreasing the friction by means of its marked lubricating properties. Graphophone, Micro A modifica- tion of the phonograph in which, instead of a single diaphragm, a number of separate non- metallic diaphragms are caused to act on a single diaphragm to record the speech, so that the separate diaphragms can be thrown into strong vibration when reproducing the speech. Graphophone, Phonograph A term sometimes applied to the graphophone. (See Graphophone, Micro. Phonograph?] Graphophone Record. (See Record, Graphophone?) Gray's Harmonic Telegraphic Analyzer. (See Analyzer, Grays Harmonic Tele- graphic?) Gray's Harmonic Telegraphy. (See Te- legraphy, Grays Harmonic Multiple?) Gravitation. A name applied to the force which causes masses of matter to tend to move towards one another. This motion is assumed to be that of attraction, that is, the bodies are assumed to be drawn to- gether. It is not impossible, however, that they may be pushed together. Gravitation, like electricity, is well known, so- far as its effects are concerned; but, as t ) the true cause of either, particularly the former, we are ia comparative ignorance. The general facts of gravitation may be suc- cinctly stated by the following law, generally known as Newton's law. Every particle of matter in the universe is at- tracted by every other particle of matter, and itself attracts every other particle of matter, witb, a force which is directly proportional to the pro- duct of the masses of the two quantities of matter Gra.] 261 [Gi and inversely proportional to the square of the distance between them. Gravity Ammeter. (See Ammeter, Grav- ity) Gravity, Centre of The centre of weight of a body. Bodies supported at their centres of gravity are in equilibrium, since their weight is then evenly distributed around the point of support. Gravity-Drop Annunciator. (See An- nunciator, Gravity-Drop?) Gravity, Voltaic Cell (See Cell, Voltaic, Gravity?) Gravity Voltmeter. (See Voltmeter, Gravity.) Great Calorie. (See Calorie, Great?) Grenet Voltaic Cell. (See Cell, Voltaic, Grenet?) Grid. A lead plate, provided with perfor- ations, or other irregularities of surface, and employed in storage cells for the support of the active material. The support provided for the active material on the plate of a secondary or storage cell. The grid receives its name from its resemblance to a gridiron. The active material is generally maintained on the grid by means of variously shaped apertures or holes. These are generally larger near the centre, so as to prevent the falling out of the material after it has been hardened by compression. (See Cell, Secondary. Cell, Stor- age.) Various forms have been given to the grid. The object of these forms, in general, is to in- sure the retention of the active material by the grid. The grids are preferably suspended from suit- able supports fastened to the top of the battery jars, instead of resting on the bottom of the bat- tery jars. Grip, Cable A grip provided for seizing the end of a cable when it is to be drawn into a duct or conduit. Grove's Voltaic Cell. (See Cell, Voltaic, Grove.) Grothnss' Hypothesis. (See Hypothesis, Grothnss'.) Ground Circuit. (See Circuit, Ground.) Ground Detector. ( S e e Detector, Ground,) Ground or Earth. A general term for the earth when employed as a conductor, or as a large reservoir of electricity. The term ground is also applied to a fault caused by an accidental and uudesired connection between an electric circuit, line or apparatus and the ground. (See Fault.) Ground Plate of Lightning Protec- tor. (See Plate, Ground, of Lightning Protector:) Ground-Return. A general term used to indicate the use of the ground or earth for a part of an electric circuit. The earth or ground which forms part of the return path of an electric circuit. The ground-return is generally used in the Morse system of telegraphy as practiced in the United States. Ground-Wire. The wire or conductor leading to or connecting with the ground or earth in a grounded circuit. This is sometimes called an earth-grounded wire. A circuit is grounded when it is completed in part by the ground or earth. Grounded Circuit. (See Circuit, Grounded.) Growth or Expansion of Lines of Force^ (See Force, Lines of, Growth or Expan- sion of.) Guard, Fan A wire netting placed around the fan of an electric motor for the purpose of preventing its revolving arms from striking external objects. Guard, Lightning A term some- times used for lightning rod. (See Rod, Lightning?) Guard, Transformer, Lightning A transformer lightning arrester. (See Ar- rester, Lightning, Transformer?) Gua.] 262 [Hal. Guard, Wire Shade A guard of wire netting provided for the protection of a shade. A form of wire shade is shown in Fig. 289. Fig. 289. Wire Shade Gu Gutta-Percha. A resinous gum obtained from a tropical tree, and valuable electrically for its high insulating powers. Gutta-percha readily softens by heat, but on cooling becomes hard and tough. Unlike India- rubber, it possesses but little elasticity. Its specific inductive capacity is 4.2, that of air being I, and of vulcanized rubber, 2.94. (See Capacity, Specific Inductive.) Gutta-percha is obtained largely from the East Indies, from a tree which yields a brownish gum. It is a fibrous and tenacious substance with but little flexibility, and is unaffected by acids. Oils produce less effect upon it than on India-rubber. Gutta-percha is one of the best insulating mate- rials known for sub-aqueous cables. Gymnotus Electricus. The electric eel. (See Eel, Electric.} Gyrometer. A speed indicator. (See In- dicator, Speed.) H. A contraction for the horizontal inten- sity of the earth's magnetism. H. A contraction proposed for one unit of self-induction. H. A contraction used in mathematical writings for the magnetizing force that exists at any point, or, generally, for the intensity of the magnetic force. The letter H, when used in mathematical writings or formulae for the intensity of the magnetic force, is always represented in bold or heavy faced type, thus : H . H-Armature Core. (See Core, Arma- ture, H.) Hail, Assumed Electric Origin of A hypothesis, now generally rejected, framed to explain the origin of the alternate coatings of ice and snow in a hail stone, by the alter- nate electric attractions and repulsions of the stones between neighboring, oppositely charged, snow and rain clouds. Ic is now generally recognized that the electric m mifestations attending hail storms are the effects and not the causes of the hail. (See Para- greles.) Hair, Electrolytic Removal of The permanent removal of hair from any part of the body, by the electrolytic destruction of the hair follicles. A platinum negative electrode is inserted in the hair follicle and the positive electrode, covered with moist sponge or cotton, is held in the hand of the patient. A current of from two to four milli-am- peres from a battery of from eight to ten Le- clanche elements is then passed for from ten to thirty seconds. A few bubbles of gas appear, and the hairs are then removed from the follicles by a pair of forceps. (See Milli- Ampere.) When the work is properly done there is no destruction of the skin and therefore no marks or scars. In the removal of hair from the face, it is pref- erable that the current should slowly reach its maximum strength. Half-Shades for Incandescent Lamps. Shades for incandescent electric lamps, in which one-half of the lamp chamber proper is covered with a coating of silver, or other reflecting surface for reflecting the light, or is ground for the purpose of diffusing the lijht. The half-shade is applicable to cases where it is desired to throw out the light, not in all direc- tions, but on one side only of any plane. Some- times the dividing plane is taken parallel to the length of the incandescing filament and sometimes at right angles to it. When the lamp is placed Hal.J 263 [Hea. within a surrounding globe the reflecting surface may be placed on this globe instead of on the lamp chamber. Hall Effect. -(See Effect, Hall.) Halleyau Lines. (See Lines, Halleyan.) Halpine-Savage Torpedo. (See Torpedo, H alpine- Savage. ) Haudhole of Conduit. A box or opening communicating with an underground cable, provided for readily tapping the cable, and of sufficient size to permit of the introduction of the hand. Hand-Lighting Argand Electric Burner. (See Burner, Argand Electric, Hand- Lighter^) Hand-Lighting Electric Burner. (See Burner, Hand-Lighting Electric?) H a n d R e gulation. ( See Regulation, Hand.) Hand-Regulator. (See Regulator, Hand) Hanger-Board. (See Board, Hanger?) Hanger, Cable A hanger or hook suitably secured to the cable and designed to sustain the weight of the cable by intermediately sup- porting it on iron or steel wires strung above the cable. A cable hanger or cable clip is shown in Fig. 290. The mode of supporting the cable C, by the hanger hook H, will be readily un- derstood from an in- spection of the figure. Fi *' 29 ~ Cable Ifan * er ' The weight per foot of an aerial cable is gener- ally so great that the poles or supports would re- quire to be very near together, unless the device of intermediate supports, by means of cable clips or hangers, were adopted. Hanger, Double-Curve Trolley A trolley hanger generally employed at the ends of single and double curves, and on inter- mediate points on double track curves, sup- ported by lateral strain in opposite directions. Hanger, Single-Curve Trolley A trolley hanger supported on a single track curve, except at the ends and on the inside curve of a double track line, by lateral strain in one direction. Hanger, Straight-Line Trolley A trolley hanger on a straight trolley line suit- ably supported by a span wire so as to have a vertical strain only. Hanger, Trolley A device for sup- porting and properly insulating trolley wires. Hard-Drawn Copper Wire. (See Wire, Copper, Hard-Drawn.) Harmonic Receiver. (See Receiver, Har- monic.) Harmonic Telegraphy. (See Telegraphy, Gray's Harmonic Multiple) Head Bath, Electric (See Bath, Head, Electric) Head Breeze, Electro-Therapeutic (See Breeze, Head, Electro-Therapeutic) Head Light, Locomotive, Electric An electric light placed in the focus of a par- abolic reflector in front of a locomotive engine. The lamp is so placed that its voltaic arc is a little out of the focus of the reflector, so that, by giving a slight divergence to the reflected light, the illumination extends a short distance on either side of the tracks. Heat. A form of energy. The phenomena of heat are due to a vibratory motion impressed on the molecules of matter by the action of some form of energy. Heat in a boly is due to the vibrations or oscillations of its molecules. Heat is transmitted through space by means of a wave motion in the univer-al ether. This wave motion is the same as that causing light. A hot body loses its heat by producing a wave motion in the surrounding ether. This process is called radiation. (See Radiation) The energy given off by a heated body cooling is called radiant energy. Radiant energy is transmitted by means of ether waves; it is of two k.nds, viz.: (I.) Obscur,: If sat, or heat which does not affect the eye, although it can impress a photo- graphic image on a sufficiently sensitive photo- graphic plate. Hea.J 264 [Hea. (2.) Luminous Heat, or heat which accompanies light ^Q Energy, Radiant.) Heat is conducted, or transmitted through bodies, with different degrees of readiness. Some bodies are good conductors of heat, others are poor conductors. Heat is transmitted through liquids by means of currents occasioned by differences in density caused by differences of temperature. These currents are called convection currents. Heat is measured as to its relative degree of in- tensity by the thermometer. It is measured as to its amount or quantity by the calorimeter. (See Thermometer, Ehctric. Calorimeter.) The heat unit most commonly employed is, perhaps, the calorie, or the amount of heat re- quired to raise one gramme of water one degree centigrade. Another heat unit, very generally employed in the United States and England, is the quantity of heat required to raise one pound of water one de- gree Fahrenheit. This is called the English heat unit. (See Calorie. Units, Heat. Joule. Volt- Coulomb.) Heat, Absorption and Generation of, in Voltaic Cell The heat effects which attend the action of a voltaic cell. The chemical action of the exciting liquid or electrolyte on the positive plate or element of a voltaic cell, like all cases of chemical combination, is attendt d by a development of heat. When, however, the circuit of the cell isclosed, the energy liberated during the chemical combi- nation appears as electricity, which develops heat in all parts of the circuit. (See Heat, Electric. Cell, Voltaic.) Heat, Atomic A constant product obtained by multiplying the specific heat of an elementary substance by its atomic weight. (See Weight, Atomic.) Dulong and Petit have discovered the remark- able fact that the product of the specific heat of all elementary substances by their atomic weights is nearly the same. The product is called the atomic heat, and is about equal to 6.4. Dulong and Petit's law may be stated as fol- ows, viz. : All elementary atoms require the same quantity of heat to heat them to the same number of degrees. The atomic heat of any body divided by its specific heat gives its atomic weight. The heat imparted to any body performs three kinds of work, viz.: (I.) That expended in external work, such, for example, as in overcoming the atmospheric pressure. (2.) That expended in internal work, or in. overcoming the attractions of the atoms and driv- ing them apart. (3.) That expended in overcoming the temper- ature, or the true specific heat, or heat expended in increasing the molecular vis-viva. The expenditure of energy is greatest in the third head. The exact value of the three factors is as yet unknown, and in the opinion of Weber and others the correctness of Dulong and Petit's law cannot be regarded as being satisfactorily established. Regnault has proved that Dulong and Petit's law is true for compound bodies, i. 4 988 2UO 2922 3422 |474I 9- 3140 851 1,78 2519 3486 4088 5 6S9 10. 34- 394 997 .380 2950 4084 4788 6626 1 Diameter in Centimetres CURRENT IN AMPERES. and Mils (thousandths ot an inch). t = 49 C. t = 81 C. Cm. Mils. Bright. Black. Bright. Black. (j 40 6.5 8.9 7-9 i ix.o .2 80 ,8.3 25-3 22.4 31.0 3 1 70 33-=; 46.4 4'-z S7-0 4 160 5<-7 7 I -5 6 t .+ 87.8 aoo 72.2 99-9 88.6 123 .6 240 94-9 131 116 161 '.I 280 310 3 165 147 203 179 248 9 I.O 35 39 "74- 204 ii 214 25' 296 347 a.o 790 577 7-9 709 3-0 life 1061 ,<68 4.0 1570 1633 2260 2006 5.0 1470 2283 3160 2802 3880 6.0 S.'o 2760 3'5> 3oo 454 4642 5100 6426 7850 9.0 354 5511 7630 6769 937C 10. 14. i 3940 6425 8935 7926 10973 70000 (Forbes.) Heat, Electric Conrection of A term employed to express the dissymmetrical distribution of temperature that occurs when a Hea.] 266 [Hea. current of electricity is sent through a metallic wire, the middle of which is main- tained at a constant temperature, and the ends at the temperature of melting ice. The distribution of heat during the pas- sage of a current through an unequally heated conductor. If the central portions of a metallic bar are heated the curve of heat distribution is sym- metrical. On sending an electric current through the wire it is heated according to Joule's law, and the curve of heat distribution is still sym- metrical. But the current in passing from the colder to the hotter parts of the wire produces an additional heating effect at this point, and in passing from the warmer to the colder parts of the wire produces a cooling effect. (See Effect, Peltier. Effect, Thomson.} The curve of heat distribution is then no longer symmetrical. The term Electrical Convection of Heat, has been given to the dissymmetrical distribution of heat so effected. Sir William Thomson, who studied these effects, found that the electrical convection of heat in copper takes place in the opposite direction to that in iron; that is to say, the elec- trical convection of heat is negative in iron, (i. e., the direction is opposite to that of the current) , and positive in copper. Heat, Irreversible Heat pro- duced in a homogeneous conductor by the passage of electricity through it. This heat, according to Joule's law, is propor- tional to the square of the current, and is produced no matter in what direction the current is pass- ing. In this respect it is unlike the heat pro- duced by the passage of electricity through a heterogeneous conductor, in which case heat is developed or liberated only by the passage of the current in a given direction : on the passage of the current in the opposite direction, heat being absorbed and the temperature lowered. (See Heat, Reversible.) Heat Lightning. (See Lightning, Heat.) Heat, Luminous A variety of radi- ant energy which affects the eye, as light. Radiant heat and light are, in reality, different effects produced by one and the same cause, viz., by vibrations or waves in the universal ether. In general the waves producing heat are of greater length and smaller frequency than are those producing light. Heat, Mechanical Equivalent of The amount of mechanical energy, converted into heat, that would be required to raise the temperature of i pound of water i degree Fahr. The mechanical equivalence between the amount of energy expended and the amount of heat produced, as measured in heat units. Joule's experiments, the results of which are generally accepted, gave 7, "2 foot-pounds as the energy equivalent to that expended in raising the temperature of I pound of water I degree Fahr. Heat, Molecular The number of calories of heat required to raise the tempera- ture of one gramme-molecule of any sub- stance i degree C. (See Molecule, Gramme. Heat, Atomic?) Heat, Obscure A variety of radiant energy which does not effect the eye. Radiant heat is sometimes divided into lumi- nous heat and obscure heat. (See Heat, Lumi- nous. ) Heat, Red The temperature at which a body, whose temperature is gradually increasing, begins to glow or to emit red rays of light. When a refractory solid body is gradually heated to incandescence, the red waves of light are first emitted, then the orange, and successively afterwards the yellow, green, blue, indigo and violet, when the body emits white light or is white hot. Heat, Reversible The heat pro- duced in a heterogeneous conductor by the passage through it of an electric current in a certain direction. Reversible heat is produced at the junction of two metals, where a difference of potential exists between them, or where their heterogeneity is greatest. It is called reversible because it de- pends upon the direction in which the :urrent is passing. If the current be passed in a certain direction across the junction, heat is liberated; while, if it be passed in the opposite direction, heat is absorbed, or cold results. Reversible heat effects are seen in the Peltier effect. (See Effect, Peltier.} Hea.J 267 [Eel. Heat, Specific The capacity of a substance for heat as compared with the capacity of an equal quantity of some other substance taken as unity. Water is generally taken as the standard for comparison, because its capacity for heat is greater than that of any other common substance. Different quantities of heat are required to raise the temperature of a given weight of dif- ferent substarices through I degree. The spe- cific heats of substances are generally compared with water or with hydrogen, the capacity of these substances for heat being very great. According to Dulong and Pettit, the specific heat of all elementary atoms is the same. For example, the heat energy of an atom of hydrogen is equal to that of an atom of oxygen, but since a given mass of hydrogen, under similar condi- tions of temperature and pressure, contains sixteen times as many atoms as an equal mass of oxygen, therefore, when compared weight for weight, hydrogen has a specific heat sixteen times greater than that of oxygen. Or, in general, co nparing equal weights, the specific heat of an elementary substance is in- versely proportional to its atomic weight. (See Heat, Atomic.} Heat, Specific, of Electricity (See Electricity, Specific Heat of.) Heat -Unit. The quantity of heat required to raise a given weight of water through a single degree. There are a number of different heat units. The most important are: ( i . ) The British Heat Unit, or Thermal Unit, or the amount of heat required to raise I pound of water I degree Fahr. This unit represents an amount of work equal to 772 foot pounds. (2.) The Greater Calorie, orthe amountof heat required to raise the temperature of 1,000 grammes of water I degree C. (See Calorie.) (3.) The Smaller Calorie, or the amount of heat required to raise the temperature of one gramme of water I degree C. (4.) The Joule, orthe quantity of heat developed in one second by the passage of a current of one ampere through a resistance of one ohm. I joule equals .0002407 large calories. I joule equals .2407 small calories. I foot-pound equals 1.356 joules. I pound-Centigrade equals 1884.66 joules. I " ' 1389.6 foot pounds, I " Fahrenheit -i 1047.03 joules. Heat Unit, English (See Units. Heat.) Heat Unit or Calorie. -(See Calorie) Heat Unit or Joule. (See Joule) Heat, White The temperature at which light of all wave lengths from the red to the violet is emitted from a heated body, and the body, therefore, glows with a white light. A solid substance heated to white incandescence emits a continuous spectrum, i. e., a spectrum in which all the wave lengths of light from the red to the violet are present. Heater, Electric A device for the conversion of electricity into heat for purposes of artificial heating. Electric heaters consist essentially of coils or circuits of some refractory metal through which the current is passed. These coils or circuits are surrounded by air or finely divided solids, and are placed inside metallic boxes or radiators, which throw off or radiate the heat produced. When employed for the heating of liquids the coils are placed directly in the liquid to be heated, or are surrounded by radiating boxes placed in the liquid. Heating Effects of Currents. (See Cur- rents, Heating Effects of) Hedgehog Transformer. (See Trans- former, Hedgehog.) Hecto-AmpSre One hundred am- peres. Heliograph. An instrument for tele- graphic communication that operates by em- ploying flashes of light to represent the dots and dashes of the Morse alphabet, or the movements of the needles of a needle tele- graph to the nght or the left. (See Alphabet, Telegraphic) The flxshes of light are thrown from the sur- face of a plane mirror. Motions to the right or left may be employed in order to distinguish between the dots and dashes, or the same may be effected by the relative durations of the flashes of Hel.] 268 [Hoi. light, or by the intervals between successive flashes. Telegraphic communication has been carried on between steamers during foggy weather by means of their fog horns; or between locomotives by their steam whistles. Helix, Dextrorsal A name some- times applied to a dextrorsal solenoid. (See Solenoid, Dextrorsal?) The magnetic polarity of a helix or solenoid depends not only on the direction in which the current is passed, but also on the direction in which the wire is coiled or wound. (See Magnet, Electro.} Helix, Sinistrorsal A name some- times applied to a sinistrorsal solenoid. (See Solenoid, Sinistrorsal.} II c MI i ht>dml Crystal. (See Crystal, Hem- ihedral.) Henry, A The practical unit of self- induction. It has been generally agreed in the United States to call the practical unit of self-induction a henry, in place of a secohm or quadrant. The name henry should be adopted, not only by American electricians, but also by ihose of other countries, since the terms secohm or quadrant are contrary to the generally adopted usage of employing for such the names of distinguished electricians, who have passed from their labors. The fact that of all discoverers in the field of self- induction, none possesses so great a claim as that of Prof. Henry, must be generally acknowledged. As early as 1832 he published in Sillimari's Jour- nal a paper in which he described experiments, showing clearly that the spark obtained by break- ing the current of a battery, in which along wire was interposed, was greater than when a short wire was employed, and that this increased length of spark was further increased by coiling the wire, and that the phenomena were ascribed to the ac- tion of the current on itself. A committee of the American Institute of Electrical Engineers, after careful consideration, recommended to the Institute that the value of the practical unit of inductance should be equal to io 9 C. G. S. units of inductance, usually ex- pressed by a length equal to one earth quadrant or i 000,000,000 centimetres. The value of the practical unit of inductance, or the "henry," may in some cases be too high for convenience; in such cases it may be expressed by some fractional dimension, such, for example, as milli-henry. Hercules Stone. -(See Stone, Hercules?) Hermetical Seal. (See Seal, Hermeti- cal.) Hertz's Theory of Electricity. (See Elec- tricity, Hertz's Theory of.) Heterostatic. A term applied by Sir William Thomson to distinguish a form of electrometer in which the electrification is measured by determining the mutual influ- ence of the attraction exerted by the charge to be measured and the attraction of an oppo- site charge imparted to the instrument by a source independent of the charge to be meas- ured. The term heterostatic distinguishes this form of electrometer from an idiostatic instrument, or one in which the measurement is effected by deter- mining the repulsion between the charge to be measured and the repulsion of a charge of the same name, i. e., positive or negative, imparted to the instrument from an independent source. ( See Electrometer ) Hick's 'Automatic Button Repeater. (See Repeaters, Telegraphic?) High-Bars. A term applied to those com- mutator segments, or parts of commutator segments, which, through less wear, faulty construction or looseness, are higher than ad- joining portions. (See Commutator?) High-Frequency Currents, Electric Light- ing by (See Lighting, Electric, by High-Frequency Currents?) High Resistance Magnet. (See Magnet, High Resistance?) High Speed Electric Motor. (See Mo- tor, Electric, High Speed?) High Tension Electric Fuse. (See Fuse, Electric High Tension?) Hissing of Arc. (See Arc , Hissing of.) Holder for Safety Fuse. A box or other receptacle of refractory material for holding a safety fuse, and catching the molten metal when fused. The holder or fuse box is provided to prevent the Hoi.] 269 [Hor. molten metal of the fuse from setting fire to any combustible material on which it might other- wise fall. Holders, Carbon, for Arc Lamps A clutch or clamp attached to the end of the lamp rod or other support, and provided to hold the carbon pencils used on arc lamps. {See Lamp, Arc, Electric.) Holders for Brushes of Dynamo-Electric Machine. A device for holding the collect- ing brushes of a dynamo-electric machine. (See Machine, Dynamo-Electric.) Hole, Armature A term sometimes .applied for armature bore or chamber. (See Bore, Armature?) Hole, Armature Bore, Elliptical An armature bore or chamber ellipsoidal in shape. Holohedral Crystal. (See Crystal, Holo- Aedral.) Holtz Machine. (See Machine, Holtz.) Home Station. (See Station, Home.) Homogeneous Current Distribution. (See Current, Homogeneous Distribution of.) Hood for Electric Lamp. A hood pro- vided for the double purpose of protecting the Fig. 3QT. Arc Lamp Hood. body of an electric lamp from rain or sun, and for throwing its light in a general down- ward direction. Hoods for arc lamps are generally conical in shape. A form of hood for an exposed arc lamp is shown in Fig. 291. Horizontal Component of Earth's Mag- netism. (See Component, Horizontal, of Earth's Magnetism) Horns, Following, of Pole Pieces of a Dynamo - Electric Machine The edges or terminals of the pole pieces of a dy- namo-electric machine towards which the armature is carried during its rotation. Fig 292. Horns of Dynamo. According to S. P. Thompson, the following horns, b, d, Fig. 292, are those towards which the armature is carried ; the leading horns, a, c, those from which it is carried. As the change in the magnetic intensity is more sudden when the armature is moved from the pole pieces, and least when moved towards them, it is clear that the leading horns in a dynamo- electric machine, and the following horns in an electric motor, become heated during rotation by the production of Foucault currents. (See Cur- rents, Foucault. Machine, Dynamo Electric.) Horns, Leading, of Pole Pieces of a Dy- namo-Electric Machine The edges or terminals of the pole pieces of a dynamo- electrical machine from which the armature is carried during its rotation. Thus, in Fig. 292, a and c, are the leading horns of the pole pieces. Horns of Pole Pieces of Dynamo-Electric Machine. The edges of the pole pieces of a dynamo-electric machine towards or from which the armature is carried during its rota- tion. These are called the following and the leading horns. Horse-Power. A commercial unit for power or rate of doing work. Hor.] 270 [Hon. A rate of doing work equal to 33,000 pounds raised i foot per minute, or 5 50 pounds raised I foot per second. A rate of doing work equal to 4,562.33 kilogrammes raised i metre per minute. A careful distinction must be drawn between work and power. The same amount of work is done in raising I pound through 10 feet whether it be done in one minute or in one hour. The power expended or the rate of doing work is, however, quite different, being in the former case sixty times greater than in the latter. I horse-power = 550 foot-pounds per second. " = 33,000 foot-pounds per min- ute. " =4,562.33 kilogramme-metres per minute. = 745,941 watts. " = 1.01385 metric horse-power. Horse-Power, Electric (See Power, Horse, Electric?) Horse-Power Hour. (See Hour, Horse- Power). Horse-Power, Metric A unit of power in which rate of doing work is equal to 75 kilogramme-metres. (See Horse- Power?) Horseshoe Electro-Magnet. (See Mag- net, Electro, Horseshoe?) Horseshoe Magnet. (See Magnet, Horse- shoe.} Hot, Red Sufficiently heated to emit red light only. (See Heat, Red} Hot St. Elmo's Fire. (See Fire, Hot, St. Elmo's?) Hot, White Sufficiently heated to emit all the colored lights of the spectrum. (Se&Heat, White.) Hotel Annunciator. (See Annunciator, Hotel.) Hour, AmpSre A unit of electrical quantity equal to one ampere flowing for one hour. The ampere-hour is in reality a unit of quanti- ty like the coulomb. It is used in the service of electric currents, and is equal to the product of the current delivered by the time in hours. The ampere-hour is not a measure of energy, but when combined with the volt, and expressed in watt hours, it is a measure of energy. The capacity of any service for maintaining a flow of current is measured in ampere-hours. Thus, if any service, such as a primary or sec- ondary battery, has a capacity of 80 ampdre- hours, it will supply 8 amperes for ten hours, or it may give 10 amperes for eight hours. The storing capacity of accumulators is gener- ally given in ampere-hours. The same is true of primary batteries. One coulomb equals .0002778 ampere-hours. One ampere-hour equals 3,600 coulombs. Hour, Horse-Power A unit of work. An amount of work equal to one horse- power for an hour. One horse power is equal to 1,980,000 foot- pounds, or 745.941 watt hours. Hour, Kilo-Watt A unit of electri- cal power equal to a kilo-watt maintained for one hour. Hour, Lamp Such a service of elec- tric current as will maintain one electric lamp during one hour. The number of lamp-hours is obtained by mul- tiplying the number of lamps by ihe average number of hours during which the lamps are burning. The use of lamp-hours is for the purpose of estimating the current supplied to a consumer by counting the number of hours each lamp is in service. To convert lamp-hours to watt-hours, multiply the number of lamp-hours by the number of watts per lamp. The watt hours, divided by 746, will then give the electrical horse-power hours. (See Hour, Watt.) Hour, Watt A unit of electrical work. An expenditure of an electrical work of one watt for one hour. Lamp-hours are converted to watt-hours by multiplying the number of lamp-hours by the number of watts per lamp. (See Hour, Lamp.) House Annunciator. (See Annunciator, House.) House Main. (See Main, House.) House-Service Conductor. (See Conduc- tor, House-Service.) Hou.] 271 [Hyp. House-Top Fixtures, Telegraphic (See Fixtures, Telegraphic House- Top.} House Wire. (See Wire, House.) Hughes' Electro-Magnet. (See Magnet, Electro, Hughes'.) Human Body, Electric Resistance of (See Body, Human, Resistance of) Hydro-Electric Bath. (See Bath, Hydro- Electric^ Hydro-Electric Machine, Armstrong's (See Machine, Armstrong's Hydro- Electric) Hydrogen, Electrolytic Hydrogen produced by electrolytic decomposition. It is the electrolytic hydrogen liberattd in a voltaic cell at the surface of the negative plate, which causes polarization and consequent de- crease in the resulting current strength, by rea- son both of the counter-electromotive force it produces and the increased resistance it produces in the cell. Electrolytic hydrogen is atomic hydrogen; i. e., hydrogen with its bonds open or free. It there- fore possesses much stronger chemical affinities than does molecular hydrogen. Electrolytic oxygen which is evolved at the same time as the electrolytic hydrogen has been successfully em- ployed in electric bleaching. Hydrogen per- oxide is also formed and acts as a bleaching agent. Hydrometer or Areometer. An appa- ratus for determining the specific gravity of liquids. (See Areometer or Hydrometer) Hydro-Plastics. (See Plastics, Hydro) Hydro-Plasty The art of hydro-plastics. (See Plastics, Hydro) Hydrotasimeter, Electric An elec- trically operated apparatus designed to show at a distance the exact position of any water level. In most forms of the electric hydrotasimeter a float placed in the liquid and connected with an electric circuit breaks this circuit, and, at intervals, sends positive impulses into the line when rising and negative impulses when falling. These are registered by means of an index moved by a step- by-step motion, positive currents moving it in one direction and negative currents moving it in the opposite direction. Hygrometer. An apparatus for determin- ing the amount of moisture in the air. Hygrometrical. Of or pertaining to the hygrometer. Hygrometrically. In the manner of the hygrometer. Hypothesis. A provisional assumption of facts or causes the real nature of which is unknown, made for the purpose of studying the effects of such causes. When the facts assumed by a hypothesis can be shown to be presumably true the hypothesis becomes a theory. A theory, therefore, gives a more correct expression of the relations between the causes and effects of natural phenomena than does a hypothesis. Hypothesis, Double-Fluid Electric (See Electricity, Double-Fluid Hypothesis of-} Hypothesis, Orothiiss' A hypothe- sis proposed by Grothiiss to account for the electrolytic phenomena that occur on closing the circuit of a voltaic cell. Grothuss' hypothesis assumes: (i.) That before the electric circuit is closed the molecules of the electrolyte are arranged in an irregular or unpolarized condition, as repre- Fig. at)3. GrotAOss' Hypothesis of Electrolytic Polari- zation. sented at (i), Fig. 293. These molecules are shaded as shown in Fig. 294, to indicate their com- position and polarity. (2.) When the circuit is closed and a current Hyp.] 272 [Hys. begins to pass, a polarization of the electrolyte, as shown at (2), ensues, whereby all the negative ends of the molecules of hydrogen sulphate, o sulphuric acid, are turned towards the positive or zinc plate, and all the positive ends towards the negative or copper plate. This, as will be seen, will turn the SO 4 ends towards the zinc, and the H 2 ends towards the copper. (3.) A decomposition of the polarized chain, whereby the SO 4 unites with the zinc and the H g liberated / reunites with the SO 4 of the molecule next to it in the chain, and its liberated H s with Fig, 294. Conventionalized the one next to it, and Molecule. so on until the last liberated H 2 in the chain is given off at the surface of the copper or negative plate. This leaves the chain of molecules as shown at (3). (4. ) A semi-rotation of the molecules of the chain, as at (3), until they assume the position shown at (4). This rotation is required, since all the molecules in (3) are turned with their similar poles towards similarly charged battery plates. Hypothesis, Single-Fluid Electric (See Electricity, Single-Fluid Hypothe- sis of.) Hypothetical. Of or pertaining to a hy- pothesis. Hypsometer. An apparatus for determin- ing the height of a mountain or other eleva- tion by ascertaining the exact temperature at which water boils at such elevation. The use of a thermometer to measure the height of a mountain or other elevation is based on the fact that a given decrease in the tempera- ture of the boiling point of water invariably at- tends a given decrease in the atmospheric press- ure. Therefore, as the observer goes further above the level of the sea, the boiling point of water becomes lower, and from this decrease the height of the mountain or other elevation may be calculated. Hypsometrical. Of or pertaining to the hypsometer. Hypsometrically. In the manner of the hypsometer. Hysteresial Dissipation of Energy. (See Energy, Hysteresial Dissipation of.} Hysteresis. Molecular friction to mag- netic change of stress. A retardation of the magnetizing or de- magetizing effects as regards the causes which produce them. The quality of a paramagnetic substance by virtue of which energy is dissipated on the reversal of its magnetization. The ratio of magnetic induction to the mag- netizing force producing it, or, in other words, the magnetic permeability, is greater when the magnetizing force is decreasing, than when it is increasing. This phenomenon is seen in the well known retention of magnetism in iron after the withdrawal of the force causing the magnetization, and was called by Ewing hysteresis, from 'vdrspeoo, to lag behind. If a curve is constructed in which the hori- zontal abscissas represent the magnetizing force, or the magnetizing current to which they are proportional, and the vertical ordinates the number of lines of induction passing through the body that is being magnetized, both in the case of gradually increasing and gradually decreasing currents, the curve will be found to have greater values for the decreasing than for the increasing current Constructing a curve in this manner for the case of a ring of iron, which has been first suddenly magnet- ized and then demag- netized, taking the magnetizing force along the line F H, Fig. 295, and the result- ing magnetization along the line M N, a loop is formed in the curve, as shown in the figure. The arrows show the direction of Fig. 293. Curves of Hy- the magnetizing force; teresis (Ewing). the shaded area the work done due to hysteresis. The area of this loop represents the amount of energy per unit of volume expended in perform- ing a magnetic cycle, i. e., in carrying the iron ring through a magnetization and subsequent demagoetiz ation. The physical meaning of the loop is that a lag- 273 ging of magnetization has occurred. This lag- ging of the magnetization is due to hysteresis. Ewing gives the value for the energy in ergs dissipated per cubic centimetre, for a complete magnetic cycle for a number of substances, as follows : Energy dissipated in ergs per cubic centimetre, during a complete c> clc of doubly revi rsed strong magnetiza- Sample of Iron operated upon. tion. Very soft annealed iron 9,300 ergs. Less soft annealed iron 16,300 " Hard drawn steel wire 60.000 " Annealed steel wire "70,500 " Same steel, glass hard 76,000 " Piano-forte steel wire, normal temper 116,000 " Same, annealed 94,000 ' ' Same, glass hard 117,000 " Approximately 28 foot-pounds of energy are required to make a double reversal of strong magnetization in a cubic foot of iron. Energy expended in this way takes the form of heat. This heat, however, is to be distinguished from heat produced by Foucault currents. According to Ewing, hysteresis is greatly de- creased by keeping the iron in a state of mag- netic vibration. In this way, the energy dis- sipated in a complete magnetic cycle is corre- spondingly decreased. This observation of Ewing agrees with the prior observation of Hughes, who noticed that tapping or twisting a bar of iron greatly accelerates the removal of its residual magnetism. The phenomena of hysteresis, according to Fleming, accounts for part of the energy which is dissipated in a dynamo-electric machine: (i.) In the field magnets. In an ordinarily constructed continuous-current dynamo, work is done in magnetizing the field magnets, not only to give the iron its initial mag- netism, but also to constantly reproduce the mag- netism which the machine loses by reason of the continual vibrations to which it is subjected dur- ing its run. If sufficient residual magnetism were retained, on the withdrawal of the magneti- zing force there would be no necessity for the current in the field magnets ; but, since this is removed by even a small vibration, the energy of the exciting current must neeJs be expended. (2.) In the armature of the dynamo. The soft iron of the core is subjected to succes- sive magnetizations and demagnetizations. Ac- cording to Fleming, in the case of a core having a volume of 9,000 cubic centimetres, with fifteen reversals per second, the loss is equal to about J horse-power. Hysteresis, Static That quality in iron, or other paramagnetic substance, by virtue of which energy is dissipated during every reversal of its magnetization. Static hysteresis is so named in order to dis- tinguish it from viscous hysteresis. (See Hystere- sis, Viscous.) Hysteresis, Tiscous = The time-lag observed in magnetizing a bar of iron, which is referable neither to induction in the iron, nor to self-induction in the magnetizing current, but to the magnetic viscosity of the substance. A sluggishness exhibited by iron for mag- netization or demagnetization due to magnetic viscosity. The difference between static and viscous hysteresis is thus stated by Fleming in consider- ing the analogous mechanical case of lifting a weight in a viscous fluid. "Apart from fluid resistance, the work done in lifting the weight against gravity, say one hundred times, is a hun- dred times the work required to be spent to lift it once ; but if fluid resistance comes into play, and if this varies as the square of the velocity of the moving body, then the total work done in lifting the weight through the fluid will be de- pendent also upon the rate at which the cycle is performed." Ihp.] 274 [111. I. H. P. A contraction for indicated horse- power, or the horse-power of an engine as obtained by the means of an indicator card. I. W. G. A contraction for Indian wire gauge. Idio-Electrics. A name formerly applied to such bodies as amber, resin or glass, which are readily electrified by friction, and which were then supposed to be electric in them- selves. This distinction was based on an erroneous conception, and the word is now obsolete. Idiostatic. A term employed by Sir Wil- liam Thomson to designate an electrometer in which the measurement is effected by de- termining the repulsion between the charge to be measured and that of a charge of the same sign imparted to the instrument from an independent source. (See Heterostatic^ Idle Poles. (See Poles, Idle.) Igniter, Jablochkoff A small strip of carbcn, or some carbonaceous material that is readily rendered incandescent by the current, placed between the free ends of the parallel carbons of a Jablochkoff candle, for the establishment of the arc on the passage of the current. The igniter is necessary in the Jablochkoff elec- tric candle, since the parallel carbons are rigidly kept at a constant distance apart by the insulat- ing material placed between them, and cannot therefore be moved together as in the case of the ordinary lamp. (See Candle, Jablochkoff.) Ignition, Electric The ignition of a combustible material by heat of electric origin. The electric ignition of wires is generally ac- complished by electric incandescence. Ignition may be accomplished by the heat of the voltaic arc. (Seeffeat, Electric. Furnace, Electric.) The ignition of combustible gases is accom- plished by the heat of the electric spark. (See Burner, Automatic, Electric.) Illumination, Artificial The em- ployment of artificial sources of light. A good artificial illuminant should possess the following properties, viz.: (i.) It should give a generator uniform illumi- nation as distinguished from sharply marked regions of light and shadow. To this end a number of small lights well dis- tributed are preferable to a few large lights. (2.) It should give a steady light, uniform in brilliancy, as distinguished from a nickering, unsteady light. Sudden changes in the intensity of a light injure the eyes and prevent distinct vision. (3.) It should be economical, or not cost too much to produce. (4. ) It sh mid be safe, or not likely to cause loss of life or property. To this intent it should, if possible, be inclosed in or surrounded by a lantern or chamber of some incombustible mate- rial, and should preferably be lighted at a dis- tance. (5 ) It should not give off noxious fumes or vapors when in use, nor should it unduly heat the air of the space it illumines. (6. ) It should be reliable, or not apt to be un- expectedly extinguished when once lighted. The electric incandescent lamp is an excellent artificial illuminant. (i.) It is cap ible of great subdivision, and can, therefore, produce a uniform illumination. (2.) It is steady and free from sudden changes in its intensity. (3.) It compares favorably in point of economy with coal oil or gas, provided its extent of use is sufficiently great. (4.) It is safer than any known illuminant, since it can be entirely inclosed and can be lighted from a distance or at the burner without the dangerous friction match. The leads, however, must be carefully insu- lated and protected by safety fuses. (See Fuse, Safety.) (5.) It gives off no gases, and produces far less heat than a gas-burner of the same candle power. It perplexes many people to understand why the incandescent electric light should not heat the air of a room as much as a gas light, since it is quite as hot as the gas light. It must be re- membered, however, that a gas-burner, when lighted, not only permits the same quantity of 111.] 275 [Imp. gas to enter the room which would enter it if the gas were simply turned on and not lighted, but that this bulk of gas is still given off, and is, indeed, considerably increased by the combina- tion of the illuminating gas with the oxygen of the atmosphere ; and, moreover, this great bulk of gas escapes as highly heated gases. Such gases are entirely absent in the incandescent electric light, and consequently its power of heating the surrounding air is much less than that of gas lights. (6.) It is quite reliable, and will continue to burn as long as the current is supplied to it. Illumination, Lighthouse, Electric The application of the electric arc light to lighthouses. A powerful arc light is placed in the focus of the dioptric lens now commonly employed in lighthouses. Since the consumption of the carbon electrodes would alter the position of the focus of the light, electric lamps for such purposes are constructed to feed both of their carbons, instead of the upper carbon only, as in the case of the ordinary arc lamp. Such lamps are called focus- ing lamps. Illumination, Unit of A standard of illumination proposed by Preece, equal to the illumination given by a standard candle .at the distance of 12.7 inches. According to Preece, the illumination of the average streets of London, where gas is employed, is equal to about one- tenth of this standard in the neighborhood of a gas lamp, and about one- fiftieth in the middle space between two lamps. The term unit of illumination, in place of in- tensity of light, was proposed by Preece in order to avoid the very great difficulty in determining the intensity of a light in a street or space where there were a number of luminous sources, and where the directions of incidence of the different lights vary so greatly. A carcel standard at the distance of a metre will illumine a surface to the same intensity of illumination as a standard candle at the distance of 12.7 inches. (See Candle, Foot.) Illumined Electrode. (See Electrode, Illumined?) Imbibition Currents. (See Currents, Jm- bibttion.} Images, Electric A term some- times applied to the charge produced on a neighboring surface by induction from a known charge. A positive charge produces, by induction, on a flat metallic surface near it, a negative charge which is distributed with varying density over the surface, but acts electrically as would an equal quantity of negative electricity placed back of the plate at the same distance the positive charge is in front of it. The correspondence of this charge with the image of an object seen in a plane mirror, has led to the term electric image. Maxwell defines electric image as follows: " An electric image is an electrified point, or system of points, on one side of a surface, which would pro- duce, on the other side of that surface, the same electrical action which the actual electrification of the surface really does produce." Impedance. Generally any opposition to current flow. The sum of the ohmic resistance and the spurious resistance of a circuit measured in ohms. A quantity which is related to the strength of the impressed electromotive force of a sim- ple periodic or alternating current, in the same manner that resistance is related to the steady electromotive force of a continuous current. In the case of steady currents, the current strength is equal to the electromotive force dl. vided by the resistance ; or, Electromotive force Current strength = =- Resistance. In the case of a simple periodic or alternating cur- rent, the average current strength is equal to the average impressed electromotive force divided by the impedance ; or, Average current strength = Average impressed electromotive force Impedance. Since impedance, like true resistance of the cir- cuit, can be measured in ohms, it is sometimes called the virtual resistance. Impedance is a quantity equal to the square root of the sum of the squares of the inductive resistance of the circuit and the ohmic resis'ance. In the case of simple periodic or alternating currents, the average current strength is equal to the average impressed electromotive force, divided by the impedance ; the maximum current strength lmp.J 276 [lUCr Is equal to the maximum impressed electromotive force, divided by the impedance. The impedance of a circuit can be repre- sented geometrically as fol lows: Draw a right angled triangle (Fig. 296), the base of which represents the ohmic resistance of the cir- cuit, and the perpendicular, the inductive resistance; Represtnt ation of Im- then the hypothenuse will fedance, represent the impedance. Since the ohmic resistance equals R, and the in- ductive resistance equals the inductance L, mul- tiplied by 2 it n, in which n, is the frequency, the value of the impedance is equal to V/R 8 -+- 4 7T 2 n* L' 1 . Impedance Coil. (See Coil, Impedance?) Impedance, Impulsive or Oscillatory The impedance which a conductor offers to an impulsive or oscillatory dis- charge. The impulsive impedance varies in simple pro- portion to the frequency of the periodic current. It depends on the form and size of the circuit, but it is independent of its resistance or permeability. Imponderable. That which possesses no weight. A term formerly applied to the luminiferous or universal ether, but now generally aban- doned. It is very questionable whether it is possible for any form of matter to be actually imponderable or to possess no attraction for other matter. An imponderable fluid, as, for example, the universal ether, as the term is now generally em- ployed, is a fluid whose weight is comparatively small and insignificant, and not a fluid an infinite quantity of which would be entirely devoid of weight. Impressed Electromotive Force. (See Force, Electromotive, Impressed?) Impulse, Electro-Magnetic An im- pulse produced in the ether surrounding a conductor by the action of an impulsive dis- charge, or by a pulsating field. Impulse, Electromotive An im- pulse producing an impulsive rush of elec- tr'city. The term is employed to distinguish between- the ordinary electromotive force which produces a steady current of electricity and an electromotive impulse which produces an impulsive rush of elec- ^ tricity or impulsive discharge. Impulsion Cell. (See Cell, Impulsion?) Impulsion Effect (See Effect, Impul- sion^) Impulsive Impedance. (See Impedance, Impulsive or Oscillatory?) Incandesce. To shine or glow by means- of heat. Incandescence. The shining or glowing of a substance, generally a solid, by reason of a. sufficiently high temperature. Incandescence, Electric The shin- ing or glowing of a substance, generally a solid, by means of heat of electric origin. Electric incandescence of solid substances differs- from ordinary incandescence, in the fact that un- less the substance is electrically homogeneous throughout, the temperature is not uniform in all parts, but is highest in those portions where the resistance is highest and the radiation smallest. The deposition of carbon in and on a carbon conductor by the flashing process is quite different as performed by electrical incandescence, than it would be if the carbons were heated by ordinary furnace or other heat. (See Carbons, Flashing Process for,") Incandescence, Thermal The shin- ing or glowing of a substance, generally a solid, by means of heat other than that of electric origin. Incandescent. Shining or glowing with heat. Incandescent Ball Electric Lamp. (See- Lamp, Electric, Incandescent Ball?) Incandescent Electric Lamp, Life Curve of (See Curve, Life, of Incandescent Lamp?) Incandescent Electric Lamp, Life of (See Lamp, Electric, Incandescent, Life of?) Incandescent Straight Filament Lamp, (See Lamp, Incandescent, Straight Fila~ ment.} Inc.] 277 [Ind Incandescing. Glowing or shining by means of heat. Inclination, Angle of The angle which a magnetic needle, free to move in a vertical and horizontal plane, makes with a horizontal line passing through its point of support. The angle of magnetic dip. A mignetic needle, supported at its centre of gravity, and capable of moving freely in a ver- tical as well as in a horizontal plane, does not retain a horizontal position at all parts of the earth's surface. The angle which marks its deviation from the horizontal position is called the angle of dip or inclination. (See Dip, Magnetic.} Incandescent Electric Lamp. (See Lamp, Electric, Incandescent?) Inclination Chart. (See Chart, Inclina- tion^) Inclination Compass. (See Compass, In- clination?) Inclination, Magnetic The an- gular deviation from a horizontal position of a freely suspended magnetic needle. (See Dip, Magnetic. Chart, Inclination?) Inclination Map. (See Map or Chart, Inclination?) Inclination of Magnetic Needle. (See Needle, Magnetic, Inclination of.) Inclinometer. A name sometimes given to an inclination compass. (See Compass, Inclination.) Incomplete Circuit. (See Circuit, In- complete?) Increased Electric Irritability.- (See Irritability, Electric, Increased?) Increment Key. (See Key, Increment?) Increment Key of a Qnadruplex Tele- graphic System. (See Key, Increment, of Qiiadruplex Telegraphic System?) India Rubber. A resinous substance ob- tained from the milky juices of several tropi- cal trees. India rubber or caoutchouc is obtained from the Siphonia elastica of "South America. India rubber is quite elastic and possesses high powers of electric insulation. When vulcanized or combined with sulphur, it still retains its powers of electric insulation in a high degree. In this state it is highly electrified by friction. (See Caoutchouc.) Indicating Bell. (See Bell, Indicating?) Indicator, Automatic Any auto- matic device for electrically indicating the number of times a circuit has been opened or closed, and thus the number of times a given operation has occurred which has caused the opening or closing of such circuit. An annunciator with an automatic drop is sometimes called an automatic indicator. (See Annunciator, Electro-Magnetic. Annunciator Drop, Automatic.} Indicator, Electric A name ap- plied to various devices, generally operated by the deflection of a magnetic needle, or the ringing of a bell, or both, for indicating, at some distant point, the condition of an electric circuit, the strength of current that is passing through it, the height of water or other liquid, the pressure on a boiler, the temperature, the speed of an engine or line of shafting, the working of a machine or other similar events or occurrences. A term sometimes used in place of annun- ciator. (See Annunciator, Electro-Magnetic.) Indicators are of various forms. They are generally electro-magnetic in character. They are automatic in action. Indicator, Electric Circuit A de- vice, generally in the form of a vertical gal- vanometer, employed to indicate the presence and direction of a current in a circuit, and often to roughly measure its strength. (See Galvanometer, Vertical.) Indicator, Electric, for Steamships An electric indicator operated by circuits connected with the throttle valve and revers- ing gear of the steam engine. The signal ' ' stop, ' ' for example, sent by the navigating officer to the engineer, causes him to close the throttle. This act places the indicator needle at "stop," and thus informs the officer that his signal has been obeyed. In the same Ind.] 278 [Ind. manner, the opening of the throttle sets the in- dicator needle to "ahead," etc. Indicator, Electric Throwback An annunciator with a drop that is electrically replaced. (See Annunciator, Electro-Mag- netic^) Indicator, Lamp An apparatus used in the central station of a system of in- candescent lamp distribution to indicate the presence of the proper voltage or potential difference on the mains. Fig, 297. Edison-Howell Lamp Indicator. The lamp indicator of Edison and Howell is shown in Fig. 297. It consists essentially of a Wheatstone bridge with the resistances arranged as shown. A galvanometer at G, serves, by the movements of its magnetic needle, to act as an indicator. This needle remains at zero, when the potential difference is the exact voltage re- quired on the circuit with which the indicator is connected. The incandescent lamp at L, being one of the resistances, and being constantly traversed by the current, will have a fixed resist- ance for the temperature at which it is designed to run. The other resistances are so proportioned as to insure the needle at G, remaining at zero. If, however, the potential varies, the temperature of the lamp L, varies, and, being carbon, its re- sistance also varies, a rise of temperature cor- responding to a fall of lamp resistance, which destroys the balance of the bridge and deflects the galvanometer needle. The attendant then regulates the potential to bring the needle back to zero. Indicator, Mechanical Throwback An annunciator with a mechanical drop. (See Annunciator, Electro-Magnetic. An- nunciator, Drop. Annunciator, Gravity) Indicator, Pendulnm An annun- ciator, the indicating arm of which is operated by means of a pendulum. (See Annunciator, Pendulum?) Indicator, Potential An apparatus for indicating the potential difference between any points of a circuit. A voltmeter is a potential indicator. It is, however, more than an indicator, since it gives the value of the potential difference in volts. (See Voltmeter.'} A lamp indicator is a potential in- dicator. (See Indicator, Lamp.) Indicator, Semaphore An annun- ciator in which a gravity drop or shutter is caused to fall by the action of the electric current, thus exposing a number of other signals back of the drop or shutter. Indicator, Speed A name some- times applied to a tachometer. (See Tachom- eter) A form of speed indicator is shown in Fig. 298. The endless screw drives the. wheel when the triangular point is held firmly against the centre of the revolving shaft or pulley. Fig. 298. Speed Indicator. Indicator, Toltaic Battery A de- vice for indicating the condition of a voltaic battery. Indifferent Point. (See Point, Indif- ferent) Indirect Excitation. (See Excitation, Indirect) Induced Atomic Currents. (See Cur- rents, Induced, Atomic or Molecular) Induced Current. (See Current, In- duced) Induced Direct Current. (See Current, Direct, Induced) Induced Electrostatic Charge. (See Charge, Induced Electrostatic) Induced Molecular Currents. (See Cur- rents, Induced Molecular) Ind.] 279 [Ind. Induced Rererse Currents. (See Cur- rent, Reverse, Induced.} Inductance The induction of a circuit on itself, or on other circuits. Self-induction. A term now generally employed instead of self-induction. That property in virtue of which a finite electromotive force, acting on a circuit, does not immediately generate the full current due to its resistance, and when the electromotive force is withdrawn, time is required for the current strength to fall to zero. (Fleming^) A quality by virtue of which the passage of an electric current is necessarily accompanied by the absorption of electric energy in the formation of a magnetic field. The inductance of a circuit depends: (i.) On the form or shape of the circuit. (2.) On the magnetic permeability of the space surrounding the circuit. (3.) On the magnetic permeability of the circuit itself. For the variations of current strength in elec- tric circuits, inductance is not unlike mass, or moment of inertia, as regards variations of velo- city. Time is required to produce velocity in a heavy body by the action of any force; so also time is required to produce a current by the action of an electromotive force. The electro-magnetic energy present in any given current is equal to the square of the current multiplied by the inductance. Since one of these factors (the current strength) represents the force, the other, the inductance, must have the dimension of a distance or length. Inductance, therefore, is measurable in units of length. If the circuits are formed of magnetizable materials, the inductance of a circuit is the ratio between the total inductance taking place through the circuit to the current producing it. If the circuit is formed entirely of non-magnetic material, surrounded entirely by materials of constant magnetic permeability (such as air, in- sulators and diamagnetic materials generally), the inductance is a constant quantity and depends only on the form or shape of the circuit. In this case, the total inductance through the circuit is pro- portional to the magnetizing force, and the mag- netic resistance, or the magnetic conductance of the magnetic circuit, is equal to the total induc- tion through the circuit, divided by the magnetiz- ing force. In cases where the magnetic circuit is partly or wholly of paramagnetic substances, where the induction bears no constant ratio to the magnetiz- ing force, and where the induction takes place partly or wholly in media of variable permeability, the co-efficient of self- induction, or the inductance, must be defined in three ways: (I.) As the ratio between the counter electro- motive force in any circuit and the time rate of variation of the current producing it. (2.) As the ratio between the total induction through the circuit and the current producing it. (3.) As the energy associated with the circuit in the form of magnetic field, due to unit current in that circuit, or as the co-efficient by which half the square of the current must be multiplied to obtain the electro-kinetic energy of the circuit at that instant. (Fleming.) A flat sheet or strip of metal possesses less in- ductance than a round conductor of equal cross- section. This may be explained by conceiving that a flat conductor presents a greater absorption sur- face to the dielectric. Therefore, the perfect form for a conductor transmitting rapidly alternating currents is that of a flat sheet or strip of copper, or preferably a copper tube. The experiments of Hughes show that the in- ductance of a conductor may be regarded as an effect due to the time required for the rapidly periodic current to penetrate the conductor, and that the decrease in the inductance, produced by forming the conductor of a strip or bar, is due to the decreased distance the current has to pass to the inner parts. Inductance, Absolute Unit of A unit of length equal to one centimetre. A length equal to an earth quadrant or IO 9 centimetres is called the practical unit of induct- ance. The practical unit of inductance was form- erly called a secohm or quadrant It is now gen- erally called a henry. (See Henry, A.) Indnctanee Bridge. (See Bridge, In- ductance) Inductance, Co-efflcient of A con- stant quantity, such that when multiplied by the current strength passing in any coil or cir- cuit, will represent numerically the induction through the coil or circuit due to that current Ind.] 280 rind. A term sometimes used for co-efficient of self-induction. (See Induction, Co-efficient of.} Inductance, Constant The induct- ance which occurs in circuits formed wholly of non-magnetic materials, immersed in or surrounded by media of constant magnetic permeability or magnetic conductance for lines of magnetic force. (See Permeability, Magnetic.) When the lines of magnetic force pass through such materials as ordinary insulators, or diamag- netic materials, such as copper, the inductance is constant, provided the geometric form of the cir- cuit remains the same. Inductance, Formal, of Circuit That part of the counter electromotive force of a circuit which depends on the form of the circuit. Inductance, or Self-induction, Practical Unit of A length equal to the earth quadrant or io 9 centimetres. The absolute unit of inductance is equal to I centimetre. Inductance, Oscillatory, Electric Inductance produced by electric oscillations. Inductance, Unit of A term now generally used for unit of self-induction. The value of the inductance may be given either in absolute or in practical units of induct- ance. The absolute unit of inductance is equal to a length of one centimetre. The practical unit of inductance is equal to 1,000,000,000 centi- metres or io 1 centimetres. The practical unit of inductance was formerly called a secohm. The term henry is generally used for this unit. (See Henry, A.) Inductance, Yariable The induc- tance which occurs in circuits formed partly or wholly of substances like iron or other paramagnetic substances, the magnetic permeability of which varies with the inten- sity of the magnetic induction, and where the lines of force have their circuit partly or wholly in such material of variable magnetic permeability. Induction. An influence exerted by a charged body or by a magnetic field on neigh- boring bodies without apparent communica- tion. A medium is necessary to connect the body producing the induction and that in which the induction is produced. (See Induction, Electro- static. Induction, Magnetic. Induction, Electro- Dynamic. ) Induction, Apparent Co-efficient of A term sometimes used for co-efficient of apparent magnetic induction. (See Induc- tion, Magnetic, Apparent Co-efficient of.) It is called the apparent co efficient of induction because its value is different from what it would be if the eddy currents were entirely suppressed. The eddy currents increase the resistance of the primary and decrease its inductance. Induction-Balance, Hughes' (See Balance, Induction, Hughes '.) Induction, Balance of, in Cable The removal of induction in a cable by neutralization by the presence of equal and opposite effects. A balance is obtained of the inductive effects of the neighboring conductors, whether in the bunched cable or outside of it. Induction-Bridge. (See Bridge, Induc- tance^) Induction, Co-efficient of A term sometimes used for co-efficient of magnetic induction. (See Induction, Magnetic, Co- efficient of.) Induction Coil. (See Coil, Induction.) Induction Coil, Inverted (See Coil, Induction, Inverted. Transformer) Induction, Current A term some- times used for voltaic induction. (See Induc- tion, Voltaic. Induction, Electro-Dynamic) Induction, Dissymmetrical, of Armature An induction produced by the passage of a different number of lines of magnetic force through adjoining halves of the arma- ture. Induction, Electro-Dynamic Elec- tromotive forces set up by induction in con- ductors which are either actually or practically moved so as to cut the lines of magnetic force. Ind.] 281 [Ind. These electromotive forces, when permitted lo act through a circuit, produce an electric current. Electro-dynamic induction may be produced in any circuit in two ways: (I.) By causing expanding or contracting lines of magnetic force to pass through that circuit. (2.) By causing the circuit or conductor to pass through the lines of magnetic force. In all cases the lines of force are made to pass through the conductor or wire. There are four cases of electro-magnetic induc- tion: (I.) That in which expanding or contracting lines of magnetic force, produced by rapidly vary- ing the current in any circuit, are caused to pass through or cut that circuit and consequently to produce differences of potential therein. (2.) That in which expanding or contracting lines of magnetic force produced by any circuit by the rapidly varying strength of the electric current passing through that circuit, are caused to pass through another neighboring circuit and thus produce differences of potential therein. (3.) That produced by moving a conductor through a magnetic field so as to cut its lines of magnetic force. In this way the strength of the magnetic field may remain practically constant, but this strength . as regards the field of the fixed conductor is varying, as the magnet producing such a field is moved toward or from such cir- cuit, and in this way differences of potential are produced in the circuit. (4.) That produced by moving an inducing field past a fixed conductor. This may be accom- plished by moving an electro-magnet, an electric circuit, or a permanent magnet past the conductor in which the difference of potential is to be in- duced. There are therefore four distinct varieties of electro-dynamic induction: (i.) Self-induction or inductance. (See/nduct- ance.) (2.) Mutual induction, or, as it is sometimes called, voltaic current induction. (See Induction, Mutual.) (3.) Electro-magnetic induction, or, as it is sometimes called, dynamo-electric induction. (4.) Magneto-electric induction. _ - If the terminals of a voltaic cell be connected with the ends of a comparatively long coil of in- sulated wire, no appreciable spark will be observed on closing the cell, because the current induced by self-induction is in the opposite direction to the current of the cell and weakens it. On breaking contact, however, a spark is readily observed. This is due to the induced current on breaking, which, flowing in the same direction as the cur- rent of the cell, strengthens it. Fig. 299. Mutual Induction The coil B, Fig. 299, consists of two parallel coils of insulated wire, the terminals of one of which, called the primary coil, are connected with the battery cell P N, and those of the otner, called the secondary coil, with the galva- nometer G. Under these circumstances it is found : ( i . ) That at the moment of closing the circuit through the primary coil, a momentary current is produced in the secondary coil in a direction opposite to that of the current through the primary, as is shown by the direction of the deflection of the needle of the galvanometer. (2.) At the moment of breaking the circuit through the primary coil, an induced current is produced in the secondary coil in the same direc- tion as that flowing through the primary coil. (3.) These induced currents are momentary, and continue in the secondary only while the in- tensity of the current in the primary is varying, *'. h . frductive.\ Inductor Dynamo. (See Dynamo, Induc- tor.) Induct orium. A name sometimes applied to a Ruhmkorff induction coil. (See Coil, Induction) Inequality, Annual, of Earth's Magnetic Tariation or Inclination Annual variations in the value of the magnetic varia- tion or inclination at any place. (See Varia- tion, Magnetic. Inclination, Magnetic?) Inequality, Annual, of Earth's Magnet- ism Variations in the value of the earth's magnetism during the earth's revolu- tion depending on the position of the sun. Annual variations in the earth's magnetism. (See Variations, Magnetic, Annual?) Inequality, Diurnal, of Earth's Magnetic Variation or Inclination Diurnal variations in the value of the earth's magnetic variation or inclination. (See Variation, Magnetic. Inclination, Magnetic?) Inequality, Diurnal, of Earth's Magnet- ism Inequalities or variations in the value of the earth's magnetism, dependent on the position of the sun during the earth's rotation. Inequality, Lunar, of Earth's Magnetic Variation or Inclination Small va- riations in the value of the magnetic variation or inclination, dependent on the position of the moon as regards the magnetic meridian. Inequality, Lnnar, of Earth's Magnet- ism Small variations in the value of the earth's magnetism dependent on the po- sition of the moon as regards the magnetic meridian. Inertia. The inability of a body to change its condition of rest or motion, unless some force acts on it. The inertia of matter is expressed in Newton's first law of motion, as follows : "Every body tends to preserve its state of rest or of uniform motion in a straight line, except in so far as it is acted on by an impressed force." All matter possesses inertia. Inertia, Electric A term some- times employed instead of electro-magnetic inertia. (See Inertia, Electro-Magnetic?) Inc.] 290 [Ills. A term employed to indicate the tendency of a current to resist its stopping or starting. By self-induction an electromotive force is pro- duced in a wire or other conductor at the moment of starting the current in it that tends to oppose the starting of such current, and also an electro- motive force at the moment of stopping the cur- rent, in such a direction as to prolong or continue the current. In other words, self induction tends to retard the rise or fall of the current. Fleming traces the following comparison be- tween the moment of inertia of a rotating wheel and the energy of its rotation on the one side, and the inductance of a circuit and the electro-mag- netic energy of the circuit on the other. (I.) The angular momentum of a fly-wheel is equal to the numerical product of its moment of inertia and the angular velocity of the wheel. Similarly the electro-magnetic momentum is equal to the product of the inductance of the circuit by the current flowing through it at any instant. (2.) The rate of change of the angular mo- mentum of the wheel, at any instant, is a measure of the rotational force of the couple acting at that instant Similarly the rate of change of the electro-mag- netic momentum of the circuit is the measure o f the electromotive force acting on it so far as mere change of current is concerned, and irre- spective of that part cf the electromotive force re- quired to overcome the ohmic resistance. An electric current does not start or stop in- stantaneously. It requires time to do either, just as a stream of water or other fluid does, and it is this property which is referred to by the term electric inertia. Inertia does not appear to be possessed by electricity apart from matter. " It is doubtful," says Lodge, "whether electricity of itself, and disconnected from matter, has any inertia." Inertia, Electro-Magnetic A term sometimes employed instead of inductance, or the self-induction of a current. (See In- ductance, Inertia, Electric?) Inertia, Electro-Magnetic, Co-efficient of A term sometimes employed in place of the co-efficient of inductance or self-induct- ance of a circuit. Inertia, Magnetic The inability of a magnetic core to instantly lose or acquire magnetism. A magnet core tends to continue in the mag- netic state in which it was plact d. The magnetic inertia is sometimes called the magnetic lag. To decrease the magnetic inertia, the strength of the magnetizing current is increased and the length of the iron core decreased. The iron should also be quite soft. (See Lag, Magnetic. Force, Coercive.) Inferred Zero. (See Zero, Inferred} Infinity Plug. (See Plug, Infinity.} Influence. A term sometimes used instead of electrostatic induction. (See Induction, Electrostatic} The word influence is used by some to apply t > the case of electrostatic induction, as distin- guished from electro-magnetic or magnetic induc- tion. Influence Charge. (See Charge, Influ- enced) Influence Machine. (See Machine, In- fluence} Inker, Morse A form of tele- graphic ink-writer. (See Ink- Writer, Tele- graphic} Ink-Writer, Telegraphic A device employed for recording the dots and dashes of a telegraphic message in ink on a fillet or strip of paper. A telegraphic ink-writer is a form of telegraphic recorder. (See Recorder, Morse.} Inside Wiring. (See Wiring, Inside} Insolation, Electric A term some- times employed for electric sunstroke, or electric prostration. (See Sunstroke, Elec- tric. Prostration, Electric} Installation. A term embracing the entire plant and its accessories required to perform any specified work. The act of placing, arranging or erecting a plant or apparatus. Installation, Electric The estab- lishment of any electric plant. An electric light installation, for example, in- cludes the steam engine and boilers, or other prime movers, the dynamo-electric machines, the line wires or leads, and the lamps. Insulated Body. (See Body, Insulated^ Jns.J 291 [Ins. Insulating Cements. (See Cements, In- sulating.) Insulating Sleeye. (See Sleeve, Insula- ting.) Insulating Stool. (See Stool, Insula- ting.) Insulating Tape. (See Tape, Insula- ting.) Insulating Tube. (See Tube, Insula- ting.) Insulating Varnish. (See Varnish, Elec- tric.) Insulation, Electric Non-conduct- ing material so placed with respect to a con- ductor as to prevent the loss of a charge, or the leakage of a current. In the case of coils the character of the insula- tion of the coil of wires through which the cur- rent is to pass must be considered from the stand- point of the cooling of the coil by radiation. In considering the safest and most economical current density to employ in any dynamo or motor, the depth of the coil, i. e., the thickness of its coils, must be considered, as well as the char- acter of the materials employed for the insulation. Such substances as silk or wool, which are char- acterized by low heat conduction, retain the heat longer than cotton. Hence the depth of a silk covered coil should necessarily be less than that of one covered with cotton. Insulation Joint. (See Joint, Insula- tion^ Insulation, Porous An insulating material containing air or gas placed between the conductor and the insulating covering. A strip of perforated paper is used for cover- ing the bare conductor, and the insulating ma- terial is placed on the outside of this ; or, a cord is wrapped separately around the conductor, and the insulating material is placed on the outside of this. By these means, as will be seen, a layer of air exists between the conductor and its insulating .covering. Insulation Resistance. (See Resistance, Insulation?) Insulation, Static A term em- ployed in electro-therapeutics for a method of treatment by convection streams or dis- charges, in which the patient is seated on an insulated stool connected to one pole or electrode of an influence machine, while the other pole or electrode is connected to the ground. Insulator Cap. (See Cap, Insulator^ Insulator, Dice-Box A name some- times applied to a double-cone insulator. (See Insulator, Double-Cone?) Insulator, Double-Cone An insu- lator in which the line wire passes through and is supported by means of a tube consisting of two inverted cones joined at their smaller bases. Insulator, Double-Cup An insula- tor consisting of two funnel-shaped cups, placed in an inverted position on the sup- porting pin and insulated from one another by a free air space, except near the ends, which are cemented. The wire is wrapped in a groove on the outside of the outer cup. This possesses the advantage of exposing it to the rain, which thus cleanses the insulator and improves its power of insulation. The inner cup is supported on a pin and the outer cup cemented to it. Any leakage must, there- fore, pass over the entire surface of bjJi cups. Insulator, Double-Shackle A form of insulator used in shackling a wire, consist- ing of two single-shackle insulators. Insulator, Double-Shed A double- cup insulator. (See Insulator, Double-Cup) Insulator, Fluid An insulator pro- vided with a small, internally placed, annular, cup-shaped space, filled with an insulating oil, thus increasing the insulating power of the support. The line wire is wrapped in a groove on the outside of the insulator. Any surface leakage between the wire and ground in wet weather must occur between the outer surface of the insu- lator, which is kept cleansed by the rain, and the inner surface, where it is supported by the pin. But to do this, the current must cross the oil in the cup, which, from its high power of insulation, effectually prevents leakage. Insulator, Invert An insulator Ins.] 292 [Int. placed on the top of the wire instead of under- neath it, as was formerly done. Insulator, Oil A fluid insulator filled with oil. (See Insulator, Fluid.} Insulator Pins. (See Pins, Insulator!) Insulator, Single-Shackle A form of insulator used for shackling a wire. (See Shackling a Wire) Insulator, Single-Shed An insula- tor with a single inverted cup. The wire is wrapped around a groove on the outside of the cup, where it is exposed to the cleansing action of the rain. The cup is inverted and supported on a pin, to which it is screwed and cemented. Insulator, Telegraphic or Telephonic A non-conducting support of tele- graphic, telephonic, electric light or other wires. Insulators are generally made of glass, earthen- Fig. 310. Glass Insulator. Fig- 3ir. Porcelain Insulator. ware, porcelain or hard rubber, and assume a variety of forms, some of which are shown in Figs. 310, 311 and 312. Of whatever material they are made, it is necessary that the surface on which the wire rests, or around which it is wrapped, should be smooth, so as to avoid abrasion, either of its insulat ing covering or of the wire i - self. Two things are to be con sidered in the selection of an insulator, viz : (I.) The insulating power of the material of which the in- sulator is composed, so as to Fig. 312. Hard reduce the leakage as much as KtMer Insulator. possible. (See Leakage, Electric.) (2.) The tensile strength of the material, so that in case of heavy wires no breaks may result from the fracture of the insulator. Some forms of insulators are shown in Figs. 310, 311 and 312. They are screwed to the pins by the threads shown. The insulating materials of which they are formed are of glass, porcelain and hard rubber respectively. Insulator, Window-Tube A tube of vulcanite or other insulating material pro- vided for the insulation of a wire entering a room. The wire conductor passes through the middle of the tube, which is firmly fixed in an opening passing through the window frame. Insulator, Z A form of double- cup insulator in which the insulating material, earthenware or porcelain, is made in a single piece, instead of in two separate pieces. The body of the insulator is conical in form r and the interior air space presents a shape ap- proximately that of the letter Z. The double form is used in order to diminish the leakage. Intensity Armature. (See Armature, Intensity?) Intensity, Connection of Voltaic Cells for A term formerly employed for series- connected voltaic battery cells. (Obsolete.) Intensity, Magnetic Density of magnetic induction. Magnetic flux per square centimetre. A committee of the American Institute of Elec- trical Engineers on "Units and Standards," pro- poses the following definition for magnetic inten- sity: The induction density at a point within an ele- ment of surface is the surface differential at that point. The practical unit of magnetic intensity i* 10^ or 100,000.000 C. G. S. lines per square cen- timetre. In practice, excluding the earth's field, intensi- ties range from 100 to 20,000 C. G. S. lines per square centimetre, and the working unit should, perhaps, have the prefix milli or micro. Intensity, Magnetic, Pole of The earth's magnetic poles as determined by means of the oscillations of a magnetic need'e. Int] 293 [Ion. The points of the earth's greatest magnetic intensity. Intensity of Current. (See Current, In- tensity of.) Intensity of Field. (See Field, Inten- sity of.) Intensity of Light. (See Light, Inten- sity of.) Intensity of Magnetization. (See Mag- netization, Intensity of) Intensity, Photometric, Unit of The amount of light produced by a candle that consumes two grains of snermaceti wax per minute. (See Candle.) Inter Air Space. (See Space, Inter Air.) Intercrossing. In a system of telephonic communication, a device for avoiding the dis- turbing effects of induction by alternately crossing equal sections of the line. (See Connection, Telephonic Cross.) Interference of Electro-Magnetic Wares. (See Waves, Electro-Magnetic, Interference of.) Interlocking Apparatus. (See Appa- ratus Interlocking) Intermittent Contact. (See Contact, In- termittent^) Intermittent Cross. A form of electric cross. (See Cross, Electric) Intermittent Current. (See Current, In- termittent) Intermittent Disconnection. (See Dis- connection, Intermittent ) Intermittent Earth. (See Earth, Inter- mittent) Internal Circuit (See Circuit, In- ternal) Internal Polarization of Moist Bodies. (See Polarization, Internal, of Moist Bodies) Interrupter. Any device for interrupting or breaking a circuit. Interrupter, Automatic An auto- matic contact breaker. (See Make-and- Break, Automatic.) Interrupter, Reed A term some- times applied to a tuning-fork interrupter. (See Interrupter, Tuning-Fork) Interrupter, Tuning-Fork An in- terrupter in which the successive makes and breaks are produced by the vibrations of a tuning-fork or reed. The tuning-fork or reed is maintained in vibra- tion by any suitable means. Such interrupters are applied to various uses. Synchronous mul- tiplex telegraphy affords an example of such "uses. Invariable Calibration of Galvanometer. (See Calibration, Invariable, of Galva~ nometer) Inverse Electromotive Force. (See Force* Electromotive, Inverse) Inverse or Make-Induced Current. (See Current, Make-Induced) Inverse Secondary Current (See Cur- rent, Inverse Secondarv) Inversion, Thermo-Electric An inversion of the thermo-electric electromotive force of a couple at certain temperatures. (See Diagram, Thermo-Electric) Invert Insulator. (See Insulator, In- vert) Inverted Induction Coil. (See Coil, Induction, Inverted) Inverted Type of Dynamo. (See Dy- namo, Inverted) Invisible Electric Floor Matting. (See Matting, Invisible Electric Floor) Ions. Groups of atoms or radicals which result from the electrolytic decomposition of a molecule. The ions are respectively electro-positive and electro-negative. The electro-positive ion ap- pears at the plate connected with the electro- negative terminal, or at the kathode, and is called the kaihion. The electro-negative ion appears at the plate connected with the electro-positive terminal, or at the anode, and is called the anion. (See Electrolysis. Kathion. Anion) Ions, Electro-Negative The neg- ative atoms, or groups of atoms, called rad- icals, into which the molecules of an electro- lon.j 294 [ISO. lyte are decomposed by electrolysis. (See Electrolysis^ The electro-negative ions are called the anions, because they appear at the anode of a decompo- sition cell. (See Anions. Anode.} Ions, Electro-Positive The pos- itive atoms, or groups of atoms, called rad- icals, into which the molecules of an electro- lyte are decomposed by electrolysis. (See Electrolysis?) The electro-positive ions are called the kathions, "because they appear at the kathode of a decom- position cell. (See Kathion. Kathode.) Iron-Clad Electro-Magnet. (See Mag- net, Electro, Iron-Clad?) Iron-Clad Magnet. (See Magnet, Iron- Clad:) Iron Core, Effect of, on the Magnetic Strength of a Hollow Coil of Wire An increase in the number of lines of mag- netic force, beyond those produced by the current itself, due to the opening out of the closed magnetic circuits in the atoms or molecules of the iron. The atoms or molecules of the iron possess naturally closed magnetic circuits, or closed lines of magnetic force, lying entirely within the mass of the iron. When the iron is placed in a magnetic field, these minute closed circuits open out and are added to the lines of force produced by the circuit itself. The opening out of these closed atomic or molecular lines of magnetic force is at- tended by the formation of lines of polarized molecules or atoms. Roughly speaking, according to Lodge, for each single line of magnetic force produced by the electric current, there are some 3,000 lines of magnetic force added to it from the iron, the ex- act number varying with the kind of iron, the physical condition of the iron and the degree of magnetization. Iron, Galvanized Iron covered by a layer of zinc by dipping it in a bath of molten zinc. The process of galvanizing iron is designed to prevent the corrosion or rusting of the iron on exposure to the air. (See Metals, Electrical Pro- tection of.} The word galvanized probably had its origin in an assumed galvanic or voltaic action, in causing the zinc to adhere to the iron. The true galvanic or voltaic action, viz., the galvanic protection, comes after the galvanizing process is completed. Iron-Work Fault of Dynamo. (See Fault, Iron- Work, of Dynamo?) Irreversible Heat. (See Heat, Irreversi- ble?) Irritability, Electric Irritability of nervous or muscular tissue by an electric discharge. Irritability, Electric, Diminished A decreased irritability of nervous or muscu- lar tissue, produced by an electric current of given strength. Diminished electric irritability is often present in certain diseases of the motor apparatus. Irritability, Electric, Increased An irritability of nervous or muscular tissue produced by a much weaker electric current than that required to produce it in normal tissue. Irritability, Faradic Muscular contractions produced by the action of a faradic current on a nerve. The action of the faradic current is to cause a prolonged tonic contraction, which continues while the current continues. Though the natural action is to produce a contraction, followed by a relaxation on each make and break, yet the makes and breaks follow one another so rapidly that the relaxation has not time to occur before the next contraction follows. Irritability, Galvanic Muscular contractions produced by the action of a gal- vanic current. The action of a galvanic current is to cause a single, quick, momentary contraction of a muscle on each starting or completion of the circuit. The contractions are stronger in the case of galvanic currents when the direction of the cur- rent is reversed with a commutator instead of by an actual break at the poles. Such a break is called a voltaic alternative, and the currents so pro- duced voltaic alternatives. (Sea Alternatives, Voltaic.} Isobaric Lines. (See Lines, Isobaric?) Isobars. Lines connecting places on the ISO.] 295 [Jar. earth's surface which have the same barome- tric pressure. The isobaric lines are generally corrected for differences of elevation of the surface. Isobars are often called isobaric lines. A study of the isobaric lines, or isobars, is of great assistance in making forecasts or predictions of coming changes in the weather. Isochasmen Curves. (See Curves, Iso- chasmen?) Isochronism. Equality of time of vibra- tion or motion. Isochronize. To produce equality of time of vibration or motion. (See Isochron- ism?) Isochronizing. Producing equality of time of vibration or motion. (See Isochron- ism?) Isochronous Yibrations or Oscillations. (See Vibrations or Oscillations, Isochron- ous?) Isoclinic Chart (See Chart, Inclina- tion?) Isoclinic Lines. (See Lines, Isoclinic?) Isodynamic Chart. (See Chart, Isody- namic?) Isodynamic Lines. (See Lines, Isody- namic?) Isodynamic Map. (See Chart, Isody- namic?) Iso-Electric Points. (See Points, Iso- Electric?) Isogonal. Pertaining to the isogonic lines. Isogonal Lines. (See Lines, Isogonal?) Isogonal Map or Chart (See Map or Chart, Isogonal?) Isogonic. Pertaining to the isogonal lines. Isogonic Chart (See Chart, Isogonic?) Isogonic Lines. (See Lines, Isogonic?) Isogonic Map. (See Map, Isogonic?) Isolated Electric Lighting. -(See Light- ing^ Electric, Isolated?) Isolatine. A kind of insulating material. Isothermal Surfaces. (See Surfaces, Iso- thermal?) Isotropic Conductor. (See Conductor, Isotropic?) Isotropic Medium. (See Medium, Iso- tropic?) J. A contraction proposed for Joule. Jablochkoff Candle. (See Candle, Jab- Jacketed Magnet. (See Magnet, Jack- eted?) Jacobi's Law. (See Law, Jacob? s?) Jar, Electric A name formerly given to the Leyden jar. Jar, Leyden A condenser in the form of a jar, in which the metallic coatings are placed opposite each other on the outside and the inside of the jar respectively. The metal coatings should not extend to more than two- thirds of the height of the jar, the rest of (he glass being varnished to avoid the creeping of the charges over the glass in damp weather. The inside coating is connected by means of a metallic chain to a knob on the top of the jar, as shown in Fig. 313. The conductor supporting the knob passes through a dry cork or plug of some insulating material. To charge the jar, the outside coating is con- nected with the earth, as by holding it in the hand, and the outside coating is connected with the conductor of a machine. (See Condenser. Accu- mulator ) The inner coating of the jar is usually con- nected with the knob by means of a chain or wire Fi "'3'3- Leyden Jar. as shown above. This necessitates a support for the ball and stem, which is generally obtained by a cork or wooden plug inserted in the mouth of Jar.] 296 [Jet. the jar. Such a form, however, is extremely ob- jectionable, since, although the top of the jar be covered with shellac varnish to avoid leakage, it affords but a poor insulation in damp weather, be- cause both the metallic rod supporting the ball and Fig. 314* Sir William Thomson's Leyden Jar. the damp wood or cork are in connection with the glass and thus facilitate leakage. To overcome these objections a form of jar has been devised by Sir William Thomson, in which the knob is supported on three feet, which rest on the inner coating. In this form the uncoated glass can he readily kept dry and clean. This form is shown in Fig. 314. A layer of sulphuric acid is sometimes employed for the inner coating of the Leyden jar. This serves the double purpose of acting as a coating and an absorber of moisture during damp weather. Jar, Leyden, Capacity of The quantity of electricity a Leyden jar will hold at a given difference of potential. The capacity of a jar is equal to the quantity of electricity divided by the difference of potential such quantity produces in the jar; or the capacity : the quantity, and V, the differ- ence of potential. Jar, Leyden, Coatings of (See Coatings of Leyden Jar.) Jar, Lightning A Leyden jar, the coatings of which consist of metallic filings. As the discharge passes, an irregular series of sparks appear, which somewhat resemble in their shape a lightning flash. Hence the origin of the term. Jar of Secondary Cell. The containing = 5, where Q vessel in which the plates of a single secondary- cell are placed. Jar, Porous A porous cell. (See Cell, Porous^ Jar, Scintillating A Leyden jar, the coatings of which, instead of being formed of continuous sheets of tin-foil or other con- ducting substances, are formed of small pieces of such substances, placed at regular intervals on the glass or dielectric so as to leave a small space between them. Such a jar has received the name of scintillat- ing jar, because when discharged by connecting its two opposite coatings the discharge appears as minute sparks, wiiLh jump across the space between the metallic pieces. Jar, Unit A small Leyden jar some- times employed to measure approximately the quantity of electricity passed into a Leyden battery or condenser. As sh wn in Fig. 315, the unit jar consists of a. small Leyden jar j, whose outer coating is con- nected with a sliding metallic a \ rod b, provided at each end with a rounded knob, and the inner coating of which is con- nected with a metallic knob c, placed as shown, inside a glass jar d, opposite a ball on the lower end of b. When, now, the inside of the unit jar, or the end con- nected with c, is connected with the charging source, such as a machine, and the outside at a, is connected with the jar or jars to be charged, for every spark that passes be-^'* ""**"' tween d and c, a definite quantity has passed a. The value of this unit charge may be varied by varying the distance between d and c. The smaller the unit jar is in proportion to the jar to be charged, and the shorter the distance between c and d, the more reliable are the com- parative results obtained. Jars, Leyden, Charging, by Cascade (See Cascade, Charging Leyden Jars by.) Jet, Gas, Carcel Standard A lighted gas jet employed for determining the candle-power of gas by measuring the height Jet] 297 [Joi. of a jet of gas burning under a given press- ure, and used in connection with the light of a larger gas burner, burning under similar conditions, for the photometric measurement of electric lights. Seven-Carcel Standard Gas Jet. Fig- 317- Cared Candle Burner. In Fig. 316 is shown a section of a seven-carcel standard gas jet, and in Fig. 317, a section of a candle burner, connected within the same service pipe. The gas for both burners is received in a chamber, from whence it passes by an opening to the burner, under the constant pressure obtained by the weight of the bell C, ard the tube A. The turner shown in Fig. 317, which is used as the standard of comparison, will give a candle-power determined from the height of the jet of the burning gas. This height is measured in milli- metres by the motion of a circular screen. The determination of the candle power of gas by means of a jet photometer is only approximately correct, unless many precautions are taken. Jet Photometer. (See Photometer, Jet.) Jewelry, Electric -- Minute incan- descent electric lamps substituted for the rarer gems in articles of jewelry. The lamps are lighted by means of small pri- mary or storage batteries, carried in the pocket or elsewhere on the person. Joint, American Twist --- A tele- graphic or telephonic joint in which each of the two wires is twisted around the other. Telegraphic or Telephonic.) The twisted joint is sometimes subsequently soldered. Fig jiS. American Twist Joint. The American twist joint is shown in Fig. 318. This joint is easi.y made and is very serviceable. Joint, Bell-Hanger's A joint for telegraphic or telephonic wires in which the ends are merely looped together. (See Joint, Telegraphic or Telephonic) Joint, Britannia A telegraphic or telephonic joint in which the wires are laid side by side, bound together and subsequently soldered. (See Joint, Telegraphic or Tele- phonic) 1111 111!! 11 F 'g' 3 f 9- Brit a Joint. The Britannia joint is shown in Fig. 319. No, 16 wire, B. W. G., is used as the binding wire. Joint, Bntt An end-to-end joint. A joint effected in wires by placing the wires end on and subsequently soldering. Butt joints are formed by bringing the ends to be joined together and securing them while in such position. Joint, Bntt and Lap, of Belts The joint in a leather belt, employed for transmit- ting power from a line of shafting where the ends are simply brought together and laced, is called a butt joint, in contradistinction to a lap joint, or a joint formed by placing one end of the belt over the other and lacing or rivet- ing the two. In using delicate galvanometers, the slightest change in the speed of the engine driving the dynamo-electric machine producing the current, causes an annoying fluctuation of the needle that prevents accurate reading, when lap joints are used in the b_lt instead of butt joints, unless the former are very carefully made. Lap joints may also cause a flickering in the lights. When, however, Inp j jints are made by cutting the belt by an oSliqne section and properly securing them so that th-. ir Joi.] 298 [Joi. elevation at the joint is no greater than elsewhere, the lap joint is preferable to the butt joint. Joint, Expansion A joint for under- ground conductors, tubes or pipes, exposed to considerable changes of temperature, in which a sliding joint is provided to safely permit a change of length on expansion or contraction. Joint, Insulation A joint in an insu- lating material or covering in which a conti- nuity is insured in the conducting as well as the insulating substance. Joint, Lap^ A joint effected by over- lapping short portions near the ends of the things to be joined, and securing them while in such position. Joint, Lap, for Wires A joint effected between two wires by overlapping their ends and subsequently soldering. Joint^Magnetic The line of junc- tion between two separate parts of magnetiza- ble materal. Magnetic joints should be of such a nature as to permit the passage of the lines of magnetic force with the least increase in the resistance of the magnetic circuit. Magnetic joints in the field magnets of a dynamo- electric machine should be as few as possible, since the resistance of the best magnetic joint to the passage of the lines of force is necessarily greater than that of the same material without such joints. Joint, Metallic Conducting A joint in a conductor in which a continuity of con- ducting power is secured. Joint Resistance of Parallel Circuits. (See Resistance, Joint, of Parallel Circuits^ Joint, Sleeve A junction of the ends of conducting wires obtained by passing them through tubes and then twisting and soldering. All joints should be soldered, but in so doing care must be taken that the soldering liquid or solid employed is free from acids or other corro- sive materials, and that all traces of the soldering liquid or solid are removed from the wire before the joint is covered with insulating material. Kerite, okonite or other insulating tape, should preferably be wrapped around the joint after it is soldered. In making a joint in a gutta-percha covered wire, such as a submarine cable, the following method may be employed: The bared and cleansed wires are twisted together and soldered. The soldered joint is then covered with a layer of plastic insulating material made of a mixture of gutta-percha, tar and rosin. (See Chattertori '.r Compound. ) In order to insure a good junction between this and the gutta-percha covering on the rest of the -wire, the outer surface of the gutta- percha is removed for about two inches from each side of the joint, so as to remove its oxidized sur- face. After the coating is put on, it is warmed gently by a warm joining tool, not by the flame of a lamp. A sheet of -warmed gutta-percha is then wrapped around the joint, and while it and the joint are still hot, another coating of the plastic insulating material is applied. Successive layers of gutta-percha and some other insulating material are generally applied in the case of sub- marine cables. (Culley.) Joint, Telegraphic, Mclntire's Parallel Sleeve A joint for telegraphic or other wires, in which the ends to be joined are slipped into parallel sleeves or tubes, which are afterward twisted around each other. A general view of the parallel sleeve joint, both before and after twisting, is shown in Fig. 320. Fig. 320. Mclntire's Parallel Sleeve Joint. The twisting is done by means of the specially devised twisting clamp shown in Fig. 321. Fig. 321. Twisting Clampfor Mclntire's Parallel Joint* Joint, Telegraphic or Telephonic A juncture of the ends of two electric con- ductors so as to insure a permanent junc- tion whose resistance shall not be appreci- ably greater per unit of length than that of the rest of the wire. Joi.J 299 [Kao. In making a joint, care should always be taken to scrape the insulating material from the wires and clean their surfaces before twisting them to- gether. Telegraph wires were formerly joined by the ordinary bell-hangers' joint; that is, the wires were simply looped together. The constant vibrations to which the wires are subjected caused such a joint to be abandoned and an improvement intro- duced by bolting the ends together, as shown in Fig. 322. Fig. 332. Telegraphic Joint. Joint, Testing of Ascertaining the resistance of the insulating material around a joint in a cable. The resistance of the insulating material of a cable at a joint is necessarily high, since the joint forms but a small part of length of the cable. It should not, however, be large as compared with an equal length of another part of the cable with a perfect core. Two methods for testing cable joints are gener- ally employed, viz. : (i.) A conductor is charged through the joints for a given time, and the deflection obtained by its discharge compared with the discharge of the same condenser charged for an equal length of time through a few feet of perfect cable. (2.) A charged conductor is permitted to dis- charge itself through the joint, and the amount lost in a given time noted. For description of different methods, see Kempe's " Handbook of Electrical Testing." Joulad. A term proposed for the Joule. This term is not generally adopted. (See Joule.} Joule. The unit of electric energy or work. The volt-coulomb. The amount of electric work required to raise the potential of one coulomb of elec- tricity one volt. The joule may be regarded as a unit of energy or work in general, apart from electrical work or energy. I joule ......... = 10,000,000 ergs. I joule .......... = . 73732 foot-pounds. I joule .......... = I volt-coulomb. I joule .......... = .24 calorie. 4.2 joules ......... = i small calorie. i joule per second = i watt. The British Association proposed to call one joule the work done by one watt in one second. Joule, as a Heat Unit. The quantity of heat developed by the passage of a current of one ampere through a resistance of one ohm. Joule Effect. (See Effect, Joule) Joule's Cylindrical Electro-Magnet. (See Magnet, Electro, Joule's Cylindrical) Joule's Law. (See Laws of Joule.) Junction Box. (See Sox, Junction.) Jump-Spark Burner. (See Burner, fump-Spark) Junction, Thermo-Electric. A junction between any thermo-electric couple. (See Cell, Thermo-Electric) K. A contraction for electrostatic capa- city. (See Capacity, Electrostatic) K. C. C. In electro-therapeutics, a brief method of writing kathodic closure contrac- tion, or the effects of muscular contraction observed at the kathode on the closure of a circuit. K. P. C. In electro-therapeutics, a brief method of writing kathodic duration con- traction, or the effects of muscular contrac- tion observed at the kathode after the current has been passing for some time. K. W. A contraction for kilo-watt. (See Watt, Kilo) Kaolin. A variety of white clay some- times employed for insulating purposes. Jablochkoff sometimes employed kaolin be- tween the parallel carbons of his electric candle Kap.] 300 [Key. for the purpose of insulating them from each other. He also devised an electric lamp in which a spark of considerable difference of potential, obtained from an ordinary induction coil, was caused to raise a surface of kaolin to incan- descence by passage over it. Kapp Lines. (See Lines, Kapp.) Eartayert. A kind of insulating material. Eatelectrotonus. A word sometimes used instead of kathelectrotonus. (See Kathe- lectrotonus^) Kathelectrotonic State. (See State, Kathelectrotonic.) Eathelectrotonic Zone. (See Zone, Kathelectrotonic^ Eathelectrotonus. In electro-therapeu- tics, the condition of increased functional ac- tivity that occurs in a nerve in the neighbor- hood of the kathode or negative electrode. (See Electrotonus.) Kathion. The electro-positive ion, atom or radical into which the molecule of an electrolyte is decomposed by electrolysis. (See Electrolysis, Jons,) Kathion is sometimes written cathion. In electrolysis the kathion, or the electro-posi- tive ion or radical, appears at the kathode or electro-negative electrode. Similarly, the anion, or the electro-negative ion or radical, appears at the anode or the electro-positive electrode. Kathodal. Pertaining to the kathode. (See Kathode) Kathode. The conductor or plate of an electro-decomposition cell connected with the negative terminal or electrode of a battery or other source. The word kathode is sometimes applied to the negative terminal of a battery or source, whether connected with a decomposition cell or not. It is preferable, however, to restrict its use to de- composition cells. (See Anode.) The word kathode is sometimes written cathode. Eathodic. Pertaining to the kathode. (See Kathode.) Eathodic Electro-Diagnostic Reactions. (See Reactions, Electro-Diagnostic?) Eeeper of Magnet (See Mag-net, Keeper Eerite. An insulating material. Eerr Effect (See Effect, Kerr.) Eey Board. (See Board, Key.) Eey, Capillary Contact A form of fluid contact in which the circuit is closed or broken by means of a wire which is dipped into or removed from the surface of a mass of mercury. In order to avoid an increase in the resistance of the circuit, due to the formation of oxide of mercury, the contact surface of the mercury is kept covered with a layer of dilute alcohol. Eey, Discharge A key employed to enable the discharge from a condenser or cable to be readily passed through a galva- nometer for purposes of measurement. Eey, Discharge, Eempe's A dis- charge key constructed as shown in Fig. 323. Fig. 323. Kempe's Discharge Key. The solid lever, hinged at one extremity, plays between two contacts connected to two terminals, and has two finger triggers at its free end marked "Discharge" and "Insulate," connected respec- tively to two ebonite hooks. The hook attached to that marked " Discharge " is a little higher than the other, so that when the lever is caught against it, the key rests in an intermediate position be- tween the contacts, and, when caught against the lower trigger, it rests against the bottom contact. When in the last position, a depression of the " Insulate " trigger causes the lever to spring up against the second hook, thus insulating it from either contact, and on the depression of the ' ' Dis- charge " trigger, the lever springs up against the top contact. Eey, Discharge, Webb's A dis- charge key constructed as shown in Fig. 324. A horizontal lever L, Fig. 324, passing between two contacts and hinged at J, is pressed upward by a spring. The free end of this lever termi- nates in two steps, I and 2. A vertical lever, pro- Key.] 301 [Key. vided with an insulating handle, is jointed at J', and has at C, a projecting metallic tongue that engages in the upper step when the lever H, is vertical, and on the lower step when it is slightly moved from the free end. When the projection C, rests on the lower step 2, the lever L, is intermediate between the top and bottom contacts, and is, therefore, discon- ff Fig, 324.. Webb's Disc/large Key. nected from either of them; but, when it rests on the upper step, it is in contact with the lower contact. When the lever H,is so moved as to have the projection C, away from both steps, the lever L, is pressed by its spring against the upper contact. The battery terminals are connected with the condenser terminals when the lever L, is touching the lower contact, but when the lever L, touches the top contact, the condenser is connected with the galvanometer terminals. Key, Double-Contact Form of Bridge, Sprague's A key designed to succes- sively close two separate circuits. K pieces, I, 2, 3 and 4, serve to make contacts with apparatus used in connection with the key. The battery circuit is connected to I and 2, and the galvanometer to 3 and 4, so that the bat- tery circuit is closed first, and the galvanometer afterwards. This form of key is used in connec- tion with the Wheatstone Bridge. Key, Double-Contact, Lambert's A key used in cable-work, and constructed as shown in Fig. 326. Sprague's double-contact key is shown in Fig. 325. On depressing K, the contacts c, c, are first closed and afterwards contacts at c' , c ' . Metallic 326. Lambert's Dou6ie-C< In Thomson's method for the determination of electrostatic capacity, the capacity of the cable is compared with that of a condenser containing a known charge. These two charges are so con- nected electrically as to discharge into and neutralize each other if equal, but if not, to pro- duce a galvanometer deflection by a charge equal to their difference. A Lambert double contact key is shown in Fig. 326. The connections are such that the pushing forward of K, depresses keys that permit a bat- tery to simultaneously charge the condenser and the cable. On drawing K, back, the two charges are allowed to mix. Then on depressing K, the difference of the charges, if any, is discharged through the galvanometer. Key, Double-Tapper The key used in a system of needle telegraphy to send electric impulses through the lines in alter- nately opposite directions. (See Telegraphy, Single-Needle) Key, Increment A telegraphic key so connected that an increase or increment in the line current occurs whenever the key is depressed. The increment key is used in duplex and quad- ruplex systems of telegraphic transmission. Key, Increment, of Quadruples Tele- graphic System A key employed to increase the strength of the current and so operate one of the distant instruments in a Key.] 302 [Key, quadruplex system by an increase in the strength of the current. (See Telegraphy, Quadruplex^ Key, Magneto-Electric A tele- graph key for sending an electric impulse into a line, so arranged that a coil of wire on an armature connected with the key lever is, by the movements of the key, moved toward or from the poles of a permanent magnet, the movements of the key thus producing the currents sent into the line. Key, Plug A simple torm of key in which a connection is readily made or broken by the insertion of a plug of metal between two metallic plates that are thus introduced into a circuit. A form of plug key is shown in Fig. 327. Fig. 327. Plug Key. Key, Reversing A key inserted in the circuit of a galvanometer for obtaining deflections of the needle on either side of the galvanometer scale. A form of reversing key is shown in Fig. 328. The galvanometer terminals are connected to the binding posts 2 and 3, and the circuit terminals to the other two posts. On depressing K, the 3 Key, Reversing, of Quadruplex Tele- graphic System A key employed to reverse the direction of the current and so operate one of the distant instruments, in a quadruplex system, by a change in the direction of the current. (See Telegraphy, Quadruple*?) Key, Short-Circuit A key which in its normal condition short circuits the gal- vanometer. Fig. 329. Short-Circuit Key. Such a short-circuit key is provided for the purpose of protecting the galvanometer from in- jury by large currents being accidentally passed through its coils. In the form shown in Fig. 329, the spring S, rests against a platinum contact ; but when depressed by the insulated head at K, it rests against an ebonite contact, and throws- the galvanometer into the desired circuit. The key is provided with double binding posts- at P and N, for convenience of attachment to re- sistance coils, batteries, etc. In the form of a short-circuit key shown in Fig, 330, a catch is provided for the purpose of keep- ing the key down when once depressed. Its arrangement will be readily understood from an inspection of the figure. 'g- 330. Sho*t-Circuit Key. Key, Sliding-Contact The key em- ployed in the slide form of Wheatstone K', it flows in the opposite direction. Clamps, bridge, to make contact with the wire over operated by handles, are provided so as to close which the sliding contact passes. (See Fig. 328. Reversing Key. current flows in one direction and on depressing either of the keys permanently, if so desired. Bridge, Electric, Slide Form of.) Key.] 303 [Kit. Key, Stationary Floor An electric key or push button placed on the floor so as to be readily closed by the foot. This form of key is especially suitable for use in connection with an electric bell and annuncia- tor for readily calling an attendant. (See Annun- ciator, Electro-Magnetic.) Key, Telegraphic The key em- ployed for sending over the line the successive makes and breaks that produce the dots and dashes of the Morse alphabet, or the deflec- tions of the needle of the needle telegraph. (See Telegraphy, American System of.) Kick. A recoil. Kicking Coil. (See Coil, Kicking.) Kilo (as a prefix). One thousand times. Kiloampere. One thousand amperes. Kiloampdre Balance. (See Balance, Kiloampere.) Kilodyne. One thousand dynes. (See Dyne.) Kilogramme. One thousand grammes, or 2.2046 pounds avoirdupois. {See Weights, French System of.) Kilojoule. One thousand joules. Kilometre. One thousand netres. Kilowatt. One thousand watts. Kilowatt Hour. (See Hour, Kilowatt) Kine. A unit of velocity proposed by the British Association. A kine equals I centimetre per second. Kinetic Energy. (See Energy, Kinetic) Kinetic Theory of Matter. (See Matter, Kinetic Theory of) Kinetics, Electro A term some- times applied to the phenomena of electric currents, or electricity in motion, as distin- guished from electrostatics, or the phenom- ena of electric charges, or electricity at rest. Kinetograph. A device for the simultane- ous reproduction of a distant stage and its actors under circumstances such that the actors can be heard at any distance from the theatre. The sounds heard by the distant audience are actual reproductions of those uttered during the performance, though not at the time of their utterance. The appearance of the stage and its actors represents the appearance of a previous reproduction of the play or opera or other per- formance, as taken by means of a Kodak camera with a film cylinder and drop shutter, operated by an electric motor, exposing, say, forty plates a second. By means of a projecting lantern these photographic pictures are thrown on a curtain on a stage at the distant theatre in regular order of sequence, while a loud- speaking phonograph puts song and speech into the mouths of the mimic actors and thus gives the phantom stage the semblance of life and reality. Kite, Franklin's A kite raised in Philadelphia, Pa., in June, 1752, by means of which Franklin experimentally demonstrated the identity between lightning and electricity, and which, therefore, led to the invention of the lightning rod. It is true that Dalibard, on the loth of May, 1752, prior to Franklin's experiment, succeeded in drawing sparks from a tall iron pole he had erected in France. This experiment was, how ever, tried at the suggestion of Franklin, to whom it must properly be ascribed. A description of this kite is given by Franklin in the following letter: Letter XI, from BENJ. FRANKLIN, Esq., of Phil- adelphia, to PETER COLLINSON, Esq., F. R. S., London. " OCT. 19, 1752. "As frequent mention is made in public papers, from Europe, of the success of the Philadelphia experiment for drawing the electric fire from clouds by means of pointed rods of iron erected on high buildings, etc., it may be agreeable to the curious to be informed that the same experi- ment has succeeded in Philadelphia, though made in a different and more easy manner, which is as follows: " Make a small cross of two light strips of cedar, the arms so long as to reach to the four corners of a large thin handkerchief when extended; tie the corners of the handkerchief to the extremities of the cross, so you have the body of a kite, which, being properly accommodated with a tail, loop and string, will rise in the air like those made of paper, but this, being of silk, is fitter to bear the wet and wind of a thunder gust without tearing. To the top of the upright stick of the cross is to Kni.J 304 [Lag. be fixed a very sharp pointed wire rising a foot or more above the wood. To the end of the twine, next the hand, is to be tied a silk ribbon, and where the silk and twine join, a key may be fastened. This kite is to be raised when a thun- der gust appears to be coming on, and the per- son who holds the string must stand \vi;hin a door or window, or under some cover, so that the silk ribbon may not be wet, and care must be taken that the twine does not touch the frame of the door or window. As soon as any of the thunder clouds come over the kite the pointed wire will draw the electric fire from them, and the kite, with all the twine, will be electrified, and the loose filaments of the twine will stand out every way, and be attracted by an approach- ing finger. And when the rain has wet the kite and twine so that it can conduct the electric fire freely, you will find it stream out plentifully from the key on the approach of your knuckle. At this key the phial may be charged, and from electric fire thus obtained spirits may be kindled, and all the other electric experiments be per- formed, which are usually done by the help of a rubbed glass globe or tube, and thereby the Sameness of the electric matter with that of light- ning completely demonstrated. 'B. FRANKLIN." Knife Break Switch. (See Switch, Knife Break) Knot or Nautical Mile. A length equal to 6,087 feet. The English statute mile is equal to 5,280 feet. The value of the nautical mile is therefore in excess of that of the statute mile. Kohlrausch's Law. (See Law of Kohl- rausch) Krizik's Bars. (See Bars, Krizik's) Kyanized. Subjected to the kyanizing process. (See Kyanizing) Kyanizing. A process employed for the preservation of wooden telegraphic poles by injecting a solution of corrosive sublimate into the pores of the wood. (See Pole, Tele- graphic) L. A contraction for co-efficient of in- ductance. (See Inductance, Co-efficient of) L. A contraction for length. Labile Galvanization. (See Galvaniza- tion, Labile) Lag, Angle of The angle through which the axis of magnetism of the armature of a dynamo-electric machine is shifted by reason of the resistance its core offers to sud- den reversals of magnetization. An armature of a bi polar dynamo- electric ma- chine has its magnetism reversed twice in every rotation. The iron of the core resists these mag- netic reversals. The result of this resistance is to shift the axis of magnetism in the direction of ro- tation. The angle through which the axis has thereby been shifted is called the angle of lag. The term, angle of lag, is sometimes incorrectly applied so as to include a similar result produced by the magnetization due to the armature current itself. It is this latter action which, in armatures with soft iron cores, is the main cause of the angle of lead. (See Brushes, Lead of. Lead, Angle of.} Lag, Angle of, of Current An angle whose tangent is equal to the ratio of the inductive to the ohmic resistance. An angle, the tangent of which is equal to the inductive resistance of the circuit, divided by the ohmic resistance of the circuit. An angle, the co-sine of which is equal to the ohmic resistance of the circuit, divided by the impedance of the circuit. Lag, Magnetic A magnetic viscos- ity as manifested by the sluggishness with which a magnetizing force produces its mag- netizing effects in iron. The tendency of the iron core of a magnet, or of the armature of a dynamo-electric ma- chine, to resist, and, therefore, retard mag- netization. This retardation, or lag, is called the magnetic lag. The lead necessary to give the brushes of a dy- namo-electric machine to insure quiet action has by I. a m. j 305 [Lam. some been erroneously ascribed to the magnetic lag. The lead, though due to lag in part, in reality is mainly due to the resultant magnetization of the armature both by the field magnets and by its own current. (See Lead, Angle of.) This dis- placement of the brushes is measured by an angle sometimes, though erroneously, called the angle of lag. (See Lag, Angle of.) Lamellar Distri- bution of Magnet- Ism. (See Magnet- ism, Lamellar Dis- tribution 0f.) Laminated Core. (See Core, Lami- nated) Laminating Core. (See Core, Lami- nation of.) Lamination of Armature Core. (See Core, Armature, Lamination of) Lamination of Cores. (See Core, Lamination of) Lamp, All-Night A term some- times applied to a double - carbon arc lamp. (See Lamp, Electric Arc, Double- Carbon) A form of all-night arc lamp is shown in % 33 * When the consumption of the first pair of carbons has Fig. 331. Att-Night Arc reached a certain limit Lamp. the current is automatically switched over to the other pair. Lamp, All-Night Electric A lamp provided with carbon electrodes so as to burn all night without recarboning. A double-carbon electric lamp. (See Lamp, All-Night) Lamp, Arc An electric lamp, the source of whose li^ht is a voltaic arc. Lamp, Arc, Electric An electric lamp in which the light is produced by a vol- taic arc formed between two or more carbon electrodes. The carbon electrodes are placed in various positions, either parallel, horizontal, inclined to one another or vertically one above the other. The latter is the form most generally adopted, since it permits the ready feeding of the upper carbon. The carbons are maintained during their con- sumption at a constant distance apart, by the aid of various feeding devices. Such devices are op- erated generally by trains of wheel- work, by me- chanical or electrical motors, or by the simple action of a spring, by gravity or by the attraction of a solenoid. The carbon pencils or electrodes are held in carbon holders, consisting of clutches or clamps, attached to the end of the lamp rods. When the lamp is not in operation the carbons are usually in contact with one another; but, on the passage of the current, they are separated the require 1 distance by the action of an electro-magnet whose coi's are traversed by the direct or main current. In order to maintain the elec- trodes a constant distance apart, the upper carbon in some lamps is held in position by the operation of a clutch, or, in others, by a detent, that engages in a toothed wheel. The position of this clutch or de- tent is controlled by the action of an electro-magnet whose coils are usually situated in a shunt or de- rived circuit, of high resistance," around the electrodes. When the carbons are at their normal dis- tance apart, the shunt current is not of sufficient strength to move the clutch or detent from the position in which it prevents the downward motion of the upper carbon rod. When, however, by the burning or consumption of the carbons, the resistance of the arc has increased to an extent which can be predetermined, the increased current that is thereby passed through the shunt circuit is now sufficiently strong to release the clutch or de- tent, thus permitting the fall or feed of the upper carbon. In a well designed lamp this occurs Lam.J [Lam. so gradually as to produce no perceptible effect on the steadiness of the light. Arc lamps are generally placed in series circuits, that is, in circuits in which the current passes suc- cessively through all the lamps in the circuit, and returns to the source. In order to avoid the break- ing of the entire circuit through the extinguish- ing of a single arc, on the breaking of its cir- cuit, an automatic safety device is provided for each lamp. This safety device consists essentially of an electro-magnet so placed in a shunt circuit, that, as the resistance of the arc becomes too great, the increased current, which will then flow through the coils of the electro-magnet, at last produces a movement of its armature which closes a short circuit around the lamp, and thus cuts it out of the circuit. Arc lamps assume a great variety of forms. A well known form is shown in Fig. 332. Lamp, Arc, Triple Carbon An arc lamp in which three carbon electrodes are used. The positive carbons consist of two ordinary cylindrical carbons, placed parallel to each other. The negative carbon is shaped like the figure 8. The arc is established between one of the positive carbons and the corresponding side of the nega- tive carbon. The feeding of the lamp is attended by a shifting back and forth of the arc between the positive carbons and from side to side of the negative carbons. The design of the triple carbon arc lamp is to produce a lamp of long life. Lamp Bracket, Electric (See Bracket, Lamp, Electric?) Lamp Bulb. (See Bulb, Lamp?) Lamp, Carcel . An oil lamp employed in France as a photometric standard. Fig. 333 shows a form of car- cel lamp. Like the standard candle, the carcel is a standard only when it consumes a given weight of the light-producing substance in a given time. Lamp, Chamber of ( The glass bulb or chamber of an incandescing electric lamp in which the incandescing conductor placed, and in which is maintained a high vacuum. The transparency of the lamp chamber and consequently the efficiency of the lamp may de- crease - ( I . ) From the settling of dust or dirt on its outer walls. (2.) From the deposit of carbon or metal on its inner walls. To obviate the first cause of diminished trans- parency the outside of the lamp chamber should be frequently cleansed. The diminished trans- parency, due to the second cause, cannot be removed. When it has reached a certain point, it is more economical to replace the old lamp by a new lamp. In a properly made lamp the dimming of the lamp chamber is not apt to occur unless a stronger current than the normal current is passed through the lamp. Lamp Clamp. (See Clamp for Arc Lamps?) Lamp, Contact A form of semi- incandescent electric lamp in which a carbon pencil is pressed against a slab of carbon or other refractory material. The source of light in an electric contact lamp is twofold, viz.: (i.) A minute arc formed at the points of im- perfect contact. (2.) The incandescence of the carbon pencil, and the points of the slab of carbon against which it is pressed. Lamp Contacts. (See Contacts, Lamp?) Lamp, Electric, Arc, Carbon Elec- trodes for (See Electrodes, Carbon, for Arc Lamps?] Lamp, Electric, Arc, Differential An arc lamp in which the movements of the carbons are controlled by the differential action of two magnets opposed to each other, one of whose coils is in the direct and the other in a shunt circuit around the carbons. Sometimes the differential coils are placed on the same magnet core. Lamp, Electric, Arc, Double Carbon An electric arc lamp provided with two pairs of carbon electrodes, so arranged that when one pair is consumed, the circuit is auto- matically completed through the other pair. lam.J 307 [Lam. Lamp, Electric Glow A term em- ployed mainly in Europe for an incandescent electric lamp. (See Lamp, Electric, Incan- descent^ Lamp, Electric, Incandescent An electric lamp in which the light is produced by the electric incandescence of a strip or filament of some refractory substance, gener- ally carbon. The carbon strip or filament is usually bent into the form of a horseshoe or loop, and placed inside a glass vessel called the lamp chamber. The lamp chamber is exhausted by means of a mercury pump, generally to a fairly high vacuum. In order to insure the complete removal from the lamp chamber of all the air it originally con- tained, the carbon strips that are placed within it are maintained at a high temperature during the process of exhaustion. This temperature, in practice, is obtained by sending the current through the carbon strip as soon as nearly all the air is removed. ' Towards the end of the pumping operation the current is increased so as to raise the carbons to their full bril- liancy. The lamp chamber is also maintained at a fa'rly high temperature. To insure this heating of the walls of the lamp chamber by the incandescent carbons during pumping, for the purpose of driving off all the air adhering to the walls of the chamber, they are sometimes covered with some readily removable preparation of lamp black. The operation of driving off the gases absorbed by the carbons is termed the occluded gas process, and is essential to the successful sealing of an incandescent lamp. By its means, a considerable quantity of air or other gaseous substances shut up or occluded by the carbon is driven out of the carbon, which it would be impossible to get rid of by the mere operation of pumping. In order to insure the success of the operation, it is necessary that the heating must take place while the lamp is being exhausted, since otherwise the expelled gases would be re-absorbed. (See Gas, Occlu- sion of. ) Both the exhaustion and the incandescence con- tinue up to the moment the lamp chamber is hermetically sealed; otherwise, some of the air mieht remain in the lamp chamber. The lamp chamber is hermetically sealed, usually by the fusion of the glass in the manner adopted in the sealing of Geissler tubes or Crookes' radiometers. For the preparation of the carbon strip, its carbonization and the flashing of the strip, see Carbonization, Processes of. Carbons, Flashing Process for. The ends of the carbon strip, or filament, are attached to lead- *-* WMVJ of platinum that pass through the glass walls of the lamp chamber, and are fused therein by melting the glass around them in the same manner as are the leading-in wires of the I Geissler tubes and other similar apparatus. Incandescent lamps are gener- ally connected to the leads or cir- Fig. 334. Incan* cuits in multiple-arc or in multi- decent Electric pie-series. They are, however, La**p' sometimes connected to the line in series. (See Circuits, Varieties of.} In the case of multiple-arc or multiple-series connection, the resistance of the filament is com- piratively high. In the case of series-connec- tion the resistance is comparatively low. Incandescent electric lamps assume a variety of different forms. In all cases, however, the shape of the filament is such that the leading-in wires that carry the current to and from the filament shall en- ter and leave the lamp chamber at points that are comparatively near together. This is for the purpose of avoiding the unneces sary production of shadows. Commercial incan- descent electric lamps are generally marked with the potential dif- ference in volts that must be applied at the terminals in order to furnish the current necessary to properly operate them. If this potential difference is made greater, the can- *'*** Lam.] 308 [Lam. tie-power of the lamp is greatly increased, but its *ife greatly decreased. The lamp chamber is more liable in such cases '/> become less transparent from the deposit of a fhin layer of carbon or metal on its inner surfaces. In the Swan lamp the filament is made of cot- ton thread. These threads are immersed in a mixture of two parts of sulphuric acid and one of water, which converts the cellulose of the thread into artificial parchment. The filaments are rap- idly washed as soon as they are removed from the sulphuric acid until all traces of the acid are re- moved. They are then parsed through discs so as to insure a uniform area of cross-section, and are then wrapped on rods of carbon or earthen- ware of the required outline, packed in a crucible filled with powdered charcoal, and carbonized. The fo-m generally given to the Swan filament is that shown in Fig. 335. Lamp, Electric, Incandescent Ball - An incandescent electric lamp in which the light is produced by a sphere or ball of carbon placed in an exhausted receiver of glass. When subjected to the effects of electrostatic waves of high frequency of alternation, such a lamp becomes luminous from the incandescence of the carbon ball or sphere. Tesla's incandescent ball electric lamp is a modifica- tion of his straight filament lamp. (See Lamp, Incan- descent, Straight Filament .) The construction of Tes- la's ball incandescent elec- tric lamp will be readily understood from an inspec- tion of Fig. 336. Lamp, Electric, In- candescent, Half-Shades for -- (See Half- Shades for Incandescent Lamps .) Lamp, Electric, Incandescent, Life of -- The number of hours that an incan- descent electric lamp, when traversed by the normal current, will continue to afford a good commercial light. The failure of an electric incandescent lamp results either Irom the volatilization or rupture of the carbon conductor, or from the failure of the ?>*&* &- ""******* vacuum of the lamp chamber. Since the em- ployment of the flashing process, and the process for removing the occluded gases, it is not unusual for incandescent lamps to have a life of several thousand hours. (See Carbons^ Flashing Pro- cess for.) The life of an incandescent electric lamp should not be considered as continuing until the filament actually breaks. As soon as the lamp chamber has become covered with such a deposit of car- bon or coating of metal as to considerably de- crease the amount of light which passes through the chamber, the lamp should be considered as- useless. Lamp, Electric, Incandescent, Three- Filament, for Multi-Phase Circuits An incandescent lamp for use on multi- phase circuits, provided with three leading-in wires, connected to the free ends of three filaments, the other ends of which are con- nected in a common joint. When properly acting, the current passing through each filament should, at any instant, equal the sum of the currents in the other two- filaments, which, as is well known, is the property of any three-phase circuit. Lamp, Electric, Outrigger for (See Outrigger for Electric Lamp.) Lamp, Electric, Pendant An in- candescent electric lamp suspended by flexible twin-wire. Lamp, Electric, Safety An in- candescent electric lamp, with thoroughly insulated leads, employed in mines, or other similar places, where the explosive effects of readily ignitable substances are to be feared. Such lamps are often directly attached to a portable battery, in which case they can be read- ily carried about from place to place. Lamp, Electric, Semi-Incandescent An electric lamp in which the light is due to the combined effects of a voltaic arc and electric incandescence. In the Reynier semi incandescent la np, shown* in Fig. 337, a thin pencil of carbon C, is gently- pressed against a block of graphite B. A lateral contact is provided at L, through a block of graphite I, by means oi which the current is con- La ii i. J 309 LLanu veyed to the lower part only of the movable rod C, which part alone is rendered incandescent. In this lamp, the light is due both to the incan- ,C F'S- 337- Semi-Incandescent Lamp. descence of the rod C, and to the small arc formed at J, between its lower end and the contact block B, though mainly from the latter. The semi- incandescent electric lamp has not as yet been in- troduced to any considerable extent. Lamp, Electric, Series-Connected Incan- descent An incandescent electric lamp adapted for use in series circuits. Fig. 338. Series Incandescent Electric Lamp. A form of series incandescent lamp, attached to pendant and shade, is shown in Fig. 338. In the series connected incandescent lamp, un- like the multiple-connected incandescent electric lamp, the resistance of the filament is low. This is done i order to prevent the total resistance of the circuit from requiring too high an electro- motive force for operation. In order to preserve the continuity of the circuit on the failure of any lamp to operate, some form of automatic cut-out is employed. This is generally some form of film cut-out. (See Cut-Out ', Film.) Lamp Hour. (See Hour, Lamp.} Lamp, Incandescent, Electric Filament of A term now generally applied to the incandescing conductor of an incandescent electric lamp, whether the same be of very small cross-section or of comparatively large cross-section. The term filament is properly applied to a con- ductor containing fibres or filaments extending in the general direction of the length of the incan- descing conductor. Such a conductor is made of carbonizable fibrous material, cut or shaped prior to carbonization so as to have its fibres extend- ing with their greatest length in the direction of length of the filament. Lamp, Incandescent, Straight Filament An incandescent electric lamp in, which a straight filament, placed in an ex- hausted glass chamber, is rendered luminous by the effects of electro- static waves or thrusts of high frequency. The straight filament in candescent lamp is the in- vention of Tesla. One form of such a lamp is shown in Fig. 339. The glass globe b, of the lamp is provided with a cylindrical neck, inside of which is placed a tube m, of conducting material, on the side and over the end of the insulating plug n. The light-giving fila- ment e, is a straight car- bon stem, connected to the plate by a conductor cov ered with a refractory in- sulating material k. An insulated tube-socket p, provided with a metallic lining s, serves to sup- port the lamp and connect it with one pole of the source of curren'. It will be noticed that the coat- Fig. 339 Tesla s Straight Filament In- candescent Lamp. Lam.] 310 [Law. ings s and m, form the plates of a condenser. The other terminal of the machine may be con- nected to the metal coated walls of the room, or to metallic plates suspended from the ceiling. Lamp Indicator. (See Indicator, Lamp.} Lamp, Pilot In systems for the operation of electric lamps, an incandescent lamp employed in a station to indicate the difference of potential at the dynamo ter- minals, by means of the intensity of its emitted light. Lamp Rod. (See Rod, Lamp} Lamp Socket Switch. (See Switch, Lamp Socket} Lamps, Bank of A term applied to a number of lamps, equal to about half the load, that were formerly placed in view of the attendant in circuit with a dynamo that is to be placed in a parallel circuit with another dynamo, one of the lamps of which is also in view. When the lamps "in bank " were judged to be of the same brilliancy as the one fed by the other dynamo, the attendant switched the dynamo par- allel with the other, and at the same time cut off the bank of lamps from the switched in dynamo. The method is, however, wrong. The proper way is to make the voltage of the dynamo equal to that of the circuit. Then connect it and finally raise its electromotive force until it takes its share of the load. Lamps, Carboning Placing carbons in electric arc lamps. When the carbons are consumed, the lamp requires recarboning. The old carbon ends are replaced by new carbons, and the lamp rods cleansed. Large Calorie. (See Calorie, Great} Latent Electricity. (See Electricity, Latent} Lateral Discharge. (See Discharge, Lateral} Lateral Induction. (See Induction, Lat- eral} Lateral Leakage of Lines of Magnetic Force. (See Leakage, Lateral, of Lines of Magnetic Force} Lateral Magnetic Leakage. (See Leak- age, Lateral, of Lines of Magnetic Force} Latitude, Magnetic The distance a place is situated north or south of the mag- netic equator All places that have the same magnetic latitude have the same value for the magnetic inclination and magnetic intensity, or are on the same isocli- nal and isodynamic lines. The magnetic latitude is the same at all points of a magnetic parallel. Launch, Electric A boat, the mo- tive power for which is electricity, suitable for launching from a ship. Up to the present time electric launches have been propelled by means of electric motors, driven by means of powerful storage batteries. A form of electric launch constructed for the English Government is shown in Fig. 340. It is Fig. 34.0. Electric Launch. 48^ feet in length over all, by 8 feet 9 inches beam, with an average draft of 2 feet 3 inches. Its speed is 8 knots per hour. It will carry forty fully equipped soldiers. Law, Jacobi's -- The maximum work done by a motor is reached when the counter- electromotive force is equal to one-half of the impressed electromotive force, or, Law, Joule's --- The heating power of a current is proportional to the product of the resistance and the square of the current strength. (See Heat, Electric} Law, Natural -- A correct expression of the order in which the causes and effects of natural phenomena follow one another. The law of gravitation, for example, correctly expresses the order of sequence of the phenomena which result when unsupported bodies fall to the earth. It should be carefully borne in mind, how- ever, that natural laws cannot be regarded as explaining the ultimate causes of natural pheno- Law.] 311 [Law. mena, but merely express their order of occur- rence or sequence. We are ignorant, for example, of the true cause of gravitation and are only acquainted with its effects. This is true of all ultimate physical causes, save for our belief in their origin in a Divine will. Law of Electro-Chemical Equivalence. (See Equivalence, Electro-Chemical, Law of) Law of Kohlrausch. In electrolytic con- duction, each atom has a rate of motion for a given liquid, which is independent of the element with which it may have been com- bined. In the following table, the rate of motion of various kinds of atoms through nearly pure water for a difference of potential of one volt per linear centimetre, is given: H .......... 1. 08 centimetres per hour. K .......... 0.205 centimetre " Na ......... 0.126 " " Li .......... 0.094 " Ag ......... 0.166 " " C ........... 0.213 1 ........... 0.216 " " SO, ........ 0.174 Law of Oliin, or Law of Current Strength. The strength of a continuous current is directly proportional to the differ- ence of potential or electromotive force in the circuit, and inversely proportional to the re- sistance of the circuit, i. e., is equal to the quotient arising from dividing the electromo- tive force by the resistance. Fig. 341. Current Strength in Circuit. Ohm's law is expressed algebraically thus: C = 5; or, E = C R. If the electromotive force is given in volts, and the resistance in ohms, the formula will give the current strength directly in amperes. The resistance of any electric circuit, as, for example, that shown in Fig. 341, consists of three parts, viz.: (i.) The internal resistance of the source, r. (2.) That of the conducting wires or leads, r'; and (3.) That of the electro-receptive, r", energized by the current. Ohm's law applied to this case would be: __ _ - r + r' + r". That is, the resistance of the entire circuit is equal to the sum of the separate resistances of its different parts. Since C= 5, (i); then E = C R, (2); R and R = 5, (3). But, since a current of one ampere is equal to one coulomb per second, then, in order to deter- mine in coulombs the quantity of electricity pass- ing in a given number of seconds, it is only neces- sary to multiply the current by the time in seconds, orQ = CT{ 4 ). Hence, referring to the above equations (i), (2), (3) and (4); according to Ohm's law: (I.) The current in amperes is equal to the electromotive force in volts divided by the resist- ance in ohms. (2.) The electromotive force in volts is equal to the product of the current in amperes and the resistance in ohms. (3.) The resistance in ohms is equal to the elec- tromotive force in volts divided by the current in amperes. (4.) The quantity of electricity in coulombs is equal to the current in amperes multiplied by the time in seconds. Law of Volta, or Law for Contact-Series. A law for the differences of electric potential produced by the contact of dissimilar metals or other substances. " The difference of potential between any two metals is equal to the sum of the differences of potential between the intervening substances in the contact series." (See Electricity, Contact. Series, Contact.) Law, Pfliiger's -- A given tract of nerve is stimulated by the appearance of kathelectrotonusandthe disappearance of an- electrotonus ; not, however, by the disap- Law.J 312 (Law, pearance of kathelectrotonus nor by the ap- pearance of anelectrotonus. (Landois and Stirling!} Law, Poynting's At any point in a magnetic field, or a conductor conveying current, the energy moves perpendicularly to the plane containing the lines of electric force or the lines of magnetic force, and the amount of energy crossing the unit of area of this plane per second is equal to the product of the intensities of the two forces multiplied by the sine of the angle between them, divided by 4*. If E, represents the electric force of a small body charged with positive electricity, and H, the magnetic force or forces of a smaller free unit north pole, and, if these forces at any point in the magnetic field are inclined at an angle, 0, then e, the flow of energy per second at this point, in a direction oerpendicular to the planes of E and II is, E H sin. 9 e = . 47t There is, therefore, a difference in the direction of the flow of electricity and the flow of electric energy. Electricity may be conceived as passing through the conductor something like water through a pipe, but electrical energy does not travel in this way. Electrical energy travels through the surrounding dielectric, which is thereby strained, and it propagates this strain from point to point until it reaches the conductor and is there dissipated. Law, Toltametric The chemical action produced by electrolysis in any elec- trolyte is proportional to the amount of elec- tricity which passes through the electrolyte. This is called the Voltametric law, because any vessel containing an electrolyte, and furnished with electrodes, so that electrolysis may take place on the passage of the current, and is provided with means for measuring the amount of the electrolysis which occurs, is called a Voltameter. (See Voltameter. Electrolysis.} Laws, AmpSre's, or Laws of Electro- Dynamic Attraction and Repulsion Laws expressing the attractions and repul- sions of electric circuits on one another or on magnets. Laws, Dub's ' The magnetism ex- cited at any transverse section of a magnet is proportional to the square root of the distance between the given section and the near end of the magnet." " The free magnetism at any given trans- verse section of a magnet is proportional to the difference between the square root of half the length of the magnet and the square root of the distance between the given section and the nearest end." Laws, KirchhofTs The laws for branched or shunted circuits. These laws may be expressed as follows: (I.) In any number of conductors meeting at a. point, if currents flowing to the point be considered as +, and those flowing away from it as , the algebraic sum of the meeting currents will be zero. This is the same thing as saying as much elec- tricity must flow away fro^n the point as flows to- ward it. (2.) In any system of closed circuits the alge- braic sum of the products of the currents into the resistances is equal to the electromotive force in the circuit. In this case all currents flowing in a certain, direction are taken as positive, and those flowing in the opposite direction as negative. All elec- tromotive forces tending to produce currents in the direction of the positive current are taken as positive, and those tending to produce currents in the opposite direction, as negative. E This follows from Ohm's law; for, since C = , R the electromotive force E = CR, and this is true, no matter how often the circuit is branched. Laws, Lenz's Laws for determining the directions of currents produced by electro- dynamic induction. The direction of the currents set up by electro- dynamic induction is always such as to oppose the notions by which such currents were pro- duced. Laws of Becquerel, or Laws of Mag- neto-Optic Rotation. Laws for the mag- neto-optic rotation of the plane of polarization of light. (See Rotation, Magneto-Optic!) Laws of Coulomb, or Laws of Electro- Law. I 313 [Lea. .static and Magnetic Attractions and Re- pulsions. Laws for the force of attraction and repulsion between charged bodies or be- tween magnet poles. The fact that the force of electrostatic attrac- tion or repulsion between two charges, is directly proportional to the product of the quantities of electricity of the two charges and inversely propor- tional to the square of the distance between them, is known as Coulomb* s Law. Coulomb also as- certained that the attractions and repulsions be- tween magnet poles are directly proportional to the product of the strength of the two poles, and in- versely proportional to the square of the distance between them. This is also called Coulomb's Law. Coulomb's law, in order to be accurate, must take into account the specific inductive capacity of the intervening medium. The correct expres- sion for the force between two quantities q and q', of electricity would be, therefore, where K, is equal to the specific inductive capacity of the medium separating the two charges. In a similar manner when the force is exerted between two magnet poles, to be accurate, we must take into account the magnetic permeability of the medium between the two magnets. The cor- rect expression for the force between two magnet poles is, therefore, _ mm' ~ r*M ' when //, is the magnetic permeability. Laws of Faraday, or Laws of Electrolysis -- Laws for the effects of electrolytic decomposition. (See Electrolysis!) These laws are as follows: (i.) The amount of an electrolyte decomposed is directly proportional to the quantity of elec- tricity which passes through it ; or, the rate at which a body is electrolyzed is proportional to the current strength producing such electrolysis. (2.) If the same current be passed through dif- ferent electrolytes, the quantity of each ion evolved is proportional to its chemical equivalent. Laws of Jonle Laws expressing the de- velopment of heat produced in a circuit by an -electric current. These laws may be expressed as follows : (i.) The amount of heit developed in any cir- cuit is proportional to its resistance, providing the current stiength is constant. (2.) The amount of heat developed in any cir- cuit is proportional to the square of the current passing, providing the resistance is constant (3.) The amount of heat developed in any cir- cuit is proportional to the time the current con- tinues. Or, H = C*Rt xo.2 4 . Where H, equals the heat in small calories, C, equals the current in ampere>, R equals the re- sistance in ohms, t, equals the time in seconds, and 0.24, the heat-units per second developed in a resistance of I ohm by the passage of i am- pdre. Lay Torpedo. (See Torpedo, Lay.) Layer, Crookes' A layer, or stratum, of the residual atmosphere of a vacuous space, in which the molecules, recoil- ing from a heated or electrified surface, do not meet other molecules, but impinge on the walls of the vessel directly opposite such heated or electrified surface. A Crookes layer may result as the effect of two different causes, viz. : (i.) The rarefaction of the gas is such that the distance between the walls of the vessel and the heated surface is less than the mean-free-path of the molecules. (2.) The wall is so near the heated surface that the distance between the two is less than the ac- tual mean-free-path of the molecules. Under these last-named circumstances Crookes' layers may result, whatever be the density of the gas. Laying-Up Cables. (See Cables, Lay- ing- Up.) Lead, Angle of The angular devia- tion from the normal position, which must be given to the collecting brushes on the com- mutator cylinder of a dynamo-electric ma- chine, in order to avoid destructive burning. (See Commutator, Burning a/.) The necessity for giving the collecting brushes a lead, arises both from the magnetic lag and from the distortion of the field of the machine by the magnetization of the armature current. The angle of lead is, therefore, equal to the sum of the angle of lag, and the angular distortion due to the magnetization produced by the armature current. Lea.] 314 [Lea, Lead, Cable A lead containing a conductor formed of several stranded con- ductors, as distinguished from a wire lead or a lead containing a single conductor. Lead, Flexible A conductor formed of a number of small stranded conductors for the purpose of obtaining flexibility. Lead, Flexible Twin A flexible conductor in which two parallel and sepa- rately insulated wires are placed. Lead of Brushes of Dynamo-Electric Machine. The angular deviation from the normal position, which it is necessary to give the brushes on the commutator of a dynamo- electric machine, in order to obtain efficient action. (See Lead, Angle of.) Lead Scoring Tool. (See Tool, Scoring, Lead.) Lead Sleeve. (See Sleeve, Lead.) Lead, Tee. (See Tee, Lead.) Lead, Wire A lead consisting of a single conductor, as distinguished from a cable lead, or a lead containing a number of stranded conductors. Lead Wire. (See Wire, Lead.) Leading Horn of Pole Pieces of Dynamo- Electric Machine. (See Horns, Leading, of Pole Pieces of a Dynamo-Electric Machined) Leading-In Wires. (See Wires, Lead- ing-In) Leading-Up Wires. (See Wires, Lead- ing- Up.) Leads. The conductors in any system of electric distribution. In distribution by parallel, the conductors through which the current flows from the source are sometimes called the leads in contradis- tinction to those through which it returns to the source. The leads, or main conductors, in a multiple system of electric lighting, must maintain a con- stant potential at the lamp terminals. The dimen- sions of the leads are, therefore, so proportioned as to absorb as small an amount of potential as pos- sible. Since, in incandescent lighting, where the lamps are connected to the leads in multiple-arc, the total resistance of the lamps is comparatively small, the resistance of the leads must be quite small in order to avoid a marked drop of poten- tial. Comparatively large conductors must, therefore, be used. The main conductor for series circuits, such as for arc-lights, has in all parts the same current strength. Since the sum of the resistances of the lamps in such a circuit is quite high, a compara- tively high resistance in the conductor may be employed without a proportionally large absorp- tion of potential. Comparatively small conduc- tors can therefore be used. (See Electricity, Dis- tribution of, by Constant Currents. Electricity, Distribution of, by Alternating Currents.) Leads, Armature, Twist in A dis- placement of the ends of the wires connected to the commutator segment, with respect to the position of the coils on the armature, for the purpose of obtaining a more convenient position for the diameter of commutation, that is, for the collecting brushes. Leak, Oscillatory A leak or grad- ual loss of electricity which takes place in alternately opposite directions. Leak, Unidirectional A gradual loss or leakage of electricity which takes place in one and the same direction. The term has been employed to distinguish such a leak from an oscillatory leak. Leakage Conductor. (See O;: :;-'>r, Leakage) Leakage, Electric The gradual dissipation of a current due to insufficient in- sulation. Some leakage occurs under nearly all circum- stances. On telegraphic lines, during wet weather, the leakage is often so great as to inter- fere with the proper working of the lines. Leakage, Electrostatic The grad- ual dissipation of a charge due to insufficient insulation. The leakage of a well insulated conductor, placed in a high vacuum, is almost inappreciable. Crookes has maintained electric charges in high vacua for years without appreciable loss. Leakage, Lateral, of Lines of Magnetic Force The failure of lines of magnetic Lea.] 315 [Len. force to pass approximately parallel to one another through a bar of iron or other mag- netizable material, when it has come to rest in a magnetic field in which it is free to move. The escape of the lines of magnetic force from the sides of a bar or other similar magnet, instead of from the poles at the end. When a bar of magnetizable material, sus- pended so as to be free to move, comes to rest in a magnetic field in which it is undergoing mag- netization, it has its greatest length parallel to the direction of the lines of force. If the bar is a long, thin, straight bar, the lines of force do not all pass in or come out at its ends. On the con- trary, many of these lines of force or induction pass in or come out at other points. The mag- netic induction is, therefore, unequal at different sections of the bar. In other words, the mag- netic flux or intensity is not constant per unit of all cross-sections of such bar. Leakage, Magnetic A useless dis- sipation of the lines of magnetic force of a dynamo-electric machine, or other similar device, by their failure to pass through the armature where they are needed. Useless dissipation of lines of magnetic force outside that portion of the field of a dynamo-electric machine through which the armature moves. Such a leakage can be detected by an instru- ment called a magnetophone. (See Magneto- phone.} Magnetic leakage results in lowering the effi- ciency of the dynamo. (See Co-efficient, Econo- mic, of a Dynamo-Electric Machine. ) Leclanch6's Voltaic Cell. (See Cell, Voltaic, LccLincht.) Leg. In a system of telephonic exchange, where a ground return is used, a single wire, or, where a metallic circuit is employed, two wires, for connecting a subscriber with the main switchboard, by means of which any subscriber may be legged or placed directly in circuit with two or more other parties. ', Leg of Circuit. (See Circuit, Leg of.) Legal Earth Quadrant. (See Quadrant, Legal Earth?) Legal Ohm. (See Ohm, Legal^ Legging-Key Board. (See Board, Leg- ging-Key) Length of Spark. (See Spark, Length of) Lens, Achromatic A lens the images formed by which are free from the false coloration produced in other lenses by dispersion. An ordinary lens can be rendered approxi- mately achromatic by the use of a diaphragm. Achromatic lenses generally consist of the com- Fig. 342. Equal and Opposite Refracting Angles. bination of a double convex lens of flint glass and a concave lens of crown glass. The ray of light entering the prism ABC, Fig. 342, suffers dispersion (separation into pris- matic colors). This dispersion in the same P C Principle of Achromatism. medium is proportional to the angle g, between the incident and emergent faces, called the re- fracting angle. If, now, another prism B C D, of the same ma- terial, with a refracting angle g', equal to g, is combined with the first prism in the manner shown in Fig. 342, it will produce an equal but opposite dispersion, so that the ray of light will emerge at R', free from rainbow tints, but par- allel to its original direction. The variety of glass called crown glass pro- duces only half as great dispersion of light as the variety called flint glass, under the same refract- Xen.] 316 ing angle g. If the prism A B C, of crown glass, Fig. 343, whose angle g, is twice as great as the refracting angle g , of the prism B C D, of flint glass, be placed together in the manner shown, then the ray R, will be transmitted at R', free from color, but will not emerge paralled to its original direction ; in other words, it suffers refraction or bending. Consequently such a combination can be used to free a pencil of light from false colora- tion and yet permit it to undergo refraction, and thus act as a lens. (See Refraction.') The construction of achromatic lenses is based on this principle. The crown glass is generally made with two Fig. 344. Piano-Convex Achromatic Lens. - 345- Achromatic Lens. Convex surfaces ; the flint glass, with one con- cave and one plane surface, as shown in Fig. 344- Sometimes both surfaces of the flint glass are made curved, as in Fig. 345. Lenz's Law. (See Law, Lcnz's.) Letter Box, Electric A device that announces the deposit of a letter in a box by the ringing of a bell, or by the move- ment of a needle or index. These devices generally act by the closing or opening of an electric circuit on the fall of the letter into the box. Leyden Jar. (See Jar, Leyden.) Leyden Jar Pattery. (See Battery, Ley- den Jar.} Lichtenberg's Dust Figures. (See Fig- ures, Lichtenberg's Dust.) Life Curve of Incandescent Electric Lamp. (See Curve, Life, cf Incandescent Electric Lamp.) Life of Electric Incandescent Lamp. (See Lamp, Incandescent, Life of.) Light, Auroral The light given off during the prevalence of an aurora. (See Aurora Horealis.) Light, Electric Light produced by the action of electric energy. Electric light is produced by electric energy in various ways, the most important of which are as follows, viz.: (I.) By the passage of an electric discharge through a gas or vapor, either in a rarefied condi- tion, at ordinary atmospheric pressure, or at pres- sures higher than that of the ordinary pressure. In any of these cases the gas or vapor is heated to incandescence by the passage of the discharge. (2.) By the incandescence of a solid by the heating power of the current, as in the incandes- cent lamp. (3.) By the incandescence of a solid by the ac- tion of a rapidly alternating electrostatic field, as in Testa's incandescent lamp. (4 ) By the volatilization of a solid and the form- ation thereby of a voltaic arc. (5.) By the combination of the effects of incan- descence and the voltaic arc. The amount of light produced in proportion to the amount of energy expended to produce it is probably least in the case of light produced by the sparks of a Wimshurst or Holtz machine, or as in (i), than in any other case in which electric energy acts to produce luminous energy. Light, Electric, Pumping of (See Pumping of Electric Light.) Light, Intensity of The brilliancy or illuminating power of a light as measured by a photometer in standard candles or other standard units. (See Photometer. Candle, Standard.) Light, Maxwell's Electro - Magnetic Theory of A hypothesis for the 317 [Lig. cause of light proposed by Maxwell, based on the relations existing between the phe- nomena of light and those of electro-magnet- ism. Maxwell's electro-magnetic theory of light as- sumes that the phenomena of light and magnet- ism are each due to certain motions of the ether, electricity and magnetism being due to its r- Shunt and Separately Excited Dynamo. the field is excited both by means of a shunt to the armature circuit, and by a current pro- duced by a separate source. A shunt and separately excited compound- wound dynamo-electric machine is shown in Fig. 356. This machine maintains a constant current in its circuit, notwithstanding changes in its ex- ternal circuit. Machine, Dynamo-Electric, Shunt- Wound A dynamo-electric machine in which the field magnet coils are placed in a shunt to the armature circuit, so that only a portion of the current generated passes through the field magnet coils, but all the difference of potential of the armature acts at the terminals of the field circuit. A shunt dynamo-electric machine is shown in. Fig. 357- D D D D Fig. 357- Shunt Dynamo. In a shunt dynamo -electric machine, an in- crease in the resistance of the external circuit in- creases the electromotive force, and a decrease in the resistance of the external circuit decreases the electromotive force. This is just the reverse of the series-wound dynamo. In a shunt-wound dynamo a continuous balanc- ing of the current occurs. The current dividing at the brushes between the field and the external circuit in the inverse proportion to the resistance of these circuits, if the resistance of the external circuit becomes greater, a proportionately greater current passes through the field magnets, and so causes the electromotive force to become greater. If, on the contrary, the resistance cf the external circuit decreases, less current passes through the field, and the electromotive force is proportion, ately decreased. Mac.] [Mac. In a shunt- wound dynamo the resistance of the Shunt should be at least four hundred times that of the armature. It is sometimes as much as one thousand fames as great. (Urjukart.) To obtain complete regulation of the machine some form of compounding is neces-ary. (See Machine^ Dynamo-Electric, Compound- Wound. ) Machine, Dynamo-Electric, Single-Mag- net A dynamo-electric machine, in which the field magnet poles are obtained by means of a single coil of insulated wire, in- stead of by more than a single coil. Machine, Dynamo-Electric, Sparking of An irregular and injurious operation of a dynamo-electric machine, attended with sparks at the collecting brushes. Sparking consists in the formation of small arcs under the collecting brushes. One cause of sparking is to be found in the brushes leaving one commutator strip before making connection with the next strip. Sparking from this cause may be avoided by so placing the brushes as to cause them to bridge over the space between two consecutive bars, thus permitting them to touch one bar before leaving the other. Two brushes, electrically connected, are sometimes employed for this purpose, or the slots between contiguous bars are slightly inclined to the axis of rotation. Sparking causes a burning of the commutat >r strips, and an irregular consumption of the brushes, both of which produce further irregulari- ties by the wear of the brushes against the com- mutator bars. At the moment the brush touches two contigu- ous commutator bars, it short circuits the coil terminating at those bars. On the breaking of this closed circuit, a spark appears under the brushes. This spark is often considerable, since from the comparatively small resistance of the coil, it is apt, when short circuited, to produce a heavy current if not exactly at the neutral point. Another cause of sparking is to be found in the Seif-induction of the armature coils. The extra Current on breaking forms an injurious spark un- der the brushes. This spark may be considerable, since the current produced in the coil on mo- mentarily short circuiting it by the brushes sim- ultaneously touching the adjoining commutator segments may be large. Sparking occurs when the brushes are not set close to the neutral line. Since the principal cause for the change in the lead of the brushes is the magnetizing effect of the armature coils, it is preferable to make the number of windings of these as few as possible, and to obtain t'.ie neces- sary differences of potential by increasing the speed of rotation and the strength of the magnetic field of the machine. Short armature coils also lessen the sparking due to self-induction. Sparking at the brushes is also caused by the jumping of improperly supported or constructed brushes When the brushes are not set close to the neu- tral point, long flashing sparks are apt to occur. A lack of symmetry of winding of the arma- ture coils will necessarily be attended by injurious flashing, from the impossibility of properly ad- justing the brushes. Machine, Dynamo-Electric, Synchroniz- ing Adjusting the phases of two alter- nating current dynamos so as to permit their being coupled or joined in parallel. Machine, Dynamo-Electric, to Short Cir- cuit a To put a dynamo-electric ma- chine on a circuit of comparatively small electric resistance. Machine, Dynamo-Electric, Unit of Out- put of A unit for the electric power furnished by the current of a dynamo-electric machine. A unit of output equal to 1,000 watts or I kilowatt. A machine furnishing a current of ico amperes at a difference of potential of 80 volts, would have an output of 8,000 watts, and would, therefore, be rated as an 8-unit machine. Machine, Electric, Rubber of A cushion of leather covered with an electnc amalgam, and employed to produce electricity by its friction against the plate or cylinder of a frictional electric machine. (See Ma- chine, Frictional Electric?) Machine, Electrostatic Induction A machine in which a small initial charge produces a greatly increased charge by its in- ductive action on a rapidly rotated disc of glass or other dielectric. An excellent type and example of such a ma- chine is found in the Hoi tz machine, which o-n- Mac.] 333 [Mac. sists of the following parts, as shown in Fig. 358, viz.: (i.) A stationary glass plate A, fixed at its edges to insulated supports. (2.) A movable plate B, capable of rapid rota- tion on a horizontal axis, by a driving pulley. Fig. 358. Holtz Electric Machine. (3.) Armatures of varnished paper f, f ', placed on opposite sides of the fixed plate at holes or windows P, P ', cut in the plate. The armatures are placed on the side of the fixed plate away from the moving plate, or on the back of the plate, so that the plate, on its rotation, moves towards tongues of paper attached to the middle of the armature. (4.) Metal combs placed in front of the movable disc opposite the armatures, and connected with the brass balls m, n, one of which is movable towards and from the other by means of a suitably supported insulating handle connected with it. A small initial charge is given to one of the armatures by holding a plate of electrified vul- canite against it, and rotating the machine while the balls m, n, are in contact. As soon as the ma- chine is charged the balls are gradually separated^ when a torrent of sparks will pass between them so long as the plate is rotated. When the balls are separated too far the sparks cease to pass. The balls must then be again brought into contact and gradually separated as before. The Holtz machine can be regarded as a re- volving electrophorus provided with means for constantly discharging and recharging the upper metallic plate. (See Electrophorus.) The action of the machine is well described by S. P. Thompson in his " Elementary Lessons on Electricity and Magnetism," as follows: "Suppose a small -4- charge to be imparted at the outset to the right armature f ; this charge acts inductively across the discs upon the metallic comb, repels electricity through it, and leaves the points negatively electrified. They discharge negatively electrified air upon the front surface of the movable disc; the repelled charge passes through the brass rods and balls, and is discharged through the left comb upon the front side of the movable disc. Here it acts inductively upon the paper armature, causing that part of it which is opposite itself to be negatively charged and re- pelling a -f charge into its farthest part, viz., into the tongue, which being bluntly pointed, slowly discharges a -f charge upon the back of the mov- able disc. If now the disc be turned round, this -f- charge on the back comes over from the left to the right side, in the direction indicated by the arrow, and, when it gets opposite the comb, in- creases the inductive effect of the already existing -f charge on the armature, and therefore repels more electricity through the brass rods and knob into the left comb. Meantime the charge, which we saw had been induced in the left armature, has in turn acted on the left comb, causing a -+- charge to be discharged by the points upon the front of the disc; and drawing electricity through the brass rods and knobs, has made the right comb still more highly , increasing the discharge of ly electrified air upon the front of the disc, neu- tralizing the -(- charge which is being conveyed over from the left. These actions result in causing the top half of the moving disc to b^ ly elcctri - fied. The charges on the front serve, as they are carried round, to neutralize the electricities let off by the poincs of the combs, while the charges on the back, induced respectively in the neighbor- hood of each of the armatures, serve, when the rotation of the disc conveys them round , to me rease the inductive influence of the charge on the other armature." The student will be aided in following Prof. Thompson's explanation by the diagrammatic sketch, shown in Fig. 359. Here the rotating plate is shown for convenience in the 1 jrm of a cylinder. The armatures are shown on the back of the plate at f and f, opposite the brass collecting combs P' and P, with their discharging rods and balls a, a. The effect of the positive charge given to the right hand armature f , directly through the comb P', rods a, a, comb P, to left hand arma- ture f, is readily seen. The rotation ot the plate being in the direction of the curved arrows, the charging of the front of the plate by convection streams from the combs, and the back of the plate Mac.] 334 [Mac. from the points of the paper armatures, as well as the character of the charge, will be understood. There thus results, as is shown, a positive charge on both the front and back of the upper half of Fig. 339. Plate of Holtz Machine. the rotating plate, and a negative charge on both sides of its lower half. A reversal of polarity of the plate occurs at the line P a a P'. Sometimes the reversal does not occur, and the machine either loses its charge entirely, or in part. A conductor S S, furnished with points, is sometimes provided to lessen the chances of lack of reversal. Machine, Faradic A machine for producing faradic currents. There are two varieties of faradic machines, viz.: magneto faradic apparatus and simple in- duction apparatus. Machine, Frictional Electric A machine for the development of electricity by friction. A frictional electric machine consists of a plate or cylinder of glass A, Fig. 360, capable of rota- tion on a horizontal axis. A rubber formed of a chamois skin, covered with an amalgam of tin and mercury, is placed at B. By the rotation of the plate the Fig. 360. Frictional Electric Machine. rubber becomes negatively and the glass posi- tively excited. An insulated conductor D, called the prime or positive conductor, provided with a comb of points, becomes positively charged by in- duction. The machine will develop electricity best if a conductor attached to the rubber is con- nected with the ground, as by a chain. Machine, Holtz A particular form of electrostatic induction machine. (See Machine, Electrostatic Induction?) Machine, Influence An electrical machine depending for its action on electro- static induction. The Wimshurst and Holtz machines are influ- ence machines. (See Machine, Electrostatic In- duction. Machine, Wimshurst Electrical. Ma- chine, Holtz.') Machine, Influence, Wimshurst's Alter- nating 1 An electrostatic induction ma- chine by means of which a series of rapidly alternating charges are produced. Although such a machine furnishes a torrent of sparks between its terminals, yet it is unable to furnish a permanent charge to a Leyden jar or condenser, since its oscillatory discharges, >^ff^\ continually undo at any M' ^. ^ \ small interval of time, J|>':/ ^JJM> what was done at the preceding interval, and thus leave the jar un- charged. Machine, Magneto Blasting A magneto-electric ma- chine employed for generating the cur- rent Used in electric^. s6f . Magneto- Electric blasting. Machine. Machine, Magneto-Electric A ma- chine in which there are no field magnet coils, the magnetic field of the machine being due to the action of permanent steel magnets. A dynamo in which currents are produced by the motion of armature coils past permanent mag- nets. (See Machine, Dynamo -Electric.} A magneto-electric machine is shown in Fig, 361. Another form of magneto-electric machine is shown in Fig. 362. This latter form of machine is known as a hand generator, in contradistinction to one driven by power and called a power generator. Mac.] 335 [Mac. The field is obtained by means of a number of separate permanent magnets so combined as to Fig. 362. Magneto- Electric Machine. act as a single magnet. The armature is rotated by hand. Machine, Mouse-Mill A form of convection induction machine, invented by Sir William Thomson to act as the replen- isher of his electrometer. (See Machine, Electrostatic Induction.} Machine, Rheostatic A machine devised by Plante in which continuous static effects of considerable intensity are obtained by charging a number of condensers in mul- tiple-arc and discharging them in series. The condensers are charged by connecting them with a number of secondary or storage bat- teries. Machine Telegraphy. (See Telegraphy, Machine?) Machine, Toppler-Holtz A modi- fied form of Holtz machine in which the initial charge of the armatures is obtained by the friction of metallic brushes against the armatures. Machine, Wimshurst Electrical A form of convection electric machine in- vented by Wimshurst. Like the Holtz machine, the Wimshurst ma- chine is a convection induction machine. It is, however, more efficient in action, and will prob- ably soon supersede the former machine. The Wimshurst machine consists of two shellac-var- nished glass plates that are rapidly rotated in op- posite directions. Thin metallic strips are placed on the outside of each of the plates, in the radial positions shown in Fig 363. These strips act both as inductors and carriers; the carriers of one plate acting as inductors to the other plate. Two curved brass rods, terminating in fine wire brushes that touch the plates, are placed as shown, one at the front of the plate, and one at the back, at right angles to each other. Pairs of conduct- Fig. 363. The Wit tt Electrical Machi* ors, connected together, provided with collecting points, are placed diametrically opposite each other, as shown. Sliding conductors, terminated with metallic balls, are provided for discharging the conductors. Leyden jars, the inner coatings of which are connected with two discharging rods, and the outer coatings together, may be em- ployed in this as in the Holtz machine. The exact action of this machine is not thor- oughly understood. Machines, Dynamo-Electric, Varieties of Dynamo-electric machines may be divided into classes according to (I.) The manner in which the magnetism of the field magnets is obtained. (2.) The character of their armatures. (3.) The nature of the current obtained, whether continuous or alternating. (4.) The form of their field magnets. (5.) The nature of their magnetic fields. (6.) The manner in which the current of the field magnets, the armature and the external circuits are connected. Mack A term proposed by Mr. Oliver Heaviside for a unit of self-induction. The term Mack is derived from Maxwell. The unit of self induction has also been a secohm and a quadrant. Mad.] The term Max would seem to be indicated. In the United States the unit of self-induction is called a Henry, after Prof. Joseph Henry. (See Henry, A.) Made Circuit (See Circuit, Made^ Magazine Fuse. (See Fuse, Magazine) Magne-Crystallic Action. (See Action, Magne-Crystallic^ Magnet. A body possessing the power of attracting the unlike pole of another mag- net or of repelling the like pole ; or of at- tracting readily magnetizable bodies like iron filings to either pole. A body possessing a magnetic field. (See Field, Magnetic!) The lines of force are assumed in passing through the magnetic field to come out at the north pole of the magnet and to go in at the south pole. All lines of force form closed magnetic circuits. If a magnetizable body is brought into a magnetic field, the lines of magnetic force are concentrated on it and pass through it. The body therefore be- comes magnetic. The intensity of the resulting magnetism depends on the number of lines of force that pass through the body, and the polarity on the direction in which they pass through it. A magnetized bar cannot be regarded as a source of energy in itself. Energy must be ex- pended to magnetize the iron, and must also be expended to demagnetize it. Magnet, Anomalous A magnet possessing more than two free poles. There is no such thing as a unipolar magnet. Fig, 364. Anomalous Magnet. All magnets have two poles. Sometimes, how- ever, several magnets are so grouped that there appear to be more than two poles in the same magnet. 336 [Mag. It is clear, however, that the central pole is in reality formed of two juxtaposed negative poles, and that ABC, actually consists of two magnets with two poles to each. The magnet A B C D, Fig. 365, which in like manner appears to possess four separate poles, in reality is formed of three magnets with two poles to each. Since unlike magnetic poles neutralize each other, it is clear that only similar poles can thus be placed together in order to produce additional magnet poles. S S Fig. 365. Anomalous Magnet. Thus, in Fig. 364, the magnet ABC, appears to possess three poles, two positive poles at A and C, and a central negative pole at B. S ffff,j66. Anomalous Magnet. The six-pointed star shown in Fig. 366, is an anomalous magnet with apparently seven poles. The formation of the central N-pole, as is evident from an inspection of the drawing, is due to the six separate north poles, n, n, n, n, n, n, of the six separate magnets Sn, Sn, etc. Such a magnet would be formed by touching the star at the point N, with the S-pole of a sufficiently powerful magnet. The extra poles are sometimes called consequent poles. Their presence may be shown by means of a compass needle, or by rolling the magnet in iron filings, which collect on the poles. Magnet, Artificial A magnet pro- duced by induction from another magnet, or from an electric current. Any magnet not found in nature is called an artificial magnet Magnet, Axial A name sometimes given to a solenoid with an axial or straight coie. Magnet, Bell-Shaped A modifica- tion of a horseshoe magnet in which the ap- proached poles are semi-annular in shape, and form a split tube. Bell-shaped magnets are used in many galva- Mag.] 337 [Mag. nometers, because they can be readily dampened by surrounding them by a mass of copper. The needle in its motion produces currents that tend to oppose, and, therefore, to stop its motion. (See Laws, Lenz's.) Magnet, Club-Footed An electro- magnet whose core is in the form of a horse- shoe and is provided with a magnetizing coil on one pole only. Magnet Coil. (See Coil, Magnet.) Magnet, Compensating A magnet placed over a magnetic needle, generally over the magnetic needle of a galvanometer, for the purpose of varying the direction and in- tensity of the magnetic force of the earth on such needle. (See Galvanometer, Reflecting^) "A magnet, called a compensating magnet, is sometimes placed on a ship, near the compass needle, for the purpose of neutralizing the local variations produced on the compass needle by the magnetism of the ship. Magnet, Compound A number of single magnets, placed par- allel and with their similar poles facing one another, as shown in Fig. 367. Compound magnets are stronger in proportion to their weight than single magnets. Magnet, Compound Horseshoe A horse- shoe magnet composed of several separate horseshoe magnets placed with their similar poles together. A compound horseshoe Fig. 36 7. Compound magnet is shown in Fig. 368. Magnet. A. horseshoe magnet possesses greater portative power than a straight bar magnet of the same weight. (See Poiver, Portative.) (i.) Because its opposite poles are nearer to- gether; and (2.) Because the magnetic resistance of its circuit is less, the lines of magnetic force closing through the armature, and thus concentrating the magnetic attraction on the armature. Electro-magnets are generally made of the horseshoe shape. Magnet, Controlling A name sometimes applied to the controller in the Thomson- Houston automatic system of cur- r ent regulation. (See Controller) Generally any mag- net which controls - some particular ac- tion. Magnet, Cylindri- cal A magnet in the shape of a cyl- inder. A helix or solenoid through which a cur- rent of electricity is passing is, so far as ex- ternal space is con- cerned, the exact mag netic equivalent of a cylindrical magnet. Magnet, Damping Any magnet employed for the pur- Fig. 368. Compound Horte- pose of checking the shoe M*?***- velocity of motion of a moving body or mag- net. Damping magnets generally act by the resist- ance which they offer to the passage of a metallic disc, so moved as to cut the lines of force of their field. Magnet, Electro A magnet pro- duced by the passage of an electric current through a coil of insulated wire surrounding a core of magnetizable material. The magnetizing coil is called a helix or sole- noid. (See Magnetism, Ampere's Theory of .) Strictly speaking, the term electro-magnet is limited to the case of a magnet provided with a soft iron core, which enables it to rapidly acquire its magnetism on the passage of the magnetizing current, and as rapidly to lose its magnetism on the cessation of such current. An electric current passed around a bar of magnetizable material, in the manner and direc- tion shown in Fig. 369, will produce the polarity N and S, at its ends or extremities as marked. The directions of the currents required to pro- duce N and S, poles respectively are shown in Fig. 370. The cause of this difference of polarity will be readily understood from a study of the direction Mag.] of lines of magnetic force in the field produced by an electric current. [Mag. Fig. 369. Polarity of Current. The direction of this polarity may be predicted by the following modification of a rule by Ampere: Imagine yourself swimming in the wire in the direction of the current; if, then, your face is Fig. 3 JO. North and South Magnet Poles. turned toward the bar that is being magnetized, its North seeking pole will be on your left. Y B Fig. 37 r. Deflection of Fig. 372. Deflection of Magnetic Needle. Magnetic Needle. If, for example, the conductor A B, be traversed by a current in the direction from B, to A, as shown in Fig. 371, the north pole N, of the needle N S, placed under the conductor, is de- flected, as shown, to the left of the observer, who is supposed to be swimming in the current, facing the needle. If the current flow in the opposite direction, as from A, to B, as shown in Fig. 372, the N, pole of the needle is deflected as shown, but still to the left of the observer supposed to be swimming as before. In any electric circuit, the lines of magnetic force, produced by the passage of the current, form circles around the circuit in planes at right angles to the direction of the current, as shown in Fig. 373. The direction of these lines of force is the same as that of the hands of a watch, if the cur- rent be supposed to flow away from the observer. (See Field, Magnetic, of an Electric Current.} Fig. 373' Direction of Lines of Force. Remembering now that the lines of force are supposed to come out at the north pole of a magnet, and to pass in at the south pole, it is evident that if the current flows in the direction shown in Fig. Fig. 374. Direction of Lines of Force. 374, the lines of force will come out at the north pole and pass in at the south pole. Since in a right-handed helix the wire passes around the axis in the opposite direction to that in which it passes in a left-handed helix, it is evident that the helices shown in Fig. 375 at I, and 2, will produce opposite polarities at the points of entrance and exit by a current flowing in the direction of the arrows. If the current be sent through the right handed helix, shown at I, from b, to a, that is, from the left to the right in the figure, a south pole will be produced at b, and a north pole at a. If, how- ever, it be sent from a, to b, the polarity will be revers"" d. If the current be sent through the left handed JUag.J 339 [Mag. helix, shown at 2, from a, to b, that is, from the left to the right in the figure, a north pole will be pro- duced at a, and a south pole at b. If, however, it be sent in the opposite direction, the polarity will be reversed. Therefore, in an electro-magnet, on the core of which several layers or thicknesses of wire are wound, in which the current flows through one layer, in, say a direction from right to left, the cur- rent must return through the next layer in the opposite direction, or from left to right. The polarities of the same extremities of the helices are, however, the same in all cases, since the layers are successively right and left handed to the current. The winding shown at 3, pro- duces consequent poles. The following laws express the more important principles concerning electro-magnets: (i.) The magnetic intensity (strength) of an electro-magnet is nearly proportional to the strength of the magnetizing current, provided the core is not saturated. (2.) The magnetic strength is proportional to the number of turns of wire in the magnetizing coil; that is, to the number of ampere turns. (See Turns, Ampere. ) (3.) The magnetic strength is independent of the thickness or material of the conducting wires. These laws may be embraced in the more gen- eral statement that the strength of an electro- F*S- 37 5- Kight-Handed, Left- Handed and Anomalous Helices. .magnet, the size of the magnet being the same, .is proportional to the number of its ampdre turns. (S-e Turns, Ampere. ) A short interval of time is required for a cur- rent to thoroughly magnetize a powerful electro- magnet. A few moments are also required for a power- ful magnet to thoroughly lose its magnetism. At the same time electro magnets are capable of acquiring or losing their magnetism with very great rapidity. It i, in fact, 0:1 this ability pos- s.ssed to so remarkable a degree Vy soft iron, that the value of an electro-magnet for many purposes depends. (See Lag, Magnetic.) A difference exists between the action of a mag- netized disc and a hollow coil of wire through which a current of electricity is passing. So far as the space outside either is concerned, the action is the same, but the coil is penetrable on the inside and the disc is not, and for the inside ot the space, therefore, there is a difference in the ac- tion. Magnet, Electro, Bar An electro- magnet, the core of which is in the form of a straight bar or rod. Magnet, Electro, Cylindrical An electro-magnet, the core of which consists of a hollow cylinder provided with a slot extend- ing parallel to its axis. The gap in the cylinder suffices for the placing of the magnetizing coils, and forms the poles. This form of electro-magnet was devised by Joule. Its construction will be understood from an inspection of Fig. 376. Fig. J/6. Cylindrical Electro- Mag net. Magnet, Electro, Horseshoe An electro-magnet, the core of which is in the shape of a horseshoe or U. Magnet, Electro, Hughes' An electro-magnet in which a U-shaped per- manent magnet is provided with pole pieces of soft iron, on which only are placed the magnetizing coils. A quick acting electro-magnet, in which the magnetizing coils are placed on soft iron pole pieces that are connected with and form the prolongations of the poles of a permanent horseshoe magnet. Hughes devised this form of electro-magnet in o-der to oMain the be t effects from currents of but short duration. He thus obtained a quick acting magnet, neces- sary to insure the success of his system of printing telegraph, where the magnetizing currents at times have a duration of but the .20 of a second. Mag.] 340 - 377- Iron-Clad Electro. Magnet. Magnet, Electro, Joule's Cylindrical An electro-magnet provided with a hollow cylindrical core. (See Magnet, Elec- tro, Cylindrical) Magnet, Electro, Iron-Clad An electro-magnet whose magnetizing coil is almost entirely surrounded by iron. The effect of the iron casing is to greatly re- duce the magnetic re- sistance of the circuit. A form of iron- clad elec- tro-magnet is shown in Fig. 377. Here one of the poles is connected with a casing of iron, external to the coils, and is thus brought nearer to the other pole. Magnet, Electro, Long-Core An electro-magnet with a long core of iron. A long-core electro-magnet magnetizes and demagnetizes much more slowly than a short- core electro-magnet. Magnet, Electro, Short-Core An electro-magnet with a short core of iron. A short-core electro-magnet possesses the power of being magnetized and demagnetized much more rapidly than a long core magnet. Magnet, Electro, Yoked-Horseshoe A horseshoe electro-magnet, in which the two straight limbs are formed of two straight rods or bars, yoked together at one pair of ends by a yoke or bar of iron. In some cases the magnetizing coils are placed on each of the limbs. Sometimes, however, a single coil is placed at the middle of the yoke and the limbs are kit bare. Even with the closest possible fiit.ng the re- sistance of the magnetic circuit is much greater in this form of electro-magnet, owing to the smaller permeability of the air gap at the joints, than it would be if the entire core weie made of a single piece of iron. A yoked electro magnet is, however, more convenient to make and use. Magnet, Electro, Zig/ag A multi- polar electro-magnet, the magnetizing coils of which are separately wound in grooves cut in the face of straight or curved bars. A form of zigzag electro- magnet devised by Joule is shown in Fig. 378. The spiral char- acter of the winding produces the alternate North and South polari- ties shown in the figure. Magnet, Equator of A point ap- proximately midway between the poles of a straight bar magnet, or Fig 37 g nearly midway from Magnet. the poles of a horseshoe magnet if meas- ured along the bar from each pole. This term was proposed by Dr. Gilbert. It is now almost entirely displaced by the term neutral point. Magnet, High-Resistance A term sometimes used in place of long-coil magnet whose coils have a high electric resistance, (See Magnet, Long-Coil) The term long-coil magnet is, perhaps, the pre- ferable one, because the resistance ot a coil, per- se, has nothing to do with its magnetizing power, which is determined by its ampere turns. (See Turns, Ampere. Magnet, Long Coil.) Magnet, Horseshoe A magnetized bar of steel or iron bent in the form of a, horseshoe or letter U. Magnet, Iron-Clad A magnet whose magnetic resistance is lowered by a casing of iron connected with the core and provided for the passage of the lines of magnetic force, (See Magnet, Tubular) Magnet, Jacketed A term some- times applied to a form of iron-clad magnet. (See Magnet, Iron-Clad.) Magnet, Keeper of A mass of soft iron applied to the poles of a magnet through which its lines of magnetic force pass. (See Field, Magnetic) The keeper of a magnet differs from its arma- ture in that the keeper while acting as such is always kept on the poles to prevent loss of mag- netization, while the armature, besides acting as a keeper, may be attracted towards, or, if an electro-magnet, be repelled from the magnet poles. While performing its functions the keeper is always fixed, the armature generally, though Mag.] 341 LMag. not always, is in motion. A keeper is, of course, only used with permanent magnets. Opinion is divided as to the efficacy of the keeper in preventing loss of magnetization m certain cases. Magnet, Long-Coil - An electro- magnet whose magnetizing coil consists of many turns of thin wire. Magnet, Low-Resistance A term sometimes used in place of short-coil mag- net. (See Magnet, Short-Coil.} This term, short-coil magnet, is the preferable one. Magnet, Marked Pole of A name for- merly applied to that pole of a magnet which points approximately to the geographical north. If the pole of the magnet that points to the geographical north be in reality the north pole of the magnet, then the earth's magnetic pole in the Northern Hemisphere is of south magnetic polarity. In the United States, and Europe generally, this is regarded as the fact. The French, however, formerly called the pole of the needle that points to the earth's geographical north the south or austral pole. In America and England it is called the north pole, the marked pole, or the north-seeking pole, and the Northern Hemisphere is assumed to possess south magnetic polarity. (See Pole, Magnetic, Austral. Pole, Magnetic, Boreal.) Magnet, Moment of The effective force of a magnetic couple as obtained by multiplying one of the forces of the couple by the perpendicular distance between the directions of the forces. The moment of a magnet is equal to the prod- uct of the volume of the magnet and the in- tensity of magnetization, or simply its magnetiza- tion. Magnet, Natural A name some- times given to a lodestone. (See Lodestone} Magnet, Neutral Line of (See Line, Neutral, of a Magnet?) Magnet, Permanent A magnet of hardened steel or other paramagnetic sub- stance which retains its magnetism for a long time after being magnetized. A permanent magnet is distinguished, in this respect, from a temporary magnet of soft iron, which loses its magnetization very shortly after being taken from the magnetizing field. Magnet, Portative Power of The lifting power ot a magnet. The portative or lifting power of a magnet, depends on the form ot the magnet, as well as on its strength. A horseshoe magnet, for example, will lift a much greater weight than the sa ne magnet if in the torm ol a straight bar. This is due not only to the mutual action of the approached poles, but also to the decreased re- sistance of the magnetic circuit, and to the greater number of lines ot magnetic torce chat pass through the armature. The portative power is proportional to the area of contact and the square of the magnetic intensity, the formula, being = 8~jTx 981, in which P, is the lifting power in grammes, A, the area of contact in square centimetres, and B, is the number of lines of force per square centi- metre. Magnet Operation. (See Operation, Magnet} Magnet, Receiving A name some- times given to the relay of a telegraphic sys- tem. (See Relay} In general, any magnet, used directly in the receiving apparatus, at the receiving end of a line connecting a system of electric communi- cation between transmitting and receiving- instruments. Magnet, Regulator A magnet, the operation of which is to automatically effect any desired regulation. The magnet in the Thomson-Houston sys-. tern of automatic regulation, by means of which the commutator collecting brushes are automatically shifted to such positions on the commutator as will maintain the current practically constant, despite the changes in the resistance of the circuit external to the machine. (See Regulation, Automatic} Magnet, Relay An electro-magnet, whose coils are connected to the main line of a telegraphic circuit, and the movements of Mag.] 342 [Mag. whose armature is employed to bring a local battery into action at the receiving station, the current of which operates the register or sounder. Magnet, Short-Coil An electro- magnet whose magnetizing coil consists of a few turns of short, thick wire. Magnet, Simple A simple mag- netized bar. The term simple magnet is used in contradis- tinction to compound magnet. (See Magnet, Compound. ) Magnet, Sluggish A magnet that magnetizes or demagnetizes sluggishly. An electro-magnet becomes sluggish when sur- rounded by a sheathing of copper, on account of the currents induced in the sheathing in a direction opposite to those passing through the magnetizing coil. Magnet, Solenoidal A thin, uni- formly magnetized straight bar of steel, of such a length that its poles, situated at ex- tremities or ends of its longer axis, act on external objects as if equal and opposite quan- tities of magnetism were concentrated at such extremities. It derives its name solenoidal from the simi- laiity between its action and that of a solenoid. Unless very carefully magnetized, a magnet will not act as a solenoidal magnet. (See Magnet, JLlectro. Magnetism, Solenoidal Distribution of.) Magnet, Tabular A form of horse- shoe magnet, in which one pole is brought near the opposite pole by a hollow cylinder or tube of iron, which is placed in contact with one of the magnetic poles, so as to com- pletely surround the other, except in the plane of cross-section of that pole. A form of iron-clad magnet. (See Mag- net, Iron-Clad.) There is thus obtained a magnet, with two concentric poles, one solid and the other annular,' the portative power of which is much greater than that of a horseshoe magnet of equal dimensions. Magnet, Field, of Dynamo-Electric Ma- chine One of the electro-magnets em- ployed to produce the magnetic field of a dy- namo-electric machine. The field magnets consist of a suitable frame, or core, on which the field magnet coils are wound. Thejietd magnet cores are made of thick and solid iron, as soft as possible. They should con- tain plenty of iron in order to avoid too ready magnetic saturation. All edges and corners are to be avoided, since they tend to cause an irregular distribution of the field. The field magnets should in general have suffi- cient magnetic strength to prevent the magnet- izing effect of the armature from unduly influ- encing the field, and thus, by causing too great a lead, produce injurious sparking. Magnetic or Magnetical. Pertaining to magnetism. Magnetic Adherence. (See Adherence, Magnetic?) Magnetic Air Circuit. (See Circuit, Air, Magnetic?) Magnetic Air Gap. (See Gap, Air, Mag- netic?) Magnetic Attraction. (See Attraction, Magnetic?) Magnetic Axis. (See Axis, Magnetic?) Magnetic Axis of a Straight Needle. (See Axis, Magnetic, of a Straight Needle?) Magnetic Azimuth. (See Azimuth, Mag- netic?) Magnetic Battery. (See Battery, Mag- netic?) Magnetic Bridge. (See Bridge, Mag- netic?) Magnetic Circuit (See Circuit, Mag- netic?) Magnetic Closed-Circuit. (See Circuit, Closed Magnetic?) Magnetic Conductance. (See Conduct- ance, Magnetic?) Magnetic Core, Closed (See Core, Closed-Magnetic?) Magnetic Core, Open (See Core, Open-Magnetic?) Magnetic Couple. (See Couple, Mag- netic?) Mag.] 343 [Mag. Magnetic Curves. (See Curves, Mag- netic.} Magnetic Day of Disturbance. (See Day of Disturbance, Magnetic?) Magnetic Declination. (See Declina- tion^) Magnetic Density. (See Density, Mag- netic^ Magnetic Dip. (See Dip, Magnetic) Magnetic Elements of a Place. (See Elements, Magnetic, of a Placed) Magnetic Equalizer. (See Equalizer, Magnetic) Magnetic Explorer. (See Explorer, Magnetic) Magnetic, Ferro Magnetic after the manner of iron or other paramagnetic body. (See Paramagnetic) Magnetic Field. (See Field, Magnetic) Magnetic Field, Reversing (See Field, Magnetic, Reversing) Magnetic Field, , Shifting (See Field, Magnetic, Shifting) Magnetic Figures. (See Figures, Mag- netic. Field. Magnetic.) Magnetic Filament. (See Filament, Magnetic) Magnetic Flow. (See Flow, Magnetic) Magnetic Flux. (See Flux, Magnetic) Magnetic Force. (See Force, Magnetic) Magnetic Inclination. (See Inclination, Magnetic) Magnetic Induction. (See Induction, Magnetic) Magnetic Induction, Dynamic (See Induction, Magnetic, Dynamic) Magnetic Induction, Static (See Induction, Magnetic, Static) Magnetic Inertia. (See Inertia, Mag- netic) Magnetic Intensity. (See Intensity, Magnetic) Magnetic Joint. (See Joint, Magnetic) Magnetic Lag. (See Lag, Magnetic) Magnetic Latitude. (See Latitude, Mag- netic) Magnetic Leakage. (See Leakage, Mag- netic) Magnetic Lines of Force. (See Force, Magnetic, Lines of) Magnetic Mass. (See Mass, Magnetic) Magnetic Memory. (See Memory. Mag- netic) Magnetic Meridian. (See Meridian, Magnetic) Magnetic Moment. (See Moment, Mag- netic) Magnetic Normal Day. (See Day, Nor- mal, Magnetic) Magnetic Observatory. (See Observa- tory, Magnetic) Magnetic Output. (See Output, Mag- netic) Magnetic Parallel. (See Parallels, Mag- netic) Magnetic Permeability. (See Permea- bility, Magnetic) Magnetic Permeance. (See Permeance, Magnetic) Magnetic Permeation. (See Permeation, Magnetic) Magnetic Poles. (See Poles, Magnetic) Magnetic Poles, False (See Pole, Magnetic, False) Magnetic Proof Piece. (See Piece, Mag- netic Proof) Magnetic Proof Plane. (See Plane, Proof, Magnetic) Magnetic Reluctance. (See Reluctance, Magnetic) Magnetic Repulsion. (See Repulsion, Magnetic) Magnetic Resistance. (See Resistance, Magnetic) Magnetic Retardation. (See Retarda- tion, Magnetic.") Mag.J 344 [Mag. Magnetic Retentivity. (See Retentivity, Magnetic) Magnetic Saturation. (See Saturation, Magnetic?) Magnetic Screen or Shield. (See Screen or Shield, Magnetic) Magnetic Screening. (See Screening, Magnetic) Magnetic Self-induction. (See Induc- tion, Self, Magnetic) Magnetic Shells. (See Shells, Magnetic) Magnetic Shunt. (See Shunt, Magnetic) Magnetic, Sidero A term proposed by S. P. Thompson to replace the term ferro- magnetic. (See Magnetic, Ferro) Magnetic Solenoid. (See Solenoid, Mag- netic) Magnetic Sounds. (See Sounds, Mag- netic) Magnetic Spin. (See Spin, Magnetic) Magnetic Storm. (See Storm, Mag- netic) Magnetic Strain. (See Strain, Mag- netic) Magnetic Stress. (See Stress, Magnetic) Magnetic Susceptibility. (See Suscepti- bility, Magnetic) Magnetic Theodolite. (See Theodolite, Magnetic) Magnetic Unit Pole. (See Pole, Unit, Magnetic) Magnetic Units. (See Units, Magnetic) Magnetic-Vane Ammeter. (See Amme- ter, Magnetic- Vane) Magnetic-Yane Voltmeter. (See Volt- meter, Magnetic- Vane) Magnetic Variations. (See Variation, Magnetic) Magnetic Variation Transit. (See Tran- sit, Magnetic Variation) Magnetic Variometer. (See Variometer, Magnetic) Magnetic Viscosity. (See Viscosity, Magnetic) Magnetic Whirl.- (See Whirls, Mag- netic) Magnetic Whirl, Expanding (See Whirl, Magnetic, Expanding) Magnetics, Electro That branch of electric science which treats of the rela- tions that exist between electric circuits and magnets. Magnetism. That branch of science which treats of the nature and properties of mag- nets and the magnetic field. (See Field, Magnetic) A property or condition of matter attended by the existence of a magnetic field. Magnetism, Ampere's Theory of A theory or hypothesis proposed by Ampere, to account for the cause of magnetism, by the presence of electric currents in the ultimate particles of matter. F'S-379' Unmagnetized Bar (after .Ampere). Fig. 380. Magnetized Bar \after Ampere). This theory assumes: (I.) That the ultimate particles of all magneti- zable bodies have closed electric circuits in which electric currents are continually flowing. (2.) That in an unmagnetized body these cir- cuits neutralize one another because they have different directions. (3.) That the act of magnetization consists in such a polarization of the particles as will cause these currents to flow in one and the same direc- tion, magnetic saturation being reached when all the separate circuits are parallel to one another. (4.) That coercive force is due to the resistance these circuits offer to a change in the direction of their planes. Figs. 379 and 380 show the circular paths of some of these circuits. Fig. 379 shows the as- Mag.] 345 [Mag. sumed condition of an un magnetized bar. Fig. 380 the assumed condition of a magnetized bar. A careful inspection of the figures will show that in a magnetized bar all the separate currents flow in the same direction. All the circuits except those on tJie extreme edge of the bar will, there- fore, have the currents flcnving in them in opposite directions to that in their neighboring circuits, and, therefore, will neutralize one another. There will remain, hoivever, a current in a circuit on the outside of the bar, which must therefore be re- garded as the magnetizing current. Guided by these considerations, Ampfere pro- duced a coil of wire, called a solenoid, which is the equivalent of the magnetizing circuit assumed by his theory. It therefore follows that an electric current sent through a coil of insulated wire surrounding a rod or bar of soft iron, or o'her readily magnet- izable material, will make the same a magnet. A magnet so produced is called an electro-magnet. {See Magnet, Electro.') The magnetizing coil is called a helix or sole- noid. (See Solenoid, Electro-Magnetic.) The polarity of the magnet depends on the direction of the current, or on the direction of winding of the helix or solenoid. (See Solenoid, Sinistrorsal. Solenoid, Dextrorsal.) The improbability of an electric current con- tinually flowing in a circuit without the expendi- ture of energy, has led, perhaps, the majority of scientific men to reject Ampere's theory of mag- netism. Lodge, however, does not agree with the ma- jority of physicists in regarding a constant flow of electricity through the molecules of magnetiza- ble substances as an impossibility. On the sup- position that the atoms or molecules possess no resistance, the current would flow through them forever. He says: " To all intents and pur- poses certainly atoms are infinitely elastic, and why should they not also be infinitely conducting ? Why should the dissipation of energy occur, in respect to an electric current circulating wholly inside an atom? There is no reason why it should." Magnetism, Animal A term some- times applied to hypnotism or artificial som- nambulism. Magnetism, Earth's, Theories as to Canse of The various theories or hypotheses respecting the cause of the earth's magnet- ism. Any theory or hypothesis which shall satisfac- torily explain the cause of the earth's magnetism must account for the following phenomena, viz.: (i.) Variations in the intensity of the earth's magnetic field. (2.) Variations in the earth's magnetic inclina- tion, declination and intensity. The following hypotheses have been proposed: 1st. That the earth's magnetism is due to the circulation round the earth of electric currents produced by differences of temperature which the earth's surface acquires from exposure to the sun during its rotation. As the earth rotates from west to east, the area of greatest heat would move round the earth in the opposite direction, or from east to west If now those differences of temperature could pro- duce, in a manner not as yet explained, thermo- electric currents circulating round the earth from east to west, such currents would produce, in the Northern Hemisphere of the earth, south mag- netic polarity, and in the Southern Hemisphere north magnetic polarity, which would account for the magnetic polarity of the earth. Differences in the intensity of the earth's mag- netic field, and in the inclination and direction of its lines of magnetic force, would be explained, according to this hypothesis, by the differences in the amount of the solar radiation at different times. The objection to this theory is to be found in the fact that by far the larger part of the earth's surface at the Equator is composed of water, so that the differences of potential at such parts, produced by the differences of temperature, are not readily set up in the earth's crust, if, indeed, they are set up at all. 2d. That the earth's magnetism is due to in- duction from an already magnetized sun. This theory was brought f >rward by Secci and others. It is not generally credited. 3d. A theory proposed by Biglow, which ac- counts for the earth's magnetism by rotation in the magnetic field of the sun's light and radia- tion. Biglow believes that the earth's magnetism is due to its rotation in the magnetic field of the sun's light. As the sun's light illumines one-hall of the earth's surface, the earth's rotation causing different portions of the surtace to pass through Mag.] this illumined area, produces, in Prof. Biglow's opinion, those differences in the direction and in- tensity of the magnetic lines of the earth's field that correspond to differences in the earth's mag- netic intensity, declination and inclination. It will be observed that in all these theories the sun is the prime factor in the production of the earth's magnetism. The evident connection between the earth's magnetism and the solar radiation is established from the well known connection between the so- called magnetic storms and variations in the in- tensity of the earth's magnetism. Magnetic storms are always attended by out- bursts of solar energy, known technically as sun-spots. A series of observations on the num- bers and frequency of sun-spots, plotted in the form of a curve, the ordinates of which represent the times of occurrence of the spots and the abscissas, the number of such spots, prove that such curve agrees, in a remarkable manner, with a similar curve representing the variations of the earth's magnetic field. An evident connection, too, exists between the earth's magnetism and the prevalence of the aurora borealis. Magnetism, Electro Magnetism produced by means of electric currents. The discovery by Oersted, in 1820, of the ac- tion of an electric current on a magnetic needle, was almost immediately followed by the simul- taneous and independent discoveries by Arago and Davy, of the method of magnetizing iron by the passage of an electric current around it. These observations were first reduced to a theory by Ampere. (See Magnetism, Ampere's Theory of. Magnet, Electro.} Magnetism, Ewing's Theory of A theory of magnetism nroposed by Prof- Ewing, based on the assumption of originally magnetized particles. Swing's theory of magnetism assumes that the ultimate particles of matter are naturally mag- netic and possess polarity. In this respect Ewing's theory agrees with the theories of Hughes and Weber. Ewing does not believe, however, in the necessity for the assumption of any arbitrary re- straining or constraining force to the movements of these ultimate magnetic particles other than those due to their own mutual magnetic attractions and repulsions. He assumes that in a magnet, the centres about which the molecular magnets rotate are maintained at constant distances from one another, save only as they are affected by the action of strain. He has experimentally demonstrated the prin- ciples of his theory by means of a model in which a number of small magnetic needles are so sup- ported as to be capable of free motion in a hori- zontal plane, when under varying magnetic forces. According to Ewing, "magnetic hysteresis" is not the result of any quasi-frictional resistance to molecular rotation, but arises from a molecule moving from one position of stable equilibrium to another position of stable equilibrium through a. position of unstable equilibrium. "This pro- cess," says Ewing, " considered mechanically, is- not reversible. The forces are different for the same displacement, going and coming, and there is dissipation of energy. In the model, the energy thus expended sets the little bars swinging, and their swings take some time to subside. In the actual solid, the energy which the molecular magnet loses as it swings through unstable posi- tions, generates eddy currents in surrounding matter. Let the magnets of the model be furnished with air vanes to damp their swings and the correspondence is complete." In Hughes' modification of Weber's theory of magnetism, it was held, that when magnetized iron was suddenly demagnetized by torsion or flexure, it lost its magnetization because the mo- lecular magnets came to rest in closed chains, wmc h produced no external effects. Experimentation with Ewing's model of a magnet shows that when the separate magnets after having been placed in any particular grouping are permitted to come to rest free from any external magnetic force, they do not arrange themselves in closed chains, but in general the tendency appears to be the formation of lines consisting of two, three or more magnets each member of a line being strongly controlled by its next member in that line, but influenced by the neighbors which lie off the line on either side. The fact that a given force, suddenly applied, produces more magnetic induction than when gradually applied, and leaves less residual mag- netism when suddenly than when gradually re- moved is presumably due to the inertia of the molecules. The influence of mechanical vibration in in- creasing the magnetic susceptibility and decreas- Mag.J 347 [Mag. ing the magnetic retentiveness, is ascribed by Ewing to the fact that the vibrations cause periodic variations in the distances between the centres of rotation of the magnetic molecules; thus making the molecular magnets respond more readily to changes of magnetic force during the time they are moving away from one another, when their magnetic stability is less, but also in- creasing the ease with which they respond to changes of magnetic force, by causing them to swing. Ewing discusses the theoretical effects of tem- perature on magnetism as follows, viz. : Suppose a moderate magnetizing force to be applied so that nothing like saturation is obtained, if now the temperature be raised ; then (i.) The magnetic permeability increases until the temperature reaches a certain (high) critical value. (2.) At this temperature there is suddenly an almost complete disappearance of magnetic quality. He explains these facts as follows, viz.: An increase of temperature by increasing the distance between the molecular centres causes a decrease in their stability. The loss of magnetic qualities, when a certain temperature is reached, is, he believes, due to the fact that at such temperatures the magnetic molecules are set into actual rotation, when, naturally, all traces of polarity would disappear. Ewing's theory of magnetism also accounts to a considerable extent for the effects of stress and consequent elastic strain on the magnetic qualities of iron, nickel and cobalt. The following general summary of his theory is taken mainly from Prof. Ewing's original articles as published in the Journal of the Society of Arts: (i.) That in considering the magnetization of iron and other magnetic metals to be caused by the turning of permanent molecular magnets, we may look simply to the magnetic forces which the molecular magnets exert upon one another as the cause of their directional stability. There is no need to suppose the existence of any quasi- elastic directing force, or any quasi-frictional re- sistance to rotation. (2. ) That the intermolecular magnetic forces are sufficient to account for all the general character- istics of the process of magnetization, including the variations of susceptibility which occur as the magnetizing force is increased. (3.) That the intermolecular magnetic forces are equally competent to account for the known facts of retentiveness and coercive force, and the characteristics of cyclic magnetic processes. (4.) The magnetic hysteresis and the dissipation of energy which hysteresis involves are due to molecular instability, resulting from intermolec- ular magnetic actions, and are not due to any- thing in the nature of frictional resistance to the rotation of the molecular magnets. (5 . ) That this theory is wide enough to admit an explanation of the differences in magnetic quality which are shown by different substances, or by the same substance in different states. (6.) That it accounts in a general way for the known effects of vibration, of temperature, and of stress, upon magnetic quality. (7 ) That, in particular, it accounts for the known fact that there is hysteresis in the relation of magnetism to stress. (8.) That it further explains why there is in magnetic metals hysteresis in physical quality generally with respect to stress. (9.) That, in consequence, any (not very small) cycle of stress occurring in a magnetic metal in- volves dissipation of energy. It can be demonstrated by means of experi- ments with a model constructed according to Ewing's hypothesis, that this hypothesis comes nearer than any which had been proposed before in explaining the following effects: (i.) The behavior of a piece of iron when placed in a magnetic field whose strength is made to pass through a cycle of changes. (2.) That nearly all reversals of sign on the change of the magnetizing force are accompanied by small changes in the magnetization. (3.) That a piece of iron submitted to vibra- tions or mechanical shocks, is magnetized and demagnetized more readily and with a smaller hysteresial area than if it had remained undis- turbed by vibrations. (4.) The phenomenon of "time lag " in mag- netization. (5.) The phenomena of stress, both those which occur when a body has first been placed in a magnetic field and the stress made to vary, and those which occur when a body is first placed in a constant stress and the magnetizing force is made to vary. (6.) The effects of heat on magnetization, both as regards the effect of comparatively low heating on increase of magnetic susceptibility, and the Mag.] 348 [Mag. effect of excessive heating to decrease the sus- ceptibility. The author is indebted for the above summary of demonstrable facts to a paper recently read be- fore the Electrical Section of the Franklin Insti- tute, by Prof. Henry Crew. Magnetism, Flux or Flow of The quantity of magnetism, or the number of lines of force which pass in any magnetic circuit under a given magneto-motive force, against a given magnetic reluctance. Magnetism, Galvano A term some- times used for electro-magnetism. Electro-magnetism is by far the preferable term, and is almost universally used in the United States. Magnetism, Horizontal Component of Earth's (See Component, Horizontal, of Earth's Magnetism?) Magnetism, Hughes' Theory of A theory propounded by Hughes to account for the phenomena of magnetism apart from the presence of electric currents. Hughes' theory, or, more strictly speaking, hypothesis of magnetism, though very similar to that of Ampere, does not assume the improbable condition of a constantly flowing electric current. Hughes' hypothesis assumes: (i.) That the molecules of matter, and, per- haps, more probably, the atoms, possess naturally opposite magnetic polarities, which are respect- ively + and , or N and S. (2.) That these molecules, when arranged in closed chains or circuits, are capable of neutral- izing one another so far as external action is con- cerned. and that, therefore, the substance can possess no magnetic properties so far as external action is concerned. i: Fig. 381. Closed Molecular Chain. Two such arrangements or groupings are shown in Figs. 381 and 382. It will be observed that the magnetic chain or circuit is complete, Fig. 382. Closed Groupings. (3. ) That the act of magnetization consists in such a rotation of the molecules that a polariza- tion of the substance is effected that is, the molecules are rotated on their axes so that one set of poles tend to point in one direction and the other set of poles in the opposite direction. Partial magnetization consists in partial polari- zation. Magnetic saturation is reached v\ hen the polarization is complete. (See Saturation, Mag- netic.') Coercive force is the resistance the body offers to the polarization or rotation of its molecules. (See Force, Coercive.) Hughes' hypothesis of magnetism would ap- pear to be strengthened by the following facts: (l.) A bar of steel or iron is sensibly elongated on being magnetized. This would naturally re- sult if the molecules be supposed to bj longer in one direction than in any other. (2.) A tube, furnished at its ends w.th plates of flat glass and filled with water containing finely divided magnetic oxide of iron, is nearly opaque to light when unmagnetized, but will permit some light to pass through it when magnetized. (3.) A magnet, if cut at its neutral point, will possess opposite polarities at the cut ends; and, no matter to what extent this subdivision is car- ried, the particles will still possess opposite polar- ities. These facts are, however, also explained by Ampere's hypothesis of magnetism, with, how- ever, the improbable assumption of a constantly flowing current in each molecule. The following experiment by Von Betz tends somewhat to confirm Hughes' hypothesis: He placed a powerful horseshoe magnet in a solution of iron and deposited a bar or plate of metallic iron between the poles by electrolysis. Here the molecules, at the time of their deposi - tion, were subjected to a polarizing force which tended to place them all in the same direction, and, as the solution from which they were ob- tained permitted great freedom of motion, they were all presumably deposited in lines parallel t one another. When this bar of iron was subs. Mag.] 349 [Mag. quently magnetized it was found to be much more powerful in comparison to its size than any other magnet. Mr. Shelford Bid well has shown that the act of magnetization produces a shortening rather than a lengthening of the magnetizable material. When the magnetization is moderate there is a true lengthening of the material, but when a more powerful magnetizing force is exerted a true contraction or shortening is observed. Fig. 383. Bidwell Apparatus. The Bidwell apparatus is shown in Fig. 383. The bar of iron to be magnetized is shown at R R. The magnetization is obtained by means of the coil of wire C. The upper end of the bar presses against the rod L, fulcrumed at F. The other end of the bar bears against a pivoted mirror M, from which a spot of light is reflected. In the case of the magnetization of nickel, the experiments of Bidwell showed the existence of contraction for both weak and strong currents. This contraction is much greater than in the case of iron. Magnetism, Lamellar Distribution of The distribution of magnetism in magnetic shells. A term sometimes applied to such a dis- tribution of magnetism in a plate, that the magnetized particles are arranged with their greatest length in the direction of the thick- ness of the plate, so that the poles are situ- ated at the faces of the plate, and conse- quently the extent of such polar surfaces is great when compared with the thickness of the plate. The term lamellar distribution of magnetism is used in contradistinction to solenoidal distribution. (See Magnetism, Solenoidal Distribution of.) A thin sheet or disc of magnetized material whose opposed extended faces are of opposite magnetic polarities, and the extent of whose sur- face is very great as compared with its thickness, is sometimes called a magnetic shell. The field produced by a magnetic shell is ex- actly similar to that produced by a closed voltaic circuit, the edges of the space inclosed by which correspond to the edges of the magnetic shell. The magnetic intensity, or the number of lines of force per unit arei of cross-section, is equal over all parts of the surface of a simple magnetic shell. A magnetic shell may be conceived as consist- ing of a very great number of short, straight magnetic needles, placed side by side, with their north poles terminating at one of the faces of the sheet and their south poles at the opposite face, the breadth of the sheet being very great as com- pared with its thickness. Such a distribution of magnetism is known as a lamellar distribution. Magnetism, Residual The magnet- ism remaining in the core of an electro-mag- net on the opening of the magnetizing cir- cuit. The small amount of magnetism retained by soft iron when removed from any mag- netizing field. When hard iron or steel is removed from a mag- netizing field it retains nearly all its magnetism. Such magnetism is also, in reality, residual mag- netism, but the term is generally limited to the case of soft iron. Magnetism, Solenoidal Distribution of A term sometimes applied to such a distribution of magnetism in a bar that the magnetized particles are arranged with their poles in the direction of the length of the bar, the ends of which are of opposite mag- netic polarities, and the extent of whose sur- faces is small as compared with the length of the bar. The term solenoidal distribution is used in con- tradistinction to lamellar distribution. (See Mag. netisrn, Lamellar Distribution of. ) Magnetism, Strength of A term sometimes used in the sense of intensity of magnetization. (See Magnetization, Inten- sity of.} The term, strength of magnetism, is sometimes u;ed for flux or quantity of magnetism. Intensity of magnetization, is the preferable term. Mag.] 350 [Mag, Magnetism, Terrestrial A name applied to the magnetism of the earth. Terrestrial magnetism has been ascribed to a variety of cause-;. (See Magnetism, Earth's, Theories as to Cause of. ) Magnetism, Vertical Component of Earth's (See Component, Vertical^ of Earth's Magnetism?) Magnetite. Magnetic oxide of iron, or Fe 3 O 4 , found in nature, as an ore or mineral. Lode-stone consists of pieces of magnetized magnetite. Magnetizable. Capable of being magnet- ized after the manner of a paramagnetic sub- stance like iron. The most magnetizable metals are iron, nickel, cobalt and manganese. (See Paramagnetism.) Magnetization. The act of calling out or of endowing with magnetic properties. Magnetizable substances are magnetized by being placed in magnetic fields. (Set Field, Mag- netic. Magnetization, Methods of ".) The act of initial magnetization is not exactly the same as the act of subsequent magnetization. A piece of steel, which has once been magnet- ized and subsequently demagnetized, is a thing en- tirely distinct, as regards its magnetization, from a piece of steel which has never before been mag- netized, and such a piece can never be placed ex- actly in the same position as regards a magnet- izing force, unless it is actually melted and recast, or, perhaps, maintained for a comparatively long time at a white heat. Magnetization, Anomalous The magnetization obtained from an oscillatory discharge, such as that of a Leyden jar. In 1842, Henry described the real character of anomalous magnetization, and showed that there was nothing anomalous in such magnetization, but rather in the fact that the magnetizing currents possessed no simple direction. He remarks on this subject as follows: "This anomaly, which has remained so long unexplained, and which, at first sight, appears at variance with all our theoretical ideas of the con- nection of electricity and magnetism, was, after considerable study, satisfactorily referred to an action ot the discharge of a Leyden jar which had never before been recognized. The discharge, whatever may be its nature, is not correctly rep- resented (employing the simplicity of Franklin) by the single transfer of an imponderable fluid from one side of the jar to the other ; the phe^ nomena require us to admit the existence of a principal discharge in one direction and then several reflex actions backward and forward, each more feeble than the preceding, until the equi- librium is obtained. All the tacts are shown to be in accordance with the hypothesis, and a ready explanation is afforded by it of a number of phe- nomena which are to be found in the older works on electricity, but whLh have until this time re- mained unexplained. ' ' Magnetization by Touch. The produc- tion of magnetism in a magnetizable sub- stance by touching it with a magnet. There are three methods of magnetization by- touch, viz.: (i.) Single touch. (2.) Separate touch. (3.) Double touch. In single touch, the magnetization of a bar of iron or other magnetizable material is effected by the touch of a single magnet. In Single Touch, the magnetizing magnet is drawn over the bar to be magnetized from end to end and returned through air, the stroke being repeated a number of times. The end of the bar the magnet leaves is magnetized oppositely to the magnetizing pole. By some writers the method of single touch is described as that effected by placing the magnet- izing magnet N S (Fig. 384) on the middle of the bar to be magnetized, and drawing it to the end and returning through the air as be- |+N S -1 fore, and then reversing the pole, placing it on Fi e- 384. Magnetization the middle of the bar * s ** u Tmtch ' and drawing it towards the other end. The- Fig. 38;. Magnetization 6y Separate Touch. former would, however, appear to be the better use of the term single touch. In Separate Touch, two magnetizing bars are placed with their opposite poles at the middle Mag.] 351 [Mag. of the bar to be magnetized and drawn away from each other towards its ends, as shown in Fig. 385. This motion is repeated a number of times, the poles being each time returned through the air. In the above, as in all cases of magnetization by touch, better effects are produced, if the bar Fig. 386. Magnetization by Double Touch. to be magnetized is rested on the opposite poles of another magnet, or, as shown in Fig. 386, placed near them. In Double Touch the two magnets are placed with their opposite poles together on the middle of the bar to be magnetized, as shown in Fig. 386. They are then moved to one end of the bar, when, instead of removing them and passing them back through the air to the other end, they are moved over the surface of the bar to be magnet- ized to the other end, and these to and-fro mo- tions are repeated a number of times. The mo- tion is stopped at the. middle of the bar, when the magnetizing magnets are moving in the opposite direction to that at which they began to move. This insures an equal number of strokes to the two halves of the bar. The method of double touch produces stronger magnetization than either of the other methods, but does not effect such an even distribution of the magnetism, and therefore is not applicable to the magnetization of needles. A variety of double touch is shown in Fig. 387, where four bars, to be magnetized, are placed in the form of a hollow rectangle, with only their ends touching at their edges, the angular spaces Fig. 387. Magnetization by Double Touch. at the corners being filled with pieces of soft iron. The horseshoe magnet N S, is then moved around the circuit several times in the same direction. This is believed to produce a more uniform mag- k= 1. netization than the ordinary method of double touch. Magnetization, Co-efficient of A number representing the intensity of magnet- ization produced in a magnetizable body, divided by the magnetizing force H. Calling k, the co-efficient of magnetization ; I, the intensity of the resulting magnetization, and H, the magnetizing force producing it, then I H The co-efficient of magnetization is sometimes called the magnetic susceptibility. A paramagnetic body when placed in a mag- netic field concentrates the lines of magnetic force on it, or causes them to pass through it. The intensity of the magnetization so produced de- pends, therefore, (I.) On the intensity of the magnetizing field. (2.) On the ability of the metal to concentrate the lines of force on it; that is," on the nature of the metal, or on its magnetic permeability. (See Permeability, Magnetic. Paramagnetism. Dia- magnelism, ) '\ he intensity of magnetization will, therefore, be equal to the product of the co- efficient of mag- netization and the intensity of the magnetizing field. It will, also, of course, depend on the area of cross-section of the magnetized body. The co-efficient of magnetization ofparamag- netic bodies is said to be positive, and that of dia- magnetic bodies to be negative, because paramag- netic bodies concentrate the lines of magnetic force on them, while diamagnetic bodies appear to repel the lines of force. (See Paramagnetic. Diamagnetic. ) Magnetization, Critical Current of The current at which any certain or definite effect of magnetization is produced. Magnetization, Intensity of A quantity showing the intensity of the magnet- ization produced in a substance. A quantity showing the intensity with which a magnetizable substance is mag- netized. The intensity of magnetization depends: (I.) On the intensity of the magnetizing field. (2.) On the magnetic permeability, or on the conducting power of the substance for lines of magnetic force. Mag.] 352 [Mag. The greater the strength of the magnetizing field, and the greater the magnetic permeability, the greater is the intensity of the magnetization produced. When, therefore, % magnetizable substance is placed in a magnetizing field, the intensity of the magnetization will depend on the magnetic sus- ceptibility of the substance; that is, on the ratio of the induced magnetization to the magnetizing force producing it. Soft iron has a high co-efficient of magnetization, or its magnetic susceptibility is high. (See Sus- ceptibility, Magnetic. Magnetization, Co-efficient of-} The intensity of magnetization through a sub- stance is measured by dividing the magnetic moment by the magnetic volume. If a bar of soft iron is placed with its greatest length extending in the direction of the lines of force in a magnetic field, it will have induced in it a certain intensity of magnetization which may be expressed as follows: Intensity of Magnetization = y i um = k H, where m, equals the strength of the magnet ; 1, its length ; k, the co-efficient of magnetization, and H, the intensity of the magnetizing field. (S. P. Thompson.") " The moment of a magnet, or of any element of a magnet, may be considered numerically to be made up of two factors, one, its volume, and the other its intensity of magnetization, or simply its magnetization, and hence, for a uniformly mag- netized small linear needle, we may define the intensity of its magnetization by saying that it has magnetic moment of unit volume." (Fleming.) Magnetization, Maximum A term sometimes used for magnetic saturation. Urquhart states, as the result of numerous ex- periments, that the number of lines of magnetic force that usually pass through a bar of soft iron I square centimetre in area of cross-section, when magnetized to a maximum, is equal to 32,000. Ewing gives the number in the particular case of a. very extraordinary magnetization as being equal to 45,350 per square centimetre area of cross- section. Magnetization, Methods of Mag- netization effected either by induction from another magnet, or by means of induction by an electric current. The substance to be magnetized is brought into a magnetic field, so that the lines of magnetic force pass through it. All methods of magnet- ization may be divided into methods of magnetiza- tion by touch and magnetization by the electric current. (See Magnetization by Touch.) Magnetization, Permanent, Intensity of A term employed for the intensity of a permanent magnetization produced in hard steel, as distinguished from the magnetization temporarily produced in soft iron. (See Mag- netization, Intensity of.) Magnetization, Temporary, Intensity of The intensity of the magnetization temporarily induced in a bar of soft iron, as distinguished from permanent magnetization induced in hard steel. (See Magnetisation, Intensity of.) Magnetization, Time-Lag of A lag which appears to exist between the time of action of the magnetizing force and the ap- pearance of the magnetism. The time which must elapse in the case of a given paramagnetic substance before a mag- netizing force can produce magnetization. In the opinion of some physicists there is no such thing as a true magnetic time-lag, the ap- parent time-lag being due entirely either to hys- teresis or to eddy currents. According to them, while the magnetizing force is increasing, it pro- duces, in the iron, reversely-directed surface- eddy-currents, which produce a reversed or opposed magnetizing force in the more deeply seated layers of the iron, the time-lag being due to the interval which is required for these eddy currents to die away and thus permit the mag- netizing force to produce its full magnetization. According to others, however, a true time- lag does exist entirely apart from the existence of surface-eddy-currents. Magnetize. To endow with magnetic properties. Magnetized. Endowed or impressed with magnetic properties. Magnetizing. Causing or producing mag- netism. Magneto-Blasting Machine. (See Ma- chine, Magneto-Blasting.) Mag.] 353 [Mag. Magneto-Electric Bell. (See Bell, Mag- neto-Electric^) Magneto-Electric Brake. (See Brake, Magneto-Electric) Magneto-Electric Call-Bell. (See Call- Bell. Magneto-Electric) Magneto-Electric Faradic Apparatus. (See Apparatus, Faradic, Magneto-Elec- tric) Magneto-Electric Induction. (See In- duction, Magneto-Electric.) Magneto-Electric Machine. (See Ma- chine, Magneto- Electric) Magneto-Electric Medical Apparatus. (See Apparatus, Magneto- Electric Medi- cal) Magneto-Electricity. (See Electricity, Magneto) Magnetograph. The permanent record obtained from the action of a self-recording magnetometer. (See. Magnetometer. Self- Recording) Magnetometer. An apparatus for the measurement of magnetic force. The magnetometer shown in Fig. 388, consists of a magnetized bar suspended by two wires pass- i ng over a pulley, as shown. The magnet is held by the frame S S, provided with a graduated scale K. The mirror S, is supported by a vertical post attached to the frame, and serves to reflect a scale placed below a distant reading telescope. This form of magnetometer, is called the bifilar mag- netometer, and was the one used by Gauss in his study of the earth's magnetism. A variety of forms have been given to delicate magnetometers. Some are self-recording. (See Magnetometer, Self -Recording.) Magnetometer, Differential A form of magnetometer in which the principles of the differential galvanometer, as applied to the electric circuit, are applied to the magnetic circuit. The differential magnetometer of Eickemeyer is shown m Figs. 389 and 390. Its principles of operation will be understood from the following considerations. Referring to Fig. 389. Suppose Fj and F 2 are two electromotive forces connected in series, and x and y, two resistances to be compared. Each of the resistances x and y, is shunted respectively by two conductors a and b, whose resistance we wish to compare. Since the action of each of them on the galvanometer G, is opposite, its nee- dle remains at zero, when the current in a, is equal to the current in b. If, instead of electric circuit, we take the idea of magnetic circuit or the number of lines of magnetic force, and instead of potential difference, Fig 388, Magnetometer. In some magnetometers the magnetic force is measured by the torsion of a wire, as in the tor- sion balance. (See Balance, Coulomb's Torsion) . 389. Eickemeyer's Differential Magnetometer. magneto-motive force, and instead of electric re- sistance, magnetic resistance, we have the princi- ples on which the Eickemeyer differential magnet- ometer is founded. The magnetic circuit of the d fferential magnet- ometer consists of two pieces ot soft iron, shaped Mag.] 354 [Mag. as shown at F t and a , Fig. 390. A magnetic coil C, surrounds the middle portion of each cir- cuit as shown. The operation as described by Mr. Chas. Steinmetz, from whom the above de- scription is mainly taken, is as follows, viz. : "The front part Sj of the left iron piece becomes south, and the back part n^ north polarity; the front part of the right iron piece n 2 becomes north, and the back part south; and the lines of magnetic force travel in the front from the right to the left, from n 2 to Sj ; in the back the opposite way, from the left to the right, or from n x to So, either through the air, or, when n 2 and s 1 , or n i and s a , are connected by a piece of magnetizable metal, through this and through the air. In the middle of the coil C, stands a small soft iron needle with an aluminum indicator, which plays over a scale K, and is held in a vertical position by the lines of magnetic force of the coil C, itself, deflected to the left by the lines of mag- netic force traversing the front part of the instru- ment from n a to s 15 deflected to the right by the lines traversing the back from n 1 to s.,. This needle shows by its zero position that the mag- netic flow through the air in front from n 8 to s t has the same strength as the magnetic flow in the back from n t to s 2 through the air. Now we put a piece of soft iron x on the front of the instrument. A large number of lines go through x, less through the air from n a to Sj ; but all these lines go from n! to s 3 through the air at the back part of the magnetometer, the front part and back part of the instrument being con- nected in series in the magnetic circuit. There- fore the needle is deflected to the right by the magnetic flow in the back of the instrument. Now, we put another piece of iron, y, on the back part of the instrument, then equilibrium would be restored as soon as the same number of lines of magnetic force go through x, as through y, because then also the same number of lines go through air in the front as in the back. As will be noted, the air here takes the place of the resist- ances a and b, influencing the galvanometer needle G, as in the diagram Fig. 389. The operation of the instrument is exceedingly simple and is as follows : Into the coil C, an elec- tric current is sent which is measured by the am- meter A, and regulated by the resistance-switch R. Then the needle, which before had no fixed position, points to zero. Now, we lay the piece of iron, the magnetic properties of which we want to determine, on the back part of the instrument. The needle is de- flected to the left. On the front of the instrument we put Norway iron rods of known cross-section and known conductivity, until equilibrium is again restored. Then the iron in the front has the same magnetic resistance as the iron in the back, and the ratio of the cross-sections gives directly the ratio of the conductivities ; so that by a single reading the magnetic conductivity of any piece of iron can be compared with that of the Norway iron standard. For absolute determinations, the iron is turned off into pieces of exactly 4 square centimetres cross-section and 20 centimetres in length, both ends fitting into holes in large blocks of Norway iron, which are laid against the pole pieces of the magnetometer, so that the transient resistance from pole face to iron is eliminated. Fig, 390. Etckemeyer's Differential Magnetometer, Magnetometer, Self-Recording A self-recording apparatus, by means of which the daily and hourly variations of magnetic needles in the earth's field, at any locality, are continuously registered. The self recording magnetometer employed in the observatory at Kew, consists essentially of means of obtaining a photographic record of a spot of light reflected fro:n a mirror, attached to the needle whose variations are to be recorded. The photographic record is received on a strip of sensitized paper, maintained in uniform and con- tinuous motion by means of suitable clock-work. The record so obtained is called a magneto- graph. Magneto-Motive Force. (See Force, Magneto-Motive!) Mag.] 355 [Mak. Magneto-Motive Force, Absolute Unit of (See Force, Magneto-Motive, Abso- lute Unit of.) Magneto-Motive Force, Practical Unit of (See Force, Magneto- Motive, Prac- tical Unit of.) Magneto-Optic Rotation. (See Rotation, Magneto-Optic) Magnetophone. A species of magnetic siren in which sounds are produced in an electro-magnetic telephone by the periodic currents produced in its coils by the rotation of a perforated metallic disc in a magnetic field. As the speed of the disc increases, the pitch of the note increases. The apparatus was invented by Prof. Carhart, in 1883. A similar apparatus is useful in studying the distribution of the mag- netic field of a dynamo-electric machine. In this case, a small, thin coil of insulated wire is held in the different regions around the machine, while the telephone is held to the ear of the observer. Magnetic leakage, or useless dissipation of lines of magnetic force outside the field proper of the machine, is at once rendered manifest by the musical note caused by variations in the intensity of the field. Since the intensity of the note heard will vary according to the intensity of the field, and also according to the position in which the coil is held, such a coil becomes a magnetic explorer, and by its use the distribution and varying intensity of an irregular field can be ascertained. Its use is especially advantageous in proportioning dynamo - electric machines and electric motors. (See Ex- plorer, Magnetic. ) Magneto-Receptive Device. (See Device, Magneto-Receptive?) Magneto-Static Current Meter. (See Meter, Current, Magneto-Static?) Magneto-Static Screening. (See Screen- ing, Magneto-Static?) Magneto-Statics. (See Statics, Magneto.) Magneto-Therapy. (See Therapy, Mag- neto.) Main Battery. (See Battery, Main.) Main-Battery Circuit. (See Circuit, Ma in-Battery.) Main. Electric The principal con- ductor in any system of electric distribution. Main Feeder. (See Feeder, Standard or Main) Main Fuse. (See Fuse, Main) Main, House A term employed in a system of multiple incandescent lamp dis- tribution for the conductor connecting the house service conductors with a centre of distribution, or with a street main. Main-Line Cut-Out (See Cut-Out, Main- Line?) Main, Street In a system of incan- descent lamp distribution the conductors ex- tending in a system of networks through the streets from junction box to junction box, through which the current is distributed from the feeder ends, through cut-outs, to the district to be lighted, and from which service wires are taken. Main, Sub A name sometimes given to the distributing conductor that is connected directly to a main. The branch nearest the main. (See Branch) Main Wire. (See Wire, Main?) Mains of Electric Railroads. The wires or conductors used for carrying the current from the feeders through the tap wires to the trolley wires. Make. A completion of a circuit. Make-and-Break. The periodic alternate completion and opening of a circuit. Make-and-Break, Automatic A term sometimes employed for such a combi- nation of contact points with the armature of any electro-magnet, that the circuit is auto- matically made and broken with great rapidity. An automatic make-and-break is used in most forms of electric alarms in connection with some form of electric bell. (See Alarm, Electric?) It is also used in the Ruhmkorff ind action cofl in order to produce the variations in the primary circuit. (See Coil, Induction.) Make-Induced Current, (See Current, Make-Induced?) Mak.] 356 [Mar. Making the Primary. (See Primary, Making the,) Mallet, Electro-Magnetic Dental (See Dental-Mallet, Electro-Magnetic.) Mangin Projector. (See Projector, Man- gin.) Man-Hole, Compartment, of Conduit A man-hole provided with suitably sup- ported shelves or compartments, guarded by locked doors that protect different cable sec- tions. Man-Hole of Conduit. An opening of sufficient size to admit a man, communi- cating from the surface of the roadbed with an underground conduit. Manipulator, Breguet's The send- ing instrument employed by Breguet in his system of step-by-step or dial telegraphy. (See Telegraphy, Step-by-Step.) Manometei. An apparatus for measuring the tension or pressure of gases. Manometers are either mercurial or metallic. Mercurial manometers are of two classes, viz., manometers with free air and manometers with comprised air. Manometers measure the presture of gases either in atmospheres, i. e., in multiples or deci- mals of 15 pounds to the square inch, or in inches of mercury. Map or Chart, Inclination A chart or map on which lines are drawn, showing the lines of equal dip or inclination, or the isoclinic lines. An inclination chart is shown in Fig. 391. It will be seen that the magnetic equator, or line of no dip, does not correspond with the geo- graphical equator, being generally north of the equator in the Eastern Hemisphere, and south of it in the Western. The figures attached to the lines indicate the value of the angle of dip. Map or Chart, Isodynamic A map of the earth on a mercator's projection, on which isodynamic lines are drawn. An isodynamic chart is shown in Fig. 392. It will be observed that the isodynamic lines do not exactly coincide with the isoclinic lines, since the line of least magnetic intensity does not correspond with the line of the magnetic equator. The point of least magnetic intensity is found at about lat. 20 degrees S., and Ion. 35 degrees W. The point of greatest magnetic intensity is found at about lat. 52 degrees N. and Ion. 92 degrees W. Another, though weaker point of magnetic in- tensity, is found in Siberia. These are distin- guished from the true magnetic poles by the term Poles of Intensity. The Poles of Verticity, as determined by the dipping needle, and the Poles of Intensity, as de- termined by the needle of oscillation, therefore do- not coincide in the Northern Hemisphere. Map or Chart, Isogonal A terra sometimes used for an isogonic map or chart. Map or Chart, Isogonic A chart on which the isogonal lines are marked. An isogonic map or chart is sometimes called a declination map or chart . In the declination or variation chart, shown in Fig. 393, the region of western declination is in- dicated by the shading. There is a remarkable oval patch in the northeastern part of Asia, in which the declination is west. A similar oval of decreased inclination is seen in the Southern Pacific. The entire earth acts like a huge magnet with south magnetic polarity in the Northern Hemi- sphere. It is not known whether the earth possesses but a single pair of magnetic poles or more than a single pair. The variations in the dec- lination, and in the intensity of its magnetism, due to the position of the sun, zs well as the marked magnetic disturbances that accompany the occurrence of sun spots, would appear to con- nect the earth's magnetism in some manner witb, the solar radiation. (See Magnetism, Earth's, Theories as to Cause of.) Marine Galvanometer. (See Galvanom- eter, Marine.) Mariner's Compass. (See Compass, Azi- muth.) Marked Pole of Magnet (See Magnet r Marked Pole of.) Markers. Colored flags, or signal lights, generally green, displayed in systems of block railway signaling at the ends of trains, in order to avoid accidents from trains breaking in two. (See Railroads, Block System for.) Jtfar.] 357 [Mar. Mar.] 358 [Mar. JLar.] [Mar. * 5 3820288 2 S S Mas.] [Mat* I. The quantity of matter contained in a body. Mass must be carefully distinguished from weight. The weight of a given quantity of matter depends on the attraction which the earth possesses for it, and this, on the earth's surface, varies with the latitude, being greatest at the poles and least at the equator. It also varies with different elevations above the level of the sea. The mass, however, is the same under all circum- stances, whether for different latitudes or alti- tudes, on the earth's surface. Mass Attraction. (See Attraction, Mass.) Mass, Magnetic A quantity of mag- netism which at unit distance produces an action equal to unit force. Mass, Unit of The quantity of mat- ter which under certain conditions will balance the weight of a standard gramme or pound. The gramme is equal to the one-thousandth part of a piece of platinum called the kilogramme, depos ted as a standard in the archives of the French Government, and intended to be equal to the mass of I cubic centimetre of water at the tem- perature of its maximum density. Massage. A treatment for the purpose of effecting changes in general nutrition or action of particular parts of the body, by kneading, rubbing, friction, etc. Massage, Electro The application of electricity to the body during its massage. Connections are established between the patient and a battery by connecting one electrode of a source to the kneading instrument, and the other electrode to the body of the patient. Masses, Electric A mathematical conception for such quantities of electricity as at unit distance will produce an attrac- tion or repulsion equal to unit force. Electrical masses are assumed to be equal when they produce on two identical bodies of small dimensions charges of the same electric force. Master Clock. (See Clock, Master.) Materials, Insulating Non-con- ducting substances which are placed around a conductor, in order that it may either retain an electric charge, or permit the passage of an electric current through the conductor without sensible leakage. Various gases, liqui Is or solids may be em- ployed as insulators. A very high vacuum affords the best known insulation. Matter. Anything which occupies space in three directions and prevents other matter from simultaneously occupying the same space. Matter is composed of atoms, which unite to form molecules. (See Atom. Molecule. ) Matter, Elementary Matter which cannot be decomposed into simpler matter. Varieties of elementary matter are called elements. (See Element. ) Matter, Kinetic Theory of A theory which assumes that the molecules of matter are in a constant state of motion or vibration towards or from one another in paths that lie within the spheres of their mutual attractions or repulsions. The molecules of gases have great freedom of motion, and are so far removed from one another as to be but little, if any, influenced by their mutual attractions. They are therefore assumed to move in straight lines with very great velocity until they collide against one another, or against the sides of the containing vessel, when they are reflected and again move in straight lines in a new path. Matter, Radiant, or Ultra-Gaseous A term proposed by Crookes for the peculiar condition of the gaseous matter which constitutes the residual atmospheres of high, vacua. This is now generally recognized as a fourth state of matter, these four states being: (I.) Solid. (2.) Liquid. (3.) Gaseous. (4. ) Ultra-gaseous or radiant. The peculiar properties of radiant matter are seen in the mechanical effects of the localized pressures produced when such residual atmos- pheres are locally heated or electrified. In Crookes' radiometer, vanes of mica, silvered on one face and covered with lampblack on the opposite face, are supported on a vertical axis so as to be capable of rotation and placed in a glass vessel in which a high vacuum is maintained. On Mat] 361 [Milt. exposing the instrument to the radiation from a candle or gas flame, a rapid rotation takes place. { See Radiometer, Crookes ' . ) The explanation is as follows: Thi lampblack covered surfaces absorb the radiant heat, and be- coming heated, the molecules of ga-> in the residual atmosphere are shot violently from them, and by their reaction drive the vanes around in the opposite direction to that from which they are thrown off. The molecules are also shot off from the silvered surfaces, but, as these are cooler, the effect is not as great as at the blackened surfaces. In a gas, at ordinary pressure, the heated sur- faces are also bombarded by oth-r molecules of the gas, but in high vacua the mean free path of the molecules is so great that there is no interfer- ence, a Crookes' layer existing between the vanes and the walls of the glass vessel. (See Layer, Crookes'.) When a Crookes' tube is furnished with suit- able electrodes, and electric discharges are sent through it between these electrodes, a stream of molecules is thrown off in straight lines from the surface of the negative electrode. Some of the effects of this molecular bombard- ment are seen by the use of the apparatus shown in Fig. 394. When the positive and negative Fig. 394. Effects of Molecular Bomiardment. terminals are arranged as shown, the paths of the molecular slreams are seen as luminous streams whose ("irections are those shown in the figures. The fi jure on the left shows the path taken in a low vacuum. Streams pass from the negative electrode to each of the positive electrodes. The figure on the right shows the discharge in a high vacuum. Here the streams pass off at right angles to the lace of the negative electrode, ana proceed therefrom in straight lines, inde- pendently of the position of the positive electrode. Since, therefore, the negative electrode at a, is in the shape of a concave mirror, the luminous particles converge to a focus near the centre of tiie glass vessel, and then diverge to the opposite wall. Refractory substances placed at such a focus of molecular bombardment, as shown in Fig. 395, are rendered incandescent. In a similar manner, phosphorescent substances exposed to such molecular streams emit a beauti- /?V. jcjj. Forces of Molecular Bombardment. ful phosphorescent light. (See Phosphorescence, Electric.) Mattel-, Thomson's Hypothesis of A hypothesis as to the structure of matter suggested by Sir William Thomson, in order to show how the extremely tenuous ether might possess rigidity. The fact that the ether, although a fluid sub- s'ance, possesses the properties of a rigid solid, has given no little trouble to physicists. Thomson explains this rigi.'.ity of the ether as being due to a rapid motion in its fluid particles. A perfectly flexible rubber tube filled with water or other fluid, possesses, when at rest, a very great degree of flexibility. When in mo- tion, however, the tubs becomes more and more rigid, as the flow increases in rapidity. Thorn- Mat.] 302 [MLed. son imagines the ether to be set in motion in minute vortex rings, and shows that a readily movable fluid body, like ether, once set in su h motion should possess the properties of a solid. I.i a perfect fluid, such as ether, these vortex rings once formed, would be practically imperish- able or indestructible. Thomson regards the atoms of matter as con- sisting of such vortex rings. Vortex rings can be formed in the air by cutting a circuhr aperture in the end of a pasteboar 1 box, and tapping sharply against the end of the box. In order to render the rings visible, the box may be previously filled with smoke. Vortex rings formed in smoky air differ from vortex rings iu the ethjr, in th^ face that air is not a perfect fluid, while ether is. Air vortex rings increase in size and decrease in energy. Vortex rings of the ether would not vary in size. According to Thomson's vortex theory of matter, the atoms of matter are the same as the ether which surrounds them. They cannot be produced in ether by any known way; therefore, they cannot be manufactured, or, as it were, created. Nor, on the other hand, can they be destroyed ; in other words, they are indestruct- ible. They are elastic, capable of definite vibra- tions, possess all the properties of matter sav.% in the opinion of some, the very important prop- erty of gravitation. As Prof. Lodge points out, the fact that this property is not present should cause Sir William Thomson's theory of matter to be accepted with considerable hesitation. Matthiessen's Metre-Gramme Standard. (See Metre-Gramme Standard, Matthies- sen's?) Matthiessen's Mile Standard. (See Mile Standard, Matthiessen's?) Matting, Invisible Electric Floor A matting or other floor covering, provided with a series of electric contacts, which are closed by the passage of a person walking over them. This matting is provided as an adjunct to a system of burglar alarms. The electric bell or annunciator, connected with the different con- tacts, is disconnected during the day-time, or while the rooms are occupied. (See Alarm, Burglar. } Maximum Magnetization. (See Mag- netization, Maximum?) Mclntire's Parallel Sleeve Telegraphic Joint. (See Joint, Telegraphic, Mclntire's Parallel Sleeve?) Measurements, Electric Deter- minations of the values of the electromotive force, resistance, current, capacity, energy, etc., in any electric circuit. Electric measurements may be either qualitative or quantitative. la qualita ive electric measurements the rela- tive values only are obtained; in quantitative measurements the actual values are obtained. Mechanical Alarm, Electric (See Alarm, Electro-Mechanical.} Mechanical Electric Bell. (See Bell, Electro-Mechanical!) Mechanical Epivalent of Heat. (See Heat, Mechanical Equivalent of.} Mechanical Mine. (See Mine, Mechani- cal.} Mechanical Throwback Indicator. (See Indicator, Mechanical Throwback?) Medical Induction Coil. (See Coil, In- duction Medical?) Medical Magneto-Electric Apparatus. (See Apparatus, Magneto-Electric Medi- cal} Medium, Anisotropic A medium in which equal stresses do not produce equal strains when applied in different directions. A medium, homogeneous in structure like crystalline bodies, but possessing different powers of specific inductive capacity in differ- ent directions. An eolotropic mediu:n. (See Medium, Eolotropic.} The latter term is used to distinguish it from an isotropic medium. (See M.dium, Iso tropic.} Medium, Eolotropic A medium in which equal stresses do not produce the same strains when applied ia different direc- tions. (See Medium, Isotropic?) Medium, Electro-Magnetic Any medium in which electro-magnetic phenom- ena occur. The medium through which electro-magnetic waves aie propagated is now universally re- Med.J 363 [Met. garded as the luminiferous or universal ether. (See Electricity, Hertz's Theory of Electro-Mag- netic Radiations or Waves.} Medium, Isotropic A medium in which equal stresses applied in any direction produce equal strains. A transparent medium which possesses the same optical or electric properties in all di- rections. An optically homogeneous, transparent medium. Such media are called isotropic to distinguish them from anisotropic or eolotropic, or those in which equal stresses produce unequal strains in different directions. (See Medium, Anisotropic, Medium, Eolotropic. } Meg or Mega (as a prefix). 1,000,000 times ; as, megohm, 1,000,000 ohms ; mega- volt, 1,000,000 volts. Megaloscope, Electric An appara- tus for the medical exploration of the cavities of the body. The light necessary for exploration is obtained from a small incandescent lamp placed at the extremity of a tube, suitably shaped for introduc- tion into the special organ for which it is devised. The organ so illumined throws its light on a prism, by means of which the light is caused to pass through a series of lenses by which it is- viewed. Megavolt. 1,000,000 volts. Megohm. 1,000,000 ohms. Meidinger Yoltaic Cell. (See Cell, Vol- taic, Meidinger?) Memory, Magnetic A term pro- posed by J. A. Fleming for coerciye force. Soft iron has but a feeble memory of its past magnetization. Mercurial Connection. (See Connection, Mercurial?) Mercurial Contact. (See Connection, Mercurial?) Mercurial Temperature Alarm. (See Alarm, Mercurial Temperature?) Mercury Break. (See Break, Mercury?) Mercury Cup. (See Cup, Mercury?) Meridian, Astronomical A great circle passing through any point in the heavens, and the North and South poles of the heavens. The astronomical meridian corresponds to the geographical meridian. The former is considered as passing around the dome of the heavens; the latter, around the surface of the earth. In order to locate any point in the heavens, a great circle of the heavens is caused to pass through that point and through the astronomical North and South poles. Meridian, Geographical The geo- graphical meridian of a place is a great circle passing through that place and the North and South geographical poles of the earth. Meridian, Magnetic The magnetic meridian of any place is the meridian which passes through the poles of a magnetic needle at that place when in a position of rest under the free influence of the earth's magnetism. The//a. A series dynamo will operate as a motor when Mot.] 372 [Mot, a current is sent through it. If the current is sent through it in the opposite direction to that which it produces when in operation as a gener- ator, the polarity of the field is reversed and the dynamo will turn as a motor in the opposite direc- tion to that required to produce the current. If the current is reversed, the polarity of both the field and the armature is again reversed, and the dynamo still rotates as a motor in the opposite direction to that in which it is rotated as a generator. A series dynamo, therefore, always rotates as a motor in a direction opposite to that of its rotation as a generator. When, however, the polarity of the field only is reversed by changing the connection between the armature and the field, the rotation is in the same direction. A shunt dynamo operated as a motor will also turn in but one direction, but this direction is the same as that in which it turns when operating as a generator; for if the direction of the current in the armature is the same as in a generator, that in the shunt is reversed. A compound wound dynamo will move in a direction opposite to that of its motion as a gene- rator if the series part is more powerful than the shunt, and in the same direction if the shunt part is more powerful than the series. To use a com- pound-wound dynamo as a differential motor the connections need not be changed. For a cumu- lative motor it is necessary to reverse the connec- tions of the series coils. Alternating-Current Dynamo. The current from an alternating-current dynamo, if sent through another similar alternating-current dy- namo running at the same speed, will drive it as a motor. Such a machine possesses the disadvan- tage of requiring to be maintained at a speed de- pending on that of the driving dynamo, and also that it requires to be brought to nearly this speed before the driving current is supplied to it. As a result of this last requirement, variations in the load are apt to stop the motor. Considerable improvements, however, are being introduced into alternate -current motors, by which these difficulties are almost entirely removed. An alternating current sent through any self- exciting dynamo electric machine, such as a shunt or series machine, will drive it continu- ously as a motor. The sudden reversals in the magnetization of its cores will, however, unless the cores are thoroughly laminated, set up power- ful eddy currents that will injuriously heat the machine, and there is also excessive sparking at the brushes. The reversibility of any dynamo -electric ma- chine, or its ability to operate as a motor if sup- plied with a current, leads to a fact of great importance in the efficiency of electric motors, viz. : that during rotation there is induced in the armature during its passage through the field of the machine, an electromotive force opposed co that produced in the armature by the driving current, or a counter electromotive force. (See Resistance, Spurious, force, Counter Electro- motive.) This counter electromotive force acts as a spurious resistance, and opposes the passage of the driving current, so that, as the speed of the electric motor increases, the strength of the driv- ing current becomes less, until, when a certain, maximum speed is reached, very little current passes. In actual practice, this maximum speed- is not attained, or is only momentarily attained, and a small, nearly constant, current is expended in overcoming friction at the bearings, air fric- tion, etc. When, however, the load is placed on the motor, that is, when it is caused to do work, the speed is reduced and the counter electromotive force is decreased, thus permitting a greater cur- rent to pass. The fact that the load thus auto- matically regulates the current required to drive the motor, renders electric motors very economi- cal in operation. The relations between the power required to drive the generating dynamo, and that produced by the electric motor, are such that the maximum work per second is done by the motor when it runs at such a rate that the counter electro- motive force it produces is half that of the current supplied to it. The maximum work or activity of an electric motor is therefore done when its theo- retical efficiency is only 50 per cent. This, however, must be carefully distinguished from the maximum efficiency of an electric motor. A maximum efficiency of 100 per cent, can be at- - tained theoretically ; and, in actual practice, con- siderably over 90 per cent, is obtained. In such cases, however, the motor is doing work at less than its maximum power. This is Jacobi's law of maximum effect, but does not apply to actual motors on account of the J imitations of current carrying capacity. For example, a motor of 9 horse power and 90 per cent, efficiency loses I horse-power in heat within. Mot.] 373 [Hot itself. Hence, if run according to Jacobi's law, it would only produce the same amount, i. e., I horse-power in useful work instead of 9. More than this would overheat it. An efficiency of too per cent, is reached when the counter electromotive force of the motor is equal to that of the source supplying the driving current. Supposing now the driving machine to be of the same type as the motor, and the two machines are running at the same speed. If now a load is put on the motor so as to reduce its speed, and thus permit it to produce a counter electromotive force of but 90 per cent., its efficiency will be but 90 per cent. In such a case, therefore, the efficiency is represented by the relative speeds of the generator and the motor. Motor, Electric, Alternating-Current An electric motor driven or operated by means of alternating currents. (See Motor, Electric?) Dr. Louis Duncan divides alternating motors into two classes, viz. : (I.) Those in which there is but one trans- formation in the machine, viz., that of the electric energy of the armature current into the mechani- cal energy of the armature's rotation. (2.) Those in which there are two transforma- tions, viz.: (a.) The transformation of electrical energy from the main current to electrical energy in the armature current. (b.) The transformation of the electric energy of the armature current into mechanical energy. Alternating motors of the first type are found in the ordinary alternating-current dynamo re- versed. Those of the second type in Tesla's or Thomson's motors. Motor, Electric, Direct-Current An electric motor driven or operated by means of direct or continuous electric cur- rents, as distinguished from a motor driven or operated by alternating currents. (See Motor, Electric?) Motor, Electric, High-Speed The ordinary electric motor. The term high-speed electric motor is used in contradistinction to low-speed electric motor. (See Motor, Electric, Low-Speed.) Motor, Electric, Low-Speed A slow-speed motor. (See Motor, Electric, Slow-Speed.) Motor, Electric, Overload of A load greater than that which an electric motor can carry while at its greatest efficiency of operation, or a load which causes injurious heating of a motor. Motor, Electric, Reversing Gear of Apparatus for so reversing the direction of the current through an electric motor as to re- verse the direction of its rotation. (See Rail- road, Electric?) Motor, Electric, Slow-Speed An electric motor so constructed as to run with fair efficiency at slow speed. The electric motor develops a counter electro- motive force when in motion, which, of course, increases with the increase of motion. The elec- tric motor has, as generally constructed, its great- est efficiency at high speed. When used on street railroads, the high speed requires to be decreased by various forms of reduction gear. The loss of power which all such gear involve, together with the noise attending their use, render any decrease in speed that can be obtained on the part of the motor, without serious loss of efficiency, desir- able. Motor-Electromotive Force. (See Force, Motor Electromotive?) Motor, Pyromagnetic A motor driven by the attraction of magnet poles on a movable core of iron or nickel unequally heated. The intensity of magnetization of iron decreases with an increase of temperature, iron losing most of its magnetization at a red heat. A disc of iron placed between the poles of a magnet, so as to be capable of rotation, will rotate, if heated at a part nearer one pole than the other, since it be- comes less powerfully magnetized at the heated part. In the form of pyromagnetic motor devised by Edison, and shown in Fig. 400, in elevation, and in Fig. 401, in vertical section, the disc of iron is replaced by a series of small iron tubes, or di- vided annular spaces, heated by the products of combustion from a fire placed beneath them. In order to render this heating local, a flat screen is placed dissymmetrically across the top to prevent Mot.] 374 [MOT. the passage of air through the portion of the iron tubes so screened. The air is supplied to the furnace by passing down from above through the Fig, 400. Pyromagnetic Motor. tubes so screened. This is shown in the draw- ings, the direction of the heating and the cooling air currents being indicated by the arrows. The Fig. 401. Pyromagnetic Motor. supply of a : r from above thus insures the more rapid cooling of the screened portion of the tubes. Motor, Rotating-Cnrrent An electric motor designed for use with a rotat- ing electric current. Unlike alternating current motors, rotary-cur- rent motors will, like continuous-current motors, readily start with a load. (See Current, Rotating. ) Motor, Series-Wound An electric motor in which the field and armature are connected in series with the external circuit as in a series dynamo. (See Machine, Dynamo- Electric, Series- Wound?) Motor, Shunt-Wound An electric motor in which the field magnet coils are placed in a shunt to the armature circuit. (See Machine, Dynamo-Electric, Shunt- Wound) Motor Standards. (See Standards, Motor) Moulded Mica. (See Mica, Moulded?) Moulding, Electric Wood Mould- ing of dried, non-conducting wood, provided with longitudinal grooves for the reception and support of electric wires or conductors. Wood mouldings are employed for the protec- tion and concealment of electric conductors. Moulding Moulding) Mouse-Mill Mouse-Mill) Mouse-Mill Machine. (See Machine, Mouse-Mill) Month Pieces. (See Pieces, Mouth) Movable Secondary. (See Secondary, Movable) Mover, Prime In a system of dis- tribution of power the motor by which sec- ondary motors or movers are driven. In a steam plant, the steam engine is the prime mover; the shafts or machines driven by the main shaft are sometimes called the secondary movers. The main shaft is called the driving shaft. Its motion is carried by means of belts to other shafts, called driven shafts. The pulleys on the driving or driven shafts are called respectively the driving and driven pulleys. Movers, Secondary The shafts or machines driven by the main shafts in order to distinguish them from the steam engine or other mover which drives it. (See Mover, Prime) Wiring. (See Wiring, Dynamo. (See Dynamo, Mul.] 375 [Mul. Multi-Cellular Electrostatic Yoltmeter. (See Voltmeter, Multi-Cellular Electro- static^ Multiphase Current. (See Current, Mul- tiphase^) Multiphase Dynamo. (See Dynamo, Multiphase) Multiphase System. (See System, Multi- phased) Multiple-Arc Circuit. (See Circuit, Multiple-Arc) Multiple-Arc-Connected Electro-Recep- tive Devices. (See Devices, Electro-Recep- tive, Multiple-Arc-Connected) Multiple-Arc-Connected Sources. (See Sources, Multiple- Arc-Connected) Multiple-Arc-Connected Translating De- vices. (See Devices, Translating, Mul- tiple-Arc-Connected) Multiple-Brush Rocker. (See Rocker, Multiple-Brush) Multiple-Brush Yoke. (See Yoke, Mul- tiple-Pair Brush) Multiple Cable Core. (See Cable, Mul- tiple-Core) Multiple Circuit. (See Circuit, Mul- tiple) Multiple Conduit. (See Conduit, Mul- tiple) Multiple-Connected Battery. (See Bat- tery, Multiple-Connected) Multiple-Connected Electro-Receptive Devices. (See Devices, Electro-Receptive, Multiple- Connected) Multiple-Connected Electro-Receptive Devices, Automatic Cut-Out for (See Cut-Out ', Automatic, for Multiple-Connected Electro-Receptive Devices) Multiple-Connected Translating Devices. (See Devices, Translating, Multiple-Con- nected) Multiple Connection. (See Connection, Mttltiple) Multiple Distribution of Electricity by Constant Potential Circuits. (See Elec- tricity, Multiple Distribution of, by Constant Potential Circuits) Multiple Electric-Gaslighting. (See Gaslighting, Multiple Electric) Multiple-Series. A multiple connection of series groups. (See Connection, Series Multiple) Usage in regard to this term is divided. By some the term multiple-series is applied to a series connection of parallel groups. This is done on account of the order of the words, multiple-series indicating, it is claimed, a series connection of multiple groups. Multiple-Series Circuit (See Circuit, Multiple-Series) Multiple-Series-Connected Electro-Re- ceptive Devices. (See Devices, Electro- Receptive, Multiple-Series-Connected) Multiple - Series Connected Sources. (See Sources, Multiple-Series-Connected) Multiple-Series-Connected Translating Devices. (See Devices, Translating, Mul- tiple-Series-Connected) Multiple-Series Connection. (See Con- nection, Multiple- Series. ) Multiple-Switch Board. (See Board, Multiple-Switch) Multiple Transformer. (See Trans- former, Multiple) Multiple Transmission. (See Trans- mission, Multiple) Multiple Working of Dynamo-Electric Machines. (See Working, Multiple, of Dynamo-Electric Machines) Multiplex Telegraphy. (See Teleg- raphy, Multiplex) Multiplicator. A word sometimes used for multiplier. Multiplier, Galvanic A term for- merly applied to a galvanometer. (See Gal- vanometer) Multiplier, Schweigger's The name first given to a coil consisting of a 1 Jttul.] 376 [Nee. number of turns of insulated wire, provided for the purpose of increasing the strength of the magnetic field produced by an electric current, and consequently the amount of its deflecting power on a magnetic needle. Schweigger's multiplier was in fact an early form of galvanometer. (See Galvanometer.} Multiplying Power of Shunt (See Shunt, Multiplying Power of.) Multipolar Armature. (See Armature, Multipolar) Multipolar Dynamo-Electric Machine. (See Machine, Dynamo-Electric, Multipo- lar) Multipolar-Electric Bath. (See Bath, Multipolar Electric?) Muscle Current (See Current, Muscle) Muscles, Electrical Excitation of (See Excitation, Electro-Muscular) Muscular, Electro Pertaining to the influence of electricity on the muscles. Muscular or Nerve Fibre, Excitability of (See Excitability, Electric, of Nerve or Muscular Fibre) Muscular Pile, Mattencci's (See Pile, Muscular, Matteucci's) Musket, Electric A gun in which the charge is ignited by a platinum wire ren- dered incandescent by the action of a bat- tery placed in the stock of the gun. Mutual Inductance. (See Inductance) Mutual Induction. (See Induction* Mutual) Mutual Induction, Co-efficient of (See Induction, Mutual, Co-efficient of) Myria (as a prefix). A million times. N. A contraction employed in mathe- matical writings for the whole number of lines of magnetic force in any magnetic cir- cuit. N. A contraction for North Pole. This N, may be distinguished from the N, used for expressing the whole number of lines of mag- netic force, by making the former light and the latter heavy. N. H. P. A contraction for Nominal Horse-Power. Nominal horse-power is a somewhat indefi- nite term for a quantity dependent on the length of stroke and the dimensions of the cylin- der. This quantity is a dependent one, be- cause it varies necessarily with the type of en- gine. Nascent State. (See State, Nascent) Natural Currents. (See Currents, Nat- ural) Natural Law. (See Law, Natural) Natural Magnet (See Magnet, Nat- Natural Unit of Electricity. (See Elec- tricity, Natural Unit of) Natural Unit of Quantity of Electricity, (See Electricity, Unit Quantity of, Natu- ral) Nautical Mile. (See Mile, Nautical) Needle Annunciator. (See Annunciator , Needle) Needle, Astatic A compound mag- netic needle of great sensibility, possessing little or no directive power. An astatic needle consisting of two separate magnetic needles, rigidly connected together and placed parallel and directly over each other, with opposite poles opposed. An astatic needle is shown in Fig. 402. The two magnets N S, and S' N', are directly opposed in their polarities, and are rigidly connected to- gether by means of the axis a, a. So disposed, the two magnets act as a very weak single needle when placed in a magnetic field. Were the two magnets N S, and S' N', of ex- actly equal strength, with their poles placed in exactly the same vertical plane, they would com- pletely neutralize each other, and the needle Nee.] 377 [Nee, would have no directive tendency. Such a sys- tem would form an Astatic Pair or Couple. In practice it is impossible to do this, so that the Fig. 402. Astat : c Needle. needle has a directive tendency, which is often east and west. The cause of the east and west directive ten- dency of an unequally bal- anced astatic system will be understood from an in- spection of Fig. 403. Un- less the two needles, N S, and S' N', are exactly op- ',$ posed, they will form a ^.403. Astatic Pair. single short magnet, N N NN, S S S S, the poles of which are on the sides of the needle. The system pointing with its sides due north and south will appear to have an east and west direc- tion. The principal use of the astatic needle is in the astatic galvanometer, in which the needle is de- flected by the passage of an electric current through a conductor placed near the needle. Therefore it is evident that one of the needles must be outside and the other inside the coil. In the most sensitive form of galvanome- ter there is also a coil surrounding the upper needle, the two coils being op- positely connected, so that the deflection on both needles is in the same direction, and the deflecting Fig- 404- Astatic System. power is equal to the sum of the two coils, while the directive power of the needles is the differ- ence of their magnetic intensities. In the astatic system, as shown in Fig. 404, the current, which flows above one needle, flows be- low the other, and therefore deflects both needles in the same direction, since their poles point in opposite directions. In some galvanometers a varying degree of sensitiveness is obtained by means of a magnet, called a compensating magnet, placed on an axis ab >ve the magnetic needle. As the compensat- ing magnet is moved towards or away from the needle the effect of the earth's field is varied, and with it the sensitiveness of the galvanometer. Such a magnet may form with the needle an astatic system. (See Magnet, Compensating. Galvanometer, Astatic. Galvanometer, Mirror. Multiplier, Schweigger's). Needle Electrode. (See Electrode, Nee- dle) Needle, Elongation of A phrase sometimes used for the angular deflection of a needle. Needle, Magnetic A straight bar- shaped needle of magnetized steel, poised near or above its centre of gravity, and free to move either in a horizontal plane only, or in a vertical plane only, or in both. A magnetic needle free to move in a vertical plane only is called a dipping needle. A mag- netic needle free to move in a horizontal plane only, as shown in Fig. 405, is the form employed S Fig. 405 Magnetic KeedU. in the mariner's compass. This form of magnetic needle is the one most commonly employed. For use as a mariner's compass the needle is supported on gimbals and placed in a box pro- vided with a card on which are marked the points of the compass. (See Compass, Azimuth, Compass, Points of.) Needle, Magnetic, Annual Variations of Variations in the value of the mag- Nee.] 378 [Nee. netic declination that take piace at regular periods of the year. The annual variations of the magnetic field were discovered by Cassini in 1786. Needle, Magnetic, Daily Variation of Variations in the value of the magnetic declination that take place at different periods of the day. It was noticed, for example, in London that ihe north pole of the magnetic needle begins to move westward between 7 and 8 A. M. and continues this movement until I P. M., when it begins to move towards the east until near 10 p. M., when it again begins its westward course. Needle, Magnetic, Damped A magnetic needle so placed as to quickly come to rt st after it has been set in motion. (See Damping?) Magnetic damping is readily effected by caus- ing the needle to move near a metallic plate. On the motion of the needle the currents set up in the plate by dynamo electric induction tend, accord- ing to Lenz's law, to oppose the motions pro- ducing them. (See Induction, Electro-Dynamic. Laws, Lenz's.} Needle, Magnetic, Declination of The angular deviation of the magnetic needle from the true geographical north. The variation of the magnetic needle. The declination of the magnetic needle is either E. or W. (See Declination, Angle of.) Declination, or variation, is different at dif- ferent parts of the earth's surface. Lines connecting places which have the same value and direction for the declination are called isogonal lines. A chart on which the isogonal lines are marked is called a variation chart. The value of the declination varies at dif- ferent times. These variations of the declination are: (i.) Secular, or those occurring during great intervals of time. Thus, in London, in 1580 the magnetic needle had a variation of about II degrees east. This eastern declination decreased in 1622 to 6 degrees E., and in 1680 the needle pointed to the true north. In 1692 the declina- tion was 6 degrees W.; in 1730, 13 degrees W. ; in 1765, 20 degrees W. ; and in 1818 the needle reached its greatest western declination and is now moving eastwards. The declination, how- ever, is still west. (2.) Annual, the needle varying slightly in its declination during different seasons of the year. (3.) Diurnal, the needle varying slightly in its declination during different hours of the day. (4.) Irregular, or those which occur during the prevalence of a magnetic storm. It has been discovered that the occurrence of a magnetic storm is simultaneous with the occur- rence of an unusual number of sun spots. (See Spots, Sun.) Needle, Magnetic, Deflection of The movement of a needle out of a position of rest in the earth's magnetic field or in the field of another magnet, by the action oT aa electric current or another magnet. The deflection of the needle is sometimes called its elongation. This latter term is, however, but little used, and is unnecessary. Needle, Magnetic, Dipping A magnetic needle suspended so as to be tree to move in a vertical plane, employed to de- termine the angle of dip or the magnetic in- clination. (See Dip, Magnetic. Inclination, Magnetic. Inclinometer. Chart, Inclina- tion?) A dipping needle is shown in Fig. 406. The Fig. 406. Dipping Needle. angle B O C, which marks the deviation of the needle from the horizontal position, is called the angle of dip. Nee.] 379 [Neg. Needle, Magnetic, Directive Tendency of The tendency of a magnetic needle to move so as to come to rest in the direction of the lines of the earth's magnetic field. The directive power of the magnetic needle is due to the attraction of the earth's magnetic poles for the poles of the needle, or to the action of the earth's magnetic field. Since the force of the earth's magnetism forms a couple, there is no tendency for the needle to move bodily forward towards either of the earth's poles. Its tendency is merely to rotate until it comes to rest within the lines of the earth's magnetic field, entering at its south pole, passing through its mass and coming out at its north pole. Of course this would be true in the case of a directing magnet only when it is at a great dis- tance from the needle. Otherwise, there would be motion towards the poles as well as rotation. Needle, Magnetic, Inclination or Dip of The deviation of a mechanically bal- anced magnetic needle from a horizontal po- sition. The direction of a magnetic needle in all parts of the earth, except at the magnetic equator, differs from a level or horizontal position. One of its ends inclines or dips towards the ground. (See Dip, Magnetic. Needle, Magnetic^ Dipping.'] Needle, Magnetic, Orientation of The coming to rest of a magnetic needle in the earth's magnetic field. Needle, Magnetic, Variation of The angular deviation of a magnetic needle from the true geographic north. The declination of the magnetic needle. (See Declination^) Needle of Oscillation. A small magnetic needle employed for measuring the intensity of a magnetic field by counting the number of oscillations the needle makes in a given time, when disturbed from its position of rest in such field. (See Magnetization, Intensity of. Lines, Isodynamic.) This use of a magnetic needle in determining the magnetic intensity of any place is analogous to the use of the pendulum in determining the in- tensity of gravity at any place. Suppose, tor example, that at a certain place the needle made 245 oscillations m ten minutes, and that at another place it made 211 in the same time. Then the relative intensities at these two- places would be as the square of these two num- bers, or as I : 1.3482. Needle, Telegraphic A needle em- ployed in telegraphy to represent by its move- ments to the left or right respectively the dots and dashes of the Morse alphabet. (See Telegraphy, Needle System of.) Needle, Throw of A phrase some- times used for the angular deflection of a needle, particularly when the needle is swing- ing. The displacement of the magnetic needle is called the deflection, the elongation, or the throw. The first will appear to be the preferable term when the needle comes to rest in a displaced posi- tion. Negative Charge. (See Charge, Nega- tive.} Negative Direction of Electrical Con- vection of Heat. (See Direction, Negative, of Electrical Convection of Heat.) Negative Direction of Simple-Harmonic Motion. (See Motion, Simple- Harmonic, Negative Direction of.) Negative Electricity. (See Electricity, Negative.) Negative Electrode. (See Electrode, Negative?) Negative Element of a Voltaic Cell. (See Element, Negative, of a Voltaic Cell.) Negative Feeders. (See Feeders, Nega- tive.) Negative Omnibus Bars. (See Bars, Negative Omnibus.) Negative Phase of Electrotonus. (See Electrotonus, Negative Phase of.) Negative Plate of Storage Battery. (See Plate, Negative, of Storage Cell.) Negative Plate of Voltaic Cell. (See Plate, Negative, of Voltaic Cell.) Negative Pole. (See Pole, Negative.) Negative Potential. (See Potential, Neg- ative) Negative Side of Circuit. (See Circuit. Negative Side of.) Neg.] 380 [Nig. Negative Wire. (See Wire, Negative.) Negatively. In a negative manner. Negatively Excited. Charged with nega- tive electricity. (See Electricity, Negative?) Nerve or Muscular Fibre, Excitability i'of (See Excitability, Electric, of Nerve or Muscular Fibre?) Nerves, Actiou of Electricity on Stimulating and other actions produced in nerves by the passage of electricity through them, dependent on the direction and char- acter of the current. (See Electrotonus. Galvanization. Faradization. Galvano- Faradization?) Net, Faraday's An insulated net of cotton gauze, or other similar material, capable of being turned inside out without being thereby discharged, employed for de- monstrating that in a charged, insulated con- ductor the entire charge is accumulated on the outer surface of the conductor. Fig. 407. Faraday's Net. Faraday's net, as shown in Fig. 407, consists of a bag N, of cotton gauze, or mosquito netting, supported on an insulating stand I. When tested by a proof plane, no free electric charge is found on the inside, though such a charge is readily detected by the same means on the outside. By the aid of the silk strings S, S, the bag can be turned inside out, when the charge will then all be found on the then inside, or the now outside. Faraday was in the habit of protecting his delicate electroscopes against outside electrifica- tion by covering them with gauze. To properly act as an electric screen, the gauze should be con- nected with the earth. Faraday constructed a small insulated room, twelve feet in height, breadth and depth, covered on the inside with tin-foil, and, on charging this room from the outside, he was unable to detect the presence of any charge on the inside, even by the aid of his most delicate instruments. This room is often referred to as Faraday's Cube. Nets, Torpedo Steel wire netting suspended from or attached to a ship's side for the purpose of ensuring protection against moving torpedoes. Network of Currents. (See Currents, Network of. Laws, Kirchhojf's.) Neutral Armature. (See Armature, Neutral?) Neutral Feeder. The feeder that is connected with the neutral or intermediate terminal of the dynamos in a three-wire sys- tem of distribution. (See Feeders?) Neutral Line of Commutator Cylinder. (See Line, Neutral, of Commutator Cylinder?) Neutral Omnibus Bars. (See Bars, Neutral-Omnibus.) Neutral Point. (See Point, Neutral.) Neutral Points of a Dynamo-Electric Machine. (SeePamts, Neutral, of Dynamo- Electric Machine?) Neutral Points of Magnet. (See Points, Neutral, of Magnet?) Neutral Points of Thermo-Electric Dia- gram. (See Points, Neutral, of Thermo- Electric Diagram?) Neutral-Relay Armature. (See Arma- ture, Neutral-Relay?) Neutral Section of Magnet (See Sec- tion, Neutral, of Magnet?) Neutral Wire. (See Wire, Neutral.) Neutral Wire Ampere-Meter. (See Am- pere-Meter, Balance or Neutral Wire?) New Ohm. (See Ohm, New.) Nickel Bath. -(See Bath, Nickel?) Nickeling, Electro Electroplating with nickel. (See Plating, Electro?) Nickel-Plating.- (See Plating, Nickel?) Night Bell.- (See Bell, tfod.] 381 [Noi. Nodal Point. (See Point, Nodal.) Nodes, Electrical Points in an open circuited conductor, through which electrical oscillations are passing, which possess a con- stant mean value of potential, while the poten- tial at its ends alternates between two fixed limits. Points on a conductor where the strength of the induced oscillatory current is equal to 2ero. The nodal points on a conductor through which electrical oscillations are passing therefore cor- respond closely to the nodes on a vibrating wire or cord. Dr. Hertz employed the following appara- tus in order to show the position of two nodes in a conductor: An induction coil, A, had its sec- ondary terminals connected as shown in Fig. 408, Fig. 408. Nodes in Conductor. to two metallic spheres, C and C ' . The spark mi- crometer circuit, a c d b, was placed near it, as ^hown, and the sparking distance of the secondary circuit of the induction eoil adjusted, so that the spark micrometer circuit was in unison with it. When sparks were passed between the terminals of the induction coil A, sparks passed between the terminals i and 2, at M, under the influence of resonant action. If, now, a second micrometer circuit, e g h f, exactly similar to a c d b, was added, as shown in the figure, and the two joined near the terminals I 2 3 4, by conducting wires, as shown, the entire system of the micrometer circuit formed a closed metallic circuit, the fundamental vibration of which would have two nodes, one at the middle point of c d, and the other at g h. The inter- nodes would be at the junctions I 3, and 2 4, and under these circumstances a true resonant ac- tion existed between the secondary circuit and the micrometer circuit, as was shown by the fact that any alteration in the circuit e g h f , whether by increasing or decreasing its length, diminished the sparking distance. Since the conductor con- necting points 2, and 4, was in the position of the node, where the strength of the excited oscil- latory current was zero, its removal from between these points should have no influence on the intensity of the vibration. This was found on trial to be the case. Electrical vibrations may therefore be excited by electrical resonance in conductors corresponding not only to the simple fundamental note or vibration, but also to the higher electrical overtones. The apparatus shown in Fig. 409, from Tesla, illustrates the phenomena of alternative path, as well as electric nodes. The terminals of an in- duction coil are connected, as shown, to a con- denser and to a thick copper conductor. Though the two incandescent lamps are placed as shown, yet they are raised to luminosity by a species of brush discharge that passes through them, al- though they would be short circuited to any cur- rent but an oscillatory discharge. Fig. 409. Nodes in a Conductor. Nodular Deposit, Electro-Metallurgical (See Deposit, Electro-Metallurgical Nodular.) Noisy Arc. (See Arc. Not'sy.} Nom.J 382 [Num, Nominal Candle-Power. (See Power, Candle, Nominal.} Non-Automatic Variable Resistance. (See Resistance, Variable, Non- Automatic.} Non-Conductors. Substances that offer so great resistance to the passage of an elec- tric current through their mass as to practi- cally exclude a discharge passing through them. Non- conductors aro called insulators, because they electrically insulate substances placed on or surrounded by them. The terms non-conductors or insulators are ordinarily used in a relative sense to mean bodies which allow no practical or appreciable current to pass through them, since there are no sub- stances known, apart, perhaps, from the universal ether, that absolutely prevent the flow of an elec- tric current, the difference of potential of which is sufficiently great The entire absence of ordinary matter, as in the case of a high vacuum, appears to render a high vacuum very nearly, if not entirely, an absolute insulator. Non-Electrics. A term formerly applied to substances like metals or other conductors which appeared not to become electrified by friction. The term non-electric, was used in contradis- tinction to electrics, or f-ubstances readily elec- trified by friction. The distinction no longer holds, since non electrics, if insulated, are readily electrified by friction. Non-Homogeneous Current-Distribu- tion. (See Current, Non-Homogeneous, Distribution of} Non-Illumined Electrode. (See Elec- trode, Non-Illumined) Non-Inductive Resistance. (See Resist- ance, Non-Inductive} Non-Oscillatory Discharge. (See Dis- charge, Non-Oscillatory) Non-Polarized Armature. (See Arma- ture, Non-Polarized} Non-Polarizable Electrodes. (See Elec- trodes, Non-Polar izable) Non-Wastin? Electrode. (See Electrode, Non- Wasting) Normal Day, Magnetic -- (See Day, Normal Magnetic} Northern Light. The Aurora Borealis. (See Aurora Borealis) Notation, Algebraic -- A system of arbitrary symbols employed in algebra. The following brief description of the notatioiv employed in algebra is for the use of the non- mathematical reader. Quantities are represented in algebra by let- ters, such as a, and b, x, and y, etc. Addition is represented thus: a + b. Subtraction is represented thus: a b. Multiplication is represented thus: a X b, or simply by writing the letters next to each other ab, Division is represented thus: a -5- b, or b An Exponent, or figure placed to the right of a letter, above it as a 8 , indicates that the quantity represented by a, is to be multiplied by itself three times, as a X a X a, or a a a. A Co-efficient, or figure placed to the lejt of a^ quantity, indicates the number of times that quan tity is to be taken; thus, 3 a, indicates that a is to- be added three t.mes, thus: a -j- a -j- a, or 3 X a. A Radical Si^n or Root, thus \/a, or *\/a., indicates that the square root of the quantity a r is to be taken. In the same manner ' v/~a, indi- cates that the cube root of a is to be taken. These expressions are sometimes written a*, or .*. Equality is indicated thus: a 8 =aXaXa, or A negative exponent a~* indicates _, or is the* a a exponent of the reciprocal of the quantity indi- cated. Null or Zero Method. (See Method, Null or Zero) Null Point. (See Point, Null) Number, Diacritical -- Such a num- ber of ampere-turns at which a given core; would receive a magnetization equal to half saturation. Obs.J 383 [Ohm. fl. A contraction for megohm. (See Ohm, Meg) oo. A contraction for ohm. (See Ohm) Obscure Heat. (See Heat, Obscure) Observation Mine. (See Mine, Observa- tion.) Observatory, Magnetic An obser- vatory in which observations of the variations in the direction and intensity of the earth's magnetic field are made. Magnetic observatories are generally furnished with self-registering magnetic apparatus, 'such as magnetographs, magnetometers, inclinometers. (See Magnetomett r. Magnetograph. Inclinome- ter) Magnetic observatories are generally con- structed entirely of non-magnetic materials; that is, of such materials as are destitute of paramag- netic properties. Obtuse Angle. (See Angle, Obtuse) Occlusion of Gas. (See Gas, Occlusion of) Odorscope. An apparatus in which the determination of an odor was attempted by the measurement of the effect the odorous vapor, or effluvia, produced on a variable contact resistance. The microtasimetcr was used in connection with the odorscope. (See Diagometer, Rous- seau's. Microtasimeter) Oerstedt, An A proposed term for the unit of electric current, in place of an ampere. The term has not been adopted. Ohm. The unit of electric resistance. Such a resistance as would limit the flow of electricity under an electromotive force of one volt to a current of one ampere, or to one coulomb per second. (See Unit, B. A. Ohm, Legal. Ohm, Standard) A value equal to 10 absolute electro-mag- netic units. A value which is represented by a velocity of i o, or i ,000,000,000 centimetres per second. It may be difficult at first to see how resistance can be correctiy represented by a velocity. The following consideration may render this clear : The formula for calculating the velocity is V = >p or the velocity equals the distance passed through in unit time. Now, by examining the formula for the value of the resistance, expressed in terms of the electro-magnetic units (see Units, Electro-Magnetic, Dimensions of), it may be seen to be that resistance = Electromotive force L Curi ent. T But this value is of the nature of a velocity, being equal to the length, divided by the time. Resistance, therefore, has the dimensions of a velocity. This is clearly expressed by Silvanus P. Thomp- son in his "Elementary Lessons in Electricity and Magnetism," as follows, viz.: " Suppose we have a circuit composed of two horizontal coils, C S, and D T (Fig. 410), I centimetre apart, joined at C D, and completed by means of a sliding piece, A B. Let this variable circuit be placed in a uniform magnetic field of unit inten- sity, the lines of force being directed vertically downwards through the circuit. "If, now, the slider be moved along towards S T, with a velocity of n, centimetres per second, the number of additional lines of force embraced by the circuit will increase at the rate of n, per second ; or, in other words, there will be an in- Fig. 410. "A T Resistance as a I'eloci'y. duced electromotive force i upressed upon the cir- cuit, which will cause a current to flow through the slider from A to B. Let the rails have no resistance, then the strength of the current will depend on the resistance of A B. Now, let A B, move at such a rate that the current shall be of unit strength. If its resistance be one absolute (electro-magnetic) unit, it need only move at the rate of I centimetre per second. If its resistance be greater, it must move with a proportionately Ohm.] 384 [Ohm. greater velocity ; the velocity at which it must move to keep up a current of unit strength being numerically equal to its resistance. The resist- ance known as " i ohm " is intended to be JO 9 ab- solute electro -magnetic units, and, therefore, is represented by a velocity of fo 9 centimetres , or 10, ooo, ooo metres (/ earth-quadrant} per second.''' 1 Ohin, B. A. A contraction for British Association ohm. Ohm, Board of Trade A unit of re- sistance as determined by a committee of the English Board of Trade. A committee consisting of Sir W. Thomson, Lord Rayleigh, Dr. J. Hopkinson and other authorities appointed by the Board of Trade (England) has recently recommended that the ohm be taken as the resistance of a column of mercury 106.3 centimetres in length and one square millimetre area of cross-section at o de grees C. and since this value agrees with the best experimental results, it will probably be generally and finally adopted. Ohm, British Association The British Association unit of resistance, adopted prior to 1884. The value of the unit of electric resistance, or the ohm, was determined by a Committee of the British Association as being equal to the resistance at o degree C. of a column of mercury I square millimetre in area of cross-section and 104.9 centimetres in length. This length was taken as coming nearest the value of the true ohm de- auced experimentally from certain theoretical considerations. Subsequent re-determinations showed the value so obtained to be erroneous. The value of the ohm is now taken internation- ally, as adopted by the International Electric Congress in 1884, as the resistance of a column of mercury 106 centimetres in length, and I square millimetre in area of cross-section. This last value is called the legal ohm, to distinguish it from the B. A. ohm, which, as above stated, is equal to a mercury column 104.9 centimetres in length. Usage now sanctions the use of the word ohm to mean the legal ohm. This value of the legal ohm is provisional until the exact length of the mercury column can be finally determined. (See Ohm, Board of Trade.} The following are the relative values of these units, viz. : I legal ohm = 1.0112 B. A. ohm. " " = 1 .0600 Siemens unit. i B. A. ohm = .9889 legal ohm. I " " = 1.0483 Siemens unit. i Siemens unit = .9540 B. A. ohm. " " = .9434 legal ohm. Ohm, Legal The resistance of a column of mercury i square millimetre in area of cross-section, and 106 centimetres in length, at the temperature of o degree C. or 32 degrees F. (See Unit, B. A.) I ohm = I.COH2 B. A. units. This value of the ohm was adopted by the International Elec- tric Congress, in 1884, as a value that should be accepted internationally as the true value of the ohm. This value, however, was provisional, and was never actually legalized. It will probably be replaced by the new (106.3 cm.) ohm. (See Ohm, Board of Trade.} Ohm, Meg One million ohms. Ohm, New A term sometimes used for .the Board of Trade ohm. (See Ohm, Board of Trade.) Ohm, Standard A length of wire having a resistance of the value of the true or legal ohm, employed in standardizing re- sistance coils. The standard ohm, as issued by the Electric Standards Committee of England, Las the form Sif. 411. Standard Ohm. shown in Fig. 411. The coil of wire is formed of an alloy of platinum and silver, insulated by silk covering and melted paraffine. Its ends are soldered to thick copper rods r, r', for ready connection with mercury cups. The coil is at B. The space above it at A, is filled with paraffine, except at the opening t, which is provided for the insertion of a thermometer. Oiim.J 335 [Ope. Ohm, Trnc An ohm having the true theoretical value of the ohm. (See Ohm.} Ohmage. The value of the resistance of a circuit expressed in ohms. Ohinic Resistance. (See Resistance, Ohmic or True.) Ohmmeter. A commercial galvanometer, devised by Ayrton, for directly measuring by the deflection of a magnetic needle, the re- sistance of any part of a circuit through which a strong current of electricity is flowing. Ayrton's ohmmeter is represente'l diagram- matically in Fig. 412. Two coils C C, and c c, Fig. 412. Ayrton's Ohmmeter. consisting of a short thick wire, and a long thin wire, respectively, are placed at right angles to each other, and act on a soft iron needle situated as shown. The short, thick wire coil C C, is con- nected in series with the resistance O, to be measured. The long, fine wire coil, of known high resistance, is placed as a shunt to the un- known resistance. Under these circumstances, it can be shown that the action on the needle is that due to the ratio of the difference of potential at the terminals of the unknown resistance and the current strength in the thick wire coil, or R = , as may be deduced from Ohm's law. The coils are so proportioned that the current when flowing through the short thick wire moves the needle to the zero of the scale, while the long thin wire produces a deflection directly propor- tional to the resistance. Ohm's Law. (See Law of Ohm) Oil, Colza An oil obtained from the seed of the Brassica oleracea, a species of cabbage. Colza oil is extensively used for purposes of il- lumination and in the carcel standard lamp. (See Lamp, Carcel.) Oil Cup. A cup containing oil for lubri eating machinery. Oil Insulator. (See Insulator, Oil.) Oil Transformer. (See Transformer, Oil.) Oiler, Automatic An oil cup or res- ervoir that automatically spreads oil over the bearings of machinery in motion. Okonite. A variety of insulating material. Omnibus Bars. (See Bars, Omnibus) Omnibus Wires. (See Wires, Omnibus.) Opacity, Selective Opaque in a cer- tain direction or directions only. Certain substances are opaque to polarized light in certain planes only. Thus, a plate of tourma- line permits light polarized in a certain p'ane freely to pass through it, but is entirely opaque in a plane at right angles thereto. S. P. Thompson and Lodge have shown that such crystals of tourmaline possess curious prop- erties in regard to the conduction of heat. While warming, the crystal conducts heat better in a cer- tain direction than in the opposite direction. While cooling, exactly the opposite effects are observed. In the same manner, while the crystal is rising i:i temperature, there is an accumulation of positive electricity at one end, anl negative at the other. While the crystal is cooling, the reverse is true. Open-Box Conduit. (See Conduit, Open- Box) Open Circuit. (See Circuit, Open) Open-Circuit Electric Oscillations. (See Oscillations, Open-Circuit, Electric) Open-Circuit Induction. (See Induction, Open-Circuit) Open-Circuit Oscillation, Period of The time in which the oscillations set up in a circuit by electrical resonance require to make a complete one to-and-fro motion. The period of an open -circuit electric oscillation is determined by the product of the co-efficients of self-induction of the conductor, and does not depend on the composition of the terminals. It is practically independent of their resistances. Open-Circuit Single-Current Signaling. (See Signaling, Single-Current, Open- Circuit) Ope.] 386 [Ore. Open-Circuit Toltaic Cell. (See Cell, Voltaic, Open-Circuit) Open-Circuit Toltmeter. (See Volt- meter, Open-Circuit.) Open-Circuited. Put on an open circuit. Open-Circuited Conductor. (See Con- ductor, Open-Circuited) Open-Circuited Thermostat. (See Ther- mostat, Open-Circuit.") Open-Coil Drum Dynamo-Electric Ma- chine. (See Machine, Dynamo-Electric, Open-Coil Drum) Open-Coil Dynamo-Electric Machine. (See Machine, Dynamo-Electric, Open-Coil.} Open-Coil Ring Dynamo-Electric Ma- chine. (See Machine, Dynamo-Electric, Open-Coil Ring) Open-Iron-Circuit Transformer. (See Transformer, Open-Iron-Circuit) Open-Iron Magnetic Circuit (See Cir- cuit, Open-Iron Magnetic) Open Magnetic Core. (See Core, Open- Magnetic) Opening Shock. (See Shock, Opening) Operation, Magnet The use of a magnet for the purpose of removing particles of iron from the human eye. Optical Strain. (See Strain, Optical) Optical Strain, Electro-Magnetic (See Strain, Optical Electro-Magnetic) Optical Strain, Electrostatic (See Strain, Electrostatic, Optical) Optics, Electro That branch of electricity which treats of the general relations that exist between light and electricity. The phenomena of electro-optics may be ar- ranged under the following heads, viz. : (i.) Electrostatic stress, produced by an electrostatic field causing an optical strain in a transparent medium, whereby such medium acquires the property of either rotating the plane of polarization of a beam of plane polarized light, or of doubly refracting light. (2.) Electro magnetic stress produced by a magnetic field causing an optical strain in a trans- parent medium, whereby such medium acquires the property of either rotating the plane of polar- ization, or of doubly refracting light. (See Re- fraction, Double, Electric) (3.) Changes in the electric resistance of bodies caused by the action of light. (S.e Cell, Sele- nium. ) (4.) The relation existing between the values of the index of refraction of a transparent medium and its specific inductive capacity. (See Refrac- tion. Capacity, Specific Inductive) This relation has been shown to be as follows : Tne specific inductive capacity is approxi- mately equal to the square of the index of re- fraction. (5.) The relation existing between the velocity of light and the value ot the ratio of electrostatic and the electro-magnetic units, thus giving a basis for an electro-magnetic theory of light. (See Light, Maxwell's Electro-Magnetic Theory of) Polarized light reflected from the surface of a magnet, although it penetrates the substance to but a trifling extent, yet has its plane of polariza- tion distinctly rotated by the magnetic whirls in the iron. Oral or Spealdng-Tube Annunciator. (See Annunciator, Oral or Speaking-Tube) Ordinate. A distance taken on a per- pendicular line called the axis of ordinates, in contradistinction to the axis of abscissas. (See Ordinates, Axis of) Thus in Fig. 413, D i, is the ordinate of the point D, in the curve O D R. Ordinates, Axis of One of the axes of co-ordinates used for determining the position of the points in a curved line. Thus in Fig. 413 the line A B, is called the axis of ordinates because it is the line on which the or- dinate 2 D, is measured. Axis of Ordi- ates. A 2 Fig- 413- Ores, Electric Treatment of Processes for the ex- traction of metals from their ores. These processes are referable to three dis- tinct classes, viz. : Org.] 387 [Osin. (I.) Those in which the reduction is effected by means of heat of electric origin. (2.) Those in which the reduction is effected by the combined action of heat and electrolysis. (3.) Those in which the reduction is effected by means of electrolysis only. Organ, Electric ^A wind organ, in which the escape of air into the different pipes is electrically controlled. In an electric organ, the keys, instead of oper- ating levers, as usual, to admit the passage of air into the pipes, merely complete the circuit of a battery through a series of controlling electro-mag- nets. With such an arrangement, the keyboard can be placed at any desired distance. Electric organs have been constructed, in which a chemical or mechanical record is made of the notes struck by the performer, as well as the musical value of such notes. By such a device the musical creations of a composer are perma- nently recorded in characters that are capable of interpretation by a compositor skilled in musical notation. Orientation of Magnetic Needle. (See Needle, Magnetic, Orientation of.) Origin, Point of The point where the axes of co-ordinates start or originate. (See Co-ordinates, Axes of.) Orthogonal. Rectangular, or right-an- gled. Oscillating Discharge. (See Disoharge, Oscillating) Oscillating Needle. (See Needle of Oscil- lation) Oscillation, Centre of A point in a body swinging like a pendulum, which is neither accelerated nor retarded, during its oscillations, by the portions of the pendulum that are situated respectively above or below it. If all the mass were concentrated at the centre of oscillation the time of oscillation would be the same. The centre of oscillation is always below the centre of gravity. The vertical distance between the centre of oscillation and the point of support of a pendulum, determines the virtual length of the pendulum, and hence its number of vibra- tions per second. (See Pendulum, Laws of.) Oscillations, Electric The series of partial, intermittent discharges of which the apparent instantaneous discharge of a Leyden jar through a small resistance actu- ally consists. These partial discharges produce a series of electric oscillations of the current in the circuit of the discharge, which consist of true to and-fro or backward -and-forward motions of the elec- tricity. This phenomenon was discovered by Joseph Henry. Oscillations, Open-Circuit, Electric Electric oscillations produced in open cir- cuits by the presence of electric pulses in neighboring circuits. Oscillatory Discharge. (See Discharge, Oscillatory) Oscillatory Electric Displacement. (See Displacement, Electric, Oscillatory) Oscillatory Electromotive Force. An electromotive force which is rapidly periodic. Oscillatory Inductance. (See Induc- tance, Oscillatory, Electric?) Oscillatory Induction. (See Induction, Oscillatory) Osmose. The unequal mixing of liquids of different densities through the pores of a separating medium. If a solution of sugar and water be placed in a bladder, the neck of which is tied to a straight glass tube, and the bladder is then immersed in a vessel of pure water with the tube in a vertical position, the two liquids will begin to mix, the sugar and the water passing through the bladder into the pure water, and the pure water passing into the sugar and water in the bladder. This latter current is the stronger of the two, as will be shown by the water rising in the vertical glass tube. The stronger of the two currents, that is, the one directed towards the higher level, or the one which produces the higher level, is called the en- dosmotic current, and the weaker current the exosmotic current. Osmose, Electric A difference of liquid level between two liquids placed on opposite sides of a diaphragm produced by the passage of a strong electric current Osm.J 388 [Ozo through the liquids between two electrodes placed therein. The higher level is on the side towards which the current flows through the diaphragm, thus appa- rently indicating an onward motion of the liquid with the current, or, in other words, the liquid is higher around the kathode than around the anode. The difference of level is most marked when poorly conducting liquids are employed. As a converse of this, Quincke has shown that electric currents are set up when a liquid is forced by pressure through a porous diaphragm. The term diaphragm currents has been proposed for these currents. Their electromotive force depends on the nature of the liquid, on the material of the diaphragm, and on the pressure that forces the liquid through the diaphragm. (See Phenomena, Electro- Capillary. Currents ; Diaphragm. ) Osmotic. Of or pertaining to osmose. (See Osmose.) Osteotome, Electric A revolving electrically propelled saw, employed in the surgical cutting of bones. An electric osteotome consists essentially of a form of revolving engine known as a dental en- gine, furnished with a circular saw, or other ro- tary cutter, driven or propelled by electricity. Outgoing Current. (See Current, Out- going^ Outlet. In a system of incandescent lamp distribution the places in a building where the fixtures or lamps are attached. The outlets are left in a building by the wire- man for the electric fixtureman to attach the de- vice intended to be used on the circuits so pro- vided. Output, Magnetic The product of the magnetic flux by the magneto-motive force. Output of Dynamo-Electric Machine. (See Machine, Dynamo-Electric, Output of.) Outrigger for Electric Lamp. -A device for suspending an electric arc lamp so as to cause it to stand out from the wall of a building. An outrigger and hood with lamp attached are shown in Fig. 414. Outrigger Torpedo. -(See Torpedo, Out- rigger.) Over-Compounded. The compounding of a dynamo-electric machine so as to produce Fig 414. Outrigger and Hood. an increase of voltage under increase Over-compounding is generally employed for compensating for drop or loss of potential in the line or conductor, and is adjusted to a definite percentage of increase from light to full load in accordance with the amount of drop, or loss, for which such compensation was designed. Overhead Lines. (See Lines, Overhead.) Overhead System, Continuous, of Motive Power for Electric Railroads (See Railroads, Electric, Continuous Overhead System of Motive Power for) Overload of Electric Motor. (See Motor,. Electric, Overload oj ".) Overtones. Additional, faint tones, ac- companying nearly every distinct musical tone, by the presence of which the peculiarity or quality of such tone is produced. (See Sound, Characteristics of) Overtones, Electric Electric vibra- tions produced in open-circuited conductors by electric resonance, of higher rates than the fundamental vibrations. The existence of electrical overtones necessitates the existence of electric nodes. (See Nodes, Elec- trical.) Overtype Dynamo. (See Dynamo, Over- type) Ozite. An insulating substance. Ozokerite. An insulating substance. Ozo.J Ozone. A peculiar modification of oxygen which possesses more powerful oxidizing properties than ordinary oxygen. Ozone is now generally believed to be tri- atomic oxygen, or oxygen in which the bonds are closed, thus: 389 [Par. The peculiar smell observed when a torrent of electric sparks passes between the terminals of a Holtz machine, or a Ruhmkorff coil, is caused by the ozone thus formed. In a similar manner ozone is formed in the at- mosphere during the passage through the air of a flash of lightning. During the so-called electrolysis of water, a com- pound formed by the union of two volumes of hydrogen with one volume of oxygen, some of the oxygen is given off in the form of ozone. Since ozone has a somewhat smaller volume than that of the oxygen forming it, the volume of the oxygen liberated is somewhat less than half the volume of the hydrogen. There are a number of different forms of ap- paratus designed for the production of ozone. They consist essentially either of means for pass- ing a torrent of electric sparks through air or for producing a species of polarization in the air. P. D. or p. d. A contraction frequently em- ployed for difference of potential. (See Poten- tial, Difference of.) Pacinotti Projections. (See Projections, Pacinotti) Pacinotti Ring. (See Ring , Pacinotti) Pair, Astatic A term sometimes applied to an astatic couple. (See Couple, Astatic?) Palladium. A metal of the platinum group. Metallic palladium has a tin-white color, and, when polished, a high metallic lustre. It is tenacious and ductile, and, like iron, can be welded at a white heat It is very refractory and possesses in a marked degree the power of ab- sorbing or occluding hydrogen and other gases. It is not affected by oxygen at any temperature, nor readily affected by ordinary corrosive agents. Palladium Alloy. (See Alloy, Pal- ladium!) Pane, Magic A condenser formed of a sheet of glass covered on one side with pieces of tin-foil with small spaces between them pasted in some design on the glass. On the discharge of a Leyden jar through these metallic pieces, the design is seen as a series of minute sparks, which bridge the spaces between the adjacent pieces of foil. Pantelegraphy. A system for the tele- graphic transmission of charts, diagrams, sketches or written characters. Pantelegraphy is more frequently called fac- simile telegraphy. (See Telegraphy, Fac-Simile.) Paper Carbons. (See Carbons, Paper.) Paper Cut-Out. (See Cut-Out, Paper) Paper Perforator. (See Perforator, Paper.) Paper Winder, Automatic A de- vice, driven by clockwork, for automatically delivering the paper fillet on which a tele- graphic message is received. Parabolic Reflector. (See Reflector, Parabolic.) Parafflne. A name given to various solid hydrocarbons of the marsh gas series, that are derived from coal oil or petroleum by the action of nitric acid. Paraffine possesses excellent powers of insula- tion, and forms a good dielectric medium. Dried wood, boiled in melted paraffine, forms a fair in- sulating material. Parafflue Wire. (See Wire, Paraffine) Paraffining. Covering or coating with paraffine. The paraffine is applied, while meUe'l by heat, either by means of a brush, or by dipping the article in the fused mass. Par.] 390 [Par. Care must be taken in paraffining wooden or other absorbent articles, to dry them before im- mersing in the melted paraffine, since, if water be pre>ent, steam is formed explosively, and the melted paraffine scattered in all directions. Paragreles. Lightning rods, intended to protect fields against the destructive action of hail. (See Hail, Assumed Electrical Ori- gin of.) It was formerly believed that hail is caused by electricity. It is now generally believed that the electricity in hail storms is caused by the hail. It will, therefore, readily be understood that para- greles can afford no real protection. Parallax. The apparent angular displace- ment of an object when seen irom two dif- ferent points of view. In reading the exact division on a scale to which a needle points, care must be taken to look di- rectly down on the needle, and not sideways, so as to avoid the error of displacement due to parallax, Parallel Circuit. (See Circuit, Parallel.} Parallel Series. (See Series, Parallel^ Parallelogram of Forces. (See Forces, Parallelogram of} Parallels, Magnetic Lines connect- ing places on the earth's surface at right angles to the isogonal lines, or lines of equal declination or variation. The magnetic parallels are at right angles to the magnetic meridians. The magnetic parallels lie in planes parallel to the magnetic equator. (See Needle, Magnetic, Declination of . Meridian, Magnetic} Paramagnetic. Possessing properties or- dinarily recognized as magnetic. Possessing the power of concentrating the lines of magnetic force. Paramagnetic is a term employed in contra- distinction to diamagnetic. (See Diamagnetic.) A paramagnetic substance, cut in the form of a bar whose length is much greater than its breadth and thickness, will, when suspended in a magnetic field in the manner shown in Fig. 415, take up a position of rest with its greatest length in the direc- tion of the lines of force, i. e. t will point axially. In other words, the lines of force will so pass through the paramagnetic substance as to reduce the magnetic resistance of the circuit as much as possible. Paramagnetic substances, therefore, concen- trate the lines of force on them. (See Resistance, Magnetic.) Diamagnetic substances, on the contrary, when placed as shown in Fig. 415, assume a position of rest with their least dimensions in the direction of the lines of force, i. e. they point equal orially. This is the position in which they are placed by the lines of force, in order to insure the least magnetic resistance in the circuit of these lines. The magnetic resistance of diamagnetic sub- stances is great as com- pared with that of par- amagnetic substances. The term ferro -mag. netic has been proposed for paramagnetic. If Polarity another term be required, which is doubtful, sidero -magnetic, proposed by S. P. Thompson, would appear to be preferable. (See Magnetic, Ferro. Magnetic, Sidero.) Tyndall believes that the magnetic polarity possessed by diamagnetic substances is the result of a distinct polar force, different in its nature from ordinary magnetism. His views, in this re- spect, are not generally accepted. (See Polarity, Diamagnetic. ) Paramagnetically. In a paramagnetic manner. (See Paramagnetism.) Paramagnetism. The magnetism of a paramagnetic substance. Parasitical Currents. (See Currents, Parasitical.) Paratonnere. A French term for light- ning rod, sometimes employed in English technical works. Lightning rod would appear to be the prefer- able term. Partial Contact (See Contact, Partial} Partial Disconnection. (See Disconnec- tion, Partial} Par.] Partial Earth. (See Earth, Partial) Partial Reaction of Degeneration. (See Degeneration, Partial Rtaction of.) Passive State. (See State, Passive) Path, Alternative The path or circuit taken by an impulsive discharge, in preference to another path or circuit, open to the discharge, although of enormously smaller ohmic resistance. The alternative path is the path taken by the discharge produced by what was formerly called lateral induction. The explanation of the reason the discharge takes the alternative path is that the counter-elec- tromotive force of self-induction of the circuit, produced by the impulsive discharge, is so great as to make the path of the circuit itself, although formed of conducting materials, practically non- conducting. It a Leyden jar is provided with discharge wires or conductors, as shown is Fig. 416, a discharge 391 [Pen. would pass across an air space in preference to a metallic circuit, was greater for a thick copper Fig. 416. Phenomena of Alternative Path. taking place at A, is accompanied simultaneously by an even longer spark at B, between the ends of two long open-circuit leads. To explain in a general manner the phenomena of the alternative path, we may say that the dis- charge at A, gives rise to electric oscillations in the leads connected with B, and that there are sent out into the surrounding medium radiations of pre- cisely the same nature as those which produce light, only of a wave length so long as to be un- able to produce on the eye the effects ol light. If the space between the balls at B, is too great for the discharge to take place, the wires glow and throw out minute sparks or brushes of light. The action of the ordinary lightning arrester depends on the principle of the alternative path. The resistance of the metallic circuit, composed of the line and the instruments, is so great in the case of the impulsive discharge of a lightning flash, that the discharge takes place between a series of points connected with the line plate and another series of points connected with the ground plate. (See Arrester, Lightning ) Dr. L'idge, who has studied the principle of alternative path in the case of lightning rods, finds that the distance at which the discharge Fig. 417. Edison Electric Pen. rod, 40 feet long, than for an iron rod of No. 27 B. VV. G. of 33.03 ohmic resistance. Patrol Alarm Box. (See Box, Patrol Alarm) Peltier Effect (See Effect, Peltier) Pen Carriage. (See Carriage, Pen) Pen, Electric A device for mani- fold copying, in which a sheet of paper is made into a stencil by minute perforations obtained by a needle driven by a small electric motor and the stencil afterwards em- ployed in connection with an inked roller for the production of any required number of copies. Mechanical pens are constructed on the same principle, the perfora- tions being obtained by mecnamcal instead of by electric power. In the Edison electric pen, Fig. 417, the per- /=" */? Elect, ic Pendant. forations are made by an electric motor driven by a voltaic battery. The manifold press with its inked pad is shown to the left of the figure. Pendant Cord. (See Cord, Pendant) Pendant, Electric A hanging fix- Pen.] 392 [Per. ture provided with a socket for the support of an incandescent lamp. A form of electric pendant is shown in Fig. 418. Pendant, Flexible Electric Light A pendant for an incandescent lamp formed by the flexible conductors which support the lamp. The advantages procured by a flexible pendant are evident in that both the length of the flexible conductor from which the lamp is hanging and position of the lamp can be changed considerably. Pendulum Annunciator. (See Annun- ciator, Pendulum or Swinging?) Pendulum, Electric A pendulum so arranged that its to-and-fro motions send electric impulses over a line, either by making or breaking contacts. An electrical tuning fork whose to-and-fro movements are maintained by electric im- pulses. Electric pendulums are employed in systems for the electrical distribution of time. Sometimes instead of using true pendulums for such purposes, coils, mounted on tuning forks, or on the ends of flexible bars of steel, called reeds, are used for the purpose of establishing cur- rents, or modifying the currents that are already passing in a circuit. The movement of a mag- netic diaphragm, as in the case of a telephone diaphragm, towards and from a coil of wire, is another illustration of an electric pendulum. Electric tuning-fork pendulums are employed in Delany's system of synchronous-multiplex teleg- raphy, and in Gray's harmonic-multiple teleg- raphy. (See Telegraphy, Synchronous-Multi- plex, Delany's System. Telegraphy, Gray' 1 ! Har- monic-Multiple.} Pendulum, Laws of The laws which express the peculiarities of the motion of a simple pendulum. A simple pendulum is one in which the entire weight is considered as concentrated at a single point, suspended at the end of a weightless, in- flexible and inextensible line. The following are the laws of the simple pen- dulum : (I.) Oscillations of small amplitude are approx- imately isochronous; that is, are made in times that are sensibly equal. (See Vibration or Wave, Amplitude of . Isochronism.) (2.) In pendulums of different lengths, the duration of the oscillations is proportional to the square root of the length of the pendulum. (3.) In the same pendulum, the length being preserved invariable, the duration of the oscilla- tion is inversely proportional to the square root of the intensity of gravity. The intensity of gravity, at any latitude, may be determined by the number of oscillations of a pendulum of a given length. In the same man- ner the intensity of a magnetic field, or the in- tensity of magnetization of a magnet, may be de- termined by the needle of oscillation, by observing the number of oscillations a needle makes in a given time when disturbed from its position of re>t. (See Needle of Oscillation.) Since a simple physical pendulum is a physical impossibility, the virtual length, of a pendulum, that is, the vertical distance between its point of support and the centre of oscillation, is taken as the true length of the pendulum. If the irregularly shaped body, shown in Fig. 419, whose centre of gravity is at G, is made to swing like a pendulum, either on S, or O, its oscillations will be performed in equal times, and the body will act as a simple pendulum, whose virtual length is SO. If, while suspended at S, it be struck at O, it will oscillate around S, without producing^. 4ry a tl(re any pressure on the supporting of Oscillation. axis at S, on which it turns. If floating entirely submerged in a liquid, a blow at O, would cause it to move in a straight line in the direction of the blow, without rotation. The point O, is called the centre of percussion,. or the centre of oscillation. The centre of oscil- lation is always below the centre of gravity . Pentane Standard. (See Standard, Pen- tane.} Percussion, Centre of That point in a body suspended so as to move as a pendu- lum at which a blow would produce rotation, but no forward motion, or motion of transla- tion. Perforator, Paper An apparatus employed in systems of automatic telegraphy for punching in a fillet of paper the circular or elongated spaces that produce the dots and Per.] I dashes of the Morse alphabet, when the fillet is drawn between metal terminals that form the electrodes of* a battery. (See Telegraphy, Automatic.) Perforator, Pneumatic A paper perforator operated by means of compressed .air. (See Perforator, Paper) Period of Open-Circuit Oscillation. (See Open-Circuit Oscillation, Period of) Period of Simple-Harmonic Motion. (See Motion, Simple-Harmonic, Period of.) Period of Vibration. (See Vibration, Period of) Period, Yibration The period of a .single or a whole vibration in a conductor, in which an oscillatory vibration is being pro- duced by electrical resonance when respond- ing to its fundamental vibration. Hertz gives the following value for the vibration period: Calling T, the single or half vibration period; L, the co-efficient of self-induction in abso- lute magnetic measure, and therefore expressed in centimetres; C, the capacity of the terminals, in electrostatic measure, and therefore also expressed in centimetres; v, the velocity of light in centi- metre- seconds, then, when the resistance of the con- ductor is small, T = it C - v Periodic and Alternate Discharge. (See Discharge, Periodic. Discharge, Alternat- ing^ Periodic Current, Power of The rate of transformation of the energy of a cir- cuit traversed by a simple periodic current. Fig. 420. Power of Periodic Current. (Fleming) If the thin line in the curve, Fig. 420, repre- sents the impressed electromotive force in an in- ductive circuit, and the thick line the correspond- ing current, then, at any instant, say at the point M, the rate at which energy is being expended on ihe circuit, is equal to the ordinate P M, multi- plied by the ordinate Q M. The mean power is [Per. the mean of all such products taken at points of time very near together. The power of a periodic current, or the work expended per second on such a circuit, is equal to half the product of the maximum values of the current, at any instant, and the maximum value of the impressed electromotive force, multiplied by the cosine of the angle of lag. Periodic Governor. (See Governor, Periodic) Periodically Decreasing Discharge. (See Discharge, Periodically Decreasing) Periodicity. The rate of change in the alternations or pulsations of an electric cur- rent. Periodicity of Auroras and Magnetic Storms. (See Auroras and Magnetic Storms, Periodicity of) Permanency, Electric The prop- erty possessed by most metallic substances, while in the solid state, of retaining a constant electric conducting power at the same tem- perature. The electric permanency of hard drawn wire is small, since such wire becomes gradually an- nealed, and thus changed in its electric resist- ance. Matthiessen showed that some specimens of annealed German silver wire increased in their conducting power at the rate of about .02 per cent, yearly. Permanent Intensity of Magnetization. (See Magnetization, Permanent, Intensity of) Permanent Magnet Voltmeter. (See Voltmeter, Permanent Magnet) Permanent State of Charge on Telegraph Line. (See State, Permanent, of Charge on Telegraph Line) Permeability Curve. (See Curve, Per- meability) Permeability, Magnetic Conducti- bility for lines of magnetic forces. The ratio existing between the magnetiza- tion produced, and the magnetizing force pro- ducing such magnetization. If u equals the permeability, B, the magnetiza- Per.] 394 [Phe. tion produced, or the intensity of magnetic induc- tion, and H, the magnetizing force; then, The permeability of n^n-magnetic materials, such as insulators, or non-magnetic metals, such as copper, etc., is assumed to be practically equal to that of air, or to unity. The magnetic permeability decreases as the magnetization increases. When a piece of iron has been magnetized up to a certain intensity, its permeability becomes less for any further magnet- ization; or, the substance shows a tendency to reach magnetic saturation. In good iron, this limit is reached at about 125,000 lines of force to the square inch of ~ rea of cross section. The magnetic permeability varies greatly, not only with different specimens of iron, but also with the previous history of the iron, as to whether or not it has before been subjected to magnetization or demagnetization, and also as to whether the value of the permeability is taken while the magnetiza- tion is increasing or decreasing. Permeameter. An apparatus devised by S. P. Thompson, for roughly measuring the magnetic permeability. Thompson's permeameter consists essentially of a rectangular piece of soft iron, provided with a slot, for the reception of the magnetizing coil. A hole bored in one end of the block serves to receive the bar or rod of iron whose permeability is to be determine!. On the magnetization of the bar to be tested, the square root of the force required to detach the rod from the lower surface of the iron block, is a measure of the permeation of the lines of magnetic forces through its end faces. Permeance, Magnetic - - Magnetic permeability. (See Permeability, Magnetic?) Permeating, as of Lines of Force. The passing of lines of force through a mag- netic substance. (See Permeability, Mag- netic?) Permeation, Magnetic The pass- age of lines of magnetic force through any permeable substance. Permissive Block System for Railroads. (See Railroads, Permissive Block System for.} Pfluger's Law. (See Law, PJlugers!) Phantom Wires. (See Wires, Phantom), Phase, Angle of Difference of, between Alternating Currents of Same Period The angle which measures the shift- ing of phase of a simple periodic current with, respect to another due to lag or other cause. Phase, Shifting of, of Alternating Cur- rent A change in phase of current due to magnetic lag or other causes. Phase of Tibration. (See Vibration* Phase of,) Phelps' Stock Printer. (See Printer* Stock, Phelps'.} Phenomena, Electro-Capillary Phenomena observed in capillary tubes at the contact surfaces of two liquids. Where acidulated water is in contact with mercury, each liquid possesses a definite sur- face tension, and each a definite shape of sur- face. The two liquids, however, do not actually touch, there being a small interval or space be- tween them. This space acts as a minute accu- mulator. But the liquid and water, being different substances in contact, possess different potentials- Any cause which alters the shape of these con- tact surfaces, and consequently the extent of the spaces between them, necessarily alters the capa- city of the condenser, and consequently the dif- ference of potential. Therefore the mere shaking of the tube, or heating it, will produce electric currents from the resulting differences of po- tential. Conversely, an electric current sent across the contact-surfaces will produce motion as a result of a change in the value of the surface- tension. An electro-capillary telephone has been constructed on the former principle, and an. electrometer on the latter. (See Electrometer, Capillary.) Phenomena, Porret An increase in the diameter of a nerve fibre in the neigh- borhood of the positive pole when traversed by a voltaic current. When a voltaic current passes through fresh living substance the contents of the muscular fibre exhibit a streaming movement in the direction the current is flowing, viz., from the positive to the IlK.J 395 [Pho. negative. This causes the fibre to swell up or increase in diameter at the negative electrode. Pherope. A name sometimes applied to a telephote. (See Telephote) Phial, Leyden A name sometimes applied to a Leyden jar. (See/ar, Leyden) Philosopher's Egg. (See Egg, Philoso- pher's) Phonautograph. An apparatus for the automatic production of a visible tracing of the vibrations produced by any sound. Phonautographic apparatus consists essentially of devices by which the sound waves are caused to impart their to-and fro movements to a dia- phragm, at the centre of which a pencil or tracing point is attached. The record is received on a sheet of paper, or wax, or on a smoked glass or other suitable surface. Leon Scott's Phonautograph, which is among the forms best known, consists of a hollow conical Fig 421. Scott's Phonautograpk. vessel A, Fig. 421, with a diaphragm of parch- ment stretched tightly like a drumhead over its smaller aperture B. A tracing point attached to the centre of the diaphragm, traces a sinuous line on the surface of a soot-covered cylinder C, that is uniformly rotated under the tracing point. As the cylinder is advanced a short distance with every rotation, a sinuous spiral line is traced on the surface. Phone. A term frequently used for tele- phone. Phonic Wheel. (See Wheel, Phonic) Phonogram. A record produced by the phonograph. (See Phonograph) Phonograph. An apparatus for the re- production of articulate speech, or of sounds of any character, at any indefinite time after their occurrence, and for any number of times. In Edison's phonograph the voice of the speaker, received by an elastic diaphragm of thin sheet iron or other similar material, is caused to indent a sheet of tin-foil placed on the surface of a cylinder C, Fig. 422, that is maintained at a uniform rate of rotation by the crank at W. In Fig. 422. the form shown in Fig. 422, the motion is by hand. In a later improved form the cylinder is driven by means of an electric motor or by clockwork. In order to reproduce the speech or other sounds the phonogram record is placed on the surface of a cylinder similar to that on which it was received (or is kept on the same surface), and the tracing point, placed at the beginning of the record and being maintained against it by gentle pressure, is caused, by the rotation of cylinder, to follow the indentations of the phono- gram record. As the point is thus moved up and. down the hills and hollows of the record surface. Fig. 423. Edison's Improved Fkettografk. the diaphragm, to which it is attached, is given to- and- fro motions that exactly correspond to the to-and-fro motions it had when impressed origin- ally by the sounds it recorded on the phono- gram record. A person listening at this dia- Pho.] 396 [Pho. -phragm will therefore hear an exact reproduction of the sounds originally uttered. In this manner the voices of relatives, dis- tinguished singers or statesmen can be preserved for future generations. In Edison's improved phonograph the record surface consists of a cylinder of hardened wax. The rotary motion of the cylinder is obtained by means of an electric motor. Two diaphragms are used, one for recording, and one for reproducing the sound waves. As shown in Fig. 423, the record- ing diaphragm is in position against the cylinder. The recording diaphragm is made of malleable glass. The reproducing diaphragm is formed of bolting silk covered with a thin layer of shellac. In the Craphophone of Bell and Tainter the point attached to the diaphragm is caused to cut Fig. 424. Bell and Tainter's Graphophont. or engrave a cylinder of hardened wax. Two separate diaphragms are employed, one for speak- ing, and the other for hearing. The recording surface is made of a mixture of beeswax and paraffine. A uniformity of rotation of the cylinder is obtained by means of a motor pro- vided with a suitable governor. An ordinary con- versation of some five minutes, it is claimed, can be recorded on the surface of a cylinder 6 inches long and I \ inch in diameter. In the Gramophone of Berliner, a circular plate -of metal, covered with a film of finely divided oil or grease, receives the record in a sinuous, spiral line. This record is subsequently etched into the metal by any suitable means, or is photographic- ally reproduced on another sheet of metal. Glass covered with a deposit of soot is some- times employed for the latter process. The ap- paratus is shown in Fig. 425, as arranged for the reproduction of speech. In Mr. Berliner's apparatus, the record surface is impressed by a point attached to the trans- mitting diaphragm, in a direction parallel to the record surface, and not, as in the instrument of Mr. Edison, in a direction at right angles to the same. This method would appear to be the best calculated for a more exact reproduction of ar- ticulate speech, since it permits comparatively loud speaking or singing, without interfering Fig. 425. Berliner's Gramophone. with the quality of the reproduced sounds. Since the resistance to indentation, or vertical cutting, increases more rapidly than the increase in the amplitude of vibration of the cutting point, it follows that the louder the 'sounds recorded by the phonograph or graphophone, the less complete would be the quality of the reproduced sounds, or the less the probability of the peculiarities of the speaker's voice being recognized. In order to avoid this, the speaker in the phonograph and the graphophone speaks in an ordinary conversa- tional tone only. (See Vibration or IVave, Am- plitude of ) For purposes of dictation, and, indeed, most commercial purposes, this is rather an advantage than otherwise. Phonograph Record. (See Record, Phonograph^ Phonoplex. Literally sound folds. A system of telegraphy. (See Telegraphy, Phonoplex.) Pho.] 397 [Pho. Phonoplex Telegraphy. (See Telegra- phy, Phonoplex?) Phonopore. A modified form of har- monic telegraph. Phonozenograph. An instrument devised by De Feltre to indicate the direction of a distant sound. A Deprez-D' Arson val galvanometer, a Wheat- stone's bridge, and a microphone of peculiar con- struction, are placed in the circuit of a voltaic battery and a receiving telephone. The observer determines the direction of the distant sound by means of the sounds heard under different condi- tions in the telephone. Phosphoresce. To emit phosphorescent light. Phosphorescence. The power of emitting light, or becoming luminous by simple ex- posure to light. Bodies that possess the property of phosphor- escence, when exposed to a bright light acquire the power, when subsequently carried into the dark, of continuing to emit light, for periods varying from a few seconds to several hours. The diamond, barium and calcium sulphides, dry paper, silk, sugar, and compounds of ura- nium, are examples of phosphorescent substances. The effects of phosphorescence appear to be due, in some cases, to sympathetic vibrations set up in the molecules of the phosphorescent body by the exciting light. (See Vibrations, Sympa- thetic.} In other cases, however, that are not exactly understood, the wave length of the emitted light is more rapid than that of the exciting light. The fire-fly, the glow-worm, and decaying animal or vegetable matter, exhibit a species of phosphorescence that appears to be due to the ac- tual oxidation or gradual burning of a peculiar, specific, chemical substance. Phosphorescence may therefore be divided into two classes, viz. : (l.) Physical phosphorescence, or that produced by the actual impact of light, and, (2.) Chemical phosphorescence, or that caused by actual chemical combination or combustion of a specific substance. This is sometimes called spontaneous phosphorescence. Physical phosphorescence may be produced in a variety of ways, viz. : (I.) By an Elevation of Temperature: A variety of fluorspar, called chlorophane, shines with a beautiful greenish blue light when heated to less than a red heat. Here the non- luminous rays are apparently transformed into luminous rays. A phosphorescent substance like fluorspar eventually loses its ability to phosphoresce. It regains it, however, on exposure to the light, i. e., if such an exhausted body be exposed to sunlight it again phosphoresces on exposure to non-luminous heat. The light emitted, during phosphorescence by heat, is, probably, wholly due to potential energy acquired during exposure to the light. (See Luminescence.) The phosphorescence by heat exhibited by fluorspar is sometimes called fluorescence. It is preferable, however, to call the phenomena phosphorescence. (See Fluores- cence.) (2.) By Mechanical Effects: The flashes of light emitted during the attri- tion or friction of some bodies, when not traceable directly to electricity, are, most probably, to be ascribed to phosphorescence. (3.) By Molecular Bombardment. The molecular bombardment due to the mole- cules of residual gas shot off from the negative electrode of an exhausted receiver through which an electric discharge is passing, produces many brilliant effects of phosphorescence. (4.) By Electricity. An electric spark produces phosphorescence in such substances as canary glass, solution of sul- phate of quinine, etc., etc. (5.) Exposure to Sunlight, or, in fact, to any light. The different rays of the sun are not equally able to excite phosphorescence. As a rule the violet or ultra violet rays excite the greatest phos- phorescence. The light excited is often, though not always, of a greater wave length than the exciting light. Phosphorescent paints for rendering the posi- tion of a push button, electric call, match safe, gas pendant or some other similar object visible at night, consist essentially of sulphides of cal- cium or barium, or of mixtures of the same. Phosphorescence, Chemical - - A variety of phosphorescence, in which the errit- ted light is produced by the actual combustion 398 [Pho, of a specific chemical substance by the oxygen of the air. Chemical phosphorescence is seen in the fire- fly and the glow-worm. (See Phosphorescence.) Phosphorescence, Electric Phos- phorescence caused in a substance by the passage of an electric discharge. The phosphorescent material is placed in an exhausted glass tube, as shown in Fig. 426, and submitted to the action of a series of discharges, as from a Ruhmkorff coil, or Holtz machine. The violet-blue light of such discharge is very efficient in producing phosphorescence. Phosphor- escence is thus effected by subjecting the phos- phorescent material to the molecular bombard- ment which is produced by such discharges in a high vacuum. (S^e Bombardment, Molecular.) Fig. 426. Electric Phosphorescence. Phosphorescence, Physical Phos- phorescence produced in matter by the actual impact of light waves resulting in a vibratory motion of the molecules of sufficient rapidity to cause them to emit light. Physical phosphorescence is distinguished from chemical phosphorescence in that in the former the energy required to produce molecular vibra- tions is imparted by the light to which the phos- phorescent body is exposed, while in chemical phosphorescence the energy producing the light is derived from the chemical potential energy of the specific substance burned. (See Phosphor- escence.} Phosphorescent. Possessing the proper- ties or qualities of phosphorescence. Phosphorescing. Emitting phosphores- cent light. (See Phosphorescence?) Phosphorescope. An apparatus for meas- uring the phosphorescent power of any sub- stance. (See Phosphorescence?) Phosphorus, Electric Smelting of An electric process for the direct production of phosphorus. In the electric smelting of phosphorus, the crude material, consisting of a mixture of bones or animal phosphates and carbon, is fed into a space between two electrodes connected to the poles of a source of powerful alternating currents. The apparatus is similar in general to the Cowles fur- nace for the reduction of aluminium. The heat produced by the alternating currents decomposes the phosphates, and the volatilized phosphorus is condensed in suitable chambers. Photochronograph. An electric instru- ment for automatically recording the transit of a star across the meridian. In a small camera connected with the eye-piece of the transit instrument is placed a sensitized plate. A sidereal clock has an electric attachment to its pendulum, so made that a shutter alternately exposes and conceals the photographic plate, and thus permits the image of a star to be formed on the plate at intervals during its passage across the field of the telescope. An image of the spider lines is afterwards fixed on the p'ate by the light of a lamp, held for a few moments before the ob- ject glass of a telescope. A shutter is provided, by means of which this light is prevented from falling on the trail of the star across the field of the glass. In this manner the time of passage of the star across the meridian is automatically re- corded on the photographic plate. The photochronograph is also adapted for similarly automatically recording the transit or passage of any heavenly body across any imagin- ary line in the heavens. Photo-Electric Cell. (See Cell, Photo- Electric?) Phot o-Electricity. ( See Electricity r Photo:) Photo-Electromotive Force. (See Force r Electromotive, Photo?) Photometer. An apparatus for measuring the intensity of the light emitted by any luminous source. There are various methods for measuring the intensity of a beam of light passing through any given space, or emitted from any luminous Pho. 399 [Pho. source; these methods are embraced in the use of the following apparatus: (I.) Calorimetric Photometer, in which the light to be measured is absoibed by the face of a thermo-electric pile, and the electric current thereby produced is carefully measured. Since obscure radiation or heat will also thus produce an electric current, it is necessary first to absorb all the heat by passing the beam of light through an alum cell. (2.) Actinic, or Chemical Photometers, in which the intensity of the light is estimated by a com- parison of the depth of coloration produced on a fillet of photographic paper under similar con- ditions of exposure to a standard light, and the light to be measured. The combination of pure hydrogen and chlorine, or the decomposition of pure mercurous chloride, have been employed for the purpose of determin - ing the intensities of two lights by measuring the amount of chemical action effected. (3.) Shadow Photometers, in which a shadow produced by the light to be measured is compared with a shadow produced by a standard candle. (See Candle, Standard.} Fig. 427. The Shadow Photometer. Rumford's photometer, shown in Fig. 427, is an example of this iorm of instrument. The standard candle, shown at L, casts a shadow C", of an opaque rod C, on the screen at B. The light to be measured L', is moved away from the screen until its shadow C', on the screen at A, is judged by the eye to be of the same depth. The distance between the screen and the lights is then measured in straight lines. The relative intensities of the two lights are then pro- portional to the squares of their distances. If, for example, the candle be at 10 inches from the screen, and the lamp at 40 inches, then the intensities are as io 8 : 40" or as too : 1,600, or the lamp is a 16 candle-power lamp. This photometer is based on the fact that the shadow of each source is illumined by the light of the other source. These results are more accurate if the two shadows are adjoining or nearly adjoining. (4.) Translucent. Disc Photometers. -The light to be measured and a standard c indie are placed on opposite sides of a sheet of paper the centre of which contains a grease spot. The standard candle is kept at a fixed dis-ance from the paper and both it and the paper are moved towards or from the light to be measured until both sides of the paper are adjudged to be equally illumined. In Bunsen's photometer a vertical sheet of paper with a grease spot at its centre, is exposed to the illumination of a standard candle on one side, and the light to be measured on the other. The sheet of paper is placed inside a dark box provided with two plane mirrors placed at such an angle to the paper that an observer can readily see both sides of the paper at the same time. This box can be slid along a graduated, hori- zontal scale towards, or from, the light to be measured, and carries with it the standard candle mounted on it at a constant distance of io inches. If the box is too near the light to be measured, the grease spot appears brighter on the side of the sheet of paper nearest the candle. If too near the candle, it appears brighter on the side of the sheet of paper nearest the light to bj measured. The position in which the spot appears equally bright on both sides, is the position in which both sides of the paper are equally illumined, and the relative intensities of the two lights are then directly as the squares of their distances from the sheet of paper. Shadow, and translucent-disc photometers being dependent on equal illumination, are re- liable only when the color of the lights compared is the same. For the determination of the photo- metric intensity of very bright lights, the standard candle is replaced by a carcel lamp, a standard gas jet, or by the light emitted by a given mass of platinum, heated to incandescence by a given current of electricity. (See Lamp, Carcel. Gas- Jet, Carcel Standard. Light, Platinum Stand- ard.) Preece's photometer belongs to the class of translucent disc photometers. A tiny incandes- cent lamp is placed in a box, the top of which has a white paper screen on which is a grease spot. The box is placed in the street where the intensity of illumination is to be measured, and the inten- riio.] 400 [Pho. sity of the light of the incandescent lamp is varied until the grease spot disappears. The current of electricity then passing through the incandescent lamp acts as the measure of the illumination. In the case of the shadow photometer, or of Bunsen's photometer, if the intensity of illumina- tion is the same, the relative intensities of the two lights may be determined as follows: Calling I, and i, respectively the relative inten- sities of the standard light, and the light to be measured, and D, and d, their respective dis- tances from the screen, then I : i : : D* : d 2 , orlxd2=ix D*; Or, the intensity of the light to be measured is ( J times the intensity of the standard light. If, for example, D and d, represent 10 and 100 inches, respectively, the intensity of i, is 100 times the intensity I, the standard light. (5.) Dispersion Photometers. -A class of pho- tometers in which, in order to more readily com- pare or measure a very bright or intense light, like that of an arc lamp, the intensity of the light is decreased by dispersion a readily measurable amount. Ayrton 6 Perry's Dispersion Photometer. A photometer in which, in order to bring an in- tensely bright light, like an electric arc light, to Fig. 428. Ayrton & Perry's Dispersion Photometer. such an intensity as will permit it to be readily compared with a standard candle, its intensity is weakened by its passage through a diverging (concave) lens. Ayrton & Perry's dispersion photometer is shown in two different positions, Figs. 428 and 429. The apparatus is supported on a tripod stand E, arranged so as to obtain exact leveling. A plane mirror H, movable around a pin placed directly under its centre, can be rotated and thus reflect the light after its passage through the diverging lens, while still maintaining its distance from the electric light ... The horizontal axis of this mirror is inclined 45 degrees to its reflecting surface in order to avoid errors arising from varying absorption at different angles of reflection. The inclination of the beam to the horizontal is indicated by means of an index attached to the mirror and moving over the graduated circle G. A black rod A, casts its shadow on a screen of white blotting paper B. A standard candle, placed in the holder D, casts its shadow alongside the shadow cast by the electric light. The lens is now displaced until the shadow of the electric light is of the same intensity as that of the candle, when viewed successively through sheets of red and green glass. A graduated scale serves to mark the distances of the candle and the lens, respectively, from the screen, from which data the intensity of the electric light may be calculated. Fig. 429. Ayrton and Ferry's Dispersion Photometer. (6.) Selenium Photometers. Instruments in which the relative intensities of two lights are de- termined by the variations produced in a selenium resistance. In Siemens' Selenium photometer a selenium cell is employed in connection with an electric circuit for determining the intensity of light. The tube A B, Fig. 430, is furnished at A, with a diaphragm, and at B, with a selenium plate, connected by wires G G, with the circuit of a battery and a galvanometer. A graduated scale L M, bears the standard candle N. The tube A B, is capable of rotation on the vertical axis F. A reflecting mirror gal- vanometer is used in connection with the selenium photometer. The light to be measured is placed Pho.J 401 [Pho. at right angles to the scale L M, and the tube A B, directed towards it, and the galvanometer de- flection compared with the deflection obtained when turned towards the standard candle. (7.) Gas-jet Photometers. Instruments in which the candle-power of a gas-jet is determined by measuring the height at which the jet burns when under unit conditions of volume and press- ure of gas consumed. Fig. 430. Siemens' Selenium Photometer. In determining the candle-power of an intense light like the electric arc light, a large gaslight is used instead of a standard candle, and the photometric power of this gaslight is carefully determined by comparison with a gas- jet photom- eter. (See Jet, Gas, Carcel Standard.) Photometer, Actinic A photom- eter in which the intensity of any light is meas- ured by the amount of chemical decomposi- tion it effects. (See Photometer.) In some actinic photometers the intensity of the light to be measured is determined by the com- parison of tbe depth of coloration of a sensi- tized film under similar conditions of exposure to a standard light and the light to be measured. Photometer, Calorimetric A pho- tometer in which the light to be measured is absorbed by the face of a thermo-electric pile, and the intensity of the light estimated from the strength of the electric current thereby produced. In order to avoid the error arising from the current produced from the absorption of the ob- scure radiation from the light, all the heat is first absorbed by passing the light through an alum cell. (See Photometer.) Photometer, Chemical A photom- eter in which the intensity of the light to be measured is determined from the amount of chemical action effected in a given time. Photometer, Dispersion A photom- eter in which the light to be measured is de- creased in intensity a known amount so as to more readily permit it to be compared with a standard light of much smaller intensity. (See Photometer) Photometer, Electric An electrical instrument for measuring the intensity of illumination. A form of electric photometer invented by C. R. Richards depends for its indications on the variations that occur in the resistance of a wire on change of temperature. An iron wire, whose change of temperature is utilized for measuring the intensity of any light to whose radiations it is opposed, is covered by a deposit of lampblack. On exposure to the light whose intensity is to be measured, the light is absorbed by the lamp- black and an increase in temperature occurs. In order to get rid of the heat rays that are associated with the light rays, the rays before falling on the soot-covered wire are caused to pass through a solution of alum ; the intensity of the light is then calculated by reference to the change in the resistance of the soot-covered wire, which is made one of the arms of a Wheatstone bridge. Photometer, Gas-Jet A photom- eter in which the candle-power of a gas jet is estimated from a measurement of the height at which the jet burns under unit conditions of volume and pressure. (See Photometer) Photometer, Jet An apparatus for determining the candle power of a luminous source by means of the height of a jet of the gas, whose candle-power is being determined, when burning under constant conditions as to pressure, etc. (See Jet, Gas, Carcel Standard.) Photometer, Selenium A photom- eter in which the intensity of a light is esti- mated by the comparison of the changes in the resistance of a selenium resistance suc- cessively exposed under similar conditions to this light and to a standard light. (See Photometer) Photometer, Shadow A photom- eter in which the intensity of the light to be Pho.] 402 measured is estimated by a comparison of the distances at which it and a standard light produce a shadow of the same intensity. (See Photometer^ Photometer, Translucent Disc A photometer in which the light to be measured is placed on one side of a partly translucent and partly opaque disc, and a standard can- dle is placed on the opposite side, and the in- tensity of the light estimated by the distances of the light from the disc when an equal illu- mination of all parts of the disc is obtained. (See Photometer) When the illumination of the opposite sides of such a disc is equal, the relative positions of the transparent and opaque portions of the disc are indistinguishable. Photometer, Yarley's A form of photometer in which the intensity of the light to be measured is determined from the rel- ative openings of two concentric circular diaphragms placed in two rotating discs, and through which the standard light and the light to be measured respectively pass. The general arrangement of Varley's photo- meter is shown in Fig. 431. The concentric cir- ring is fully open, the <- ther is completely closed ; or, if one ring, say the outer, is opened 1 60 de- grees, the inner is opened 20 degrees. The quantity of light then which passes through the outer ring from the light to be measured is eight times that passed through the inner ring. The circle is divided into 2,000 parts, instead of into 360 degrees, and, t>y means of a vernier, these parts are further divided into 10 parts, permitting a reading of the 20,000 divisions. Two collimeters placed in front of the disc, project a disc with a black centre and a luminous spot respectively. The discs are regulated until the light projected on the screen produces a uni- form disc. This is readily ascertained, since if one or the other predominate, a disc with gray spot, or a gray marginal ring with a bright spot, will appear. The general appearance of the circular dia- phragm, corresponding to different relative posi- tions of the two discs, is shown in Fig. 432. Fig. 43 /. Varley's Photometer. cular apertures extend circumferentially 180 de- grees, and are reversed so that when one half Fig. 432. Circular Diaphragm of Varley's Photometer. Photometric. Of or pertaining to the photometer. (See Photometer) Photometrically. In a photometric man- ner. Photophone. An instrument invented by Bell for the telephonic transmission of artic- ulate speech along a ray of light instead of along a conducting wire. A beam of light, reflected from a diaphragm against which the speaker's voice is directed, is caused to fall on a selenium resistance inserted in the circuit of a voltaic battery, and a telephone. The changes thus effected in the resistance of the circuit by the varying amounts of light reflected on the selenium resistance from the diaphragm, while moving to-and-fro under the influence of the speak- er's v :ce, produce in the receiving telephone a series of to-and fro movements similar to those im- pressed on the transmitting diaphragm. One lis- tening at the telephone can hear whatever has been spoken in the neighborhood of the transmitting diaphragm. Telephonic communication can, therefore, by such means be carried on along a Pho.] 403 [Pie. ray or beam of light, theoretically through any distance. (See Resistance ; Selenium.) A block of vulcanite or of certain other sub- stances may be used as the receiver, since it has been discovered that a rapid succession of flashes of light produces an audible sound in small masses of these substances. The term sonorescence has been proposed for the property possessed by such substances of emitting sounds when subjected to such inter- mittent flashes of light. (See Sonorescence.} Photophore, Trouve's An appa- ratus in which the light of a small incandescent electric lamp is employed for purposes of medical exploration. A small incandescent lamp is placed in a tube containing a concave mirror and a converging lens. Photo-Telegraphy. The electric produc- tion of pictures, writing, charts or diagrams at a distance. Photo-Telegraphy is sometimes called telepho- tography; it is a species of fac-simile telegraphy. (See Telegraphy, Fac- Simile. Telephotography.} Photo- Voltaic Effect. (See Effect, Photo- Voltaic^ Physical Change. (See Change, Phy- sical^) Physical Phosphorescence. (See Phos- phorescence, Physical!) Physiological. Pertaining to physiology. Physiological Rheoscope. (See Rheo- scope, Physiological.} Physiologically. In a physiological man- ner. Physiology, Electro The study of electric phenomena of living animals and plants. Living animals and plants present electric phenomena, due to the electricity naturally pro- duced by them. It is the province of electro- physiology to ascertain the causes and effects of these phenomena. Piano, Electric A piano in which 'he strings are struck by hammers actuated by means of electro-magnets, instead of by the usual mechanical action of levers. An electric piano-action is mainly useful in per- mitting the instrument to be played at any dis- tance from the key-board, it is also of value from the ease it affords in recording the pieces played. It fails, however, to properly preserve the vari- ous modulations of force so requisite for brilliant instrumentation. Pickle. An acid solution in which me- tallic objects are dipped before being gal- vanized, or electroplated, in order to thoroughly cleanse their surfaces. The pickle used for the preparation of iron for galvanization is a weak solution of sulphuric acid in water. Various acids, or acid liquids, are em- ployed for insuring the thorough cleansing of metallic surfaces so necessary in order to ensure an even, uniform, adherent coating of metal by the process of electroplating. (See Plating, Electro ) Piece, Magnetic Proof A para- magnetic rod, ellipsoid or sphere employed for ascertaining the distribution of magnetism over a magnet by the force required to de- tach the same. (See Paramagnetic!) Prof. S. P. Thompson points out the fact that the presence of the proof-piece so alters the distribution of magnetism on the magnet to be measured as to render this method unreliable. He also shows that the force required for detach- ment depends on the magnetic permeability of the proof-piece, as well as on its shape and its position in the magnetic circuit. Pieces, Month Openings into air chambers, generally circular in shape, placed over the diaphragms of telephones, phono- graphs, gramophones or graphophones to permit the ready application of the mouth in speaking, so as to set the diaphragm into vibration. The mouth-piece may be also utilized by the ear of an observer listening so as to be affected by its vibrations. Pieces, Pole, of Dynamo-Electric Ma- chine Masses of iron connected with the poles of the field magnet frames of dynamo-electric machines, and shaped to conform to the outline or contour of the armature. PH.] 404 [PiU The pole pieces are made in a variety of forms, but in all cases are so shaped as to conform to the outline of the space in which the armature rotates. The pole pieces are brought as near as possible to the armature, so as to increase the intensity of the magnetic induction. The intervening air space should be as thin as possible, but of as large an area as convenient. The opposite pole pieces should not have their extensions brought too near together, as this will permit of serious loss through magnetic leakage. The distance between them should be as many times the depth of the armature windings as possible. (See Leakage, Magnetic. ) Rounded edges are preferable to sharp edges for the same reason. Pile, Dry A voltaic pile or battery consisting of numerous cells, the voltaic couple in each of which consists of sheets of paper covered with zinc-foil on one side and black oxide of manganese on the other. Various modifications of the above form have been made. The term dry-pile is a misnomer, since all such piles contain substances moistened by liquid electrolytes. Pile, Muscular, Matteueci's A vol- taic battery or pile, the elements of which are formed of longitudinal and transverse sections of muscle alternately connected. Matteueci's experiments appear to show that the lower the animal is in the scale of creation, the stronger is the current produced, and the longer its duration. Du Bois-Reymond has shown that the muscular current is not due to contact, but to the differences of electric poten- tial naturally possessed by the muscles them- selves. The nerves also possess the power of producing differences of electromotive force, and hence cur- rents. (See Electrotonus. ) Pile, Thermo, Differential A ther- mopile in which the two opposite faces are exposed to the action of two nearly equal sources of heat in order to determine accu- rately the differences in the thermal intensities of such sources of heat. Pile, Thermo-Electric A number of separate thermo-electric couples, united in series, so as to form a single thermo-electric source. (See Couple, Thermo-Electric) A thermo-electric pile is sometimes called a thermo-electric battery. Fig. 433 shows Nobili's thermopile, in which. a number of bismuth- antimony thermo-elec- tric couples connected in a continuous se- ries, as shown parly in Fig. 434, are insu- lated from one another, except at their junc- tions, and packed in a metallic box, supported as shown in Fig. 433. The free terminals of Fig. 433. f her mo- Electric the series are con- file- nected to binding posts. Differences of tem- perature between the two faces of the pile, where the junctions are exposed, result in a difference of potential equal to the sum of the differences of potential of all the thermo-electric couples. A careful inspec- tion will show that the junctions are formed successively at opposite faces of the pile, so that if the junctions be numbered succes- sively, the even junc- (ions will come at one face, and the Fig. 434. Series -Connected Thermo-Electric Couples. odd junctions at the other. This is necessary in order to permit all the thermo-electric couples to add their differences of potential ; for, if, as in Fig. 435, a thermo-electric chain be formed, Fig- 435- Thermo-Electric Circuit. no currents will result from equally heating anjr two consecutive junctions J, J, of the metals A and B, since the electromotive forces so produced oppose each other. Thermopiles have been constructed by Clamond, of couples of iron and an alloy of zinc and antimony, of sufficient power to produce a voltaic arc whose illuminating power equaled 40 Pil.] 405 [Pla. carcel burners. Many practical difficulties exist which will have to be surmounted, however, before such piles can be employed as commercial electric sources. Pile, Voltaic A battery consisting of a number of voltaic couples connected so as to form a single electric source. A form similar to Volta's original pile, consist- ing of alternate discs of copper and zinc, separated from each other by discs of wet cloth, and piled on one another, so as to form a number of separate voltaic couples connected in series, is shown in Fig. 436. The thick plates marked Zn, are of zinc ; the copper plates, marked Cu, are much Fig. 436. Voltaic Pile. thinner. The discs of moistened cloth are shown at d d. One end of such a pile would then be terminated by a plate of copper, and the other by a plate of zinc. The copper end forms the positive electrode, and the zinc end the negative electrode. (See Cell, Voltaic.} Pilot Lamp. (See Lamp, Pilot.) Pilot Transformer. (See Transformer, Pilot.) Pilot Wires. (See Wires, Pilot.) Pin, Insulator A bolt by means of which an insulator is attached to the tele- graphic support or arm. The insulator pins or bolts are generally fixed to the insulator by means of screw threads turned on their ends. They are then cemented to the insulators by any suitable moisture-proof cement. The pin and insulator con- nected to one another by means of a screw thread are shown in Fig. 437. Pin, Switch - -A metallic pin or plug pro- vided for insertion in a telegraphic switch board. A form of switch pin is shown in Fig. 438. The metallic end is conical in form, and is provided with two longitudinal slots at Fig. 437. Insulator right angles to each other in '>' order to insure a light spring connection with the metallic contact plate in which the pin is in- serted. Pith. A light, cellular material, forming the central portions of most exogenous plants. An excellent pith, suitable for electrical purposes, is furnished by the dried interior of the elder- berry stick. Pith Ball. (See Balls, Pith.) Pith - Ball Electroscope. (See Electroscope, Pith-Ball.) Pivot Snspension. (See Sus- pension, Pivot) Plain-Pendant Argand Elec- tric Burner. (See Burner, Plain-Pendant Electric) Plain-Pendant Electric Burner. (See Burner, Plain-Pendant Electric) Plane Angle. (See Angle, Plane) Plane, Proof A small insulated conductor employed to take test charges from the surfaces of insulated, charged conductors. Pla.] 406 [Pla. The proof-plane is used in connection with some form of electrometer. (See Balance, Cou- lomb' 1 s Torsion."] Plane, Proof, Magnetic A small coil of wire placed in the circuit of a delicate galvanometer, and used for the purpose of exploring a magnetic field. When the coil is suddenly inverted in a mag- netic field, if a long-coil galvanometer provided with a heavy needle is used, the number of lines of force which pass through the area of cross-sec- tion of the coil will be proportional to the sine of half the angle of the first swing of the needle. Plant. A word sometimes used for in- stallation, or for the apparatus required to carry on any manufacturing operation. An electric plant includes the steam engines or other prime motors, the generating dynamo or dynamos, the lamps and other electro-receptive devices, and the circuits connected therewith. Plant Electricity. (See Electricity, Plant. Plants, Electricity of.) Plants, Electricity of Electricity produced naturally by plants during their vig- orous growth. DuBois-Reymond and others have shown that plants while in a vigorous vital state are active sources of electricity. If one of the terminals of a galvanometer be inserted into a fruit near its stem, and the other terminal into the opposite part of the fruit, the galvanometer at once shows the presence of an electric current. Buff has shown that the roots and interior por- tions of plants are always negatively charged, while the flowers, fruits and green twigs are posi- tively charged. Plant tissue or fibre, like the muscular fibre of animals, exhibits in many cases a true contraction on the passage through it of an electric current. This is seen in the Mimosa sensitiva, or Sensitive Fern, in the Venus' Fly-Trap, and in several other species of plants. Pouillet concludes from numerous observations that the free positive electricity of the atmosphere is partly due to the vapors disengaged by grow- ing plants. The peculiar geographical distribution of thun- der storms, however, does not favor this assump- tion. (See Storm, Thunder, Geographical Dis- tribution of.) Plastics, Galvano A term some- times employed for electrotyping, that is where the deposits are sufficiently thick to permit of ready separation from the object which forms the mould. Literally, the cold moulding or shaping of metals by electrotyping. (See Plating, Elec- tro. Metallurgy, Electro?) The word galvano-plastics is sometimes used as synonymous with electrotyping, electro -plat- ing, or electro-metallurgy generally. Plastics, Hydro The art of elec- trically shaping or depositing metals in the wet by electrotyping. (See Plastics, Gal- vano.) Plate, Arrester, of Lightning Protector That plate of a lightning protector which is directly connected with the circuit to be protected, as distinguished from the plate that is connected with the ground. (See Arrester, Lightning?) Plate Condenser. (See Condenser, Plated) Plate, Ground, of Lightning Arrester That plate of a comb lightning arrester which is connected to the earth or ground. (See Arrester, Lightning, Comb.) Plate, Negative, of Storage Cell That plate of a storage cell which, by the action of the charging current, is converted into or partly covered with a coating of spongy lead. That plate of a storage battery which is connected with the negative terminal of the charging source, and which is therefore the negative pole of the battery on discharging. The usage is the reverse of that in the case of the primary battery. Plate, Negative, of Yoltaic Cell The electro-negative element of a voltaic couple. (See Couple, Voltaic.) That element of a voltaic couple which is negative in the electrolyte of the cell. (See Electrolyte) The negative plate of a voltaic cell is the plate not acted on by the electrolyte. In a zinc-carbon Pla.] 407 [Pla. couple in dilute sulphuric acid, the carbon plate is the negative plate. (See Cell, Voltaic.) The negative plate is to be carefully distin- guished from the negative pole, which is the ter- minal connected to the positive plate. The terminal connected to the negative plate is the positive pole. (See Cell, Voltaic.) Plate, Positive, of Storage Battery That plate of a storage battery which is converted into, or covered by, a layer of lead peroxide, by the action of the charging current. That plate of a storage battery which is connected with the positive terminal of the charging source and which is, therefore, the positive pole of the battery on discharging. It will be noticed that the usage in this respect is the reverse of that in the case of primary bat- teries, in which the positive plate is positive in the liquid only; the end which projects from the liquid, or the terminal connected with it being negative. In storage batteries, the positive plate is con- nected with the positive pole. (See Battery, Storage. Cell, Voltaic.) Plate, Positive, of Yoltaic Cell The electro-positive element of a voltaic couple. (See Couple, Voltaic.} That element of a voltaic couple which is positive in the electrolyte of the cell. (See Electrolysis.} The positive plate of a voltaic cell is the plate out from which the current flows through the electrolyte. The zinc plate of a zinc-carbon couple is the positive plate. (See Cell, Voltaic.) The current leaves the cell, however, to flow or pass through the external circuit at the wire or terminal connected with the negative plate. (See Cell, Voltaic.) Plate, Primary, of Condenser That plate of a condensing transformer in which the inducing charge is placed in order to induce a charge of different potential in the secondary plate. Plate, Secondary, of Condenser That plate of a condensing transformer in which the induced charge is produced by the induction of a charge on the primary plate. Plat?, Zinc, of Voltaic Cell. Amalgama- tion of Covering the surface of the zinc plate of a voltaic cell with a thin layer of amalgam in order to avoid local action. (See Action, Local, of Voltaic Cell. Zinc, Amal- gamation of.} Plates, Arrester A term sometimes applied to the two plates of an ordinary comb lightning arrester. (See Arrester, Lightning, Comb) The plate that is connected to the line to be protected, is more correctly called the arrester plate, and that connected to the ground the ground plate. Plates of Secondary or Storage Cell, Forming of Obtaining a thick coating of lead peroxide on the lead plates of a storage battery, by repeatedly sending the charging current through the cell alternately in opposite directions. The effect of sending a current between two lead plates immersed in dilute sulphuric acid, is to coat one of the plates with lead peroxide. On the sending of the current in the opposite direction, the other plate is coated with lead peroxide. If now the current is sent in the opposite direction, more peroxide is deposited on one of the plates, and the peroxide at the other plate is converted into spongy lead. At the end of charging, the battery will form an independent source of current. (See Cell, Storage.) Platform, Pole A platform, capable of supporting several men, placed on a termi- nal pole provided with a cable box, for the purpose of affording a ready means of inspect- ing and arranging the conductors in the box. Plating Balance. (See Balance, Plating.} Plating Bath, Electro (See Bath, Electro-Plating) Plating, Copper - Electro-plating with copper. (See Plating, Electro. Bath, Copper.} Plating, Electro The process of covering any electrically conducting surface with a metal by the aid of the electric current. By the aid of electro-plating, the baser metals are covered with silver, gold or platinum, or with any other metal, such as nickel or copper. Pla.] 408 [Pla. The process of electro-plating is carried on as follows: The object to be plated is connected with the negative terminal of a battery and placed in a so- lution of the metal with which it is to be plated, opposite a plate of that metal connected to the positive terminal of the battery. If, for example, the object is to be plated with copper, it is placed in a solution of copper sulphate or blue vitriol, opposite a plate of copper. By this arrangement the object to be plated forms the kathode of the plating bath, and the plate of copper forms the anode. On the passage of the current the copper sul- phate (Cu SO 4 ) is decomposed, metallic copper being deposited in an adherent layer on the arti- cles attached to the kathode, and the acid radical (SO 4 ) appearing at the anode, where it combines with one of the atoms of the copper plate. Since for every molecule of copper sulphate decomposed in the electrolyte, a new molecule of copper su! phate is thus formed, by the gradual solution of the copper anode, the strength of the solution in the bath is maintained as long as any of the copper plate re- mains at the anode, and the ordinary activity of the cell is not otherwise interfered with. When any other metals, such as gold, silver or nickel, for example, are to be deposited, suitable solutions of their salts are placed in the bath, and plates of the same metal hung at the anode. The character and coherence of the metallic coatings thus obtained depend on the nature and strength of the plating bath, and on the density of the current employed. The size and position of the anode, as compared with the size and posi- tion of the objects to be plated, must therefore be carefully attended to, as well as the strength of Fig. 439. Electro- Plating the metallic solution and the current strength passing. (See Current Density.} Fig. 439, shows a bath arranged for silver- plating. The anode consists of a plate of silver. The spoons, forks, etc., to be plated are immersed in a suitable silver solution and connected with the kathode. The electro-plating process when employed for the production of electrotype plates is called electro typing. Here the object is to obtain a re- production in metal of any particular form, such as of type or of some natural object. It was called by Jacobi the galvanoplastic process. The term electrotyping is, however, more generally adopted. (See Electrotyping, or the Electrotype Process.) Plating 1 , Gold Electro-plating with gold. (See Plating, Electro. Bath, Gold.) Plating-, Nickel Electro - plating with nickel. (See Plating, Electro. Bath, Nickel) Plating-, Sectional Plating an article with a greater thickness of metal at certain points than at the rest of the surface. Sectional plating is employed for such objects as spoons, etc., which are, by this method, given a greater thickness of deposit at the under portions of the bowl and handle, where the spoon usually rests, and is, therefore, exposed to the greatest wear. Sectional plating is effected by means of sec- tional plating frames. (See Plating, Electro. Frames, Sectional Plating. ) Plating 1 , Silver Electro-plating with silver. (See Plating, Electro. Bath, Silver^ Platinoid. An alloy consisting of German silver containing i or 2 per cent, of metallic tungsten. Platinoid is suitable for use in resistance coils on account of the comparatively small influence pro- duced on its electric resistance by changes of temperature. Its resistance is 60 per cent, higher than that of German silver. Platinum. A refractory and not readily oxidizable metal, of a tin-white color. The co-efficient of expansion of platinum by heat is very nearly that of ordinary glass. Pla- tinum is, therefore, generally employed for the leading-in conductors of an incandescent lamp. These conductors are fused into the glass of the lamp chamber. On the heating of the wires by Pla.] 409 [Pin. the current, the glass expands equally with the wires, and the vacuum in the lamp chamber is not, therefore, injured. Platinum Alloy. (See Alloy, Platinum- Silver) Platinum Black. Finely divided platinum that possesses, in a marked degree, the power of absorbing or occluding gases. Platinum black is obtained by the action of potassium hydrate on platinum chloride. Unlike metallic platinum it is of a black color. Platinum Fuse. (See Fuse, Platinum) Platinum-Silver Alloy. (See Alloy, Plat- inum-Silver) Platinum Standard Light. (See Light, Platinum Standard) Platymeter. An instrument invented by Sir William Thomson for comparing the capacities of two condensers. Plow. The sliding contacts connected to the motor of an electric street car, and placed within the slotted underground conduit, and provided for the purpose of taking off the current from the electric mains placed therein, as the contacts are pushed forward over them by the motion of the car. Similar contacts, placed in the rear of the motor car and drawn after the train, form what is techni- cally known as the sled, or when rolling on over- head wires as trolleys. (See Railroad, Electric.) Plow, Electric A plow driven by an electric motor placed either on a wagon to which the plow is attached, or by a stationary electro-motor, by the aid of cords or other flexible belts. One of the first practical applications of the elec- tric transmission of energy was for the operation of a plow, driven electrically, by an electric current generated at some distance, and transmitted to the electric motor by suitable conductors. Pliicker Tube. (See Tube, Pliicker) Plug 1 . A piece of metal in the shape of a plug, provided for making or breaking a cir- cuit by placing in, or removing from, a con- ical opening formed in the ends of two closely approached pieces of metal which are connected with the circuits to be made or broken. As the plug is inserted in the opening it bridges over the opening and thus closes the circuit con- nected with the separate pieces of metals. On removing the plug the circuit is opened or broken. Plug. In telegraphy, an inexpert operator. Plug, Double A plug so constructed that when inserted in a spring-jack it makes two connections, one at its point and one at its shank. (See Spring-Jack) Plug, Fusible A term sometimes applied to a safety fuse. (See Plug , Safety) Plug, Infinity A plug hole in a box of resistance coils, in which the two pieces of brass it connects are not connected by any resistance coil, and which, therefore, leaves, when withdrawn, an open circuit of an in- finite resistance. Plug, Safety A wire, bar, plate or strip of readily fusible metal, capable of con- ducting, without fusing, the current ordinarily employed on the circuit, but which fuses, and thus breaks the circuit, on the passage of an abnormal current. (See Fuse, Safety) A safety plug is only used on circuits in which the electro-receptive devices are connected with the leads in multiple. In this case the fusing of the safety plug, and the consequent opening of the circuit with which it is connected, does not affect the rest of the circuit. On series-connected circuits a different form of safety device is used. (See Cut -Out, Automatic, for Series-Connected Elec- tro-Receptive Devices. ) Plug, Short-Circuiting A plug by means of which one part of a circuit is cut out by being short-circuited. Plug Switch. (See Switch, Plug) Plug, Wall A plug provided for the insertion of a lamp or other electro-re- ceptive device in a wall socket, and thus con- necting it with a lead. Plugging. Completing a circuit by means of plugs. Plugs, Grid Plugs of active ma- terial that fill the spaces or apertures in the lead grid or plate of a storage battery. Plu.] 410 [PoL The active material forming the plugs is placed in the spaces in the grid while in the plastic con- dition. On the subsequent hardening of this ma- terial, these grid plugs cannot readily fall out, since the spaces are so shaped that their interior portions are of greater diameter than at the sur- face of the plates. Plumbago. An allotropic modification of carbon. Plumbago, the material commonly known as black lead, is the same as graphite. Powdered plumbago is employed in electrotyping processes for rendering non-conducting surfaces electrically conducting. For this purpose powdered plum- bago is dusted on the surfaces, which thus acquire the power of receiving a metallic lustre by fric- tion. Stove polishes are formed of mixtures of plumbago and other cheap materials. (See Graphite.') Strictly speaking, the term graphite is properly applied to such varieties of plumbago as are suit- able for direct use for writing purposes, as in lead pencils. Plumbago, Coppered Powdered plumbago coated with copper, for use in the metallization of objects to be electro-plated. (See Metallization^ Plumbago, Gilt Powdered plum- bago whose conducting power for electricity has been increased by coating it with metallic gold. Gilt plumbago is used for rendering non-con- ducting surfaces electrically conducting and thus preparing them for electro-plating. To prepare gilt plumbago, dissolve in 100 parts of sulphuric ether I part of chloride of gold, mix in this 60 parts of powdered plumbago, and ex- pose to air and light until all ether has volatilized. Then dry in an oven. Plumbago, Silvered Powdered plumbago coated with metallic silver for use in the metallization of objects to be electro- plated. Plunge Battery. (See Battery, Plunge^ Pneumatic Perforator. (See Perforator, Pneumatic?) Pneumatic Signals, Electro (See Signals, Electro-Pneumatic^) Pockets, Armature Spaces pro- vided in an armature for the reception of the armature coils. (See Coils, Armature, of Dynamo-Electric Machine?) Poggendorff's Voltaic Cell. (See Cell* Voltaic, Poggendorff's.) Point, Carbon A term formerly applied to the carbon electrodes used in the production of the voltaic arc. Point, Indifferent A point in the intra-polar regions of a nerve where the ane- lectrotonic and kathelectrotonic regions meet, and where the excitability is therefore un- changed. This is sometimes called the neutral point. Point of Lightning Rod. (See Rod,, Lightning, Points on.) Point of Origin. (See Origin, Point of.) Point, Neutral In electro-thera- peutics, a term sometimes used instead of in- different point. (See Point, Indifferent.) Point, Nodal The null point in a circuit traversed by electric oscillations. (See Point, Null.) Point, Null Such a point on a micrometer circuit, that when joined or con- nected with the second- ary circuit of an in- duction coil, the sparks in the micrometer cir- cuit are either very greatly decreased or are entirely absent. The null point on the micrometer circuit is situ- ated symmetrically with respect to the micrometer knobs. If the induction coil A, Fig. 440, has its second- ary circuit connected as shown with the microm- Fig. 440. Null Point. eter circuit at the point e, situated at the centre of the micrometer circuit, the point will be a null point, and the effects of sparks at the micrometer knobs, at M, will be greatly decreased. Under the conditions shown in the figure, the electrical oscillations in the micrometer circuit must be re- garded as in the condition of stationary waves or vibrations. It would seem, therefore, that defi- nite waves or vibrations are set up in the microm- Poi.] 411 [Pol. eter circuit, in the same way as are the vibra- tions produced in an elastic bar set in vibration by a violin bow, or by a blow from a hammer. Points, Consequent The points or places in an anomalous magnet where the consequent poles are situated. (See Magnet, Anomalous. Pole, Anomalous!) Points, Corresponding- Points where the lines of electrostatic force sur- rounding an insulated charged conductor enter the surfaces of neighboring conductors. Points on the surface of a body placed in an electrostatic field where the lines of elec- trostatic force enter its surface, and thus pro- duce a charge equal and opposite to that of the surface of the body at the points from which they came. Corresponding points receive, in accordance with the laws of electrostatic induction, charges equal and opposite to those of the surfaces from which the lines of electrostatic force originate. Points, Electric Action of The effect of points placed on an insulated, charged conductor, in slowly discharging the conductor by electric convection. (See Con- vection, Electric) The cause of this action of points is to be at- tributed to the increased density of a charge on the surface of a conductor at the points and the consequent production of convection streams of air, which thus gradually carry off the charge. (See Charge, Distribution of.) Points, Iso-Electric A term some- times used in electro-therapeutics for points of equal potential. Points, Neutral, of Dynamo-Electric Ma- chine Two points of greatest differ- ence of potential, situated on the commutator cylinder, at the opposite ends of a diameter thereof, at which the collecting brushes must rest in order to carry off the current quietly. These are called the neutral points because the coils that are short-circuited by the brushes lie in the magnetically neutral points of the armature. (See Line, Neutral, of Commutator Cylinder.) Points, Neutral, of Magnet Points approximately midway between the poles of a magnet. (See Line, Neutral, of a Magnet. Magnet, Equator of.) Points, Neutral, of Thermo-Electric Dia- gram The points on a thermo-electric diagram where the lines representing the thermo-electric powers of any two metals cross one another. A mean temperature for any two metals in a thermo-electric series, at which, if their two junctions are slightly over and slightly under the mean temperature (the one as much above as the other is below), no effective electromotive force is developed. (See Dia- gram, Thermo-Electric. Couple, Thermo- Electric) Points or Rhumbs of Compass. (See Compass, Points of) Polar Region. (See Region, Polar) Polar Tips. (See Tips, Polar) Polarity, Diamagnetic A polar- ity the reverse of ordinary magnetic polarity, the existence of which was assumed by Fara- day to explain the phenomena of diamag- netism. (See Diamagnetism) Faraday assumed that diamagnetic substances, when brought into a magnetic field, acquired north magnetism in those parts that were nearest the north pole, instead of south magnetism, as with ordinary magnetic substances. The north pole thus obtained would, he thought, explain the apparent repulsion of a slender rod of any di- amagnetic material delicately suspended in a strong magnetic field, and cause it to point equa- torially, or with the lines of force passing through its least dimensions. This supposition was subse- quently abandoned by Faraday. It has recently been revived by Tyndall. (See Diamagnetism.) The action of a diamagnetic body, when placed in a magnetic field, is now generally ascribed to- the fact that the atmosphere, by which such body is surrounded, is more powerfully paramagnetic than the diamagnetic substance. The diamag- netic substance comes to rest in an equatorial posi- tion, because in that position there is the greatest length of air in the path of the magnetic lines, which has a smaller magnetic resistance than the diamagnetic substance. Polarity, Magnetic The polarity acquired by a magnetizable substance when brought into a magnetic field. Pol.] 412 [Pol. The direction of magnetic polarity, acquired by a substance when brought into a magnetic field, depends on the direction in which the lines of magnetic force pass through it. Where these lines enter the substance a sou h pole is pro- duced, and where they pass out, a north pole is produced. The axis of magnetization lies in the direction of the lines of force as they pass through the body, and the intensity of magnetiza- tion depends on ihe number of these lines of force which pass through the body. The cause of magnetic polarity is not definitely known. Hughes' hypothesis attributes it to a property inherent in all matter. Ampere at- tributes it to closed electric circuits in the ultimate particles. Whatever its cause, it is invariably manifested by a magnetic field, the lines of force of which are assumed to have the direction already mentioned. (See Magnetism, Hughes' Theory of. Magnetism, Ampere 's Theory of. Magnet- ism, Ewing's Theory of.} Polarization, Galvanic A term sometimes applied to the polarization of a voltaic cell. (See Cell, Voltaic, Polariza- tion of.) Polarization, Internal, of Moist Bodies A polarization exhibited by such moist bodies as the nerves, muscular fibres, the juicy parts of vegetables and animals, or in general by all bodies possessing a firm struc- ture filled with a liquid, on the passage through them of a strong electric current. Polarization, Magnetic Rotary The rotation of the plane of polarization of a beam of plane-polarized light consequent on its passage through a plate of glass subjected to the stress of a magnetic field. (See Rota- tion, Magneto-Optic.) Polarization of Dielectric. (See Dielec- tric, Polarization of.) Polarization of Electrolyte. (See Elec- trolyte, Polarization of.) Polarization of Toltaic Cell. (See Cell, Voltaic, Polarization of.) Polarized Armature. (See Armature, Polarized?) Polarized Relay. (See Relay, Polarized?) Polarizing Current. (See Current , Polarization.) Polarizing Electro-Therapeutic Current. (See Current, Electro-Therapeutic Polar- izing?) Pole, Analogous That pole of a pyro-electric substance, like tourmaline, which acquires a positive electrification while the temperature of the crystal is rising. (See Electricity, Pyro.) Pole, Anomalous A name some- times given to those parts or poles in an anomalous magnet which consist of two simi- lar free poles placed together. (See Magnet, Anomalous?) Pole, Antilogous That pole of a pyro-electric substance, like tourmaline, which acquires a negative electrification when the temperature of the crystal is rising, and a positive electrification when it is falling. (See Electricity, Pyro?) Pole, Armature (See Armature, Pole?) Pole Changer. A switch or key for chang- ing or reversing the direction of current pro- duced by any electric source, such as a bat- tery The commutator of a Ruhmkorff coil is a sim- ple form of pole changer. It is, however, usu- ally called a commutator. (See Coil, Induction. ) Pole-Changing and Interrupting Elec- trode Handle. (See Electrode-Handle, Pole-Changing and Interrupting?) Pole-Changing Switch. (See Switch, Pole- Changing?) Pole Climbers. (See Climbers, Pole?) Pole, Consequent A magnet pole formed by two free north or two free south poles placed together. (See Magnet, Anom- alous?) Pole, Magnetic, Austral A name formerly employed in France for the north- seeking pole of a magnet. That pole of a magnet which points to the earth's geographical north. It will be observed that the French regarded the magnetism of the earth's Northern Hemisphere Pol.] 413 [Pol. as north, and so named the north-seeking pole of the needle the austral or south pole. The north-seeking pole of the magnet is some- times called the boreal or north pole. (See Pole, Magnetic, Boreal.") Pole, Magnetic, Boreal A name formerly employed in France for the south- seeking pole of a magnet, as distinguished from the austral or north-seeking pole. That pole of a magnet which points to- ward the geographical south. If the earth's magnetic pole in the Northern Hemisphere be of north magnetism, then the pole of a needle that points to it must be of the oppo- site polarity, or of south magnetism. In this country we call the end which points to the north, the north-seeking pole or marked pole. In France the end which points to the north was formerly called the austral pole. Austral means south pole. (See Pole, Magnetic, Austral.) Pole, Magnetic, False A term pro- posed by Mascart and Joubert to designate the place or places on the earth which appar- ently act as magnetic poles, in addition to the two true magnetic poles, near the earth's geographical poles. According to these authorities, the earth pos- sesses two magnetic poles only, viz., a negative pole in the Northern Hemisphere and a positive pole in the Southern Hemisphere. The addi- tional poles are called by them the false magnetic poles. Pole, Magnetic, Free A pole in a piece of iron, or other paramagnetic sub- stance, which acts as if it existed as one mag- netic pole only. A free magnetic pole has in reality no physical existence. The conception, however, is of use in describing certain magnetic phenomena. If the bar of iron be so long as to practically place one pole beyond the sensible action of the other, either pole may be regarded as a free pole. Pole, Magnetic, Marked That pole of a magnetic needle which points approxi- mately to the earth's geographical north. (Obsolete.) The north-seeking pole of a magnetic needle. Pole, Magnetic, North That pole of a magnetic needle which points approxi- mately to the earth's geographical north. The north-seeking pole of a magnetic needle. Pole, Magnetic, North-Seeking That pole of a magnetic needle which points approximately towards the earth's geographi- cal north. Pole, Magnetic, Salient A term sometimes applied to the single poles at the ex- tremities of an anomalous magnet, in order to distinguish them from the double or consequent pole formed by the juxtaposition of two simi- lar magnetic poles. (See Magnet, Anoma- lous.) Pole, Magnetic, South That pole of a magnetic needle which points approxi- mately towards the earth'sgeographical south. The south-seeking pole of a magnetic "needle. Pole, Magnetic, South-Seeking That pole of a magnetic needle which points approximately toward the geographical south. Pole, Negative That pole of an electric source through which the current is assumed to enter or flow back into the source after having passed through the circuit ex- ternal to the source. Pole-Pieces of Dynamo-Electric Machine. (See Pieces, Pole, of Dynamo-Electric Machine) Pole Platform. (See Platform, Pole.) Pole, Positive That pole of an electric source out of which the electric cur- rent is assumed to flow. Pole Steps. Short rods or bars shaped so as to be readily inserted in holes near the base of telegraph or electric light poles, so as to serve as steps to enable a lineman to reach the permanently placed steps. Permanent steps are placed only at some dis- tance from the ground, in order to prevent the ready climbing of the poles by unauthorized persons. Pole, Telegraphic A wooden or iron upright on which telegraphic or other wires are hung. Wooden poles are generally round. Pol.] 414 [Pol. The terminal pole, or the last pole at each end of the line, or where the wires bend at an angle of nearly 90 degrees, is made larger than usual and is often cut square. The holes for the poles must be dug in the true line of the wires, and not at an angle to such line. As little ground should be disturbed in the dig- ging as possible. Earth borers, or modifications of the ordinary ship auger, are generally em- ployed for this purpose. When the pole is placed in position the ground should be rammed or punned around the pole. In setting the pole, it is generally buried at least 5 feet in the ground. In England the poles are planted to a depth of about one- fifth of their length. In embankments and loose ground, they are planted deeper than in more solid earth. On curves, the poles should be inclined a little so as to lean back against the lateral strain of the wire, since by the time the ground has completely set, the strain of the wire will have pulled them into an erect position. Care must be taken to so plant the poles on that side of a road or railway that the prevailing winds will blow them off the roadbed, should it overturn them. As to location, the top of steep cuttings is preferable to the slope. In all exposed positions, it is preferable to strengthen the poles by stays attached to both sides. Where the number of wires is unusually large, heavy timber, or in case of its absence, double A Fig. 441. Telegraphic Brackets. Fig. 442. Telegraphic Arms. poles suitably braced together, must be employed. In long lines the poles should all be numbered in order to afford ease of reference in case of repair. When, even with the best punning, and other precautions, the pole is judged to be unable to resist the strain on it, stays and struts are em- ployed. A stay is used when it is desired to re- move the pull or tension from the pole ; a strut, when it is desired to remove the thrust or pressure. The arms or brackets, or the cross-pieces that support the insulators, should all be placed on the same side of the poles. Some common forms- of brackets are shown in Fig. 441, and of tele- graphic arms in Fig. 442. Saddle brackets should be placed on alternate sides of the poles. When the strain on an insula- tor is too great, on account of the wire going off at a sharp angle, a shackle is used. This is a special form of insulator which confines the strain to one spot. 443- Double Shackles. A form of double shackle is shown in Fig. 443. The wire passes around the recess at B r between the two insulators. On curves, or in any situation where there is a probability, in case of the breaking of an insula- Fig* 4-44-' Hook Guard, tor, of a wire getting into a dangerous position^ guards should be employed. Guards are of two kinds, viz.: hoop guards and hook guards. A form of hook guard i* shown in Fig. 444. When wooden poles are employed various pre- servative methods are adopted to protect the wood from decay, which is very apt to occur, especially where the pole enters the ground. Some of these forms are as follows, viz. : (l.) Charring and tarring the butt end of the pole where it enters the ground, so as to expel the sap and destroy injurious plant or animal germs. Pol.] 415 [For. The charred end is then cleansed and dipped in a mixture of tar and slaked lime. (2.) Btirnetizing, or the introduction of chloride of zinc into the pores of the wood, by placing the poles in an open tank filled with a solution of this salt. (3.) Kyanizing, or the similar introduction of corrosive sublimate, or mercuric chloride. (4.) Boucherizing, or the injection of a solution of copper sulphate into the pores of the wood. (5.) Creosoting, or the application of creosote to well seasoned poles. Pole, Telegraphic, Punning of Ramming or packing the earth around the base of a telegraph pole for the purpose of more securely fixing it in the ground. Pole, Telegraphic, Terminal The pole at either end of a telegraphic line. As the first or last pole in a telegraphic line is not supported on opposite sides by the line wires, it is generally made stouter than the intermediate poles, and greater care is taken to fix it securely in the ground. Pole, Testing A term sometimes employed in electro-therapeutics for the in- different pole or electrode. (See Electrode, Indifferent?) Pole, Trolley The pole which sup- ports the trolley bearing and rests on the socket in the trolley base frame in an over- head wire electric railway system. Pole, Unit, Magnetic A magnetic pole of such a strength that it would act with a unit or dyne of force on another unit pole at a distance of one centimetre. Poles, Consequent The name given to single magnetic poles formed by two free N. poles or two free S. poles placed together. (See Magnet, Anomalous?) Poles, Idle Poles or electrodes in Crookes' tubes, between which discharges are not taking place. The idle poles have no connection with the in- duction coils or other sources from which the elec- tric discharges areobtaint d. These poles are pro- vided for attaching galvanometer wires, etc., in the study of the Edison effect, or for the study of the electrical condition of the dark space and other regions of the atmosphere of the tube. Poles, Magnetic The two points where the lines of magnetic force pass from the iron into the air, and from the air into the iron. The two points in a magnet where the magnetic force appears to be concentrated. In reality the magnetic force is most concen- trated at the neutral points of a m agnet, through which all the lines of force pass. All magnets possess at least two poles, one positive or north, and the other negative or south. The lines of magnetic force are assumed to come out of a magnet at its north pole, and to enter it at its south pole. Poles, Magnetic, of Yerticity (See Verticity, Poles of, Magnetic?) Poles of Condenser. The terminals of a condenser. (See Condenser.} Poles of Magnetic Intensity. (See In- tensity, Magnetic, Pole of.) Polyphase Current. (See Current, Multi-Phase?) Polyphotal Arc Light Regulators. (See Regulator, Polyphotal Arc-Light?) Popgun, Electro-Magnetic A mag- netizing coil, provided with a tubular space for the insertion of a core, much shorter than the length of the coil, which, when the ener- gizing current is passed through the coil, is thrown violently out from the coil. The movement and consequent expulsion of the core is due to the action of the lines of magnetic force which complete their circuit through the core. Porcelain. A variety of insulating ma- terial. A translucent variety of earthenware. Porous Cell. (See Cell, Porous?) Porous Cup. (See Cup, Porous?) Porous Insulation. (See Insulation, Porous?) Porous Jar. (See far, Porous.) Porret's Phenomena. (See Phenomena, Porret?) For.] 416 fPos. Portative Power. (See Power, Porta- tive) Portelectric. An electric carrier. A system of electric transportation by means of the successive attractions of a num- ber of hollow helices of insulated wire on a hollow solenoidal iron car. The solenoidal car forms the movable core of the helical coils. As it moves through these coils it automatically closes the circuit of an electric cur- rent through the coils in advance of it and opens the circuit of the coils in its rear. In this way the solenoidal car advances in a line coincident with the axis of the helical coils, being virtually sucked through them by their magnetic attractions. This system of electric propulsion is unique in systems of electric traction. The motor becomes a mere mass of iron or other paramagnetic material. The system is suitable for the carriage of mail or other comparatively light articles at a high speed. In an experimental plant at Dorchester, Mass., a track of 2,784 feet in length was laid in the ap- proximate form of an oval. The track was formed by an upper and lower rail of steel, suit- ably supported by stringers. The car, which forms the movable core of the solenoidal coils, was of wrought iron, and was cylindrical in shape, with conical ends. It was placed on the top of the carrier and connected the several helices successively with the electric Fig. 445. Portelectri< Track. 12 feet in length and 10 inches in diameter, and weighed about 500 pounds. It would carry about 10,000 letters. It had two flanged wheels above and two below. The solenoidal coils, by the attractive power of which the core was moved, embraced the track and the movable core or carrier. They were fixed along the track at intervals of 6 feet from centre to centre. Each coil was formed of 630 turns of No. 14 copper wire. The upper track rail is divided into sections which form conductors for the driving current. A central wheel was Fig. 446. Portelectric Car. source as the carrier was drawn forward. A speed of about 34 miles an hour was reached. A section of the track is shown in Fig. 445, and the shape and general structure of the carrier in Fig. 446. Portrait, Electric A portrait formed on paper by the electric volatilization of gold or other metal. An electric portrait is obtained by cutting on a thin card a portrait in the form of a stencil. A sheet of gold leaf is then placed on one side of the Fig. 447. Electric Portrait. paper stencil, and a sheet of paper on the other side ; sheets of tin-foil are then placed on the out- side, as shown in Fig. 447, and the whole firmly pressed together. If, now, a disruptive discharge is passed through from one sheet of tin-foil to the other, the gold leaf is volatilized, and a purplish stain is left on the paper of the outlines of the stenciled card, thus forming an electric portrait. Position, Energy of A term used for stored energy, or potential energy. (See Energy, Potential) Positive Direction of a Simple-Harmonic Motion. (See Motion, Simple-Harmonic, Positive Direction of) Pos.] 417 [Pot. Positive Direction of Lines of Magnetic Force. (See Force, Magnetic, Lines of, Positive Direction of.) Positive Direction of the Electrical Con- vection of Heat. (See Direction, Positive, of Electrical Convection of Heat?) Positive Direction Round a Circuit. (See Direction, Positive, Round a Cir- cuit^ Positive Direction Through a Circuit. (See Direction, Positive, Through a Cir- cuit^ Positive Electricity. (See Electricity, Positive) Positive Electrode. (See Electrode, Positive?) Positive Feeders. (See Feeders, Posi- tive.) Positive-Omnibus Bars. (See Bars, Posi- tive Omnibus?) Positive Phase of Electrotonus. (See Electrotonus, Positive Phase of.) Positive Plate of Storage Battery. (See Plate, Positive, of Storage Battery.) Positive Plate of Toltaic Cell. (See Plate, Positive, of Voltaic Cell.) Positive Pole. (See Pole, Positive.) Positive Potential. (See Potential, Posi- tive) Positive Side of Circuit (See Circuit, Positive Side of) Positively. In a positive manner. Positively Excited. Excited or charged with positive electricity. (See Electricity, Positive?) Post, Binding A device for con- necting the terminal of an electric source with the terminal of an electro-receptive de- vice, or for connecting different parts of an electric apparatus with one another. The conducting or circuit wire is either intro- duced in the opening a, or c', Fig. 448, and clamped by the screw b, or b', or is placed in the space d, d, and kept in place by means of a thumbscrew. Sometimes two openings are provided at c, and c', for the purpose of connect- ing two wires together. A device for coupling or connecting the ends of two wires to each other. It is then called a coupler. (See Couple, Voltaic.) J' Fig. 448. Binding Posts. Pot, Porous The porous jar or cell of a voltaic cell. (See Cell, Porous) Potential, Alternating A poten- tial, the sign or direction of which is alter- nately changing from positive to negative. An alternating potential may be obtained either in the case of an electrostatic field, or in that of a magnetic field. Potential, Alternating Electrostatic The potential of a charge that is under- going rapid alternations. Potential, Alternating, Magnetic The difference of magnetic potential pro- duced by alternating electric currents. Potential, Constant A potential which remains constant under all conditions. A machine or other electric source is said to have a constant potential when it is capable, while in operation, of maintaining a constant difference of electric pressure between its two terminals on changes of load. (See Circuit, Constant-Potential. ) Potential, Difference of A term employed to denote that portion of the electromotive force which exists between any two points in a circuit. The difference of potential at the poles of any electric source, such as a battery or dynamo, is that portion of the total electromotive force which is available, and is equal to the total electromotive force, less what is lost in the source. Some difference of opinion exists as to the exact meaning that is attached to the phrase difference of potential. A positively electrified body is said to have a higher electric potential than the earth, whose potential is taken as zero. Pot] 418 [Pot Potential, Difference of, Methods of Measuring Methods employed for de- termining differences of potential. These methods are as follows: (i.) By the Method of Weighing, that is, by obtaining the -weight required to overcome the attraction between two oppositely charged plates, or oppositely energized coils; or by measuring the repulsion between similarly charged surfaces, or similarly energized coils. (2.) By the Use of Electrometers, or apparatus designed for measuring differences of potential. (See Electrometers. ) (3.) By the Use of Galvanometers. Differences of potential, in the case of currents, may be determined from the quantity of electri- city which flows per second through a given circuit, that is, by the number of amperes, just as the pressure of water at any point in the side of a containing vessel can be determined by the quantity of water that flows per second. Differ- ence of potential in the case of currents, there- fore, may be measured by any galvanometer which measures the current directly in amperes, provided the resistance of the circuit is known. Potential, Drop of A term some- times used instead of fall of potential. (See Potential, Fall of.) Potential, Electric The power of doing electric work. Electric level. Electric potential can be best understood by comparison with the case of a liquid such as water. The ability of a water supply or source to do work depends: (I.) On the quantity of water. (2.) On the level of the water, as compared with some other level; or, in other words, on the dif- ference between the two levels. In 2 like manner the ability of electricity to do woik depends: (I.) On the quantity of electricity. (2.) On the electric potential at the place where the electricity is produced, as compared with that at some other place; or, in other words, on the difference of potential. In the case of water flowing through a pipe, when its flow has been fully established, the quan- tity which passes in a given time is the same at any cross-section of the pipe. In the case of electricity, the quantity of elec- tricity flowing through any conductor, or part of a circuit, is the same at any cross-section. A gal- vanometer introduced into a break in any part of the conductor would show the same strength of current. But, though the quantity of water which passes is the same at any cross-section of a pipe, the pressure per square inch is not the same, even in the case of a horizontal pipe of the same diameter throughout, but becomes less, or suffers a loss of head, or difference of pressure, at any two points along the pipe. This difference of pressure causes the flow of water between these two points against the resistance of the pipe. So, too, in the case of a conductor carrying an electric current, when the full current strength has been established, the quantity of electricity that passes is the same at all cross-sections. Fig. 449. Hydraulic Gradient. The electric pressure or potential, however, is by no means the same at all points in the conductor, but suffers a loss of electric head or level, in the direction in which the electricity is flowing. It is this electric head or level, or dif- ference of electric potential, that causes the elec- tricity to flow against the resistance of the con- ductor. These analogies can be best shown by the fol- lowing illustration: In Fig. 449, a reservoir, or source of water, at C, communicates with the horizontal pipe A B, furnished with open vertical tubes at a, b, c, d, e, f, g, and B. If the outlet at B, is closed, the level of the water in the communicating vessels is the same as at the source; but if the liquid escape freely from B, the level of the water in the branch pipes will be found on the inclined dotted line, or at a', b', c'. d', e', f , g', which may be called the hydraulic gradient. The pressure per square inch, at any cross sec tion of the horizontal pipe, which is measured by the height of the liquid in the vertical pipe at that point, decreases in the direction in which the liquid is flowing. The force that urges the liquid Pot] 419 rpot. through the pipe between any two points, may be called the liquid-motive force (Fleming) and is measured by the difference of pressure between these points. In Fig. 450, the dynamo-electric machine at D, has its negative pole grounded, and its positive pole connected to a long lead, A B, the positive pole of which is also grounded. A fall of poten- tial, represented by the inclined dotted line, occurs between A and B, in the direction in -which the electricity is flowing. Fig. 450. Fall of Electric Potential. The dynamo-electric machine may be regarded as a pump that is raising the electricity from a lower to a higher level, and passing it through the lead A B. The electric pressure or potential producing the flow is greatest near the dynamo and least at the further end, the differences at the points a, b, c, d, e, f, and g, being represented by the vertical lines a a', bb', c c', d d', ee', f f, and gg'- The electricity flows between any two points as a and b, in the conductor A B, in virtue of the -difference of electric pressure or potential be- tween these two parts, or the difference between a a' and b b'. Differences of potential must be distinguished from differences in electric charge, or electrostatic density. If two conductors at different potentials are connected by a conductor, a current will flow through this conductor. When their potential is the same, no current flows. The density of a charge is the quantity of electricity per unit of area. The electric potential is the same at all points of an insulated charged conductor; the density is different at different points, except in the case of a sphere. The potential, however, is the same, since no current flows, or the charge does not re- distribute itself. The density on an insulated, isolated sphere, is uniform over all parts of the surface, and its potential is the same at all points. If now the sphere be approached to another body, its density will vary at different parts of its sur- face, and while the charge is redistributing itself so as to produce these differences in density the potential will vary. As soon, however, as this redistribution is effected and no further current exists, the potential is the same over all points, though the density differs at different points. An electric source not only produces but also maintains a difference of potential. In the case of the flow of liquid in a pipe, if a continuous current of the liquid be maintained from the higher level in the reservoir to a lower level, as, for example, by means of a pump, it must flow through the pump to the reservoir, from the lower level towards the higher level. In case of an electric source, since the thing called electricity flows through a closed circuit, if its direction of flow in that part of the circuit extern il to the source i. e. , in the external or useful current be from a higher to a lower level, then its flow through the remainder of the circuit i. e., through the source must be from the lower to the higher level. Since, however, the electrical po- tential of a body represents the work the elec- tricity is capable of doing, the work done by the e'ectricity may be regarded as being that done when it passes from the higher to the lower level. Potential, Electrostatic The power of doing work possessed by a unit quantity of positive electricity charged or re- siding on an insulated body. Potential, Electrostatic, Difference of Difference of potential of an electric charge. (See Potential, Difference of. 'Electrostatics?) Potential Energy. (See Energy, Poten- tial^ Potential, Fall ot A decrease of potential in the direction in which an elec- tric current is flowing, proportional to the re- sistance when the current is constant. (See Potential, Electric!) Potential Galvanometer. (See Galva- nometer, Potential?) Potential Indicator. (See Indicator, Potential!) Potential, Magnetic The amount of work required to bring up a unit north- seeking magnetic pole from an infinite dis- tance to a given point in a magnetic field. Pot.] 420 [Pow. Potential of Conductor, Methods of Varying 1 (See Conductor, Potential of, Methods of Varying?) Potential of Conductors. (See Conduc- tor, Potential of.} Potential, Negative That potential in the circuit external to the source towards which the electric current flows. Generally the lower potential, or lower level. Potential, Positive That potential in the circuit external to the source, from which the electric current flows. The higher potential or higher level. Potential, Uniform A potential that does not vary. A constant potential. (See Potential, Con- stant.} An electric source is said to generate a uniform potential when it maintains a constant difference of potential at its terminals. Potential, Unit Difference of - Such a difference of potential between two points that requires the expenditure of one erg of work to bring a unit of positive elec- tricity from one of these points to the other, against the electric force. (See Erg.} The practical unit of difference of potential is the volt. (See Volt.) Potential, Zero An arbitrary level from which electric potentials are measured. As we measure the heights of mountains from the arbitrary mean level of the sea, so we measure electric levels from the arbitrary level of the po- tential of the earth. Potentiometer. An apparatus for the galvanometric measurement of electromotive forces, or differences of potential, by a zero method. (See Method, Null or Zero.) In the potentiometer the difference of potential to be measured is balanced or opposed by a known difference of potential, and the equality of the balance is determined by the failure of one or more galvanometers, placed in shunt circuits, to show any movement of their needles. The principle of operation of the potentiometer will be understood from an inspection of Fig. 451. A secondary battery S, has its terminals con- nected to the ends of a uniform wire A B, of high resistance called the potentiometer wire. There will, therefore, occur a regular drop or fall of po- tential along this wire, which, since the wire is uniform, will be equal per unit of length. This drop of potential can be shown by connecting the terminals of a delicate galvanometer, generally of high resistance, to different parts of the wire, when the deflection of the needle will be propor- S Fig. 431. Potentiometer. tional to the drop of potential between the two points of the wire touched. If, now, the terminals of a standard cell be inserted in the circuit of the galvanometer, so as to oppose the current taken from the potentiometer wire, and the con- tacts of the potentiometer wire be slid along the wire until no deflection of the galvanometer needle is produced, the drop of potential between these two points on the wire will be equal to the differ- ence of potential of the standard cell. (See Cell, Voltaic, Standard.) Suppose, now, it be desired to measure the dif- ference of potential between two points a and b, on the wire C, through which a current is flow- ing. Connect the points b and d, and a and c, as shown, with the delicate high resistance gal- vanometer G, in either of them. Now slide C T towards d, until the needle of G, shows no deflec- tion. The potential between a and b, is then equal to that between c and d. Potentiometer Wire. (See Wire, Po- tentiometer?) Power. Rate of doing work. Mechanical power is generally measured in horse power, which is equal to work done at the rate of 550 foot-pounds per second. The C. G. S. unit of power is one erg per second. The practical unit of power is the watt, or 10,000,000 ergs per second. The kilowatt is even more frequently used as the unit of power than the watt. (See Power, Unit of.) Power, Absorptive The property Pow.] 421 [Pow. possessed by many solid bodies of taking in and condensing gases within their pores. Carbon possesses marked absorptive powers. The absorption of gases in this manner by solid bodies is known technically as the occlusion of gases. (See Gas, Occlusion of.) One volume of charcoal, at ordinary tempera- tures and pressures, absorbs of Ammonia 90 volumes Hydrochloric acid 85 " Sulphur dioxide 65 " Hydrogen sulphide 55 " Nitrogen monoxide 40 " Carbonic acid gas 35 " Ethylene 35 " Carbon monoxide 9.42 " Oxygen 9.25 " Nitrogen 6.50 " Hydrogen 1 .25 " {Sous sure.) Power, Candle An intensity of light emitted from a luminous body equal to the light produced by a standard candle. (See Candle, Standard.) The light-giving power of one standard candle. Power, Candle, Nominal A term sometimes applied to the candle-power taken in a certain favorable direction. This term is generally used in arc lighting. In the ordinary arc lamp the greatest amount of light is emitted at a particular point, viz., from the crater in the upper or positive carbon. (See Arc, Voltaic.) Power, Candle, Rated A term sometimes used for nominal candle-power. Power, Candle, Spherical The average or mean value of candle power taken at a number of points around the source of light. Power, Conducting The ability of a given length and area of cross-section of a substance for conducting light, heat, elec- tricity or magnetism, as compared with an equal length and area of cross-section of some other substance taken as a standard. Power, Conducting, for Electricity The ability of a given length and area of cross-section of a substance to conduct elec- tricity, as compared with an equal length and area of cross-section of some other substance, such as pure silver or copper. No substance is known that does not offer some resistance to the passage of an electric current. The following table is taken from Sylvanus P. Thompson's ' ' Elementary Lessons in Electricity and Magnetism": GOOD COXDUCTORS. Silver, Copper, Other metals, Charcoal. PARTIAL CONDUCTORS. Water, Wood, The human body, Marble, Cotton, Paper. NON-CONDUCTORS. Oils, Gutta-percha, Porcelain, Shellac, Dry wood, Ebonite, Silk, Paraffine, Resins, Glass, Dry air. Heat decreases the conducting power of ele- mentary substances. This decrease in the con- ducting power is approximately proportional to the increase of temperature. Carbon is an ex- ception to the law, being a better conductor at a red or white heat than when cold. The resistance of some alloys, such as German silver and platinoid, is but little affected by mod- erate changes of temperature. These alloys are, therefore, employed in the construction of resist- ance coils. At a red heat insulators become fairly good conductors of electricity. At very low temperatures the conducting powers of the metals increase. Wroblewski has shown that at extremely low temperatures copper increases in its conducting power for electricity. He cooled copper to 200 degrees C., the temperature of the solidification of nitrogen, and found that at this temperature its conducting power increased to about nine times its conducting power at O degrees C. It may be remarked here that at exceedingly low temperatures a metal would take in or absorb heat from the surrounding medium with very, great rapidity. In this sense it might be said that Pow.J 422 [Pow. its conducting power for heat was greatly in- creased. Kohlrausch estimates the conducting power of distilled water at .000000000025, that of mer- cury being taken as unity. The best conductors of electricity are the best conductors of heat. This fact is well illustrated by the following table from Ayrton : RELATIVE CONDUCTIVITIES PER CUBIC UNIT. Name of Metal. Electricity. Heat. Copper, " 94-1 74-8 Gold, 73 54.8 Platinum 16.6 9-4 ic.c IO. I Tin H.4 15.4 Lead 7-6 7 Q Bismuth . . . I.I 1.8 The electric conductivity of porous conductors decreases much more rapidly than the heat con- ductivity. Practically perfect insulators for electricity can "be obtained, but are unknown for heat. Edlund believes the universal ether to be al- most a perfect conductor. He bases this belief on the phenomena of sun spots, the occurrence of which is almost immediately followed by the occurrence of magnetic disturbances on the earth. Lodge regards the luminiferous ether as being almost a perfect non-conductor, because he thinks that conductors must be opaque. It may be sug- gested in this connection that Edlund's hypothesis as to the conductibility of magnetic effects through the e.her is also capable of an explanation by the effects of magnetic induction. The conducting power for alternating currents is not the same as for steady currents. When the alternations become very high, the difference between these conducting powers of the metals becomes almost inappreciable. Iron is an enormously worse conductor of electricity than copper for rapidly alternating currents, at least when the alternations are not too great. When, however, the alternations are extremely high, such as those which are produced by the discharge of a Leyden jar or lightning flash, the iron is as good a conductor as the cop- per. The reason for this is evident. The dis- charge in such cases keeps to the extreme outer layer of the conductor, so that the composition of the substance is practically of no effect. Hughes has shown that the resistance of an iron telephone line of the usual diameter, to periodic currents of about 100 per second, is somewhat more than three times its resistance for steady currents. There is no such thing as conduction of elec- tricity in gases. Electricity makes its way through a gas by a sudden piercing of the dielectric, or, in other words, by a disruptive discharge. (See Discharge, Disruptive.') In such a disruptive discharge it may be assumed that the gas be- comes a conductor of electricity while the dis- charge is passing. It would then partake of the nature of an electrolytic conductor, since the dis- charge takes place by means of a true locomotion of atoms. (See Conduction, Electrolytic.') Power, Conducting, for Heat The ability of a substance to transmit heat through its mass. The metals are good conductors of heat. They are also good conductors of electricity. The conducting powers for heat and electricity are nearly identical. As the temperature of a body increases, its conducting power for heat is de- creased. Carbon forms an exception to this statement. The flow of heat across a wall formed of a homogeneous material, the exposed faces of which are of equal extent and are maintained at a con- stant difference of temperature, takes place in accordance with the following laws : (i.) The rate of flow across all perpendicular sections is the same. (2.) A uniform drop of temperature occurs from one side of the wall to the other in the direc- tion in which the flow is taking place. (3.) The rate of flow is proportional to the dif- ference in temperature. The similarity between the laws of the flow of heat under the circumstances just named and the flow of electricity through a conductor is evident; the electrical current being the same in all parts of the circuit, a drop of potential occurring in the direction in which the current is moving, and the flow being proportional to the difference of potential. Power, Conducting, Tables of Tables in which the relative conducting Pow.] 423 [Pow. powers of different substances are given. (See Resistance, Tables of.) Power, Electric Power developed by means of electricity. Power, Electric, Distribution of The distribution of electric power by means of any suitable system of generators, connect- ing circuits and electric motors. Power, Electric Transmission of The transmission of mechanical energy by converting it into electric energy at one point or end of a line, and reconverting it into mechanical energy at some other point on the line. (See Energy, Electric, Transmission of.} Power, Horse A rate of doing work equal to 550 foot-pounds per second, or 33,- ooo foot-pounds per minute. I horse-power=745.94 X io 7 ergs per second. (See Erg.) " =745.941 watts. (See Watt.) " =42.746 Ib. Fahr. heat units per min. (See Units, Heat.) " =23.748 Ib. Cent, heat units per min. (See Units, Heat.) Power, Horse, Electric Such a rate of doing electric work as is equal to 746 watts or 746 volt-coulombs per second. This rate is equivalent to 33,000 foot-pounds per minute, or 550 foot-pounds per second. Just as I pound of water raised through the vertical distance of I foot requires the expendi- ture of a foot-pound of energy, so I coulomb of electricity acting through the difference of poten- tial of I volt requires a certain amount of work to be done on it. (See Coulomb. Volt. Po- tential, Electric.) This amount is called a volt-coulomb or joule, and measured in foot-pounds is equal to .737324 foot-pounds. The volt coulomb, or joule, is there- fore the unit of electric work, just as the foot- pound is the unit of mechanical work. The electric work of any circuit in joules is equal to the product of the volts by the coulombs. If we determine the rate per second at which the coulomb ; pass, and multiply this product by the volts, we have a quantity which represents the electrical power, or rate of doing electrical work. But I ampere is equal to I coulomb per therefore, if we multiply the current in am- peres by the difference of potential in volts, the product is equal to the electrical power or rate of doing electrical work. The product of an ampdre by a volt is called a volt-ampere, or a watt. One watt = .0013406 horse-power, or On- horse-power = 745.941 watts. C* F Therefore the electrical horse-power = z ' where C = the current in amperes and E = the difference of potential in volts. Power, Multiplying, of Shunt (See Shunt, Multiplying Power oj ".) Power of Periodic Current (See Cur- rent, Periodic, Power of.) Power, Portative The carrying power of a magnet. (See Magnet, Porta- tive Power of.) Power, Projecting, of Magnet The power a magnet possesses of throwing or pro- jecting its lines of magnetic force across an intervening air space or gap. The greater the air space the greater the mag- netic reluctance, and consequently the greater the magnetizing force required to overcome it. Mag- nets of great projecting power are generally of great length, to accommodate the long coils of wire required. Power, Resuscitating, of Secondary Bat- tery Cell The power possessed by an apparently completely discharged secondary or storage cell of furnishing additional current after a protracted rest. This resuscitating power is probably due to depolarization. It is therefore present in primary as well as in secondary batteries. Power, Stray That part of the power employed in driving a dynamo, which is lost through friction, air churning or air currents, eddy currents, hysteresis, etc. Power, Thermo-Electric A num- ber which, when multiplied by the difference of temperature of a thermo-electric couple, will give the difference of potential thereby generated in micro-volts. (See Diagram, Thermo-Electric) Pow.] 4 Power, Units of Various units em- ployed in the measurement of power. The following table of units of power is taken from Hering's work on dynamo-electric machines. Unit of Pffwer. I erg per second. . = .000000 1 watt. I watt, or i volt- ampere, or I joule per second, or I volt-coulomb per second = looooooo ergs per second. " =44.2394 foot-pounds per min. " =6.11622 kilogram - metres per min. " ==. 0573048 Ib.-Fah., heat unit per min. " = .318360 Ib.-Cent., heat unit per min. " = .0144402 klgr.-Cent. heat unit per min. " = .0013592 metric horse- power. ' = .0013406 horse power. I foot-pound per min = 226043 ergs per second. " = .0226043 watt. " = .13825 kilogram-metre per min. " = .00003072 metric horse- power. " = .000030303 horse-power. I kilogram - metre per min = 1635000 ergs per second. " = .163500 watt. " = 7.23314 foot-pounds per min. " = .0002222 metric horse- power. ' = .0002192 horse-power. I metric horse- power, or I French horse- power, or I che- val-vapeur, or I force de cheval, or i Pferdekraft. = 735 75 X io 7 ergs per second. " = 735-75 watts. " = 32549.0 foot-pounds per min. " = 4500 kilogram-metres per t [Pri. I metric h.-p., etc. =42.162 Ib.-Fah., heat units per min. " = 23.423 Ib.-Cent., heat units per min. " = 10.625 klg.-Cent., heat units per min. " = -98634 horse-power heat units per min. i horse-power =1745.94 X io 7 ergs per second. = 745-941 watts. " . . . . = 33000 foot-pounds per min. " = 4562.33 kilogram - metres per min. " = 42.746 Ib.-Fah., heat units per min. " = 23.748 Ib.-Cent., heat units per min. " = 10.772 klg. - Cent., heat units per min. " = 1.01385 metric horse- power, i Ib.-Fih., heat unit per min = 17.45 X io 7 ergs per sec. " = 17.4505 watts. " = .23718 metric horse-power, " = .023394 horse-power. I Ib. Cent., heat unit per min =31.41 X io 7 ergs per sec. " = 31.4109 watts. " = .04269 metric horse power. " = .042109 horse-power, i klgr.-Cent., heat unit per min = 69.25 X io 7 ergs per sec. " = 69.249 watts. = .09412 metric horse-power, " = .092835 horse-power. Poynting's Law. (See Law, Poynting's.) Practical Unit of Inductance, or Self- induction. (See Inductance, or Self -Induc- tion, Practical Un it of.) Practical Unit of Magneto-Motive Force, (See Force, Magneto-Motive, Practical Unit of.) Practical Units. (See Units, Practical.} Pressel. A press switch or push connected to the end of a flexible, pendant conductor. Pressure Wires. (See Wires, Pressure.) Primary Battery. (See Battery, Prim- ary) Pri.] 425 [Pro. Primary, Breaking- the Breaking or opening the circuit of the primary of an induction coil. (See Primary, The.) Primary Coil. (See Coil, Primary) Primary, Making- the Closing or completing the circuit of the primary of an induction coil. (See Primary, The) Primary Plate Condenser. (See Plate, Primary, of Condenser) Primary Spiral. (See Spiral, Primary) Primary, The That conductor in an induction coil, or transformer, which re- ceives the impressed electromotive force, or which carries the inducing current. On changes in the :urrent intensity in the primary, currents are induced in the secondary. (See Induction, Electro-Dynamic. Coil, Induc- tion. Transformer) Prime Conductor. (See Conductor, Prime) Prime Motor. (See Mover, Prime) Prime Mover. (See Mover, Prime) Printer, Stock, Callahan's A form of printing telegraph used in sending stock quotations telegraphically. (See Telegraphy, Printing. Ticker, Stock) Printer, Stock, Phelps' A form of printing telegraph used in sending stock quo- tations telegraphically. (See Ticker, Stock. Telegraphy, Printing) Probe, Electric A metallic con- ductor inserted in the body of a patient in order to ascertain the exact position of a bullet, or other foreign metallic substance. Two conductors are placed parallel to each other, and are separated at the extremity of the probe by any suitable insulating material. On contact with the metallic substance, an electric bell is rung by the closing of the circuit, or the same thing is more readily detected by the de- flection of the needle of a galvanometer, or by a telephone placed in the circuit. Process, Electrotyping (See Elec- trotyping, or the Electrotype Process) Processes of Carbonization. (See Car- bonization, Processes of) Production of Electricity by Light. (See Electricity, Production of, by Light) Prog-nosis, Electric In electro- therapeutics, a prognosis, or prediction of the fatal or non-fatal termination of a disease, from an electro-diagnosis based on the exag- gerated or diminished reactions of the excit- able tissues of the body when subjected to the varying influences of electric currents. (See Diagnosis, Electro) Projections, Paeinotti -Radial projections or teeth in an armature core ex- tending from the central shaft, so as to form slots, pockets, or armature chambers, for the reception of the armature coils. The term Paeinotti projections was given to these teeth because they were first introduced by Paeinotti in his dynamo-electric machine. Projector, Mangin A special form of search light. The Mangin reflector consists of a concavo- convex mirror, the convex surface of which is silvered and acts as a reflector. The radii of curvature of the two surfaces are such that the light undergoes the two refractions, i. e., on en- tering and on passing out of (he mirror, in such a manner as to pass out of the mirror in absolute parallelism, and thus destroy all aberration. Fig. 432. Mangin Projector. The Mangin projector is shown in longitudinal and in cross-section in Fig. 452, and the projector B, is placed in one end of the cylinder A, furnished with the openings for the ventilation of the cham- ber. The cylinder is supported on trunnions, and by means of screws can be given any desired inclina- tion, in a manner which will be readily under- stood from an inspection of the drawing. The source of light is an arc lamp of the focus- ing type. A small disc is placed in front of the Pro.] 426 [PuL arc in order to stop the direct light from the arc which would have divergent rays. The door C, is formed of a number of cylindrical lenses, placed parallel to one another, which cause the rays to diverge horizontally, when so desired. Prony Brake. (See Brake, Prony.) Proportional Coils. (See Coils, Propor- tional) Proportionate Arms. (See Arms, Pro- portionate.) Proportionate Arms of Electric Bridge. (See Arms, Proportionate) Prostration, Electric Physiological exhaustion or prostration, resembling that produced by sunstroke, resulting from pro- longed exposure to the radiation of an unusu- ally large voltaic arc. (See Sunstroke, Electric) Protection, Electric, of Houses, Ships and Buildings Generally Means for protection against the destructive effects of a lightning discharge, consisting essentially in the use of lightning rods. (See Rod, Light- ning^ Protection, Electric, of Metals (See Metals, Electrical Protection of) Protectiye Sheath. (See Sheath, Pro- tective^) Protector, Cable A device for the safe discharge of the static charge produced on the metallic sheathing of a cable, or on conductors surrounding or adjacent to the cable, consequent on changes in the electro- motive force applied to the conducting core of such cable. The cable protector is provided for the purpose of preventing the discharge of the charge from piercing and thus injuring the insulation of the cable itself. Protector, Comb A term some- times applied to a lightning protector or ar- rester, in which both the line and ground plates are furnished with a series of teeth, like those on a comb. (See Arrester, Light- ning) Protector, Voltaic Battery A de- vice for automatically disconnecting a voltaic battery, whenever the circuit in which it is. placed becomes grounded. The battery protector is used in systems of elec- tric gaslighting, where, unless great care is exer- cised in insulating the circuits, considerable annoy- ance is often experienced from the readiness with which grounds are established. This arises from the high electromotive force of the spark ob- tained from the spark coil, piercing the insula- tion and establishing a ground through the gas- pipes. Protoplasm, Effects of Electric Current* on Contractions observed in all pro- toplasm on the passage of an electric current through it. Protoplasm, the basis of plant and animal life, or the jelly-like matter that fills all organic cells, whatever may be the origin of such cells, suffers contraction when traversed by an electric cur- rent. An increased activity in the movements of a form of microscopic life called the amoeba is occa- sioned by slight shocks from an induction coil ; stronger discharges produce tetanic contractions, with, in some cases, expulsion of food or even of the nucleus. A uniform strength of current pro- duces contraction and imperfect tetanus. Pull. A contact maker, similar in general construction to a push button, but operated by means of a pulling rather than a pushing force. The pull is preferable to the push in exposed positions, such as outer doors, where moisture is apt to injure pushes. Pull, Chain -A chain pendant at- tached to a pendant burner for the move- ment of the wipe-spark spring and the ratchet in an electrically lighted gas burner. Pull, Door Bell, Electric A cir- cuit-closing device attached to a bell pull and operated by the ordinary motion of the pull. Pull, Electric Bell A circuit-clos- ing device operated by a pull. Fig 453 shows a form of electric bell pull. On pulling the bell handle, contact springs, that rest on a ring of insulating material when the Pul.] 427 [Pum. pull is in its normal position, are brought into con- tact with a metal ring, thus completing the cir- Fig. 453. Electric Bell Pull. cuit. The bell pull is often used to replace the ordinary push button. Pulley, Driven A pulley attached to the driven shaft. (See Mover, Prime?) Pulley, Driving A pulley attached to the driving shaft. (See Mover, Prime?) Pulsating Current. (See Current, Pul- sating?) Pulsation. A quantity of the nature of an angular velocity, equal to 2 n multiplied by the frequency of the oscillation, or, equal to 2 it divided by the duration of a single period. Pulsatory Current. (See Current, Pul- satory?) Pulsatory Magnetic Field. (See Field, Magnetic, Pulsatory?) Pulse, Electrical An electric oscil- lation. A momentary flow of electricity from a conductor, which gradually varies from the zero value to the maximum, and then to the zero value again, like a pulse or vibration in an elastic medium. Electric pulses are set up in conductors con - nected with the coatings of a Leyden jar, on the discharge of the same. Such pulses produce a series of electrical oscillations, which move alter- nately backwards and forwards, until the dis- charge is gradually dissipated. (See Oscillations, Electric:) The circumstances influencing the rate of propagation of an electric pulse through different parts of a closed circuit, according to Lodge, are (i.) The extra inertia, or the so-called magnetic susceptibility in the conducting substance, es- pecially at its outer parts. (2. ) An undue constriction or throttling of the- medium through which the disturbance is pass- ing. (3.) The nature of the insulating medium. Pump, Air, Oeissler Mercurial A mercurial air pump, in which the vacuum is attained by the aid of a Torricellian vacuum . In the Gassier Mercury Pump, Fig. 454, a vacuum is obtained by means of the Torricellian, vacuum produced in a large glass bulb that forms the upper ex- tremity of a barome- tric column. The lower end of this tube or column is con- nected with a reser- voir of mercury by means of a flexible rubber tube. To fill the bulb with mer- cury the reservoir is raised above its level, i. e., above thirty inches, the air it con- tains being allowed to escape through an opening governed by a stopcock. The ves- sel to be exhausted is connected with the bulb, and by means of a two-way exhaus- tion cock, communi- Fig. 434. Geissler's Mer- cation can be made cttrial Air Pump. with the bulb, when it contains a Torricellian vacuum, and shut off from it while its air is being expelled. In actual practice the mercury is mechanically pumped into the barometric column, and the valves are opened either by hand, or automati- cally by electrical means. Pump, Air, Mechanical A mechan- ical device for exhausting or removing the air from any vessel. An excellent form of air pump is shown in Fig. 455, which is a drawing of Bianchi's pump. Three valves, all opening upwards, are placed Pum.] 428 at the top and bottom of the cylinder, and in the piston, respectively. These valves are mechan- ically opened and closed at the proper moment by the movements of the piston, *'. e., their action is automatic. This enables a much higher vacuum to be obtained than when the valves open and close by the tension of the air. Mechanical pumps are unable to readily pro- duce the high vacua employed in most electric lamps. Mercury pumps are employed for this purpose. (See Pump, Air, Mercurial.) rump, Air, Mer- curial A de- vice for obtaining a high vacuum by the use of mercury. Mercury pumps are in general of two types of construction, viz. : (I.) The Geissler Btancht's Air Pump. pump. (2.) The Sprengel pump. (See Pump, Air, Geissler Mercurial. Pump, Air, SprengePs Mercurial.} Pump, Air, Sprengel's Mercurial A mercurial air pump in which the vacuum is obtained by means of the fall of a stream of mer- cury. In the Sprengel mercury pump, Fig. 456, the fall of a mer- cury stream causes the exhaustion of a reservoir connected with the vertical tube, by the mechan- ical action of the mercury in entang- ling bubbles of air. These bubbles are largest at the begin- ning of the exhaus- tion, but become smaller and smaller Fig. 456. SprengeFs Mer- near the end, until, curial Air Pump. at last, the characteristic metallic click of mer- cury or other liquid falling in a good vacuum is heard. The exhaustion may be considered as completed when the bubbles entirely disappear from the column. The Sprengel pump produces a better vacuum than the Geissler pump, but is slower in its action. In actual practice, the mercury that has fallen through the tube is again raised to the reservoir connected to the drop tube by the action of a mechanical pump. Pumping of Electric Lights. A term sometimes applied to a pulsating or period- ical increase and decrease in the brilliancy of the light. This action is generally due to the periodic slip- ping of- the belt or other driving mechanism. In the case of arc lamps it may also be caused by the improper action of the feeding device of the lamp. Puncture, Electro The application of electrolysis to the treatment of aneurisms or diseased growths. The blood is decomposed by the introduction of a fine platinum needle connected with the anode of a battery, and insulated, except near its point, by a covering of vulcanite. The kathode is a sponge-covered metallic plate. Puncture, Galvano A term some- times applied to electro-puncture. (See Puncture, Electro?) Punning of Telegraph Pole. -(See Pole, Telegraphic, Punning of.} Push. A name sometimes applied to a push button, or to a floor push. (See Push, Floor. Button, Push.*) Push Button. (See Button, Push.) Push-Button Rattler. (See Rattler, Push-Button?) Push, Floor A push button placed on the floor of a room so as to be readily operated by means of the foot. (See But- ton, Push.) Pyknometer. A term sometimes used for the specific gravity bottle employed in determining the specific gravity of a liquid. Pyrheliometer. An apparatus for mea- suring the energy of the solar radiation. 429 [Qua. The pyrheliometer consists essentially of a short cylinder, the area of whose base is accu- rately determined. The cylinder being filled with a known weight of water, the water surface is ex- posed for a definite time to the sun's radiation, and the increase in temperature carefully deter- mined. The product of the weight of the water thus heated by the increase in degrees, gives the number of heat units, from which the total energy absorbed is readily calculable. In order to avoid loss by reflection or diffusion from the water surface, it is covered by a layer of lamp- black. (See Units, Heat. Calorimeter.'] Pyro - Electricity. (See Electricity, Pyro) Pyro-Magnetic Generator or Dynamo. (See Generator, Pyro-Magnetic?) Pyro-Magnetic Motor. (See Motor, Pyro- Magnetic?) Pyrometer. An instrument for deter- mining temperatures higher than those that can be readily measured by thermometers. Pyrometers are operated in a variety of ways. A common method is by the expansion of a metal rod. Pyrometer, Siemens' Electric An .apparatus for the determination of tempera- ture by the measurement of the electric resist- ance of a platinum wire exposed to the heat whose temperature is to be measured. The platinum wire is coiled on a cylinder of fire-clay, so that its separate convolutions do not touch one another. It is protected by a platinum shield, and is exposed to the temperature to be measured while inside a platinum tube. The resistance of the platinum coil at O degree C. having been accurately ascertained, the temper- ature to which it has been exposed can be calcu- lated from the change in its resistance when ex- posed to the unknown temperature. Pyrometer, Siemens' Water : A pyrometer employed for determining the tem- perature of a furnace, or other intense source of heat, by calorimetric methods, /. e., by the increase in the temperature of a known weight of water, into which a metal cylinder of a given weight has been put, after being exposed for a given time to the source of heat to be measured. When copper cylinders are employed, the in- strument possesses a range of temperature of 1, 800 degrees F.; when a platinum cylinder is used, it has a range of 2,700 degrees F. Q Q. A contraction for electric quantity. Quad. A contraction sometimes em- ployed in place of quadruplex telegraphy. (See Telegraphy, Quadruplex?) Quadrant. A term proposed for the unit of self-induction. An earth quadrant is equal to io 9 centi- metres. In the United States the word henry is used for the unit of self-induction. (See Henry, A.) Quadrant Electrometer. (See Electro- meter, Quadrant?) Quadrant Electroscope, Henley's. (See Electroscope, Quadrant, Henley 's.) Quadrant, Legal A length equal to 9,978 kilometres, instead of the assumed 10,000 kilometres. Quadrant, Standard A length equal to 10,000 kilometres. Quadrature, In A term employed to express the fact that one simple periodic quantity lags 90 degrees behind another. The electromotive force of self-induction is said to be in quadrature with the effective electro- motive force or current. Quadruplex Telegraphy, Bridge Method of - (See Telegraphy, Quadruplex, Bridge Method of.) Qualitative Analysis. (See Analysts, Qualitative?) Quality or Timbre of Sound. (See Sound, Quality or Timbre of.) Quantitative Analysis. (See Analysis, Quantitative?) Qua.] 430 [Rad. Quantity Armatnre. (See Armature, Quantity!) Quantity, Connection of Battery for (See Battery, Connection of, for Quantity) Quantity Efficiency of Storage Battery. (See Efficiency, Quantity, of Storage Bat- tery) Quantity, Unit of Electric A definite amount or quantity of electricity called the coulomb. (See Coulomb?) Although the exact nature of electricity is un- known, yet, like a fluid (a liquid or gas), electricity can be accurately measured as to quantity. A current of I ampere, for example, is a- current in which one coulomb of electricity passes in every second. A condenser of the capacity of I farad, is large enough to hold I coulomb of electricity if forced into the condenser under an electro- motive force of I volt. (See Capacity, Electro- static. Farad. Volt. Ampere.} Quiet Arc. (See Arc, Quiet) Quiet Discharge. (See Discharge, Si- lent) Quicking Solution. (See Solution* Quicking) R. A contraction used for ohmic resist- ance. p. A contraction used for specific resist- ance. Radial Armature. (See Armature, Radial) Radially Laminated Armature Core. (See Core, Armature, Radially-Laminated) Radiant Energy. (See Energy, Radiant) Radiant Matter. (See Matter, Radiant, or Ultra-Gaseous) Radiate. To transfer energy by means of waves. Radiating. Transferring energy by means of waves. Radiation. Transference of energy by means of waves. When an elastic body is set into vibration, whether it be the vibrations that produce light, heat or electricity, energy is charged on the body, and the body will then continue to vibrate until it imparts to some medium surrounding it an amount of energy exactly equal to that orig- inally imparted to itself. In the case of a sonorous body the energy is transferred from the vibrating body to the air around it. For example, in the case of an elastic metallic wire set into vibration, the wire will con- tinue to vibrate until it does as much work on the surrounding air as was originally done on it, in order to set it into vibration. In the case of a heated body the energy is transferred from the body to the luminilerous- ether around it. For example, in the case of the same wire heated above the temperature of the air, the energy imparted to the molecules of the metal by the source of heat causes them to move towards and from one another. These to and- fro motions of the molecules cause the surrounding ether to be set into waves, and as much energy is imparted to the ether, as was originally imparted to the wire in order to heat it. In the case of a luminous body the energy is transferred from the body to the luminiferous ether. For example, if the wire is heated to luminosity by a certain amount of energy im- parted to it, the surrounding ether is now set into waves of both light and heat, which differ from one another only in their wave length, and the luminous body will continue to radiate light and heat until it imparts to the surrounding ether an amount of energy exactly equal to that originally imparted to it. So, too, in the case of a body charged with electricity. If disruptively discharged, the im- pulsive rush of electricity, so produced, causes the energy charged on it to be radiated as electro- magnetic waves into the surrounding ether. The discharging body is, to all intents and purposes, in the same condition as the vibrating elastic wire, and dissipates or radiates its energy in much the same manner. Radiation, Electro-Magnetic The sending out in all directions from a con- Had.] 431 [Rad. ductor, through which an oscillating discharge is passing, of electro-magnetic waves in all respects similar to those of light except that they are of much greater length. (See Elec- tricity, Hertz's Theory of Electro-Magnetic Radiations or Waves.) Radiation of Electricity. (See Electri- city, Radiation of.) Radiation of Lines of Force. (See Force, Lines of, Radiation of.) Radical, Compound A group of unsaturated atoms. A group of elementary atoms, some of the bonds of which are open, or not connected or joined with the bonds of other atoms. (See Atomicity?) For example, hydroxyl, HO, is a compound radical, with one of the two bonds of the diad oxygen atom, open or unsaturated. Radical, Simple An unsaturated atom with its bond or bonds free. A single unsaturated atom as distinguished from an unsaturated group of atoms. Radicals. Unsaturated atoms or groups of atoms, in which one or more of the bonds are left open or free. Radicals are either Simple or Compound. The radical may be regarded as the basis to which other elements may be added, or as the nucleus around which they may be grouped. Thus H 3 O, forms a complete chemical molecule, because the bonds of all its constituent atoms are saturated, thus H O H. But H O , or hydroxyl, is a radical, because its oxygen atom possesses one unsaturated or free bond. By combining with the radical (NO 2 ), it forms nitric acid, thus H O (NO 2 ) or II NO 8 . During electrolysis, the molecules of the elec- trolyte are decomposed into two groups of simple or compound radicals, called ions. These ions are respectively electro-positive and electro-negative, and are called kathions and onions. (See Ions. Electrolysis . ) Radiometer, Crookes' An appara- tus for showing the action of radiant matter in producing motion from the effects of the reaction of a stream of molecules escaping from a number of easily moved heated sur- faces. (See Matter, Radiant, or Ultra- Gaseous^) Radiometer, Electric, Crookes A radiometer in which the repulsion of the molecules of the residual atmosphere takes place from electrified instead of from heated surfaces. (See Radiometer, Crookes .) Radio-Micrometer, Boys' An elec- trical apparatus for measuring the intensity of radiant heat. The action of the radio-micrometer depends on the deflection, by a magnetic field, of a suspended thermo-electric circuit composed of three metals, viz. : two bars of antimony and bismuth, or of their alloys, which are soldered side by side to the end of a minute disc or strip of copper foil, as shown in Fig. 457. This disc or foil of copper is Fi S- 437- Boys' Radio-Micrometer. provided for the purpose of receiving the radia- tion that is to be measured. The upper ends of the thermo-couple are soldered to the ends of a long, narrow, inverted U-shaped piece of copper wire, which completes the thermo-electric circuit. The absorption of radiant energy by the cop- per disc connected to the thermo-electric couple produces an electric current, and the circuit, being suspended in a magnetic field, is at once deflected to a degree dependent on the intensity of the radiation, or of the current generated at the thermo-electric junction. The means adopted for the suspension of t e system are s'lown in Figs. 457 and 458. A small piece of straight wire is soldered to the up- Rad.j 432 [Rai. QUARTZ FIBRE GLASS TUBE COPPER. WIRE per end of the copper stirrup, which completes the thermo-electric circuit. This wire is cemented to the lower end of a glass tube, the upper end of which is provided with a mirror, and the whole suspended, as shown, by a quartz fibre in the field of a powerful magnet. In a radio-micrometer made by Prof. Boys, the minuteness of the suspended circuit may be judged from the following ac- tual dimensions, viz.: Thermo- electric bars, x ^ x ^ ff inch ; copper circuit of number 36 copper wire, I inch long and about ^,5 inch wide ; copper heat-receiving surface, black- ened on the face exposed to the radiation, ^ inch in diameter, or J x ^ inch; receiver, ^ inch square, yfa inch thick ; quartz fibre 4 inches long, -^-^ inch in diameter. This instrument, when pro- perly adjusted for extreme sen- sitiveness, should give clear in- c / o ,' dications when the blackened \Cti surface is warmed but the Fig, 438. Boys' sircffffffff degree Centigrade. It Radio-Micrometer. will respond to the heat radiated on the surface of a half penny from a candle flame at a dis- tance of 1,530 feet. In order to avoid the disturbance due to the magnetic qualities of the antimony and bismuth bars, the central portions of the metallic block, inside which the system is suspended, is made of iron, as shown by the heavier shading in Fig- 457- This mass of iron serves as a magnetic screen to the thermo-electric bars, but permits the action of the field on the circuit. Radiophone. A name sometimes given to the photophone. (See Photophone) Radiophony. The production of sound by a body capable of absorbing radiant energy when an intermittent beam of light or heat falls on it. The action of radiant energy, when absorbed by matter, is to cause its expansion by the conse- quent increase of temperature. This occurs even when the body is but momentarily exposed to a flash of light, but the instantaneous expansion thus produced immediately dies away, and by itself is indistinguishable. If, however, a suffi- ciently rapid succession of such flashes fall on the body, the instantaneous expansions and contrac- tions produce an appreciable musical note. The sounds so produced have been utilized by Bell and Tainter in the construction of the Phtto- phone. (See Photophone.') Railroad, Electric A railroad, or railway, the cars on which are driven or pro- pelled by means of electric motors connected with the cars. The electric current that drives the motor is derived either from storage batteries placed on the cars, or from a dynamo-electric machine, or battery of dynamo-electric machines, conveniently situated at some point on the road. The current from the dynamo is led along the line by suitable electric conductors and is passed into the electric motor as the car runs along the tracks in various ways, viz.: Systems for the electric propulsion of cars may, therefore, be divided into the dependent system, in which the driving current is obtained from conduc- tors placed somewhere outside the cars, and the independent system, where the current is derived from primary or secondary batteries placed on the cars. (See Railroads, Electric, Dependent System of Motive Power for. Railroads, Electric, Independent System of Motive Power for.} In the dependent system, the conductors which supply the car with current are placed either overhead, on the surface of the road-bed or un- derground. Thus arise three divisions of the dependent system: (I.) The Surface System. (2.) The Underground System. (3. ) The Overhead System. (i.) The Surface System, By placing one or both rails in the circuit of the dynamo and taking the current from the tracks by means of sliding or rolling contacts connected with the motor. (2.) The Underground System. By placing the conducting wires parallel to each other in a longi- tudinally slotted underground conduit in the road- bed, and provided with two central plates, insu- lated from one another and connected respectively to the motor terminals, and taking the current by means of a traveling brush or roller, called a plow, sled or shoe. On the movement of the car over the track, these traveling contacts touch the Kai.j 433 [Rai. two parallel line conductors in the> conduit and Safiine. ) Recoil Circuit. (See Circuit, Recoil.} Record, Chronograph A record made by means of a chronograph for the pur- pose of measuring and recording small inter- vals of time. (See Chronograph, Electric?) Record, Gramophone The irregular indentations, cuttings or tracings made by a point attached to the diaphragm spoken against, and employed in connection with the receiving diaphragm for the reproduction of articulate speech. Record, Graphophone The record made by the movement of the diaphragm of the graphophone. (See Phonograph.} Record, Phonographic The record produced in a phonograph, for the subse- quent reproduction of audible articulate speech. Record, Telephonic The record produced by the diaphragm of a receiving telephone. Various methods have been proposed for ob- taining telephonic records, but none of them have yet been introduced into actual commercial use. Recorder, Chemical, Bain's An ap- paratus for recording the dots and dashes of Rec.] 441 [Bee. a Morse telegraphic dispatch, on a sheet of chemically prepared paper. A fillet of paper soaked in some chemical sub- stance, such as ferro-cyanide of potassium, is moved at a uniform rate between the two ter- minals of the line, one of which is iron tipped, so that on the passage of the current, a blue dot, or a dash, will be made on the paper according to the length of time the current is passing. In order to insure a moist condition of the paper fillet, some deliquescent salt, like ammonium nitrate, is generally mixed with the ferro-cyanide of potassium. Fig. 467. Bain Recorder '. A Bain recorder is shown in Fig. 467. A, is a drum of brass, tinned on the outside. The paper fillet is drawn from the roll and kept pressed against the cylinder A, by a small wooden roller B. The needle, which is a metallic point, is placed in connection with one end of the line wire, and the brass drum is connected with the other end through the earth. Care must be ob- served to connect the needle point with the posi- tive electrode, as otherwise the paper will not be marked. (See Electrolysis.} The Bain recorder is now almost entirely re- placed by the Morse sounder. (See Sounder, Morse Telegraphic.} Recorder, Morse An apparatus for automatically recording the dots and dashes of a Morse telegraphic dispatch, on a fillet of paper drawn under an indenting or marking point on a striking lever, connected with the armature of an electro-magnet. This apparatus is sometimes called a Morse register. The Morse recording or registering apparatus is shown in Fig. 468. The paper fillet passes between a pair of rollers r, driven by the clockwork W. The upper roller is provided with a groove, so that the movement of the stylus at the b.nt end of the lever L, by the electro-magnet M, moving its armature attached to the lever L, may indent or emboss the paper fillet. When no current is passing, the armature of the magnet and the lever L, are drawn back bj the action of an adjustable spring at n. Fig. 468. Morse Recorder. In the drawing, the ordinary Morse sounder is shown on the right. The sounder has almost entirely replaced the recording apparatus. Recorder, Siphon An apparatus for recording in ink on a sheet of paper, by means of a fine glass siphon supported on a fine wire, the message received over a cable. One end of the siphon dips in a vessel of ink. The record is received on a fillet of paper moved mechanically under the siphon. The ink is dis- charged from the siphon by electric charges im- parted to the ink by a static electric machine. Fig. 469. The Siphon Recorder. In the annexed sketch of the siphon recorder, Fig. 469, a light rectangular coil b b, of very fine wire, is suspended by a thin wire f f, between the poles N, S, of a powerful compound permanent magnet, and moving on the vertical axis of the supporting wire f f, and adjustable as to tension, at h. A stationary soft iron core a, is magnetized SIPHON RECORDER Fig. 470. Record of Siphon Recorder. by induction and strengthens the magnetic field of N, S. The cable current is received by the Rec.] 442 [Ref. coil b b, through the suspending wire f f", and is moved by it to the right or the left, according to its direction, to an extent that depends on the current strength. The fine glass siphon n, which dips into a reservoir of ink at m, is capable of movement on a vertical axis 1, and is moved backwards or for- wards, in one direction by a thread k, attached S E T T L ED Fig, 471- Record of Siphon Recorder. to b, and in the opposite direction by a retractile spring attached to an arm of the axis 1. As the paper is moved under the point of the siphon, an irregular curved line is marked thereon. Two records as actually received by a siphon, recorder are shown in the Figs. 470 and 471. Movements upwards correspond to the dots, and downwards to dashes. Rectification of Alcohol, Electric (See Alcohol, Electric Rectification of.} Rectified. Turned in one and the same direction. The alternate currents in a dynamo-electric machine are rectified or caused to flow in one and the same direction by means of a commutator. The word commuted, generally used in this connection, would appear to be preferable to the word rectified. (See Commutator.') Rectilinear Co-ordinates, Abscissa of (See Abscissa of Rectilinear Co-ordinates!) Rectilinear Current. (See Current, Rec- tilinear^) Red Heat (See Heat, Red.) Red Hot. (See Hot, Red) Redncteur or Resistance for Voltmeter. A coil of known resistance as compared with the resistance of the coils of a voltmeter, and connected with them in series for the purpose of increasing the range of the instru- ment. (See Voltmeter) Redncteur or Shunt for Ammeter. A shunt coil connected in multiple with the coils of an ammeter for the purpose of changing the value of the readings. The ratio of the resistance of the reducteur and the ammeter coils is known. A reducteur in- creases the range of current measured by the am- meter. Refining of Metals, Electric The refining of metals by the application of elec- trolysis. When certain precautions are taken, metals thrown down from their solutions, are obtained in a chemically pure condition. This fact is utilized in the electrical refining of metals. If, for exam- ple, a plate of impure copper is to be refined electroly tically, it is used as the anode of a copper bath, and placed opposite a thin plate of pure cop- per forming the kathode. The passage of the current gradually dissolves the copper from the plate at the anode, and deposits it in a chemically pure condition on the plate at the kathode. Somewhat similar principles are employed for electrically refining other metals. Reflect. To throw off from a surface, ac- cording to the laws of reflection, as of waves in an elastic medium. (See Reflection, Laws of) Reflecting. Throwing off from a surface, according to the laws of reflection. (See Reflection, Laws of) Reflecting Galvanometer. (See Gal- vanometer, Reflecting) Reflection. The throwing back of a body or wave from a surface at an angle equal to that at which it strikes such surface. (See Reflection, Laws of) Reflection, Laws of The laws gov- erning the reflection of light (l.) The angle of reflection, or the angle in- cluded between the reflected ray and the perpen- dicular to the reflecting surface at the point of incidence, is equal to the angle of incidence, or the angle included between the striking ray and the perpendicular to the reflecting surface at the point of incidence. (2.) The plane of the angle of incidence co- incides with the plane of the angle of reflection. Reflection of Electro-Magnetic Wares. (See Waves, Electro-Magnetic, Reflection, of) Reflection of Induction. (See Induc- tion, Reflection of) Reflector. A plane or curved surface, capable of regularly reflecting light. Reflector, Parabolic A reflector, Ref.] 443 [Reg. w or mirror, the reflecting surface of which is a paraboloid, or such a surface as would be obtained by the revolution of a parabola about its axis. A parabolic curve, which may be regarded as a section of a parabola, is shown in Fig. 472. A parabola has the following properties: If lines F P, F P, etc., be drawn from the point F, called the focus, to any point, P, P, etc., in the curve, and the lines Pp, Pp, Pp, etc., be then drawn severally parallel to the axis, V M, then all such angles, F P p, F P p, will be bisected by verticals to tangents at the point P, P, and P. Therefore, if a light be placed at the focus of a parabolic reflector, all the light reflected from the surface of the parabola will pass off sensibly par- allel to the axis V M. In Locomotive Headlights, a lamp is placed at the focus of a parabolic reflector, and the parallel beam so obtained is utilized for the illumination of the track. In a search light an electric arc lamp is placed at the focus of a parabolic reflec- tor, or at the focus of a lens. A parabolic reflector is used for search lights, some- Fig. 472. Parabolic times in connection with an Reflictor. arc lamp. A focusing arc lamp must be used for this purpose, so as to maintain the voltaic arc at the focus of the parabolic reflector, notwithstand- ing the unequal consumption of the positive and negative carbons. (See Arc, Voltaic,} Refract. To change the direction of waves in any elastic medium in accordance with the laws of refraction. (See Refraction^) Refracting. Changing the direction of waves in an elastic medium in accordance with the laws of refraction. Refraction. The bending of a ray of sound, light, heat, or electro-magnetism at the surface of any medium whose density differs from that through which such ray was previously passing. Rays of sound, light, heat or electro-mag- netism are transmitted or propagated in straight lines as long as the density of the homogeneous medium through which they are pissing under- goes no change. That is, as long as the medium is homogeneous or isotropic. (See Medium, Iso- tropic.) As the rays enter the surface of a medium which differs in density from that through which they have been passing, they are bent or refracted at the surface of such a medium. This bending takes place towards a perpen- dicular to the refracting surface at the point of in- cidence, when the medium into which the rays are entering is of greater density than that they are leaving, and from the perpendicular when the medium they are entering is of less density than that they are leaving. The refraction or bending of the ray is caused by the difference in the velocity with which the waves are propagated through the two media. There is no refraction or deviation when the two rays enter the new medium at right angle > to its surface, or when there is no angle of inci- dence. Refraction, Double The property possessed by certain substances of splitting up a ray of light passed through them into two separate rays, and thus doubly refracting the ray. Certain specimens of calc spar possess the prop- erty of double refraction. Each of the two rays into which the original ray is separated is polar- ized. Such calc spar is called doubly refracting calc spar. Refraction, Double, Electric The property of doubly refracting light acquired by some transparent substances while in an electrostatic or electro-magnetic field. Transient or momentary powers of double refraction, acquired by a transparent sub- stance while placed in an electric field. The intensity of double refraction is propor- tioned to the square of the electric force. The action of an elect-ic field in endowing a substance with the power of double refraction while kept in such field, is due to the strain pro- duced by the electrostatic stress of the field. A similar transient power of double refraction is acquired by many bodies when subjected to the strain produced by a simple mechanical stress. Refreshing Action of Current (See Ac- tion, Refreshing, of Current '.) Region, Extra-Polar A term ap- plied in electro-therapeutics to the region Reg.] 444 [Reg. which lies outside or beyond the therapeutic electrode. The term extra-polar region is used in contra- distinction to polar region. (See Region, Polar.) Region, Polar A term applied in electro-therapeutics to that region or part of the body which lies directly below the thera- peutic electrode. Register, Double-Pen Telegraphic A telegraphic register provided with two separate styluses or pens for recording the telegraphic message on a fillet of paper. (See Register, Telegraphic?) Register, Morse A name sometimes given to a Morse recorder. (See Recorder, Morse?) Register, Telegraphic An appa- ratus employed at the receiving end of a tele- graphic line for the purpose of obtaining a permanent record of the telegraphic dispatch. The telegraphic register consists essentially of means whereby a fillet or tape of paper is drawn mechanically under a pen or stylus attached to the armature of an electro-magnet and moving therewith. The pen or stylus presses against the paper whenever the armature is attracted to the elec- tro-magnet, and is held there while the cur- Fig. 473 /** Writing Register. rent is passing through the coils of the electro- magnet. By these means the dots and dashes of the telegraphic alphabet are recorded on the paper fillet as embossed or printed dots and dashes. The Morse register is an apparatus of this description. (See Recorder, Morse.) A form of ink-writing telegraphic register is shown in Fig. 473. It is self -starting. Register, Time, for Railroads A telegraphic recording apparatus or register designed to record all telegraphic messages transmitted over a line. The record is received on an endless band or fillet of paper. It is useful in case of disputes as to the time certain messages were sent over the line. Register, Watchman's Electric A device for permanently recording the time of a watchman's visit to each of the dif- ferent localities he is required to visit at stated intervals. These registers are of a variety of forms. They consist, however, in general, of a drum or disc of paper driven by clockwork, on which a mark is made by a stylus or pencil, operated on the clos- ing of a circuit by the pressing of a push button or the pressing of a key by the watchman at each station. Registering Apparatus, Electric (See Apparatus, Registering, Electric?) Registering Electrometer. (See Elec- trometer, Registering?) Regulable, Automatically Capa- ble of being automatically regulated. (See Regulation, Automatic?) Regulate, Automatically To regu- late in an automatic manner. (See Regula- tion, Automatic?) Regulation, Automatic Regulation automatically effected. Regulation, Automatic, of Dynamo-Elec- tric Machine Such a regulation of a dynamo-electric machine as will automati- cally preserve constant either the current or the potential difference. The automatic regulation of dynamo-electric machines may be accomplished in the following ways, viz.: (I.) By a Compound Winding of the Machine. This method is particularly applicable to con- stant-potential machines. By this winding, the magnetizing effect of the shunt coils is maintained approximately constant, while that of the series eoils varies proportionally to the load on the ma- chine. The series coils are sometimes wound close to Reg.] 445 [Beg- the poles of the machine, and the shunt coils nearer the yoke of the magnets. Custom, how- ever, varies in this respect, and very generally the shunt coils are placed nearer the poles than the series coils. (See Machine, Dynamo-Electric, Compound- IVoitnd.) (2.) By Shifting the Position of the Collecting Brushes. In the Thomson-Houston system of current regulation, the current is kept practically con- stant by the following devices: The collecting brushes are fixed to levers moved by the regula- tor magnet R, as shown in Fig. 474, the arma- ture of which is provided with an opening for the entrance of the paraboloidal pole piece A. A dash-pot is provided to prevent too sudden move- ment. When the current is normal, the coil of the regulator magnet is short-circuited by contact points at S T, which act as a shunt of very low re- sistance. These contact points are operated by the solenoid coils of the controller, traversed by the main current. The cores of this solenoid are suspended by a spring. When the current be- comes too strong, the contact point is opened, and the current, traversing the coil of the regu- lar magnet A, attracts its armature, which shifts tbe collecting brushes into a position in which a smaller current is taken off. A carbon shunt, r, of high resistance, is pro- vided to lessen the spark at the contact points S T, which occurs on opening the circuit. Fig. 474. Thomson-Houston Regulator. In operation the contact points are continually opening and closing, thus maintaining a practi- cally constant current in the external circuit. (3.) By the Automatic Variation of a Resist- ance shunting the field magnets of the machine, as in the Brush system. In Fig. 475 the variable resistance C, forms a part of the shunt circuit around the field mag- nets F M. This resistance is formed of a pile of carbon plates. On an increase of the current, such, for example, as would result from turning out some of the lamps, the electro- magnet B, placed in the main circuit, attracts its armature A, and, compressing the pile of carbon plates C, lowers their resistance, thus diverting a propor- tionally larger portion of the current from the field magnet coils F M, and maintaining the cur- rent practically constant. In some machines the same thing is done by hand, but this is objectionable, since it requires the presence of an attendant. (4.) By the Introduction of a Variable Resist- ance into the shunt circuit of the machine, as in the Edison and other systems. Fig- 47 S- The Brush Regulator. This resistance may be adjusted either auto- matically by an electro-magnet whose coils are in an independent shunt across the mains, or may be operated by hand. In Fig. 476, the variable resistance is shown at R, the lever switch being in this case operated by hand whenever the potential rises or falls be- low the proper value. Fig. 476. The Edison Regulator. The machine shown is thus enabled to main- tain a constant potential on. the leads to which the lamps L, L, L, etc., are connected in multiple arc. (5.) Dynamometric Governing, in which a series dynamo is made to yield a constant cur- rent by governing the steam engine that drives it, by means of a dynamometric governor. This governor operates by maintaining a constant torque or turning moment, instead of by means of Reg.] 446 [ReU the usual centrifugal governor which maintains a constant speed. (6.) Electric Governing of the Driving Engine, in which the governor is regulated by the cur- rent itself instead of by the speed of rotation, as usual. Regulation, Hand Such a regula- tion of a dynamo-electric machine as will pre- serve constant, either the current or the potential, said regulation being effected by hand as distinguished from automatic regu- lation. Regulator, Automatic A device for securing automatic regulation as dis- tinguished from hand regulation. (See Regulation, Hand. Regulation, Automatic?) Regulator, Hand A resistance box, the separate coils or resistances of which can be readily placed in or removed from a circuit by means of a hand-moved switch. The term hand regulator is used as distin- guished from automatic regulator. (See Regu- lator, Automatic. Regulation, Automatic.} Regulator Magnet. (See Magnet, Regu- lator) Regulator, Monophotal Arc-Light A term sometimes employed for an electric arc lamp in which the whole current passes through the arc-regulating mechanism, and which is usually operated singly in circuit with a dynamo. Regulator, Polyphotal Arc-Lamp A regulator for an arc lamp suitable for maintaining a number of lamps in series cir- cuit with the dynamo. Polyphotal regulators differ from monophotal regulators in that their regulating electro-mag- nets are energized by a shunt circuit around the electrodes of the lamp, while in monophotal regu- lators such electro-magnets are placed in the di- rect circuit The terms monophotal and poly- photal are not generally used in America. Reguline Electro-Metallurgical Deposit. (See Deposit, Electro-Metallurgical, Reg- uline) Rejuvenation of Luminescence. (See Luminescence, Rejuvenation of) Relative Calibration. (See Calibration, Relative) Relay. An electro-magnet, employed in systems of telegraphy, provided with contact points placed on a delicately supported arma- ture, the movements of which throw a battery, called the local battery, into or out of the circuit of the receiving apparatus. A relay is sometimes called a receiving magnet. Fig. 477 . Telegraphic Relay. The use of a relay permits much smaller cur- rents to be used than could otherwise be done, since the electric impulses, on reaching a distant station, are required to do no other work than- attracting a delicately poised movable contact, and thus, by throwing a local battery into the circuit of the receiving apparatus, to cause such local battery to perform the work of register- ing. Its use is especially required in the Morse system of telegraphy in order 10 cause the sounder to be distinctly heard. A form of relay that is much used is shown in FIJI. 477- The electro- magnet M, is wound with many^ turns of very fine wire. In the form used by the Western Union Telegraph Company, there are about 8, 500 turns, having resistance of 150 ohms. A screw m, is provided for moving the electro- magnet M, a slight distance in or out, for the pur- poses of adjustment A semi-cylindrical arma- ture A, of soft iron, is attached to the insulated armature lever a, the lower end of which is sup- ported by a steel arbor, which is pivoted between two set screws. A retractile spring S', regulable at S, is pro- vided for moving the armature away from the electro-magnet. There are four binding posts, two of which are placed in the circuit of the electro-magnet, and two in that of the local bat- tery. The ends of the line wire are connected with the former, and the receiving instrument placed in the circuit of the latter. A platinum- Rel.] 447 [Rel. contact is placed on the end of a screw supported at F, opposite a similar contact, near the end a, of the armature lever. The contact is regulable by means of a screw c. On the energizing of the electro -magnet, the attraction of its armature closes the platinum contact, and, by thus completing the circuit of the local battery, causes an attraction of the armature of the receiving apparatus. On the cessation of the current in the main line, the spring S , pulls the armature away from the magnet, breaks the circuit of the local battery, and thus permits a similar spring on the receiving instrument to pull its armature away. Thus all the movements of the armature of the relay are reproduced with in- creased intensity by the armature of the receiving instrument. The connections of the relay to the local bat- tery and the registering apparatus, will be better understood from an inspection of Fig. 478, which represents a form of relay much used in Germany. Relay, Differential A telegraphic ' 47 S. Telegraphic Relay, German Pattern. The retractile spring f, is regulated by the up- and-down movements of its lower support, which slides in the vertical pillar S. The line wire is shown at m m, connected at one end to earth by a ground wire. . The registering apparatus R, is connected in the circuit of the local battery L, as shown. The contacts are made by the end B, of the lever B B', attached to the armature A, of the electro- magnet M M. Relay Bell. (See Sell, Relay, Electric^ Relay, Box-Sounding Telegraphic - A relay the magnet of which is surrounded by a resonant case of wood for the purpose of increasing the intensity of the sound made by the armature of the magnet. A form of box-sounding relay is shown m Fig. 479- V Box- Sounding Relay relay containing two differentially wound coils of wire on its magnet cores. When the currents which pass through these two coils are of the same strength, there is no movement of the armature, since the fields of the two coils neutralize each other. The differencial relay is used in the differential method of duplex and quadruplex telegraphy. (See Telegraphy, Duplex Differential Method of. Telegraphy, Quadruplex Differential Method of '.) Relay Magnet. A name sometimes given to a relay. (See Relay.) Relay, Microphone A device for automatically repeating a telephonic message over another wire. Fig. 480. Microphone Relay. A form of microphone relay is shown in Figs. 480 and 481. Several minute microphones mounted on the Fig. 481. Microphone Relay. diaphragm of the telephone whose message is to be repeated, so vary the resistance of a local bat- tery included in their circuit as to automatically repeat the articulate speech received. The microphones may DC connected either in Rel.] 448 [Bel. multiple arc or in series, as shown respectively to the left and right in Fig. 480. Relay, Pocket Telegraphic A form of telegraphic relay of such small dimensions as to permit it to be readily carried in the pocket. Relay, Polarized A telegraphic re- lay provided with a permanently magnetized armature in place of the soft iron armature of the ordinary instrument. In the form of polarized relay shown in Fig. 482, N S, is a steel magnet, whose magnetism is consequently permanent, with its north and south poles at N, and S, respectively. The cores of the electro-magnet m, m', are of soft iron, and, since they rest on the north pole of the permanent steel magnet, the poles, brought very near to- gether by the armatures at n, n', will be of the same polarity as N, when no current is passing through the coils m, m' ; but when such current does pass, one of these poles becomes of stronger north polarity, while the other changes its polar- ity to south. By these means to-and fro movements of the armature lever, with its contact point, are effected without the use of a retractile spring ; movement in one direction occurring on the closing of the circuit due to the electro-magnetism developed Fig. 482. Polarized Relay. by the coils m, m', and movement in the opposite direction, on the losing of this magnetism on breaking the circuit, by the permanent magnet- ism of the steel magnet N S. These movements are imparted to the soft iron lever c, c', pivoted at B, and passing between the closely approached soft iron poles at n, n'. This lever rests at the end c', against a contact point when moved in one direction, and against an in- sulated point when moved in the opposite direc- tion. It rests against the insulated point when no current is passing through the coils m, m'. If the armature lever were placed in a position exactly midway between the poles n, and n', it would not move at all, being equally attracted by each; but if moved a little nearer one pole than the other, it would be attracted to, and rest against, the nearer pole. When alternating currents are employed on the line, the lever c, c', must be adjusted as nearly as possible in the middle of the space between n and n', in which case it will remain on the side to which it was last attracted, until a current in the opposite direction moves it to the other side. Fig. 483. A Detail of the Polarized Relay. The space between the magnet poles n, n', and the contacts of the armature lever at D, and D', are shown in detail in Fig. 483, which is a plan of Fig. 482. The binding posts for the line battery are shown at L B, I, and 2, and those for the local battery at A and B. The dotted lines show the connections. Since the polarized relay dispenses with the re- tractile spring, it is far more sensitive than the ordinary instrument. Once adjusted, no further regulation is required, in which respect it differs very decidedly from non-polarized relays. There are other forms of polarized relays, but the above will suffice to illustrate the general principle of their operation. Relay Shunt, Steam's (See Shunt, Relay, Steam's.} Reluctance, Magnetic A term re- cently proposed in place of magnetic resist- ance to express the resistance offered by a Rel.] 449 [Rep. medium to the passage through its mass of lines of magnetic force. The term reluctance, in the sense of resistance to passage of lines of magnetic force, has been proposed in place of resistance, for the purpose of carrying out the conception of regarding the flow of lines of force in a magnetic circuit as being due to a magneto-motive force, and being opposed by a reluctance of the substances form- ing such circuit to the passage of such lines. According to this conception, The magnetic flux = The magneto-motive force The reluctance. Reluctance, Magnetic, Unit of Such a magnetic reluctance in a closed cir- cuit that permits unit magnetic flux to traverse it under the action of unit magneto- motive force. In present practical work reluctances vary from 100,000 to 100,000,000 of the practical units. Reluctivity. A term proposed for mag- netic reluctance. (See Reluctance, Mag- netic?) This term is not generally adopted. Removable Key Switch. (See Switch, Removable Key) Renovation of Secondary Cell. (See Cell, Secondary or Storage, Renovation of,) Renovation of Secondary or Storage Cell. (See Cell, Secondary or Storage, Renovation of.) Reofore. A rheophore. (See Rheophore.) Repeaters, Telegraphic Tele- graphic devices, whereby the relay, sounder or registering apparatus, on the opening and closing of another circuit, with which it is suitably connected, is caused to repeat the signals received. Repeaters are employed to establish direct communication between very distant stations, or to connect branch lines to the main line. Fig. 484, shows Wood's Button Repeater. This repeater consists simply of a three-point switch L, capable of being placed on the points I, 2 and 3 ; and a ground switch at 4. The circuits are arranged between the sounders S, S', relays M, M', main batteries B, B', and the two main lines E, and W, in the manner shown. Fig. 484. Wood's Button Repeater. If the lever L, is in the position shown in the drawing, the lines E and W, form independent circuits. If the ground switch 4 is closed, and the lever L, is placed on 2, 2, the eastern line repeats into the western. If the lever L, is placed on the plates 3, 3, the western line repeats into the eastern. This repeater is non- automatic and can be worked in but one direction at a time ; moreover, it requires the services of an attendant. The automatic repeater can be operated in both directions, and dispenses with the constant ser- vices of an attendant at the repeating station. In sending a dispatch through a repeater, the dots and dashes are prolonged so as to give the lever of the repeating instrument time in which to move backwards and forwards. Fig. 48s- Hick's Automatic Button Repeater. In Hick's Automatic Repeater, shown in Fig. 485, the switch or circuit- changer is automatic in its action. The relay magnets are shown at M, M', the sounders at R and R' ; f, f, are platinum con- tacts operated by levers 1 and 1', and L and L', are extra local magnets, that act on armatures Rep.] 450 [Rep. placed directly opposite the armatures of the relay magnets. The extra local magnet L, is cut out of the circuit of B', the extra local battery, when the main circuit is broken, and the armature is in contact with c. As soon as this happens, how- ever, the spring s, drawing away the armature, and thus opening the short-circuit of no resist- ance between c and a, establishes a circuit through L. On a, coming in contact with c, the circuit is again broken. The tension of the spring s, is so regulated that a very rapid vibration of a, is maintained so con- stantly, that it is impossible to close the main cir- cuit when L, is not cut out. The armature a, will therefore respond to very weak impulses of the relay magnet. On breaking the western main circuit N, the lever a, vibrates very rapidly. The lever 1, of the sounder R, first breaks the circuit of L, and after- wards that of the eastern main circuit E, which passes through M. Both L' and M', being broken, a slight tension of s', will hold a, in place, thus avoiding the breaking of the western main circuit through the closing of the local cir- cuit through R. On the closing of the western circuit, the reverse of these operations occurs. The author has taken the above explanation mainly from Pope's work on " Modern Practice of the Electric Telegraph." Repeating Sounder. (See Sounder, Re- peating?) Replenisher. A static influence machine devised by Sir William Thomson for charging the quadrants of his quadrant electrometer. Two brass carriers C and D, shown in Fig. 486, are electrically fixed to the end of the vulcanite rod E, which is capable of ro- tation by the thumb screw at M, in the direction shown by the arrow. Hol- low metal half-cylinders, p . A and B, act as inductors, a strip of brass fixed around Fig. 486. The Replen- the edges of a piece of vul- isher - canite P, connecting the metallic springs S, and S', as shown. The action of the replenisher is readily under- stood from the following considerations, as sug- gested by Ayrton in his " Practical Electricity " : A and B, Fig. 487, are two insulated hollow metallic vessels having a small difference of po- tential between them, A, being the higher. C, and D, are two small uncharged conductors held by insulating strings. If C and D, be held near A and B, as shown, the potential of C, will, by induction, be raised somewhat above that of D, so that when connected by a conductor, such as fie metallic wire W, a small quantity of positive electricity will flow from C, to D, thus leaving D, positively, and C, negatively charged. If, now, C and D, are removed from W. and placed in the bottom of B and A, as shown in Fig. 488, the difference of potential between A, and B, will be thereby increased, and if they are then withdrawn, and totally discharged, and Fig. 487. Action of Replenisher. again placed in the first position shown, an ad- ditional charge can be given to A and B, and this can be repeated as often as desired. In the replenisher, A and B, correspond to the vessels A and B ; the brass carriers C and D, to the balls C and D, and the spring S S, and M, Fig. 48 8. Action of Replenisher. to the wire W. No initial charge need be given to A and B, since they are invariably found to Hep.] 451 [Res. be at a sufficient difference of potential to build up the charge. Replenishes Carriers of The moving conductors of a replenisher which carry the charges and thus permit of an ac- cumulation of such charges. (See Re- plenisher} Repulsion, Electric The mutual driving apart or tendency to mutually drive apart existing between two similarly charged bodies, or the mutual driving apart of similar electric charges. Repulsion, Electro-Dynamic The mutual repulsion between two electric circuits whose currents are flowing in opposite direc- tions. Parallel currents flowing in opposite directions repel one another, because their lines of magnetic force have the same direction in adjoining parts of the circuit. (See Dynamics, Electro.) Repulsion, Electro-Magnetic The mutual repulsion produced by two similar electro-magnetic poles. Repulsion, Electrostatic The mutual repulsion produced by two similar electric charges. Repulsion, Magnetic The mutual repulsion exerted between two similar mag- netic poles. Repulsion, Molecular The mutual repulsion existing between molecules arising from their kinetic energy. (See Matter, Ki- netic Theory of.} Residual Atmosphere (See Atmosphere, Residual?) Residual Charge. (See Charge, Resid- ual.} Residual Magnetism. (See Magnetism, Residual} Resin. A general term applied to a variety of dried juices of vegetable origin. Resins are, in general, transparent, inflamma- ble solids, soluble in alcohol, and, in general, excellent non-conductors of electricity. Rosin is one of the varieties of resin. Resinous Electricity. (See Electricity, Resinous} Resistance. Something placed in a circuit for the purpose of opposing the passage or flow of the current in the circuit or branches of the circuit in which it is placed. The electrical resistance of a conductor is that quality of the conductor in virtue of which there is a fixed numerical ratio be- tween the potential difference of the two opposing faces of a cubic unit of such con- ductor, and the quantity of electricity which traverses either face per second, assuming a steady flow to take place normal to these faces, and to be uniformly distributed over them, such flow taking place solely by an elec- tromotive force outside the volume considered. The term is used in the first definition in the concrete sense of something intended for or used as a resistance. For the physical definitions and facts see Resistance, Electric. Gases offer very high resistance to the flow of an electric current. Their non-conducting power causes the increase of resistance which attends the polarization of a voltaic cell. (See Cell, Voltaic, Polarization of.} Resistances consist of coils, strips, bars or spirals of metal, or plates of carbon, or metallic powders, powdered or granulated carbon, or liquids. Resistance, Absolute Unit of The one thousand millionth of an ohm. (See Ohm. Units, Practical} Resistance, Assyminetrical Con- ductors or parts of conductors, which offer a greater resistance to the flow of an electric current in one direction than in another. Assymmetrical conductors are unknown, so far as structural peculiarities are concerned, but can be obtained by the use of counter electromotive forces, acting as resistance. This term was pro- posed by Wilke in discussing the obtaining of continuous currents by commutatorless dynamo- electric machines. The resistance of the human body is possibly an assymmetrical resistance. An evident application of an assymmetrical re- sistance is to direct alternating currents so as to cause the current that passes to flow in and to the same direction. Resistance, Balanced A resistance so placed in a circuit as to be balanced or made equal to another resistance connected therewith. Res.] 452 [Res. Resistance, Balanced, for Dynamos A resistance that possesses a range suf- ficient to balance one dynamo against another with which it is desired to run in parallel. ( Urquhart?) Resistance Box. (See Box, Resistance!) Resistance Bridge. (See Bridge, Resist- ance?) Resistance Coil. (See Coil Resistance) Resistance Coil, Standard (See Coil, Resistance, Standard?) Resistance, Conductivity The re- sistance offered by a substance to electric conduction, or to the passage of electricity through its mass. Resistance, Dielectric A term sometimes employed for the resistance of a dielectric to mechanical strains produced by electrification. The dielectric resistance of the glass, or other dielectric of a Leyden jar or condenser, is fre- quently overcome by the passage of the charges on the conducting surfaces, and the glass is thus pierced. The term dielectric resistance would appear to be badly chosen; for, like all substances, dielec- trics possess a true ohmic resistance, which in creases with the increase of length, and decreases with the increase of area of cross-section. The resistance of the dielectric, however, differs from the ordinary ohmic resistance of conductors, in that the resistance of the dielectric is suddenly overcome, and the discharge passes disruptively as a spark. Resistance, Effect of Heat on Electric Nearly .all metallic conductors have their electric resistance increased by an in- crease of temperature. The carbon conductor of an incandescent elec- tric lamp, on the contrary, has its resistance decreased when raised to electric incandescence. The decrease amounts to about three-eighths of its resistance when cold. The effects of heat on electric resistance may be summarized as follows: (i.) The electric resistance of metallic conduc- tors increases as the temperature rises. In some alloys this increase is small. (2.) The electric resistance of electrolytes de- creases as the temperature rises. (3.) The electric resistance of dielectrics and non-conductors decreases as the temperature rises. RESISTANCE AND CONDUCTIVITY OF PURE COPPER AT DIFFERENT TEMPERATURES. If 1 >l ;| if 8 1 I! ti j ! if H 1 '5 o" .OOOOO I OOOOO 16 .06168 .94190 I .00381 .99624 17 06563 .93841 2 .00756 .99250 18 .06959 93494 3 01135 .98878 '9 07356 93H8 4 .01515 .98508 20 .07742 .92814 5 .0,896 .98139 21 .08164 62452 6 7 02280 . 02663 97771 .97406 22 23 08553 .08954 .92121 .91782 8 03048 97042 24 09365 91445 9 -03435 .96679 25 .09763 .91110- 1C .03822 .96319 26 .I0!6l .90776 i .0 4 IQ9 9597 27 10567 9443 2 .04599 . 05603 28 11972 90113 3 4 .04990 .05406 95247 .94893 2 9 30 .1.382 .11782 .89784 89457 5 05774 94541 (Latimer Clark.} Resistance, Electric The ratio be- tween the electromotive force of a circuit and the current that passes therein. The reciprocal of electrical conductivity. Resistance can be defined as the reciprocal of electrical conductivity, because even the best electrical conductors possess appreciable resist- ance. Ordinarily the resistance of a circuit may be conveniently regarded as that which opposes or resists the passage of the current. Strictly speak- ing, however, this is not true, since from Ohm's law (See Law of Ohm, or Law of Current' Strength.) C = , from which we obtain R E R = , which shows that resistance is a C ratio between the electromotive force that causes the current and the current so produced. Resistance may be expressed as a velocity. The dimensions of resistance in terms of the electro-magnetic units are L (See Units, Electro. Magnetic.) But these are the dimensions of a velocity, which is the ratio of the distance passed over in unij time. Resistance may therefore be expressed as a velocity. Res.] 453 [Res. ' ' The resistance known as ' one ohm ' is in- tended to be lo 9 absolute electro-magnetic units, and, therefore, is represented by a velocity of icP centimetres or 10,000,000 metres (one earth quad- rant) per second." (Sylvanus Thompson.) Resistance may be represented by a velocity, one ohm being the resistance of a wire, which, if moved through a unit field of force at the rate of 1,000,000,000 (lo 9 ) centimetres per second will have a current of one ampere generated in it. (See Resistance, Ohmic. Resistance, Spurious.) The true value of the ohm is exactly io centi- metres. The material standards employed, i. e., the B. A. and "legal " ohms, are not absolutely of this value. One mil-foot of soft copper at 10.22 degrees C. or 50.4 degrees F. has the standard resistance of exactly 10 legal ohms ; at 15.56 or 59.9 degrees F., it has a resistance of 10.20 legal ohms, and at 23.9 degrees C. or 75 degrees F., 10.53 le g al ohms. RESISTANCE. Resistance of Wires of Pure Annealed Copper at O C. (Density = 84.) Diameters in 1 1 Millimetres. o,.S S f|Jg j| = (l Resistance of Wire of Pure An- nealed Copper at O degree C. Ohms per Kilometre. Metres Ohm. Ohms per Kilogramme. 5 175 5-7 .8 1230.5 .00456 4-4 ,35.28 7-4 1.06 944.38 .00784 3-9 106.35 9-5 i-35 722 .0x28 3-4 3 .7 80.8 62.93 51 12.5 iti 19.8 i. 80 1:1 563-92 439-7 355-65 .0222 0365 557 4 40.23 25 3-6 281 .088 .2 33-82 29 4.2 236.08 "3 27-95 36 5* i 195- *5 .185 .8 22.7 44 .278 .6 7.89 56 8 124.9 .448 5 5.75 63 9- 1 109-75 574 4 3-7 73 10.5 95-651 .763 -3 1.84 85 12 82.42 - 1.03 .8 0.06 00 M 70.247 1.42 .1 8-47 19 17 59.024 2.O2 6-99 44 20 48.782 "95 '2 5-66 78 25 39-5'S 4.19 .8 4-47 25 32 31.225 7.21 .7 2.83 294 42 23-9 "3 .6 5 2.52 i-74 400 576 \\ I7-56 12.305 22.78 46.8, .4 I-I75 902 122.4 8-173 110.41 34 .808 1251 177.9 5.O22 222.55 3 .24 .7.8. .4026 228.5 357 4-377 2.801 Pf .a 2797 3614 5'4 1-945 1.857.6 .if .179 5590 803.1 1-245 .4.489 " .1007 .0699 9929 14369 1428 2056 : 4 7 86 I4.I79 29,549 '.oS .0447 24570 3213 3" 78,943 .06 0252 39824 5713 173 227,515 .04 0112 88878 12848 .078 "42,405 The following table, based on Matthiessen's measurements, gives the relative resistances of equal lengths and cross-sections of a number of different substances used in electricity as com- pared with silver. LEGAL MICROHMS. Resistance in Microhms NAMES OF METAL. at o degree C. Relative Resistance. Cubic Centimetre. Cubic Inch. Silver, annealed... I. W4 . SQ2I Copper, annealed. Silver, hard drawn Copper, h'rd dr'wn Gold, annealed.... Gold, hard drawn. 1-598 1.634 1.634 2.058 2.094 .6292 6433 6433 .8102 .8247 .'063 .086 .086 369 393 Aluminium, ann'ld 2.Q12 .147 935 Zinc, pressed Platinum, annealed 5-626 9.057 .215 .565 3-741 6.022 Iron, annealed.. . 9.716 .825 6.460 Nickel, annealed. 12.47 .907 8.285 Tin, pressed 13.21 8.784 Lead, pressed.... 19.63 7.728 13-05 German silver.... 20.93 8.24O I3-9 2 Antimony, pressed 35-50 13-98 23-60 Mercury Bismuth, pressed. 94-32 I3I-2 37-15 51.65 62.73 (Hospitalier.) (Ayr ton.) The above resistances are for chemically pure substances only. Slight impurities produce a very considerable increase in the resistance. Resistance, Electric, of Liquids The resistance offered by a liquid mass to the passage of an elec- tric current. As a rule the electric re- sistances of liquids, with the single exception of mer- cury, are enormously high- er than those of metallic bodies. To roughly determine the resistance of a liquid, a section is taken between two parallel metallic plates A and B, Fig. 489, placed as shown in the figure, and an electric current is pass- ed between them. In order to accurately vary the size of the plates Fig. 489. Resistance of immersed in the liquid, and Liquid. hence the area of cross-section of the liquid con- ductor, as well as the distance between the plates, the apparatus shown in Fig. 490 may be used, in 454 [Res. TABLE OF CONDUCTING POWERS AND RESISTANCES IN OHMS B. A. UNITS. NAMES OF METALS. Conducting power at o de- gree C. Resistance of a wire one foot ong weighing one grain. Resistance of a wire one metre Ion weighing on gramme, Resistance of a wire one foot long .Tifcu inch m diameter. Resistance of a wire one metre long, one milli- metre in diam- eter. Approximate percentage of variation in re- sistance for i de- gree of tempera- ture at 20 deg. .1544 .1689 :% .4080 415 05759 .3983 .464 .7522 .8666 .9184 257 3295 525 13.071 2.959 9.936 9.151 9.718 9.940 12.52 12.74 17.72 32.22 55-09 59 40 75.78 80.36 119.39 216.0 798.0 600.0 ^S-SS 127.32 66.10 0.01937 .02103 .02057 .02104 02650 .02697 03751 .07244 .1166 .1251 .1604 .1701 2527 457' .689 .270 0.3140 0.2695 0.1399 0.377 Silver, hard drawn loo.oo 0.2421 0.2064 O.2IOO 0.5849 0-5950 0.06822 0.5710 3-536 1.2425 1-0785 Ull 3-32+ 5-054 18.740 4.243 0.388 Copper, hard drawn Gold annealed 99-55 0-355 Gold, hard drawn 77.96 Zinc presse'd 29.02 0.365 16.81 12.36 8.32 4.62 1.24 Nickel, annealed Tin, pressed 0.365 0.387 0.389 0-354 0.072 0.031 0.044 0.06S Antimony, pressed Bismuth, pressed Platinum - silver, alloy, German silver, hard or Gold, silver, alloy, hard 2.391 1.668 which these distances are readily adjustable, as shown. Resistance, Equivalent A single resistance which may replace a number of separate resistances in a circuit without alter- ing the value of the current traversing it. Resistance, Essential A term sometimes used instead of internal resist- ance. Fig. 4QO. Apparatus for Measuring Resistance of Liquid, Resistance, External Secondary A term proposed by Du Bois Reymond for the change in the resistance of a circuit external to the electric source when cataphoric action takes place. (See Action, Cataphoric?) " If the copper electrodes of a constant battery be placed in a vessel filled with a solution of cupric sulphate and from each electrode there projects a cushion saturated with this fluid, then, -(Jenkin.) on placing a piece of muscle, cartilage, vegetable tissue, or even a prismatic strip of coagulated albumen across these cushions, we observe, that very soon after the circuit is closed, there is a considerable variation of the current. * * * This phenomenon is called ' external secondary resistance.' " (Landois and Sterling.} Resistance, Extraordinary A term sometimes employed instead of external re- sistance. (See Resistance, External Secon- dary?) Resistance, False A resistance aris- ing from a counter electromotive force and not directly from the dimensions of the circuit, or from its specific resistance. The false resistance of any circuit is sometimes called its spurious resistance. (See Force, Electro- motive, Counter. Resistance, Spurious.) Resistance, Indnctionless A term sometimes used instead of non-inductive re- sistance. (See Resistance, Non-Inductive.} Resistance, Inductive A resistance which possesses self-induction. Resistance, Insulation The re- sistance of a line or conductor existing be- tween the line or conductor and the earth through the insulators, or between the two Res.] 455 [Res. wires of a cable through the insulating material separating them. The insulation resistance of a telegraph line is the resistance that exists between the line and the earth, through its insulators. The insulation re- sistance will decrease as the length of line in % creases, since for any increase in the number of poles and insulators there is a proportional in- crease in the area of cross-section of the insula- ting supports. If the insulation resistance is 1,000,000 ohms per mile, in a line 200 miles in length, the insula- tion resistance is only 5,000 ohms, that is, 1,000,000 = 5,000 ohms. 200 Resistance, Joint, of Parallel Circuits -- The joint resistance of two parallel circuits is determined by means of the follow- ing formula : Where R = the joint resistance of any two cir- cuits whose separate resistances are respectively r and r . When there are three resistances r, r and r*, in parallel, the joint resistance, r r -- r r --r r (See Circuits, Varieties of. ) Resistance, Magnetic -- The recipro- cal of magnetic permeability or conducti- bility for lines of magnetic force. Resistance offered by a medium to the passage of the lines of magnetic force through it. The magnetic resistance of the circuit of the lines of force is reduced by forming the circuit of a medium having a high magnetic permeability, such as soft iron. This is accomplished by the armature or keeper of a magnet, or by the iron in an iron-clad magnet. (See Magnet, Iron-Clad.} Resistance, Measurement of Methods employed for determining the re- sistance of any circuit or part of a circuit. Numerous methods are employed for this pur- pose. Among these are : (I.) The use of a resistance box with a Wheat- stone bridge, by opposing or balancing the un- known resistance against a known resistance. (See Balance, Wheat stone's Electric.) (2.) The differential galvanometer. (See Gal- vanometer, Differential.) (3.) The method of substitution. (4.) Comparison of the deflections of a gal- vanometer. Method of Substitution. A resistance -box R, Fig. 491, galvanometer G, and the resistance x, that is to be measured, are placed in the direct circuit of the battery B, by means of conductors of such thick wire that their resistance can be neglected. The deflection of the galvanometer is first measured with x, in circuit, and no resistance in tue box R. The resistance x, is then cut out of the circuit by placing a thick copper wire across the terminals of the mercury cups at mm', and resistances unplugged in R, until the same deflec- tion is obtained. Then, if the electromotive force of the battery has remained constant, the resist- ances unplugged equal the unknown resistance. For full description of the various methods of determining resistance the reader is referred to ''Ayrtorfs Practical Electricity,'* ^'Kempe's Handbook of Testing," or other standard books on electrical measurements. Fig 4Qr Substitution Method. When several resistances are placed in series in any circuit, by measuring the difference of poten- tial at their terminals, their values can be deter- mined by simple calculation, being directly pro- portional to these differences of potential. This method is especially applicable to the measurement of such low resistances as the arma- tures of dynamo-electric machines. Resistance, Non-Indnctive A re- sistance in which self-induction is practically absent. An incandescent lamp filament is practically a non-inductive resistance when compared with a coil on the helix of an electro-magnet. Resistance of Human Body. (See Body, Human, Resistance of.) Res.] 456 [Res. Resistance of Toltaic Arc. (See Arc, Voltaic, Resistance of.} Resistance, Ohmic The true resist- ance of a conductor due to its dimensions and specific conducting power, as distin- guished from the spurious resistance produced by a counter electromotive force. (See Force, Electromotive, Counter. Resistance, Spuri- ous?) The term ohmic resistance must be regarded as a pleonasm. Its use can only be permitted in contradistinction to counter electromotive force resistance. True and spurious resistance would seem preferable. Resistance or Cell, Selenium A mass of crystalline selenium, the resistance of which is reduced by placing it in the form of narrow strips between the edges of broad conducting plates of brass. The selenium employed for this purpose is the vitreous variety which has been fused and main- tained for several hours at about 220 degrees C., by means of which its resistance is reduced. By exposure to sunlight, the resistance of a selenium cell is decreased fully one-half its re- sistance in the dark. The selenium cell is used in the photophone. (See Photophone} Resistance or Reducteur for Toltmeter. (See Reducteur or Resistance for Volt- meter} Resistance, Secondary A term sometimes used in place of external secon- dary resistance. (See Resistance, External Secondary} Resistance Slide. (See Slide, Resist- ance} Resistance, Specific The particular resistance which a substance offers to the passage of electricity through it. In absolute measure, the resistance in ab- solute units between the opposite faces of a centimetre cube of the given substance. In the practical system the resistance given in ohms. Resistance, Specific Conduction A term sometimes used instead of specific resistance. (See Rest 'stance, Specific} Resistance, Specific, of Liquids The resistance of a given length (one centi- metre) and area of cross-section (one square centimetre) of any liquid as compared with the resistance of an equal length and cross- section of pure silver. The resistance of a few common liquids and so- lutions is here given from Lupton: Water, pure, at 75 degrees C . . 1. 188 X io 8 ohms, i. e., 118,800,000. Water at 4 degrees C 9. ioo X io 6 " Water at 1 1 degrees C 3.400 X io 5 Dilute hydrogen sulphate (sul- phuric acid) at 1 8 degrees C., 5 per cent, acid 4.88 Dilute hydrogen sulphate at 18 degrees C., 3 per cent, acid 1.38 ohms. Nitric acid at 18 degrees C., density 1.32 1.61 " Saturated solution of copper sulphate (blue vitriol) at io degrees C 29.30 " Saturated solution of zinc sul- phate at 14 degrees C 21.50 " Hydrochloric acid, 20 per cent, acid, at 18 degrees C 1.34 " Sal ammoniac, 25 percent, salt 2.53 " Common salt, saturated, at 13 degrees C 5.30 " It will be observed that the resistance varies considerably with differences of temperature. Resistance, Spurious A false re- sistance arising from the development of a counter electromotive force. (See Resist- ance, False. Force, Electromotive, Coun- ter} The spurious resistance is also called the false resistance, in order to distinguish it from the true or ohmic resistance. (See Resistance, Electric.) Resistance, Standard A resistance used for comparison with or the determina- tion of unknown resistances. A committee appointed by the American Insti- tute of Electrical Engineers in 1890 reported the following values for the standard resistance of copper wire; at O degree C. in B. A. U. and legal ohms, viz.: Res.] 457 [Res. STANDARD RESISTANCE AT o" C. B. A. U. Legal Ohms. * ' Meter- millimetre, " " soft copper "... .02057 .02034 Cubic centimetre. .. .000001616 .000001598 "Mil-foot" 9.720 9.612 Resistance, Tables of Tables in which the resistance of equal lengths and cross-sections of different substances is given in ohms, or other units of resistance. Resistance Thermometer. (See Ther- mometer, Electric Resistance^) Resistance, Transition A term sometimes used in electro-therapeutics for a change in the value of the resistance caused by polarization. Whenever an electric current passes through a fluid substance and decomposes the fluid, the decomposition products collect on the electrodes and produce an increase in the resistance of the circuit. Resistance, True The resistance which a conductor offers to the passage of a current by reason of its dimensions and spe- cific conducting power, as distinguished from a spurious resistance produced by a counter electromotive force. The true resistance is sometimes called the ohmic resistance. (See Resistance, Spurious. Resistance, Ohmic.) Resistance, Unit of Such a resist- ance that unit difference of potential is re- quired to cause a current of unit strength to pass. (See Ohm. Potential, Electric. Potential, Difference of.} Resistance, Unit of, Absolute The one thousand millionth of an ohm. (See Ohm. Units, Practical.} Resistance, Unit of, Jacobi's The electric resistance of 25 feet of a certain copper wire weighing 345 grains. Another unit of electric resistance proposed by Jacobi was the resistance of a copper wire one metre in length and one millimetre in diame- ter. Resistance, Unit of, Matthiessen's The resistance of one statute mile of pure annealed copper wire r B inch in diameter at 15.5 degrees C, and determined by him to be 13.59 B. A. ohms. Resistance, Unit of, Varley's The resistance of one statute mile of a special copper wire f, inch in diameter. Varley's unit was afterwards adjusted by him to equal 25 Siemens Mercury Units. Resistance, Yariable A resistance the value of which can be readily varied. Variable resistances are either : (i.) Automatically variable resistances; or (2.) Non-automatically variable resistances. Resistance, Variable, Automatic A resistance the value of which can be auto- matically varied. A pile of carbon plates resting on one another, in loose contact, offers a high resistance, but when compressed as by an electro-magnet their resist- ance is lowered. Brush employs such an auto- matic resistance in the regulation of his dynamo- electric machine. (See Regulation, Automatic.) Resistance, Variable Non- Automatic A resistance the value of which is regulated by hand. (See Rheostat.) Resistance, Virtual A term some- times employed instead of impedance. (See Impedance.} Resonance, Electric The setting up of electric pulses in open-circuited con- ductors, by the action of pulses in neighboring conductors. Electric resonance, like acoustic resonance, takes place when a correspondence exists between the time-rate of vibration of the body producing the resonance, and the body in which the reso- nance is produced. In other words, when the wave lengths are the same in the two bodies, or when the wave length in one is equal to a half wave length, or some definite multiple of a half wave length of the other. Partial resonance may occur, when there is a small difference between the wave lengths of the two bodies. Beyond certain limits, however, this is so small as to be practically absent. When an electrical pulse is started in a con- ductor by the discharge of a Leyden jar, a side flash spark is obtained in the alternative path, between the discharge points. The length of this spark has its greatest value, when the time required for the Res.] 458 [Kes. pulse to travel backwards and forwards along the conducting wires, is exactly equal to the time of a complete oscillation in the circuit, or when the length of the open-circuit wires is equal to half a wave length, or some multiple 01 half a wave length. The fact that the length of the spark is greatest when certain relations exist between the dimen- sions of the two circuits, shows that the time-rate of an electrical pulse in any circuit depends on the dimensions of that circuit. In the case of acoustic resonance, in order that one tuning fork may be able to excite vibrations in another, the fork producing or exciting the vibra- tion must be strictly in unison with the fork in which the vibrations are excited, and any varia- tions produced in the rate of vibration of the sounding fork, by overloading it, or, in other words, by altering its dimensions, checks the effects of its resonance. In a similar manner, any alterations in the di- mensions of the circuit, checks or diminishes the effects of electric reson- ance in a neighboring cir- cuit, which was previously in unison with it. This has been experimentally shown by Hertz as fol- lows: An induction coil A, Fig. 492, has the terminals of its secondary connected to an open rectangular cir- cuit provided with spark- ing terminals, I, and 2, called a spark micrometer. Under certain conditions, when the discharge oc- curs at the terminals B, Fig. 4Q2. Electrical Resonance. of the ordinary discharger, sparks are produced by electric resonance in the electric resonator formed by the spark micrometer at M. Supposing, now, that a certain character of spark is obtained at the terminals B, that is, a cei tain velocity of electrical pulsations is obtained which depends on the nature of the spark; sup- pose, moreover, that the dimensions of the spark micrometer or electric resonator are such that the greatest length of spark is obtained. Then, any alteration in the character of these sparks, be- tween the terminals at B, varies the intensity of the sparks in the park micrometer. If, for example, the apparatus be arranged as shown in Fig. 493, in which one of the sec- ondary terminals of the induction coil has con- nected with it a copper wire i g h. The sparks at M, decrease considerably. When, however, the conductor C, is connected with the free end H, of this additional conductor, then this effect is not observed, as is shown by the fact that when the conductor C, is attached at the point G, it produces no effect on it. Fig. 493, Electric Resonance. In another experiment with the same apparatus, matters may be arranged that the sparks in the micrometer circuit pass singly. When, now, an- other conductor C', is attached to K, a stream of sparks immediately passes. It would appear, therefore, from the above ex- periments, that when two circuits are taken, having as nearly as possible the same vibration periods, any alteration in the dimensions of either will prevent one from producing electrical reso- nance in the other. In the above experiments Hertz demonstrated the following facts, viz., (I.) The sparks in the micrometer circuit are smaller when the discharges take place between points, or a point and a plate, instead of between knobs. (2.) The micrometer sparks are feebler in rare- fied gas than in air at ordinary pressures. (3.) Extremely slight differences in the nature of secondary sparks produce considerable differ- ence in the length of the micrometer sparks. Hertz found the above results were obtained when the secondary sparks were of a brilliant color, and were attended by a sharp crack. (4.) The length of the spark in the micrometer Res.] 459 [Ret. circuit varies with the length of the micrometer circuit. This, of course, follows from the fact that any alteration of the length in the micrometer circuit, produces, by electrical retardation, a correspond- ing alteration in the time of the electrical pulses. (5.) No effect is produced in the length of the micrometer spark by variations in the material, the resistance, or the diameter of the wire forming the micrometer circuit. This is probably because the rate of propaga- tion of electrical pulses along a conductor, de- pends mainly on the capacity of the conductor, and on its co-efficient of self-induction, and only to a slight extent on its resistance. (6. ) The length of wire connecting the microm- eter circuit with the secondary circuit has but little effect, provided such length does not exceed a few metres. Local disturbances, therefore, must traverse conductors without undergoing any appreciable change. (7.) The position of the point on the micrometer circuit connected with the secondary circuit, is of the greatest importance. When the point on the micrometer circuit is situated symmetrically with respect to the two mi- crometer knobs, variations of potential will reach the terminals in the same phase, and there will be but little effect, as seen by the sparks between the micrometer knobs. Such a point on the microm j eter knobs is called the null point, or it is called as in a corresponding case in acoustics, a nodal point. (See Point, Null. Point, Nodal.) (8.) When the conductors are of sufficient length, their approach produces disturbances in a previously adjusted and quiet spark microm- eter, just as the approach of a conductor would. Probably one of the most curious effects con- nected with the phenomena of electrical resonance is that pointed out by Lodge, viz. : that when the spark from a secondary circuit is so placed that the light is visible from a micrometer circuit, the effects of the discharge are greatly increased. Lodge also found that the light from burning magnesium wire, or, in general, light rich in the ultra-violet rays, produces the same effect. Resonator, Electric An apparatus employed by Hertz in his investigations on electric resonance. (See Resonance, Elec- tric) An electric resonator consists essentially of an open-circuited conductor, or circuit of such dimen- sions that electro-magnetic waves or pulses are propagated through it at the same rate as those which are occurring in a neighboring circuit from which electro-magnetic radiation is tak- ing place. Under these circumstances electro- magnetic pulses are set up sympathetically by resonance in the open circuit of the resonator, like the sympathetic vibrations in a tuning foxk, when placed near another vibrating tuning fork, which is giving off sound waves of exactly the same period of vibration as its own. Resonator, Electro-Magnetic A term applied to the Hertz spark micrometer, in which electro-magnetic waves are produced by electric resonance. (See Resonance, Elec- tric^ Resultant. In mechanics, a single fonfe that represents in direction and intensity the effects of two or more separate forces. The separate forces are called the components. (See Components.} Retardation. A decrease in the speed of telegraphic signaling caused either by the induction of the line conductor on itself, or by mutual induction between it and neighbor- ing conductors, or by condenser action, or by all. The line must receive a certain charge before a current sent into it at one end can produce a signal at the other end. This charge will de- pend on the length and surface of the wire, on the neighborhood of the wire to the earth or other wires, and on the nature of the insulating mate rial between the wire and neighboring conductors. This results in a charge given to the wire which is lost as a current for signaling. The greater the electrostatic capacity of the line wire, the greater will be the retardation in signaling. (See Capa- city, Specific Inductive. Dielectric. Capacity, Electrostatic. Induction, Electro-Dynamic.} Retardation in signaling is produced by the following causes : (I.) Self-induction which produces extra cur- rents. (See Induction, Self. Currents, Extra.} The extra current on making, retards the be- ginning of the signal ; the extra current on break- ing, retards its stopping. (2.) Mutual Induction between the line con- ductor and neighboring conductors. Ret] 460 [Rhe. (3.) The Magnetic Inertia or Lag, or the time required to magnetize or demagnetize the core of the electro-magnetic receptive devices used on the line. (4.) By Condenser Action, the cable acting as a condenser. Retardation, Electric A retarda- tion in the starting or stopping of an electric current, arising from self-induction. (See In- duction, Self. Retardation?) Retardation, Inductive A retarda- tion in the appearance of a signal at the dis- tant end of a cable, produced by the action of induction. (See Retardation?) Retardation, Magnetic A retarda- tion in the magnetization or demagnetization of a substance due to magnetic lag. (See Retardation. Lag, Magnetic?) Retarding, Electrically Decreas- ing the speed of telegraphic signaling, by means of induction. (See Retardation?) Retentivity, Magnetic A term pro- posed by Lament in place of coercive force, or the power possessed by a magnetizable substance of resisting magnetization or de- magnetization. (See Force, Coercive?) Return Circuit (See Circuit, Return?) Return, Earth (See Earth Re- turn?) Return Ground. (See Ground-Return?) Return Wire or Conductor. (See Wire, Return?) Returns. In a system of distribution, those conductors through which the current flows back from the electro-receptive devices to the source. (See Leads?) The word returns is sometimes used in a sys- tem of distribution by parallel circuits, to distin - guish between the conductor by which the cur- rent goes back or returns from the receptive de- vices to the dynamo, and the conductor that leads it to the receptive devices. The term leads is, however, often applied to both conductors. Reverse-Induced Current. (See Current, Reverse-Induced?) Reversed Currents. (See Currents, Re- versed.) Reverser, Current A switch, or other apparatus, designed to reverse the di- rection of a current. Reversible Bridge. (See Bridge, Rever- sible?) Reversible Heat. (See Heat, Reversible.) Reversibility of Dynamo. The ability of a dynamo to operate as a motor when tra- versed by an electric current. (See Motor, Electric.) Reversing Gear of Electric Motor. (See Motor, Electric, Reversing Gear of.) Reversing Key. (See Key, Reversing.) Reversing Key of Quadruples Tele- graphic System. (See Key, Reversing, of Quadruplex Telegraphic System?) Reversing Magnetic Field. (See Field, Magnetic, Reversing.) Rheochord. A word formerly employed instead of rheostat. (See Rheostat?) Rheometer. A word formerly employed for any device for measuring the strength of a current. This word is now obsolete and is replaced by the word galvanometer. (See Galvanometer.) Rheomotor. A word formerly employed to designate any electric source. This word is now obsolete, apd replaced by the various names of the different electric sources. (See Source, Electric.) Rheophore. A word formerly employed to indicate a portion of a circuit conveying a cur- rent and capable of deflecting a magnetic needle placed near it. (Obsolete.) Rheoscope. A word formerly employed in place of the present word galvanoscope, for an instrument intended to show the presence of a current, or its direction, but not to measure its strength. (Obsolete.) Rheoscope, Physiological A sensi- tive nerve-muscle preparation employed to determine the presence .of an electric current. (See Frog, Galvanoscope.) Rhe.] 461 [Rin. A term sometimes applied m electro-thera- peutics to the frog's legs preparation adapted to show the presence of any electric current. The physiological rheoscope is adapted to show the presence of an electric current without the use of a galvanometer. On the passage of the electric current the frog's legs twitch con- vulsively. Rheostat. An adjustable resistance. A rheostat enables the current to be brought to a standard, i. 7 7-1 f *f' 495" Discharging (See Discharge, Dzs- Rod rupti-ve. Jar, Leyden?) The insulated handles H, H, Fig. 495, permit the balls at M, M, to be readily applied to the opposite coatings of the jar or condenser. The name discharging tongs is sometimes ap- plied to this apparatus. Rod, Lamp A metallic rod pro- vided in electric arc lamps for holding the carbon electrodes. When the upper carbon only is fed, as is the case in most arc lamps, there is usually but one lamp rod provided. The clutch or clamp of the feeding device acts against this rod, which must of necessity be at least as long as the upper carbon. (See Lamp, Arc, Electric.) Rod, Lightning A rod, or wire cable of good conducting material, placed on the outside of a house or other structure, in order to protect it from the effects of a light- ning discharge. Lightning rods were invented by Franklin. The results of a very extended inquiry on the subject, leave no room for doubt that a lightning rod, properly placed and constructed, affords an efficient protection to the buildings on which it is placed. To insure this protection, however, the fol- lowing conditions were, until very recently, gen- erally insisted on in order to permit the rod to properly act, viz. : (I.) The rod, generally of iron or copper, should have such an area of cross- section as to enable it to carry without fusion the heaviest bolt it is liable to receive in the latitude in which it is located. When of iron, the area of cross-section should be about seven times greater than when of copper. (2. ) The rod should be continuous throughout, all joints being carefully avoided. When joints are used, they should be made of as low resistance as possible, and should be pro- tected against corrosion. (3.) The upper extremity of the rod should terminate in one or more points formed of some metal that is not readily corroded, such as pla- tinum or nickel. (4.) The lower end of the rod should be car- ried down into the earth until it meets perma nently damp or moist ground, where it should be attached to a fairly extended metallic surface buried in the ground. Metallic plates will answer for grounding the Rod.] 463 [Rod. rod, but, if gas or water pipes are available, the rod should be placed in good electrical connec- tion therewith, by wrapping it around and soldering\t to such pipes. This fourth requirement is of great importance to the proper action of a lightning rod, and un- less thoroughly fulfilled, may render the rod worthless, no matter how carefully the other re- quirements are attended to. When a bolt strikes a lightning rod which is not properly grounded, the discharge is almost certain to destroy the building to which the rod is connected. (5.) The rod should not be insulated from the building, unless to prevent stains from the oxi- dation of the metal. On the contrary, the rod should be directly connected with all masses of metal in its path, such as tin roofs, gutter spouts, metallic cornices, etc. In this way only can dan- gerous disruptive lateral discharges from the rod to such masses of metal be avoided. (6.) The rod should project above the roof or highest part of the building, or, in other words, the height of the rod should bear a certain pro- portion to the size of the building to be pro- tected. A rod will protect a conical space around it, the radius of whose base is equal to the vertical height of the rod above the ground, but whose sides are curved inwards instead of being straight. Where the building is very high, a number of separate rods all connected to one another should be employed. A lightning rod sometimes fails to protect a house or barn, from the fact that a heated, ascend- ing current of air from a fire in the house, or from the gradual heating of green hay or grain in the barn, acting as a conductor, increases the vir- tual height of the house beyond the ability of its rods to protect it. (7.) A stranded conductor is much better than an equal cross-section of a solid rod of the same metal. A copper tape is better than a copper rod for lightning rods, because a rapidly periodic current, whose periodicity is sufficiently great, passes practically over the surface of the conductor only. Considering an electric current as taking its energy from the surrounding dielectric, a tape is better, because the surface which absorbs the energy is greater in the case of a tape than of a solid rod. (See Law, Poynting's.) A lightning rod more frequently acts to quietly discharge an impending cloud by connective dis- charge than by an actual disruptive discharge of the same. (See Discharge, Connective. Dis- charge, Disruptive, ,) Lightning rods should be frequently tested to see that no breaks or oxidation of their joints have occurred. Professor Lodge takes exception to some of the heretofore generally received notions concerning the action of lightning rods. He distinguishes between two distinct kinds of discharge that may occur between a charged cloud and the earth, viz.: (i.) A steady strain or current. (2.) An impulsive rush or oscillatory discharge. A discharge by a steady strain or current oc- curs when the cloud gradually approaches a point on the earth ; or, in the case of the cloud being stationary, when it receives its charge gradually by the approach of another cloud. In steady discharge, the lightning rod, with its pointed end, either quietly discharges the cloud by a convective discharge, or by a harmless con- ductive discharge through the rod, after a spark has passed disruptively between the cloud and the rod. (See Discharge, Convective. Dis- charge, Conductive. Discharge, Disruptive. ) The impulsive discharge or rush occurs when- ever the cloud that discharges to the earth re- ceives its charge suddenly, as by the discharge into it of a neighboring cloud, or when a bound charge, produced by the presence of a neighbor- ing charged cloud, is suddenly liberated by dis- harge, and, thus becoming free, impulsively dis- charges to the earth. In all cases of an impulsive discharge or rush, a counter electromotive force is set up in the rod, which resists the discharge through the rod and causes the electricity to rush back and spit off in lateral discharges. In this case the conducting power of the rod has no effect in facilitating the discharge. Indeed, the smaller its resistance, and the longer the oscillations last, the greater the danger from lateral discharges. (See Discharge, Lateral. Path, Alternative.) The following principles adyanced by Lodge differ from the views heretofore generally re- ceived, viz.: (I.) Iron is a better substance for a lightning rod than copper, because it is equally as good a. conductor as copper for very rapidly alternating currents, and is more difficult to fuse. (2.) All neighboring metallic conductors should be connected to earth. These connections should. Rod.] 464 [Rot. preferably be by separate conductors rather than by the rod itself. (3.) The lightning conductors should have a good separate earth, but should be connected to water pipes, gas pipes, etc., if near them, by an underground connection. (4.) The lightning conductor should be de- tached from the building and not close against it. (5.) The rod should be of flat section, or a stranded conductor. Rod, Lightning, for Ships A system of rods designed to afford electric protection for vessels at sea. Since the lightning discharge takes place be- tween the points of greatest difference of poten- tial, and these points are generally the cloud and the nearest point of the earth, tall objects are especially liable to be struck. Ships at sea should, therefore, be thoroughly protected from lightning. In Harris' system of lightning protection for ships, the rods are connected with a series of copper plates and rods so placed on the masts as to readily yield to strains. These plates or rods are electrically connected with the copper sheath- ing of the vessel and with aZ2 large masses of metal in the vessel. This latter precaution is especially necessary in the case of men-of-war, in order to protect the powder magazine. Harris' method for the lightning protection of ships was adopted only after very considerable opposition. It proved, however, so efficacious in practice that serious effects of lightning on vessels so protected are now almost unknown. In 1845, Harris received the honor of knighthood from the English Government for his services in this respect Rod, Lightning, Points on Points of inoxidizable material, placed on lightning rods, to effect the quiet discharge of a cloud by convection streams. (See Rod, Lightning. Convection, Electric?) .Rod, Thunder A term formerly used for lightning rod. (See Rod, Light- ning) Rods, Bus Heavy copper rods em- ployed in a central or distributing station, to which all the terminals of the generating dy- namos are connected, and from which the cur- rent passes to the different points of the dis- tribution system over the feeders. Bus rods are often called bus bars or bus wires. (See Wires, Bus.) Rodding a Conduit. (See Conduit, Rod- ding a.) Rolling Contact. (See Contact, Rolling) Rose, Ceiling An ornamental ceil- ing plate through which an electric conductor passes. Rosette. An ornamental plate provided with contacts connected to the terminals of the service wires, and placed in a wall for the ready attachment of the incandescent lamp. A word sometimes used in place of rose. Rosette Cut-Out (See Cut-Out, Rosette) Rotary Magnetic Polarization. (See Polarization, Magnetic Rotary) Rotary-Phase Current. (See Current, Rotating) Rotary-Phase Dynamo. (See Dynamo, Rotary-Phase) Rotary-Phase Motor. (See Motor, Ro- tating Current) Rotary-Phase Transformer. (See Trans- former, Rotary-Phase) Rotating Brushes of Dynamo-Electric Machine. (See Brushes, Rotating, of Dynamo-Electric Machines) Rotating Current. (See Current, Rota- ting) Rotating Current Field. (See Field, Rotating Current) Rotating Current Motor. (See Motor, Rotating Current) Rotating Current Transformer. (See Transformer, Rotatory Current) Rotation, Electro-Magnetic A rotation obtained by electro-magnetic attrac- tions and repulsions. (See Disc, Arago's. Disc, Faraday's. Motor, Electric) Rotation, Magneto-Optic A rota- tion of the plane of polarization of a beam of polarized light on its passage through a transparent medium when placed in a strong magnetic field. The medium only possesses such properties while in the field. Rub.] 465 [Sai. In a ray of ordinary light the vibrations of the ether particles are at right angles to the direction of the ray, or to the direction in which the light is moving. But the vibrations occur indiscrimi- nately in all planes passing through the line of direction. Under certain circumstances, all the ether particles may be caused to move in planes that are parallel to one another. Such a beam of light is called a. plane polarized beam. A plane polarized beam of light, when passed through many transparent substances, will have its ether particles vibrating in the same plane when it emerges from the medium, as it had before it entered. Some transparent substances, how- ever, possess the property of rotating or turning the plane of polarization of the light to the right Fig. 496. Magneto- Optic Rotation. or to the left. . This property is called respec- tively right-handed rotary polarization, and left- handed rotary polarization. Many substances that ordinarily possess no power of rotary polarization acquire this power when placed in a magnetic field. This property of a magnetic field was discovered by Faraday. The effect is to be ascribed to the strain produced in the transparent medium by the stress of the magnetic field. It may be caused in solid bodies by mechanical force. The apparatus for demonstrating the rotation of the plane of polarization by a magnetic field is shown in Fig. 496. A powerful electro-magnet, M, M, is provided with a hollow core. The substance c, is placed in the field produced by the approached poles, and its action on the light of a lamp, placed at the end 1, is observed by suitable apparatus at a. Rubber of Electrical Machine. A cushion of leather, covered with an electric amalgam, and employed to produce electricity by its friction against the plate or cylinder of a frictional electric machine. (See Machine, Frictional Electric?} Rubbing Contact (See Contact, Rub- bing^) Ruhmkorff Coil. (See Coil, Ruhmkorff.) RnhmkorfFs Commutator. (See Com- mutator, Ruhmkorjf ~'s.) Rule, Ampere's, for Effect of Current on Needle A magnetic needle, when placed near a conductor through which a current is flowing, has its north pole deflected to the left of the observer, who is supposed to be swimming with the current and facing the needle. s S. A contraction employed for second. S. H. M. A contraction employed for simple harmonic motion. S. N. Code. A contraction for single needle code. S. W. G. A contraction for Standard Wire Gauge. Saddles, Telegraphic Brackets placed on the top of telegraphic poles for the support of the insulators. Saddle brackets are usually employed for the wire attached to the top of a telegraph pole. (See Pole, Telegraphic.) Safe Carrying Capacity of a Conductor. - (See Capacity, Safe Carrying, of a Con- ductor?) Safety Catch. (See Catch, Safety) Safety Device for Multiple Circuits.-(See Device, Safety, for Multiple Circuits.) Safety Fuse. (See Fuse, Safety.) Safety Lamp, Electric (See Lamp, Electric Safety) Safety Plug. (See Plug, Safety.) Safety Strip. (See Strip, Safety.) Saint Elmo's Fire. (See Fire, St. El- mo's.) Sal.] 466 [Seta. Salient Magnetic Pole. (See Pole, Mag- netic, Salient?) Saline Creeping. (See Creeping, Saline.} Salts, Electrolysis of The decom- position of a salt into its electro-positive and negative radicals or ions. (See Electrolysis.) Sandy Deposit, Electro-Metallurgical (See Deposit, Electro-Metallurgical, Sandy.) Saturated Solution. (See Solution, Sat- urated.) Saturation, Magnetic The max- imum magnetization which can be imparted to a magnetic substance. The condition of iron, or other paramag- netic substance, when its intensity of mag- netization is so great that it fails to be further sensibly magnetized by any magnetic force, however great. When the core of an electro-magnet is saturated by the passage of an electric current, the only further increase of its magnetization that is possi- ble, is that due to the magnetic field of the in- creased current which may be sent through its coils. This is comparatively insignificant. A permanent magnet is sometimes said to be super-saturated, that is, to have received more magnetism than it can retain for any considerable time after its magnetization. In the saturated field magnets of a dynamo-elec- tric machine the magnetic density is seldom taken at a larger value than 16,000 lines per square cen- timetre of area of cross-section. But this is only practical saturation, since Ewing has forced 45,300 lines per square centimetre by using an enormously high magnetizing force (H = 24,500). Saturation, Magnetic, Diacritical Point of A term proposed by S. P. Thomp- son for such a value of the co-efficient of magnetic saturation, that the core is mag- netized to exactly one-half its possible max- imum of magnetization. Saw, Electric A platinized steel wire, employed while incandescent for cut- ting hard substance. Scale, Tangent A scale designed for use with a galvanometer, on which the values of the tangents are marked, instead of equal degrees as ordinarily, thus avoiding the necessity of finding from tables the tangents corresponding to the degrees. Such a scale may be constructed as follows: Draw the tangent B T, to the circle, Fig. 497, and lay off on it any number of equal divisions or parts, as, for example, the thirty shown in the annexed figure. Connect these parts with the centre C, of the circle. The arc of the circle will C Fig. 497. Tangent Scale. thus be divided into parts proportional to the value of the tangents of the angles. These parts are more nearly equal the nearer they are to B, and grow smaller and smaller the further they are from B. In tangent galva- nometers it is therefore very difficult to accurately determine the current strength when the deflec- tions of the needle are very large. Scale, Thermometer, Centigrade A thermometer scale, in which the length of the thermometric tube between the 'melting point of ice and the boiling point of water is divided into one hundred equal parts or degrees. Centigrade degrees are indicated by a C., thus O degree C, or 100 degrees C., to distinguish them from Fahrenheit degrees that are marked F. In the Fahrenheit scale the freezing point of water is taken at 32 degrees, and the boiling point at 212 degrees. Scale, Thermometer, Fahrenheit's A thermometer scale in which the length of the thermometer tube between the melting point of ice and the boiling point of water is divided into 180 equal parts called degrees. Fahrenheit degrees are indicated by an F., thus, 32 degrees F. The freezing point of water in Fahrenheit's scale is marked 32 degrees F., and the boiling point of water is marked 2 1 2 degrees F. Schiseophone. An electro-mechanical ap- pliance for detecting flaws and internal de- fects in rails or other metallic masses. The schiseophone consists essentially in the combination of a microphone and telephone with a mechanical hammer and induction balance. Sch.] 467 [Scr. Schweigger's Multiplier. (See Multi- plier, Schweigger's^) Scintillating Jar. (See Jar, Scintillat- ing.) Scratch Brush. (See Brush, Scratch.) Scratch Brush, Circular (See Brush, Scratch, Circular.) Scratch Brush, Hand (See Brush, Scratch, Hand.) Scratch Brushing. (See Brushing, Scratch.) Screen, Electric A closed conduc- tor placed over a body to screen or protect it from the effects of external electrostatic fields. An electric screen is sometimes called an elec- tric shield. The ability of a closed, hollow conductor to act as a screen, arises from the fact that all points on its inner surface are at the same potential, and therefore are not affected by an increase or de- crease in the potential of the outside of the con- ductor as compared with that of the earth. (See Net, Faraday's.) No considerable thickness is required for the efficient operation of an electric screen. Screen, Magnetic A hollow box whose sides are made of thick iron, placed around a magnet or other body so as to cut it off or screen it from any magnetic field ex- ternal to the box. Magnetic screens are placed around delicate galvanometers to avoid any variations in their field due to extraneous masses of iron or neigh- boring magnets. They are also sometimes placed around watches to shield or screen the works from the effects of magnetism. To act effectively, when the external fields are at all powerful, magnetic screens must be made of thick iron. They differ in this respect from electrostatic shields, which will afford protection against electrostatic charges although they may be but mere films. Screen, Methven's A vertical rec- tangular metallic screen used in connection with a standard argand burner, for furnish- ing a standard amount of light for photo- metric purposes. In a rectangular screen a small vertical slot is made of such dimensions as to permit an amount of light to pass just equal to two standard candles. The proper burning of the argand lamp is de- termined by supplying sufficient gas to produce a flame exactly 3 inches high. The glass chimney used in the burner is 6 inches high, and is provided with two horizontal wires placed on each side of the burner at the required height. Methven's screen possesses the advantage of being easily used and of furnishing a reliable standard of light. Extended experiments made with it appear to show that the amount of light produced depends rather on the height of the gas flame than on the quality of the gas itself. In using Methven's screen care should be taken (i.) To see that the gas flame is of exactly the required height. (2.) That the chimney on the lamp is quite clean. .(3.) That the top of the flame is as regular as possible. As this last point is almost impossible to obtain in actual practice, the flame is ad justed so that the highest point extends about one- eighth of an inch above the height of the horizontal wires. (4.) That the lamp and apparatus be permitted to acquire its normal temper- ature before the readings are taken. Fig. 498 shows the con- struction of the ordinary Methven standard screen. The vertical slot in the screen is placed as shown before the standard argand F 'f- 4<)S. burner. Horizontal wires for the adjustment of the height of the flame are placed one on each side of the gas chimney. Screening, Electrostatic Screening or shielding from the inductive effects of a charge. A continuous metallic surface surrounding an air space to be shielded, completely protects any body placed within such air space from electro- static influence. (See Cube, Faraday* s.) Screening, Magnetic Preventing magnetic induction from taking place by in- terposing a metallic plate, or a closed circuit of insulated wire, between the body producing Methven Standard Screen. Scr.] 468 [Scr. the magnetic field and the body to be mag- netically screened. A magnetic needle is screened from the action of the earth's field by placing it inside a hollow iron box, which prevents the lines of force of the earth's field from passing through it by concen- trating them on itself. This action is dependent on the fact that iron is paramagnetic and there- fore offers the lines of force less resistance through its mass than elsewhere. A plate of copper would not effect any such magnetic shielding or screening. In any magnetic field, however, in which the strength of the field is undergoing rapid, periodic variations, a plate of copper or other electric conductor may act as a screen to protect neigh- boring conductors from the effects of magnetic induction, and its ability to thoroughly effect such a screening will depend directly on .its conducting power. If, for example, the copper plate c (Fig. 499), be interposed between a coil of copper ribbon a, and the fine wire coil b, it will greatly reduce the intensity of the induced currents, produced when rapidly alternating currents are sent through a. If, however, the copper plate be slit, as shown to the right at a, the screening effect is lost, but is regained if the slit be connected by a conductor. Similarly a flat coil of insulated wire effects no screening. action when open, but when closed acts as the uncut copper plate. Here the screening action is due to the fact that the energy of the field is spent in producing eddy currents in the interposed metal screen or coils. If the metal screen is discontinuous in the direction in which the eddy currents tend to flow, the inability of the screen to absorb the energy as eddy currents prevents its action as a screen. induction from occurring in a neighboring con- ductor, by interposing some conducting substance in which eddy currents can be freely established. As to the efficiency of the screening action, if the makes-and -breaks do not follow one another very rapidly, the following principles can be proved : (I.) If the screening material have absolutely no electrical resistance it will effect a perfect mag- netic screening when placed between the primary and secondary, no matter what its thickness may be. (2.) If the screen have a finite conductivity, the screening will be imperfect, unless the thick- ness of the material employed is considerable. If, however, the makes-and-breaks follow one another very rapidly, then The screening effect of even imperfect conduc- tors will become manifest with comparatively thin screens of metal. As to magnetic screening, therefore, it follows that the less the conductivity, the greater must be the speed of reversal, in order that the screen- ing action may be effective. Where a screen of iron is employed, an ad- ditional effect is produced by the fact that the small magnetic resistance of the metal, or its con- ductivity for lines of magnetic force, causes the lines of induction to pass through its mass, and thus effect a screening action for the space on the other side. This action is, by some, called mag- netic screening. In the case of iron screens, considerable thick- ness is required in the metal plate, in order to- obtain efficient screening action of this latter character. On account of this action of iron, in conducting away lines of force, a much smaller speed of reversal is required, in order to obtain effective screening action, where plates of iron are used, than in the case of plates of other metal. The apparatus shown in Fig. 500 was employed Fig. 499. The word magnetic screening is generally em- ployed in the latter sense of preventing magnetic Fig> 500. Willoughby Smith's Apparatus. by Mr. Willoughby Smith, in studying the effects- of magnetic screening. The flat coils A, and B, were employed for the primary and secondary coils respectively, and were connected to the battery C, and the galva^ Scr.] 469 [Sec. nometer F, as shown. Current reversers, D and E, were so arranged as to reverse galvanometer and battery alternately, and so cause the oppo- site induced currents to affect the galvanometer in the same direction. If the commutators were caused to reverse the current slowly, a plate of copper interposed between A and B, produced but little effect on the galvanometer, but if the re- versers were driven at a very rapid rate, a marked decrease of deflection occurred. The screening action of the metals, or their ability to diminish the galvanometer deflection, is in the order of their electrical conductivity, ex- cept in the case of iron, which, as we have seen already, has an additional screening power, due to its conducting away the lines of magnetic force. It follows from the preceding principles that the use of lead covered cables, for the conveyance of periodic currents, of the frequency of, say, sixty to one hundred alternations per second, is of but little or no advantage for protecting neighboring telephones from inductive action, because (i.) Lead is a poor conductor. (2.) The rapidity of alternation is too slow. J. J. Thomson made some experiments with electrical oscillations produced by resonance, of about 10 s in frequency. He obtained this fre- quency of oscillation from oscillations set up in the primary of an induction coil, in a secondary circuit of suitable dimensions. The presence of these secondary vibrations or waves was shown by means of the sparks seen at the terminals of a spark-micrometer circuit. Under these circum- stances he found that the interposition of a thin sheet of tin foil or gold leaf at once completely stopped the secondary sparks by the shielding action it exerted. Screening 1 , Magnetostatic Screen- ing from the inductive effect of a stationary magnetic field. Magnetostatic screening differs from electrostatic screening in that the plate of iron or other para- magnetic material surrounding the space to be screened must have a fairly considerable thick- ness. This arises from the fact that the magnetic susceptibility of the substance is not infinitely great. Screw, Binding A name some- times applied to a binding post. (See Post, Binding?) Seal, Hermetical Such a sealing of a vessel, designed to hold a vacuum, or gas- eous atmosphere under pressures greater or less than that of the atmosphere, as will pre- vent either the entrance of the external at- mosphere into the vessel, or the escape of the contained gas into the atmosphere. Hermetical sealing may be accomplished either by the use of suitable cements, or by the direct fusion of the walls of the containing vessel. The latter method is generally employed. Search Light, Automatic (See Light, Search, Automatic?) Searchlight, Electric (See Light, Search, Electric?) Secohm. The practical unit of self-induc- tion, or the practical unit of inductance. The secohm is equivalent to a length equal to- that of an earth quadrant, or 10 ' centimetres. The word secohm is a contraction for second, ohm, and implies the fact that the product of the ohm and the second are taken. The word henry is now generally used in the United States for secohm. (See Henry.) Secohmmeter. An apparatus for measur- ing the co-efficient of self-induction, mutual induction and capacity of conductors. (See Secohm. Induction, Mutual. Induction, Self.) The principle of the secohmmeter depends upon successively performing the cycleof magnetic operations, by making and breaking the circuit of a galvanometer by means of a commutator capable of working at a definite speed. Second, Ampere One ampere flow- ing for one second. (See Hour, Ampere.) Second, Watt A unit of electrical work. A watt -second equals the work due to the ex- penditu re of an electrical power of one watt for one second. It is the same as a volt-coulomb. The watt-second and the H. P. hour, etc., are units of work, since Power = - ?L , Time therefore, power X time = work. Secondary Battery. (See Battery, Sec- ondary.) Secondary Battery, Cell of (See Cell, Secondary.) Sec.] 470 [Sec. Secondary Cell. (See Cell, Secondary?) Secondary Cell, Jar of (See Jar of Secondary Cell,) Secondary Clock. (See Clock, Second- ary.) Secondary Coil. (See Coil, Secondary) Secondary Currents. (See Currents, Secondary?) Secondary, Fixed : The secondary of an induction coil, that, as is common in such coils, is fixed, as contradistinguished from a movable secondary. (See Secondary, Movable) Secondary Generator. (See Generator, Secondary?) Secondary Impressed Electromotive Force. (See Force, Electromotive, Second- ary Impressed?) Secondary, Movable The second- ary conductor of an induction coil, which, in- stead of being fixed as in most coils, is mova- ble. The peculiar movements observed in the secondary of an induction coil when the second- ary is free to move, have been carefully studied by Prof. Elihu Thomson. The secondaries employed for this purpose are in the shape of rings, discs, spheres, wedges, bars, wheels, etc., etc. The primary is in the form of a straight cylin- drical coil surrounding a straight core. The coils are traversed by rapidly alternating currents and possess considerable impedance. Among the many phenomena concerning the behavior of movable secondaries in such a rapidly alternating field are the following, viz.: (i.) A metallic ring, resting on lugs attached to the coils of the primary, is thrown violently off the magnet on the passage of alternating currents through the primary. (2.) Two metallic rings of the same diameter brought into the field are mutually attracted to ach other, with sufficient force to sustain the weight of one of the rings when the other ring is held in the field. (3.) Metallic spheres are set into rotation when so held near the primary pole as to be shielded from the action of part of the rapidly alternating field. When held on one side of the pole, this rotation occurs in the opposite direction to that when held on the opposite side. (4.) Metallic discs similarly placed are simi- larly set into rotation. (5.) The speed ot rotation of spheres or discs varies in different positions. (6.) Spheres or discs of diamagnetic substances attain their maximum rotation when held in posi- tion at right angles to those of paramagnetic sub- stances. (7.) Bars of steel or substances possessing high coercive power, placed dissymmetrically on the primary as regards their centres of gravity, ex- hibit the phenomena of a shifting magnetic field. (See Field, Magnetic, Shifting.) (8.) A wedge-shaped piece of steel placed with a flat face on the primary, exhibits a shifting magnetic field, and acts on movable metallic masses near it, just as though a fluid substance was escaping with great velocity from its edges. Secondary Movers. (See Movers, Second- ary) Secondary Plate of Condenser. (See Plate, Secondary, of Condenser?) Secondary Spiral. (See Spiral, Second- ary) Secretion Current. (See Current, Secre- tion?) Section Line of Electric Railway. (See Railroads, Electric, Section Line of.) Section, Neutral, of Magnet A section passing through the neutral line or equator of a magnet. (See Line, Neutral, of a Magnet. Magnet, Equator of.) Section, Trolley A single contin- uous length of trolley wire, with or without its branches. Sectional or Divided Overhead System of Motive Power for Electric Railroads. (See Railroads, Electric, Sectional Over- head System of Motive Power for) Sectional or Divided Surface System of Motive Power for Electric Railroads. (See Railroads, Electric, Sectional Surf ace System of Motive Power for?) Sec.] 471 [Sep. Sectional or Divided Underground System of Motive Power for Electric Rail- roads. (See Railroads, Electric, Sectional Underground System of Motive Power for.) Sectional Plating. (See Plating, Sec- tional.) Sectional Plating Frame. (See Frames, Sectional Plating) Seebeck Effect. (See Effect, Seebeck) Seismograph, Electric An appa- ratus for electrically recording the direction and intensity of earthquake shocks. Seismograph, Micro An electric apparatus for photographically registering the vibrations of the earth produced by earth- quakes or other causes. The micro-seismograph consists essentially of a microphone placed on the ground and connected with a telephone. A small concave mirror mova- ble about a horizontal axis is supported on a plate of aluminium supported on a platinum wire connected with the diaphragm of the telephone. The movements of the diaphragm of the telephone are permanently recorded on a strip of sensitized paper that is moved before the mirror. Selective Absorption. (See Absorption, Selective?) Selenium. A comparatively rare element generally found associated with sulphur. Selenium Battery. (See Battery, Selen- ium) Selenium Cell. (See Cell, Selenium) Selenium Eye. (See Eye, Selenium) Selenium Photometer. (See Photometer, Selenium) Self-Induced Current. (See Currents, Self-Induced) Self-induction. (See Induction, Self) Self-induction, Co-efficient of (See Induction, Self Co-efficient f) Self-Recording Magnetometer. (S e e Magnetometer, Self -Recording.) Self-Registering Wire Gauge. (See Gauge, Wire, Self-Registering) Self-Winding Clock. (See Clock, Self- Winding) Semaphore. A variety of signal apparatus employed in railroad block systems. The semaphore used on the Pennsylvania Rail- road consists of a wooden post, in the neighbor- hood of twenty feet in height, on which a wooden arm or blade, six feet in length and a foot in width, is displayed. When the block is clear, during the day the arm is placed pointing downwards at an angle of 75 degrees with the horizontal ; during night semaphore displays a white light. When the block is not clear, the arm or blade is placed in a horizontal position by day, or displays a red light at night. (See Railroads, Block System for.) Semaphore Arm. (See Arm, Semaphore) Semaphore Indicator. (See Indicator, Semaphore) Sender, Zinc A device employed in telegraphic circuits, by means of which, in order to counteract the retardation produced by the charge given to the line, a momen- tary reverse current is sent into the line after each signal. A zinc sender generally consists of a low resist- ance Siemens relay introduced between the line and the front contact of the signaling key. Sensibility, Electro An effect pro- duced on a sensory nerve by its electrization. Sensibility of Galvanometer. (See Gal- vanometer, Sensibility of) Sensitive Thread Discharge. (See Dis- charge, Sensitive Thread) Separate Coil Dynamo-Electro Machine. (See Machine, Dynamo-Electric, Separate Coil) Separate Touch, Magnetization by (See Touch, Separate) Separately Excited Dynamo. (See Dy- namo, Separately Excited) Separately Excited Dynamo-Electric Machine. (See Machine, Dynamo-Electric, Separately Excited) Separator. An insulating sheet of ebonite, or other similar substance, corrugated and perforated so as to conform to the outline of the plates of a storage battery, and placed between them at suitable intervals, in such a Sen] 472 [Ser. manner as to avoid short-circuiting, without impeding the free circulation of the liquid. Series and Magneto Dynamo-Electric Machine. (See Machine, Dynamo-Electric, Series and Magneto?) Series and Separately Excited Dynamo- Electric Machine. (See Machine, Dynamo- Electric, Series and Separately Excited?) Series and Shunt-Wound Dynamo-Elec- tric Machine. (See Machine, Dynamo- Electric, Series and Shunt- Wound?) Series Circuit (See Circuit, Series) Series-Connected Battery. (See Battery, Series-Connected?) Series-Connected Electro-Receptive De- vices. (See Devices, Electro-Receptive, Se- ries- Connected. ) Series-Connected Electro-Receptive De- vices, Automatic Cut-out for (See Cut-out, Automatic, for Series-Connected Electro-Receptive Devices?) Series-Connected Sources. (See Sources, Series-Connected?) Series-Connected Translating Devices. (See Devices, Translating, Series-Con- nected?) Series-Connected Voltaic Cells. (See Cells, Voltaic, Series-Connected?) Series Connection. (See Connection, Series?) Series, Contact A series of metals arranged in such an order that each becomes positively electrified by contact with the one that follows it. The contact values of some metals, according to Ayrton and Perry, are as follows: CONTACT SERIES. Difference of Potential in Volts. Zinc ) Lead f 2I Lead ) Tin *[ 069 Tin I Iron \ 313 Iron... ... ) Copper \ *4 6 Copper Platinum Platinum Carbon .238 The difference in potential between zinc and carbon is equal to 1.089, an ^ * s obtained by add- ing the successive differences of potential between the intermediate couples, thus: .210 +.069 +.313 + .146-1- .238 +.113 =1.089. This fact is known technically as Yalta's Law, which may be formulated as follows: The difference of potential, produced by the con- tact of any two metals, is equal to the sum of the differences of potentials between the intervening metals in the contact series. Series Distribution of Electricity by Constant Currents. (See Electricity, Se- ries Distribution of, by Constant Current Circuit?) Series-Multiple. A series of multiple connections. (See Circuit, Series-Multiple?) Series-Multiple Circuit. (See Circuit, Series-Multiple?) Series - Multiple-Connected Electro-Re- ceptive Devices. (See Devices, Electro-Re- ceptive, Series-Multiple- Connected?) Series-Multiple-Connected Sources. (See Sources, Series-Multiple-Connected.} Series-Multiple-Connected Translating Devices. (See Devices, Translating, Series- Multiple- Connected.) Series-Multiple Connection. (See Con- nection, Series-Multiple.) Series, Parallel A term some- times applied to a multiple-series connection. (See Connection, Multiple-Series.) Series, Thermo-Electric A list of metals so arranged according to their ther- mo-electric powers, that each metal in the series is electro-positive to any metal lower in the list. Series-Transformer. (See Transformer, Series.) Series Turns of Dynamo-Electric Ma- chine. (See Turn-s, Series, of Dynamo- Electric Machine.) Series Winding. (See Winding, Series.) Series-Wound Dynamo. (See Dynamo,. Series.) Series-Wound Dynamo-Electric Machine. (See Machine, Dynamo-Electric,, Series- Wound?) Sen] 473 [She. Series-Wound Motor. (See Motor, Se- ries- Wound.) Service Conductors. (See Conductors, Service.) Service, Street In a system of in- candescent lamp distribution that portion of the circuit which is included between the main and the service cut-out. Serving, Cable The covering of hemp or jute spun around the insulated core of a cable to act as a protection against the pressure of the iron wire which forms the armor of the cable. Shackling a Wire. Inserting an insula- tion between the two ends of a cut wire. Shaded or Screened. Cut off or screened from the effects of an electrostatic or mag- netic field. (See Screening, Magnetic. Screen, Magnetic. Screen, Electric.) Shadow, Electric A term some- times used for molecular shadow. (See Shadow, Molecular.) Shadow, Molecular The compara- tively dark space on those parts of the walls of Crookes' tubes, which have been protected from molecular bombardment by suitably placed screens. Fig. 501. Molecular Shadow. If a, in the Crookes tube, shown in Fig. 501, be connected with the negative pole of an elec- tric source, and the cross-shaped mass of alu- minium at b, be connected with the positive elec- trode, on the passage of a series of rapid discharges, phosphorescence is produced by the molecular bombardment from a, in all parts of the vessel opposite a, except those lying in the projection of its geometrical shadow. (See Phos- phorescence, Electric.) Shadow Photometer. (See Photometer, Shadow?) Shaft, Driven A shaft which re- ceives its power from the driving shaft. (See Mover, Prime?) Shaft, Driving The main line of shafting which takes its power directly from the prime mover. Shallow-Water Submarine Cable. (See Cable, Submarine, Shallow- Water?) Sheath, Protective A device at- tached to a transformer or converter, to pre- vent any connection from taking place between the high-potential primary circuit and the low-potential secondary circuit. The protective sheath devised by Prof. Elihu Thomson consists essentially in an earth -con- nected copper strip or divided plate interposed between the windings for the secondary and pri- mary circuit. Should the primary circuit lose its high insulation it becomes grounded. Sheet, Current The sheet into which a current spreads when the wires of any source are connected at any two points near the middle of a very large and thin con- ductor. A continuous electric current does not flow through the entire mass of a conductor in any single line of direction. If the terminals of any source are connected to neighboring parts of a greatly extended thin conductor, the current spreads out in a thin sheet known as a cur- rent sheet, and instead of flowing in a straight line between the points, spreads over the plate in cttrved lines of flow, which, so far as shape is concerned, are not unlike the lines of magnetic force. Sheet Lightning. .(See Lightning, Sheet) Shellac. A resinous substance possessing valuable insulating properties, which is ex- uded from the roots and branches of certain tropical plants. The specific inductive capacity of shellac as compared with air is 2.74. She.] 474 [Shu. Shell, Magnetic A sheet or layer consisting of magnetic particles, all of whose north poles are situated in one of the flat surfaces of the layer, and the south poles in the opposite surface. (See Magnetism, La- mellar Distribution of.) Shell Transformer. (See Transformer, Shell.) Shield, Magnetic, for Watches A hollow case of iron, in which a watch is per- manently kept, in order to shield it from the influence of external magnetic fields. (See Screen, Magnetic.) Shifting Magnetic Field. (See Field, Magnetic, Shifting.) Shifting Zero. (See Zero, Shifting.) Ships, Lightning Rods for (See Rod, Lightning, for Ships.) Ship's Sheathing, Electric Protection of Attaching pieces of zinc to the copper sheathing of a ship for the purpose of prevent- ing the corrosion of the copper by the water. (See Metals, Electrical Protection of.) Shock, Break A term sometimes employed in electro-therapeutics for the physiological shock produced on the opening or breaking of an electric circuit. Shock, Electric The physiological shock produced in an animal by an electric discharge. Shock, Opening The physiological shock produced on the opening or breaking of an electric circuit. Shock, Static A term employed in electro-therapeutics for a mode of applying Franklinic currents or discharges, by placing the patient on an insulating stool and apply- ing one pole of a static machine provided with small condensers or Leyden jars, to an insulated platform" on which the patient is placed, while the other pole is applied to the body of the patient by the operator. The electrode applied to the body of the pa- tient is provided with a ball electrode. Shocks are given to the patient on the approach of this electrode by the discharge of the Leyden jars. Short-Arc System of Electric Lighting. (See Lighting, Electric, Short-Arc Sys- tem.) Short-Circuit. To establish a short cir- cuit. (See Circuit, Short.) Short-Circuit Key. (See Key, Short- Circuit.) Short-Circuiting. Establishing a short circuit. (See Circuit, Short.) Short- Circuiting Plug. (See Plug, Short-Circuiting?) Short-Coil Magnet (See Magnet, Short- Coil) Short-Core Electro-Magnet (See Mag- net, Electro, Short-Core?) Short-Shunt Compound-Wound Dyna- mo-Electric Machine. (See Machine, Dy- namo-Electric, Compound- Wound, Short- Shunt) Shunt. An additional path established for the passage of an electric current or dis- charge. Shunt. To establish an additional path for the passage of an electric current or dis- charge. Shunt and Separately Excited Dynamo- Electric Machine. (See Machine, Dynamo- Electric, Shunt and Separately Excited) Shunt Circuit (See Circuit, Shunt.) Shunt Dynamo-Electric Machine. (See Machine. Dynamo-Electric, Shunt- Wound.) Shunt, Electric Bell (See Sell. Shunt, Electric.) Shunt, Electro-Magnetic In a sys- tem of telegraphic communication an electro- magnet whose coils are placed in a shunt circuit around the terminals of the receiving celay. The electro -magnetic shunt operates by its self-induction. Its poles are permanently closed by a soft iron armature so as to reduce the resist- ance of the magnetic circuit (See Induction, Self.) Shu.] 475 [Shu. On making the circuit in the coils of a receiv- ing relay, a current is produced in the coils of the electro -magnetic shunt in the opposite direction to the relay current ; and, on breaking the circuit in the relay, a current is produced in the coils of the electro-magnetic shunt in the same direction as the current in the relay. The connection of the coils of the electro-mag- netic shunt with those of the receiving relay, how- ever, is such that on making the circuit in the relay the current in the shunt coils flows through the relay in the same direction, and on breaking the circuit it flows in the opposite direction. Therefore this shunt produces the following effects: (I.) At the commencement of each signal in the receiving relay, it produces an induced cur- rent in the same direction which strengthens the current in the relay. (2.) At the ending of each signal in the receiv- ing relay, it produces a current in the opposite direction, which hastens the motion of the tongue of the polarized relay. (See Relay, Polarized.} Shunt, Galvanometer A shunt placed around a sensitive galvanometer for the purpose of protecting it from the effects of a strong current, or for altering its sensi- bility. (See Shunt^ The current which will flow through the shunt wire depends on the relative resistance of the gal- vanometer and of the shunt. In order that only TV rk> or TT.W of the total current shall pass through the galvanome- ter, it is necessary that the resistances of the shunt shall be the \, fa or 3-^, of the galvanom- eter resistance. Fig. 502 shows a shunt, in which the re- sistances, as compared with that of the galva- nometer, are those above referred to. The galva- nometer terminals are connected at N, N. Plug keys are used to connect one or another of the shunts with the circuit. (See Shunt, Multiplying Power of.} Sli 11 nt. Magnetic An additional path of magnetic material provided in a mag- Fig. 302. Galvanometer Shunt. netic circuit for the passage of the lines of force. Shunt, Multiplying Power of -- A quantity, by which the current flowing through a galvanometer provided with a shunt, must be multiplied, in order to give the total cur- rent. The multiplying power of a shunt may be de- termined from the following formula, viz.: A= X C, in which = the mul- tiplying power of a shunt whose resistance is s; g, is the galvanometer resistance; C, the current through the galvanometer, and A, the total cur- rent passing; s and g, are taken in ohms, and C and A, in amperes. Suppose, for example, that but -^ the entire current is to flow through the galvanometer; then the resistance of the shunt must evidently be \ g, for, s + g ~~ i+9 or, 10 s = s -f- g. 10 s s .. 9 s=g; or, Shunt or Reducteur for Ammeter. (See Reducteur or Shunt for Ammeter?) Shunt Ratio. The ratio existing between the shunt and the circuit which it shunts (See Shunt, Multiplying Power of.) Shunt, Relay, Stearns' -- A shunt employed in the differential method of duplex telegraphy to short-circuit the relay and then permit the line current to be cut off directly after it has completed its work in closing the local circuit. The use of the relay shunt permits the slacken- ing of the armature spring of the relay, because the decreased duration of the line current does not produce so strong a magnetization of the iron. Shunt-Turns of Dynamo-Electric Ma- chine. (See Turns, Shunt, of Dynamo- Electric Machine.) Shunt-Wound Dynamo-Electric Ma- chine. (See Machine, Dynamo-Electric, Shunt- Wound.) Shunt-Wound Motor. (See Motor, Shunt- Wound.) Shu.] 476 [Big. Shunting. Establishing a shunt circuit. Shuttle Armature. (See Armature, Shuttle) Side A, of Quadruplex Table. (See Table, Quadruplex, A, Side of.) Side B, of Quadruplex Table. (See Table, Quadruplex, B, Side of.) Side Flash. (See Flash, Side) Sidero-Magnetic. (See Magnetic, Side- ro) Siemens' - Armature Electro-Magnetic Bell. (zzBell,Electro-Magnetzc, Siemens' Armature Form) Siemens' Differential Voltameter, (See Voltameter Siemens' Differential) Siemens' Electric Pyrometer. (See Py- rometer, Siemens' Electric) Siemens-Halske Yoltaic Cell.- (See Cell, Voltaic, Siemens-Halske) Siemens' Water Pyrometer. (See Py- rometer, Siemens' Water) Signal Arm. (See Arm, Signal) Signal, Electric Tell-Tale An electrically operated signal, generally silent, whereby the appearance of a white or colored disc, on a black or otherwise uniformly colored surface, indicates the occurrence of a certain predetermined event. Signal Service for Electric Railways. (See Railroads, Electric, Signal Service System for) Signals, Electro-Pneumatic Sig- nals operated by the movement's of dia- phragms or pistons moved by compressed air, the escape of which is controlled electri- cally. Signaling, Balloon, for Military Pur- poses Transmitting intelligence of the movements of an enemy's army obtained from observations made in balloons by means of tel- ephone circuits connected with the balloon. Signaling, Curb In cable teleg- raphy a system for avoiding the effects of retardation by rapidly discharging the cable before another electric impulse is sent into it, by reversing the battery, before connecting it to earth, and then connecting to earth be- fore beginning the next signal. Signaling, Double-Curb In curb signaling, a method by which the cable, after being connected with the battery for sending a signal, is subjected to a reverse battery, but instead of being put to earth after this con- nection, as in single-curb signaling, the bat- tery is again reversed and connected to earth. The time during which the cable is connected to the reversed battery before being put to earth, that is, the time during which it receives the positive and negative currents, may be made of any suitable duration. Signaling, Double-Current Signal- ing by means of currents that alternately change their direction. Double-current signaling was devised by Var- ley in order to avoid the effects of the induction of underground conductors on Morse tele- graphic apparatus. The idea of reversing the direction of the current was to hasten the dis- charge of the wire, which was prolonged by in- duction. Double-current working, however, possesses other advantages, and is used in duplex and quadruplex transmission. Signaling, Single-Curb In curb signaling, a method by which the cable, after connection with the battery for sending a signal, is subjected to a reverse battery cur- rent, and then put to earth before again being connected to the battery for sending the next signal. Signaling, Single-Current Signal- ing by making or breaking the circuit of a single current. Single-current signaling is of two kinds, viz. : (l.) Open-Circuit Signaling, in which the bat- teries are fixed at each station, and are in circuit only when signaling. (2.) Closed-Circuit Signaling, where the bat- teries are divided, one half generally being at each end of the line, and so connected that both sets flow in the same direction. Signaling, Single-Current, Closed-Circuit A system of single-circuit signaling in which the sending batteries are placed at each end of the line and are so connected as 477 [Sin. to remain always in circuit. (See Signaling, Single- Current?) Signaling, Single-Current, Open-Circuit A system of single-current signaling in which the sending batteries, fixed at each station, are in circuit during signaling only. (See Signaling, Single-Current?) .Signaling, Velocity of Transmission of The speed or rate at which successive signals can be sent on any line without the retardation producing serious interference. (See Retardation:) Silent Discharge. (See Discharge, Si- lent) Silver Bath. (See Bath, Silver.) Silver Chloride Voltaic Cell. (See Cell, Voltaic, Silver Chloride?) Silver Plating. (See Plating, Silver) Silver Voltameter. (See Voltameter, Silver?) Silvered Plumbago. (See Plumbago, Sil- vered?) Silvering, Electro Covering a sur- face with a coating of silver by electro-plat- ing. (See Plating, Electro?) Electro-plating with silver. Silurus Electricus. The electric eel. (See Eel, Electric?) Simple Arc. (See Arc, Simple) Simple Circuit. (See Circuit, Simple?) Simple Electric Candle-Burner. (See Burner, Simple Candle Electric?) Simple-Harmonic Current. (See Cur- rent, Simple-Harmonic.) Simple-Harmonic Curve. (See Curve, Simple-Harmonic?) Simple-Harmonic Motion. (See Motion, Simple-Harmonic?) Simple Magnet. (See Magnet, Simple?) Simple-Periodic Current. (See Cur- rents, Simple-Periodic?) Simple-Periodic Electromotive Force. (See Force, Electromotive, Simple- Periodic?) Simple-Periodic Motion. (See Motion, Simple-Periodic.) Simple Radical. (See Radical, Simple.) Simple-Sine Motion. (See Motion, Simple-Sine) Simple Voltaic Cell. (See Cell, Voltaic, Simple) Simplex Telegraphy. (See Telegraphy, Simplex) Sims-Edison Torpedo. (See Torpedo, Sims-Edison) Sine Galvanometer. (See Galvanometer, Sine) Single-Brush Rocker. (See Rocker, Single-Brush ) Single-Cup Insulator. (See Insulator, Single-Shed) Single Curb. (See Curb, Single) Single-Current Signaling. (See Signal- ing, Single-Current) Single-Curve Trolley Hanger. (See Hanger, Single-Curve Trolley) Single-Fluid Hypothesis of Electricity. (See Electricity, Single-Fluid Hypothesis of) Single-Fluid Voltaic Cell. (See Cell, Voltaic, Single-Fluid) Single-Loop Armature. (See Armature, Single-Loop) Single-Magnet Dynamo-Electric Ma- chine. (See Machine, Dynamo-Electric, Single-Magnet) Single-Pair Yoke. (See Yoke, Single- Pair) Single-Shackle Insulator. (See Insula- tor, Single-Shackle) Single-Shed Insulator. (See Insulator, Single-Shed) Single-Stroke Electric Bell. (See Bell, Single-Stroke Electric) Single Touch. (See Touch, Single) Single-Wire Cable. (See Cable, Single- Wire) Sin.] 478 [Sme. Single-Wire Circuit. (See Circuit, Single- Wire) Sinistrorsal Solenoid or Helix. (See So- lenoid, Sinistrorsal) Sinuous Currents. (See Current, Sinu- ous?) Siphon, Electric A siphon in which the stoppage of flow, due to the gradual accumulation of air, is prevented by electrical means. In the electric siphon, an opening is provided at the highest part of the bend of the siphon tube, and a chamber is attached thereto, provided with a float. Contact points are so connected with the float that when it falls, contact is made, and when it rises, contact is broken. The closing of the circuit, on the fall of the float, operates an electric motor which drives an air pump which exhausts the air from the siphon. Or the float being raised in the siphon, the con- tact is broken and the operation of the pump is stopped. Siphon Recorder. (See Recorder, Si- phon) Sir William Thomson's Standard Cell. (See Cell, Voltaic, Standard, Sir William Thomson's?) SkinEffect.-(See Effect, Skin.) Skin, Faradization of The thera- peutic treatment of the skin by a faradic cur- rent. For efficient faradization the skin should be thoroughly dried and a metallic brush or elec- trode employed. For very sensitive parts, as, for example, the face, the hand of the operator, first thoroughly dried, is to be preferred as an electrode. Skin, Human, Electric Resistance of The electric resistance offered by the skin of the human body. The electric resistance of the skin is subject to marked differences in different parts of the body, where its thickness or continuity varies. It varies still more with variations in its condition of moisture. Even in the same individual the re- sistance varies materially under apparently similar conditions. Sleeve, Insulating A tube of treated paper or other insulating material, provided for covering a splice in an insulated con- ductor. Sleeve Joint (See Joint, Sleeve.) Sleeve, Lead A lead tube provided for making a joint in a lead-covered cable. Sled. The sliding contacts drawn after a moving electric railway car through the slotted underground conduit containing the wires br conductors from which the driving current is taken. Slide Bridge. (See Bridge, Electric t Slide Form of.) Slide, Resistance A rheostat, in which the separate resistances or coils are placed in or removed from a circuit by means of a sliding contact or key. Apparatus employed in telegraphy for charging a conductor to a given fraction of the maximum potential of the battery so as to adjust its charge in order to balance the varying charge of a cable. The resistance slide consists essentially of a set of resistance coils of high insulation and of equal resistance. Suppose, for example, ten such equal coils to be connected in series, then if connected to the charging battery the potential will vary by one-tenth at the junction between each pair. A condenser, therefore, will be charged to any number of tenths of the potential of the charging battery by connecting it at suitable points. A second set of coils of equal resistance is ar- ranged so as to subdivide any of the lower coils, thus permitting an adjustment to within a hun- dredth of the potential of the battery. Slide Wire. (See Wire, Slide.) Sliding Contact. (See Contact, Sliding.) Slow-Speed Electric Motor. (See Motor, Electric, Slow-Speed:) Sluggish Magnet. (See Magnet, Slug- gish) Small Calorie. (See Calorie, Small) Smee Yoltaic Cell. (See Cell, Voltaic, Smee.) Smelting, Electro The separation or reduction of metallic substances from their ores by means of electric currents. Sna.] 479 [Sol. Snap Switch. (See Switch, Snap.) Soaking-Iu. A term sometimes employed by telegraphers to represent the gradual penetration of an electric charge by a neigh- boring dielectric. An electric displacement occurs in the neigh- boring dielectric, and produces thereby what is generally called the residual charge. Soaking-Ont. A term sometimes em- ployed by telegraphers to represent a gradual discharge which occurs in the case of a charged conductor in a neighboring dielec- tric. When a condenser, or other similar conductor, is discharged, the discharge is not instantaneous. The charge which soaked in, gradually recovers, or soaks-out. Socket, Electric Lamp A support Fig. j 03. Lamp Socket. for the reception of an incandescent electric lamp. Incandescent lamp sockets are generally made so that the mere insertion of the base of the lamp Fig. jo hy. Henry z. Electrochemical 1. Intensity of mag P. Power. fl.lb. Footpound. gramme second (System) A.W.6. American Wire Gauge L. Inductance (Coeffic. of) A.M. Amperemeter. V.BI. Voltmeter equivalent i. Joule K.W. Kilowatt li. Magnetic per- meability K. Magnetic sus- B.W.G. Birmingham F.M. Field Magnet ^Complete period cepttbility Wire Gauge -f- Positive pole or termina t (^//. < ^.) H. Horizontal Negative *' " " H Dynamo intensity of Earth 's 4U- Arftoy magnetism Siemens \Anxatnr? [**, {'** f Vi ^ i 1 telephone Clmiit ^ : Jllltrnatmg Current Transformer Diagram fru^y SMf Sym.J 503 [Sym. t-pat*tSIUk " ^ Storage Battery Systu* Ihuuuf*- Fig. Sib- Crocker's Chart of Standard Electric Symbols and Diagrams. Sym.] 503 [Sys. Symmetrical Indnctiou of Armature. (See Induction, Symmetrical, of Armature. ,) Symmetrical Magnetic Field. (See Field, Magnetic, Symmetrical^] Sympathetic Electrical Vibrations. (See Vibrations, Sympathetic Electrical^ Sympathetic Vibrations. -(See Vibra- tions, Sympathetic) Synchronism. The simultaneous occur- rence of any two events. A rotating cylinder, or the movement of an index or trailing arm, is brought into synchronism with another rotating cylinder or another index or trailing arm, not only when the two are mov- ing with exactly the same speed, but when in ad- dition they are simultaneously moving over simi- lar portions of their respective paths. In the Breguet Step-by-Step or Dial Telegraph (See Telegraphy, Step-by-Step), the movements of the needle on the indicator are synchronized with the movements of the needle on the manipulator. In systems of Fac- Simile Telegraphy the move- ments of the transmitting apparatus are syn- chronized with those of the receiving apparatus. In Delany's Synchronous Multiplex Telegraph System, the trailing arm that moves over a cir- cular table of contacts at the transmitting end, is accurately synchronized with a similar trailing arm moving over a similar table at the receiving end. Delany, who was the first to obtain rigorous synchronism at the two ends of a telegraphic line hundreds of miles in length, accomplishes this by the use of La Cour's phonic wheel, through the agency of correcting electric im- pulses, automatically sent in either direction over the main line, when one trailing arm gets a short distance in advance or back of the other. With alternating current dynamos, where one dynamo is feeding incandescent lamps connected to the leads in multiple, and it is desired to couple another alternating current dynamo in parallel with the first, it is necessary to obtain a complete synchronism of the two dynamos before coupling them, since otherwise the lamps will show variations in their light, and the machine may suffer. Synchronizable. Capable of being syn- chronized. (See Synchronism) Synchronize. To cause to occur or act simultaneously. (See Synchronism.} Synchronized. Caused to occur or act simultaneously. (See Synchronism.) Synchronizing Dynamo-Electric Ma- chine. (See Machine, Dynamo-Electric, Synchronizing) Synchronous Multiplex Telegraphy. (See Telegraphy, Synchronous Multiplex, Delany's System) System, Astatic An astatic com- bination of magnets. An astatic needle consists of an astatic system of two magnetic needles. The needles are rigidly fixed together with their opposite poles facing each other. The two needles form an as- tatic pair or couple. (See Needle, Astatic.) System, Block, for Railways (See Railroads, Block System for) System, Centimetre - Gramme - Second (See Units, Centimetre - Gramme - Second) System, Continuous Underground, of Motive Power for Electric Railroads (See Railroads, Electric, Continuous Un- derground System of Motive Power for) System, Dependent, of Motive Power for Electric Railroads (See Railroads, Electric, Dependent System of Motive Power for) System, Independent, of Motive Power for Railroads (See Railroads, Elec- tric, Independent System of Motive Power for) System, Multiphase A term fre- quently applied to a system of rotating elec- tric currents. (See Current, Rotating) System of Distribution of Electricity by Commutatiiig Transformers. (See Elec- tricity, Distribution of, by Commutating Transformers) System of Distribution of Electricity by Condensers. (See Electricity, Distribution of, by Alternating Currents by Means of Condensers. Electricity, Distribution of, by Continuous Current by Means of Condens- ers.) System of Distribution of Electricity by Means of Alternating Currents. (See Elec- Sys.] tricity, Distribution of, by Alternating Cur- rents.} System of Distribution of Electricity by Motor Generators. (See Electricity, Dis- tribution of, by Motor Generators} System, Three-Wire A system of electric distribution for lamps or other trans- lating devices connected in multiple, in which three wires are used instead of the two usually employed. In the three-wire system two dynamos are gen- erally employed, which are connected with one another in series. The three conductors are connected as shown in Fig. 527, the central conductor to the junction of the two dynamos and the two others to their free terminals, and the difference of potential be- tween the central and the two outer conductors is maintained the same. The lamps, or other electro-receptive devices, are placed in multiple- arc between either branch, and so distributed that the current hi each branch is the same. When such balance is established no current flows through the central or neutral conductor. But when that balance is disturbed, the surplus current in one branch is taken up by the central conductor. The three-wire system effects considerable [Tau economy in the weight of wire required. Since in the multiple- series-connection of electro -receptive devices whatever difference of potential is im- pressed on the mains is fed to each device, no higher difference of potential can be employed on the mains than that which the devices are capa- ble of taking. In the case of an incandescent lamp, if such difference be exceeded, too strong a current is passed through the lamps with a, consequent decrease in their life. In the three-wire system of distribution a higher difference of potential can be maintained on the mains than is required for any lamp placed in Fig- J27- Three- Wire System connection therewith, and in this manner a con- siderable saving is effected in the cot of the leads. T. A symbol used for time. T-shaped Spark. (See Spark, T-Shaped.} Table, Quadruplex, A-Side of That side of a quadruplex system which is worked by means of reverse currents. (See Telegraphy, Quadruplex^) Table, Quadruplex, B-Side of That side of a quadruplex system which is worked by means of strengthened currents. (See Telegraphy, Quadruplex} Tables of Conducting Powers. (See Powers, Conducting, for Electricity. Re- sistance, Electric.} Tachograph. An apparatus for recording the number of revolutions per minute of a shaft or machine. Tachometer. An apparatus for indicating at any moment on a revolving dial the exact number of revolutions per minute of a shaft or machine. A tachometer is sometimes called a speed in- dicator. Tachyphore. A term proposed by Wurtz for a system of electric transportation, in which a carriage, formed of magnetic ma- terial, is propelled by the sucking action of solenoids placed along the track and ener- gized in succession during the passage of the car. This is generally called the portelectric sys- tem. (See Portelectric.) Tail Light. (See Light, Tail.} Tai.] 505 [Tag. Tailings. False markings received in sys- tems of automatic telegraphy, due to retard- ation. (See Retardation?) Tailings. A term applied to the current that runs out of a line at the receiving end. The current that continues to run out at the receiving end of the circuit after the send- ing current is broken. The tailings in a telegraphic line are due to the effects of self-induction and static capacity follow- ing the breaking of the circuit which produce a current in the same direction as that sent into the line. Consequently, on the breaking of the cir- cuit, the current continues to flow out of the line at the distant or receiving end. This prolongation of the original current is known technically as the tailing or the tailing current. Talk, Cross In telephony an indis- tinctness in the speech transmitted over any circuit, due to this circuit receiving, either by accidental contacts or by induction, the speech transmitted over neighboring circuits. Tangent. One of the trigonometrical functions. (See Function, Trigonometrical?) Tangent and Sine Galvanometer, Com- bined (See Galvanometer, Combined Tangent and Sine?) Tangent Galvanometer. (See Galva- nometer, Tangent?) Tangent Scale. (See Scale, Tcmgent?) Tangentially Laminated Armature Core. (See Core, Armature, Tangentially Lam- inated?) Tank, Cable A water-tight tank in which a section of a cable is placed for pur- poses of testing. The cable is tested either when merely covered by water, or when subjected to a pressure ap- proximately equal to or in excess of that to which it will be subjected when laid in the water. Reid has constructed cable tanks for testing under pressures as great as 4,500 pounds per square inch. The pressure is obtained by means of force pumps. When a cable section is subjected to these pressures any flaws or defects would be at once detected by the entrance of the water. Tanning, Electric An application of electric currents to tanning leather. The dressed hides are steeped in a solution of tannin through which an electric current is passed. It is claimed, that by this process, the hides are thoroughly tanned in from one to four days, in place of from four to twelve months, as re- quired by the ordinary process. The tanning solution is placed in a vat fur- nished with suitable electrodes and filled with the tanning liquid, and the articles to be tanned are placed between the electrodes and a motion of revolution given to the vat. By these means the time required for the completion of the pro- cess is considerably shorter than that required by the ordinary process. Tap. A conductor attached to a larger conductor in a shunted circuit. Tap, AmpSre A tap provided for carrying off a current of one ampere. Tap Wires. (See Wires, Tap.) Tape, Insulating A ribbon of flexible material impregnated with kerite, okonite, rubber or other suitable insulating material, employed for insulating wires or electric conductors at joints, or other exposed places. Sometimes the tape is formed entirely of some or another the above named insulating materials. Taped Wire. (See Wire, Taped,} Tapper, Double-Key (See Key, Double Tapper?) Target, Electric A target in which the point struck by the ball is automatically registered by means of electric devices. A variety of targets have been devised. Gen- erally, however, the target is divided into a num- ber of separate sections provided with circuits of wires, on the making or breaking of any of which, by the impact of the ball, the section struck is au- tomatically indicated on an electric annunciator. (See Annunciator, Electro-Magnetic.') Taste, Galvanic A sensation of taste produced when a voltaic current is passed through the tongue or in the neighborhood of the gustatory nerves, or nerves of taste. Tea.] 506 [TeU Teaser. An electric current teaser. (See Teaser, Electric Current?) Teaser, Electric Current A coil of fine wire placed on the field magnets of a dynamo-electric machine, underneath the se- ries coil wound thereon, and connected as a shunt across the main circuit. The name teaser was applied by Brush to the coil of fine wire used as above described to main- tain constant electromotive force under variations of load. Technics, Electro The science which treats of the physical applications of electricity and the general principles applying thereto. Tee, Lead A tee-shaped lead tube provided for the purpose of taking a branch joint from a main cable to a service line. Tee, Split-Lead A tee-shaped lead tube that is split for readily covering a joint at a loop in a cable. Tel-Autogram. The recorded message obtained by means of a tel-autograph. (See Tel-Autograph) Tel-Autograph. A telegraphic system for the fac-simile reproduction of handwriting. Teleautograph. An orthography some- times employed for tel-autograph. (See Tel- Autograph^) Tele-Barometer, Electric An elec- tric recording barometer for indicating and recording barometric or other pressures at a distance. Telegrapher's Cramp. (See Cramp, Telegrapher's?) Telegraphic. Pertaining to telegraphy. Telegraphic Alarm. (See Alarm, Tele- graphic) Telegraphic Alphabet. (See Alphabet, Telegraphic) Telegraphic Alphabet, Continental Code (See Alphabet, Telegraphic : Inter- national Code.) Telegraphic Alphabet, Morse's (See Alphabet, Telegraphic : Morse's) Telegraphic Arm. (See Arm, Tele- graphic?) Telegraphic Bracket. (See Bracket* Telegraphic?) Telegraphic Cable. (See Cable, Tele- graphic) Telegraphic Code. (See Code, Tele- graphic?) Telegraphic Earth-Circuit. (See Cir- cuit, Earth, Telegraphic) Telegraphic Embosser. (See Embosser, Telegraphic) Telegraphic Fixtures. (See Fixtures, Telegraphic?) Telegraphic Fixtures, House-Top (See Fixtures, Telegraphic House- Top.) Telegraphic Ground Circuit. (See Cir- cuit, Ground, Telegraphic) Telegraphic Joints. (See Joint, Tele- graphic or Telephonic) Telegraphic Key. (See Key, Telegraph- ic) Telegraphic Line Circuit. (See Circuit, Line, Telegraphic) Telegraphic Needle. (See Needle, Tele- graphic) Telegraphic Paper Winder. (See Wind- ers, Telegraphic Paper?) Telegraphic Pocket Relay. (See Relay, Pocket Telegraphic?) Telegraphic Register. (See Register, Telegraphic) Telegraphic Switch Board. (See Board, Switch, Telegraphic?) Telegraphic Translator. (See Trans- later, Telegraphic) Telegraphically. In a telegraphic manner. Telegraphing. Sending a communication by means of telegraphy. Telegraphy, Acoustic A non-re- cording system of telegraphic communica- tion, in which the dots and dashes of the Morse system, or the deflections of the needle in the needle system, are replaced by sounds Tel.] 507 [TeU that follow one another at intervals, that represent the dots and dashes, or the de- flections of the needle, and thereby the letters of the alphabet. Morse invented a sounder, for this purpose, which is used very generally. (See Sounder, Morse Telegraphic.) Steinheil and Bright each invented acoustic systems of telegraphy in which electro-magnetic bells are used. For details of the apparatus and system see Telegraphy, Morse System of. Telegraphy, American System of A term sometimes applied to the Morse sys- tem of telegraphy. (See Telegraphy, Morse System of.) Telegraphy and Telephony, Simultane- ous, Over a Single Wire Any system for simultaneous transmission of telegraphic and telephonic messages over a single wire. These systems are based, in general, on the fact that a gradual make-and-break in a tele- phone circuit fails to appreciably affect a tele- phone diaphragm. By the use of graduators the makes and breaks required for the transmission of the telegraphic dispatch are effected so grad- ually that they fail to appreciably influence the telephone diaphragm, and thus permit simultane- ous telegraphic and telephonic transmission over a single wire. (See Graduators.) Telegraphy, Autographic A name sometimes applied to fac-simile telegraphy. (See Telegraphy, Fac-Simzle.} Telegraphy, Automatic A system by means of which a telegraphic message is automatically transmitted by the motion of a previously perforated fillet of paper contain- ing perforations of the shape and order re- quired to form the message to be transmitted. The paper passes between two terminals of (he main line, the circuit of which is completed when the terminals come into contact at the perforated parts, and is broken when separated by the unperforated parts of the paper. In the automatic telegraph some form of regis- tering apparatus is employed. In the Wheatstone system, the perforations mechanically control the movements of the levers which make contacts between the line and the battery. The advantage of automatic telegraphy arises from the fact that the rate of transmission or re- ception of signals does not depend on the expert- ness of the operators, and the messages may be perforated on the slips preparatory to transmis- sion. Type printing telegraphs are often used for registering apparatus, in which case the im- pulses required for the transmission of the dif- ferent letters are automatically sent into the line by the depression of corresponding keys on a suitably arranged key -board. Telegraphy, Chemical A system by means of which the closings of the main- line-circuit, corresponding to the dots and dashes of the Morse alphabet, are recorded on a fillet of paper by the electrolytic action of the current on a chemical substance with which the paper fillet is impregnated. (See Recorder, Chemical, Bain's?) Telegraphy, Contraplex Duplex telegraphy in which transmissions are simul- taneously made from opposite ends of the line. When the transmissions are simultaneously made from the same end of the line, the system is called diplex telegraphy. (See Telegraphy, Di- plex.) Telegraphy, Dial A system of telegraphy in which the messages are received by the motions of a needle over a dial plate. (See Telegraphy, Step-by- Step.) Telegraphy, Diplex A method of simultaneously sending two messages in the same direction over a single wire. Diplex telegraphy is to be distinguished from duplex telegraphy, where two messages are simul- taneously transmitted over a single wire in oppo- site directions. Telegraphy, Double-Needle A sys- tem of needle telegraphy in which two sepa- rate and independently operated needles are employed. This system diners from the single-needle sys- tem only in the fact that two needles, entirely in- dependent of each other, are mounted side by side, on the same dial, so as to permit their simultane- ous operation by the right and left hand of the Tel.] 508 [lei. operator. Each needle has therefore a separate wire. The increase in speed of signaling thus obtained is not, however, sufficiently great to balance the increased expense of construction. Single-needle instruments, therefore, are preferred to those with two needles. Telegraphy, Duplex, Bridge Method of A system whereby two telegraphic messages can be simultaneously transmitted over a single wire in opposite directions. Various duplex telegraphs have been devised. The Bridge Duplex is shown in Fig. 528. The receiving relay is placed in the cross wire of a Wheats tone bridge. (See Bridge, Electric.} Fig. 328. Duplex Telegraphy, Bridge, Method. When the ends of this cross wire are at the same potential, whicn will occur when the resist- ances in the four arms are proportionately equal, no current passes. The battery is connected through the trans- mitter K, which is arranged so that the battery contact is made before the connection of the line to earth is broken, to H, where the circuits branch to form the arms of the bridge. Adjust- able resistances A, B, are placed in the two arms of the bridge. The line wire L, connected as shown, forms the third arm, and a rheostat or other adjustable resistance R, connected to a condenser C, as shown, forms the fourth arm. (See Rheostat.} The relay M, is placed in the cross wire of the bridge thus formed. Small resistances V, and W, are placed in the circuit of the battery to pre- vent injurious short circuiting. A similar disposition of apparatus is provided at the other end of the line. If, now, the four re- sistances at one end are suitably adjusted, the relay will not respond to the outgoing current ; but, since an earth circuit is employed, it will respond to the incoming current. The relay at either end, therefore, will only respond to signals from the other end. The operator may thus signal the distant station while, at the same time, his relay, not being affected by his sending, is in readiness to receive signals from the other end. Telegraphy, Duplex, Differential Method of A system of duplex telegraphy in which the coils of the receiving and transmit- ting instruments are differentially wound. A differential system of duplex telegraphy is shown in Fig. 529. The coils of the receiving and transmitting galvanometers at A and B, are differentially wound. One of the coils of A, is connected to that of B, through the line, as shown; and the other, in each to the rheostats at R, and R'. As these coils are differentially wound, when equal currents flow in opposite directions through either of the instruments at A B, no deflection of the galvanometer occurs. The battery at A, has its copper terminal, and that at B, its zinc terminal, connected to earth. When the keys at A and B, are depressed simul- taneously, the currents sent into the line flow in the same direction and strengthen each other. Suppose now that only the key at A, be de- pressed. The current divides equally between rheostat and line, the resistance e a b b a' e', r', being made equal to the resistance e c d R. This current passes through both coils of the instrument at A, and produces no deflection of the needle; but since it only passes through one coil at B, it deflects the galvanometer needle, and produces a signal. Earth Duplex Telegraphy, Differenti If the keys at A, and B, are simultaneously closed, the effect on the line is to add the current of the two batteries, but each rheostat circuit is traversed by its own battery current only. The line-connected coils of the ga'vanometer have, therefore, the stronger currents flowing through them, and the needles of both are moved, just as if, with a single battery discharging into the line, its resistance had been decreased. Each Tel.J 509 [Tel. sender's instrument is unaffected by the currents he sends into the line, and is, therefore, ready to be operated by the currents sent into the line by the sender at the other end of the line. The two currents in duplex telegraphy, there- fore, do not pass each other on the line; on the contrary, they are sent into the line in the same direction. Since, \vhen either key is moving there is a small interval of ti.ne when the circuit is broken for incoming currents, the keys are generally made so as to close the second contact before breaking the fir.*t. In order to avoid disturbing the balance on the introduction of the resistance of the batteries at A or B, on closing the circuits, an equal resistance is added at r and r', between the back stop and the earth. Si:ice the proper operation of duplex telegraphy requires a balance in the resistance of the circuits of the differentially wound coils, a rheostat at R, and R', is necessary. Besides balancing the line for resistance, it is necessary to balance it for capacity. A condenser is, therefore, necessary when the circuit exceeds in length about 100 miles, or has much cable or underground wire. Telegraphy, Fac-Simile A system whereby a fac-simile or copy of a chart, diagram, picture or signature is telegraphically transmitted from one station to another. Fac-simile telegraphy is sometimes called auto- graphic telegraphy, or pantelegraphy. Bakewell's fac-simile telegraph, which was one of the first devised, consists of two similar metal cylinders c, c', arranged at the two e:ids of a telegraph line L, at M and M', as shown in Fig. 530. These cylinders are synchronously rotated . , Fig. jjo. Bakmvell's Fac-Simile Telegraphy. and provided with metallic arms or tracers r, r', placed on a horizontal screw in the line circuit and moved laterally over the surface of the cylinder on its rotation. At the transmitting station the chart, writing, or other design is traced with varnish, or other non-conducting liquid, on the surface of the metallic cylinder, as at M, and a sheet of chemi- cally prepared paper, similar to that employed in the Bain chemical system is placed on the surface of the receiving cylinder at M'. (See Recorder, Chemical, Bains.) The two cylinders being synchronously rotated, the metallic tracer breaks the circuit in which it is placed when it moves over the non-conducting lines on the cylinder, and thus causes correspond- ing breaks in the otherwise continuous blue spiral line traced on the paper-covered surface of M'. The telegraph keys at R, R', are used for the purposes of ordinary telegraphic communication before or after the rec >: d is transmitted. Caselli's Pan Telegraph is an improvement on Bakewell's Cop>i .g Telegraph. Better methods are employed for maintaining the synchronism between the transmitting and receiving instru- ments, for which purpose a pendulum, vibrating between two electro-magnets, is employed. Telegraphy, Fire Alarm A system of telegraphy by means of which alarms can be sent to a central station, or to the fire engine houses in the district, from call boxes placed on the line. The alarms are generally sounded by an ap- paratus similar to a district call, so that the pull- ing back of a lever rotates a whe.l, by means ot which successive makes and breaks are produced, the number and sequence of which enable the receiving stations to locate the particular box from which the signal is sent. . In the case of some buildings, the alarms are automatic, and either call for help from the central office, or for the watchman in the build- ing, or else turn on a series of water faucets or jets, in order to extinguish the fire. I these cases thermostats are used. (See Thermostat.) Telegraphy, Gray's Harmonic Multiple A system for the simultaneous trans- mission of a number of separate and distinct musical notes over a single wire, which separate tones are utilized for the simultane- ous transmission of an equal number of tele- graphic messages. The separate tones are thrown into the lines by means of tuning forks automatically vibrated by electro- magnets. Th.se forks interrupt the Tel.] 510 [Tel. circuit of batteries connected with the main line at the sending end of the line. The composite tone thus formed, is separated into its component tones by receiving electro- magnets called harmonic receivers, the armature of each of which consists of a steel ribbon or plate tuned to one of the separate notes sent into the line. As the complex or undulatory current passes through the coils of each harmonic re- ceiver, that note only affects the particular arma- ture that vibrates in unison with its ribbon or reed. The operator, therefore, at this receiver is in communication only with the operator at the key of the circuit that is sending this par- ticular note into the line. The same is true of the other receivers. The Morse alphabet is used in this system, the dots and dashes being received as musical tones. In practice it was found that there was no diffi- culty in each operator recognizing the particular sound of his cwn instrument in receiving, although many instruments were in the same room. By a subsequent invention the signals received are converted into the regular Morse characters by means of an ingenious device. Telegraphy, Induction A system for telegraphing by induction between moving trains and fixed stations on a railroad, by means of impulses transmitted by induction between the car and a wire parallel with the track. Two systems of inductive telegraphy are in actual use, viz., (i.) The Static Indtiction system of W. W. Smith and Edison, and (2.) The Current or Dynamic Induction system of Willoughby Smith and Lucius J. Phelps. In the System of Static Induction, one of the condensing surfaces which receives or produces the charge, consists of a wire placed on the road so as to come as near the top of the cars of the moving train as possible. The other condensing surface is composed of the metal roofs of the mov- ing cars. Each condensing surface is connected to suit- able instruments and batteries, and to the earth ; the line wire at the fixed station being connected to earth through a ground plate, and the metal roof of the cars to earth through the wheels and track. Under these circumstances variations in the charge of either of the condensing surfaces pro- duce inductive impulses that are received by the other surface as telegraphic signals. The Morse alphabet is employed, but in place of the ordinary receiver or sounder, a telephone is used. In the System of Current Induction, the line wire is placed near the track, so as to be parallel with a coil of insulated wire placed on the side of the car, and which receives the inductive impulses. The coil of wire on the train is connected with instruments and batteries, and forms a metallic circuit. The line wire is also connected with suitable batteries and receiving and transmitting instruments. An induction coil is generally employed, since the greater and more rapidly varying difference of potential of its secondary wire renders it better suited for producing effects of induction. A tele- phone is employed as a receiver, as in the system of static induction. The metallic car roof and the lower truss rods have been successfully used as the secondary conductor of the induction coil. The automatic make-and break used for operat- ing the induction ceil, causes the Morse characters employed in this system to be received in the receiving telephone as shrill buzzing sounds. The receiving telephones used on the trains have a resistance of about 1,000 ohms. Telegraphy, Induction, Current System of A system of induction telegraphy depending on current induction between a fixed circuit along the road, and a parallel circuit on the moving train. The circuit on the train generally consists of a coil of wire. (See Telegraphy, Induction.} Telegraphy, Induction, Dynamic System of A term sometimes used in place of a system of telegraphic current induction. (See Telegraphy, Induction?) Telegraphy, Induction, Static System of A system of inductive telegraphy de- pending on the static induction between the sending and receiving instrument. A fixed wire placed along the road so as to come near another wire or metallic surface on the mov- ing train, imparts to the latter a static charge, which is utilized for the transmission of dispatches. The metal roof of the car is generally used for the condensing surface receiving the charge. (See Telegraphy, Induction.) Tel.] 511 [Tel. Telegraphy, Machine A term some- times applied instead of automatic telegraphy. (See Telegraphy, Automatic?) A system of telegraphy is properly called ma- chine telegraphy when both the transmission and the receiving of the telegraphic messages are ac- complished by machine, instead of by the hand, as usual. Telegraphy, Morse System of A system of telegraphy in which makes and breaks occurring at intervals corresponding to the dots and dashes of the Morse alphabet are received by an electro-magnetic sounder or receiver. A metallic lever A, Fig. 531, is supported on a pivot at G, between two set screws D, D, so as to liave a slight movement in a vertical plane. This motion is limited in one direction by a stop at C, called theanvi/or front contact, and in the other direction by a set screw F, which constitutes its back stop. The front stop C, is provided with a platinum contact or stud, which may be brought into contact with, or separated from, a similar stud placed directly opposite it. These contacts are connected to the ends of the circuit so that on Fig- S3i' Telegraphic Key. the movements of the key, by the hand of the operator placed on the insulated head B, the line ii closed and broken in accordance with the dots and dashes of the Morse alphabet. A spring, the pressure of which is regulated by the screw F', is provided for the upward movement of the key. A switch H, is provided for closing the line when the key is not in use. The system generally used in the United States is known as the " Closed -Circuit System, " the bat- tery being connected to line whether the line is in use or not This battery is generally placed at both ends of the line. In Europe, the " Open-Circuit System " is gen- erally used. Alternating currents and polarized relays are employed. One pole is connected to the line at the front of the key, and the other pole to the back of the key. When the line is not in use, it is connected to earth at both ends by switches conveniently placed for the operators. With this system, intermediate stations must each have a main battery, while in the closed -circuit system, the terminal batteries answer for all inter- mediate offices, which in some cases amount to as many as fifty. In the Morse system, each station is provided with a key, relay, sounder or register, and local battery. The closed-circuit, connecting one station with another, being broken by the open- ing of the switch H, or the working of the key, so as to open and close its contacts, the armature of the relay opens or closes the circuit of the local battery and operates the sounder or register- ing apparatus connected therewith. (See Sounder, Morse Telegraphic. Apparatus, Registering, Telegraphic.} Telegraphy, Multiplex A system of telegraphy for the simultaneous transmis- sion of more than four separate messages over a single wire. (See Telegraphy, Syn- chronous-Multiplex, Delanys System.) Telegraphy, Needle System of A system of telegraphy in which signals are transmitted by means of the movements of needles under the influence of the electric current. (See Telegraphy, Single-Needle.) Telegraphy, Phonoplex A system of telegraphic transmission in which pulsatory currents, superposed on the ordinary Morse currents, actuate a modified telephonic re- ceiver, and thus permit the simultaneous transmission of several separate messages over a single wire without interference. Telegraphy, Printing A system of telegraphy in which the messages received are printed on a paper fillet. In Callahan's Printing Telegraph, two type wheels are employed, one of which carries letter type and the other numerals on its circumference. These printing wheels are placed alongside of each other, as shown in Fig. 532, but on separ- ate and independent axes. The type wheels are moved by a step-by-step device. The impulses necessary to bring the Tel.] 512 [TeU desired letters in position for printing are auto- matically sent by a circuit maker and breaker. These impulses are sent into the line by the de- pression of keys on a suitably arranged key- board. When the proper letter or r.cTr.eral is reached at the receiving end, the printing wheel is stopped, and a paper fillet is pressed against its surface. The printing wheel is kept covered with ink by means of an inked roller. The transmitting instrument is similar in its operation to the Breguet manipulator. Separate transmitters are used for each of the wires. (See Telegraphy, Step-by -Step.) Fig. S3 2. Callahan's Prntin- Tdegraph. Telegraphy, Quadrnplex A system for the simultaneous transmission of four mes- sages over a single wire, two in one direction and the remaining two in the opposite direc- tion. Quadruplex telegraphy consists in fact of du- plex telegraphy duplexed. There are various systems of quadruplex teleg- raphy. The most important are the bridge method and the differential method. (See Teleg- raphy, Quadruplex, Bridge Method of. Telegra- phy, Quadruplex, Differential Method of.) Telegraphy, Qnadruplex, Bridge Method of A system of quadruplex telegraphy by means of a double bridge duplex system. (See Telegraphy, Quadruplex?) In the bridge method of quadruplex telegraphy, as in the differential method, changes in the polar- ity and strength of the current are utilized to establish a double duplex system of transmission. Fi g- 533 from Prescott's" Electricity and Electric Telegraphy, "from which the following desciiption is taken, shows tic method first employed by the Western Union Telegraph Company in 1874. A double current transmitter, or pole changer, is shown at T', with its operating key K' and local battery e'. This instrument interchanges- the poles of the main battery E' , when K, is de- pressed, and thus reverses the polarity of current on the line. The increment transmitter T 2 , is connected ta the battery wire 12 of T', in such a way that when K', is depressed, the main battery E', is placed in series with battery E, of say twice the strength of E', thus permitting a current of three- fold the original strength to be sent into the line. Fig. 5 33. Quadruplex Telegraphy, Bridge Method. Two receiving instruments R' and R 2 , are placed at the distant end of the line. R', is a polarized relay whose armature is deflected in one direction by positive currents, and in the opposite direction by negative currents, independ- ently of their strength. That is to say, R', re- sponds to changes in the direction of the currents that pass through its coils, but not to changes in their strength. (See Relay, Polarized.} Relay R 2 , is non-polarized and the movements of its soft iron armature depend on a change in the strength of the current only. That is to say, R a , responds to changes in the strength of the current passing through its coils, but not to- changes in their direction. These two relays R and R 8 , are placed in the bridge wire of a Wheatstone bridge. Tiiemiire apparatus of transmitting keys and relays is duplicated at each end of the line. Under these conditions, signals transmitted from either end of the line affect the instruments at the other end of the line, but not their own instruments, in the same manner as in the case of the bridge du- plex. (See Telegraphy, Duplex, Bridge Method of-} Telegraphy, Quadruplex, Differential Tel.] 513 [Tel. Method of A system of quadruplex telegraphy by means of a double differential duplex system. Quadruplex telegraphy depends for its opera- tion on the use of two differentially wound relays at each station. One of these relays A, as shown in Fig. 534, which shows the general arrangement of the system, gives signals on a change in the direction of the current, but none on a change in the current strength. The other B, gives signals on changes in current strength, but none on changes in direction. They are, therefore, in- dependent of each other, and operate sounders that are under the independent control of two distinct receiving operators. A table, divided into four sections, is provided with places for two sending and two receiving clerks. The name " A side " is given to the side worked by the reversed currents, and the "B side " to that worked by the strengthened cur- rents. LEX RHEOSTAT BATTERY 1, BATTERY Z. Fig- S3 4- Quadruplex Telegraphy, Differential Method. Referring to Fig. 534 the reversing key on the *' A side " is merely indicated so as to avoid con- fusion by too great detail ; as is also the case with the increment key or the strengthening key at B. From the connections it will be seen that when the increment key is at rest, the reversing key sends currents from battery I. When the incre- ment key is depressed, the reversing key is shifted from battery I, and connected by its copper con- nection C, with the battery 2, of double the strength of I. Since, however, I, is thus connect- ed in series with C, the current strength is in- creased threefold. From the reversing key the current passes to the junction of the two coils with which the relay B, is differentially wound. It divides here between these coils, which are connected to simi- lar coils on relay A, as shown. The current from one coil on A, is sent to line, while that from the other coil goes to earth through the compen- sating rheostat. This arrangement forms a du- plex system, the outgoing currents of which have no effect on the home relays. Resistances R* and R 3 , are connected to the batteries I and 2, and the stops in the increment key in the manner shown, to the resistance of R and R 3 . The former is used in order to main- tain the resistance of the circuit, whether the bat- tery is in or out of circuit. The latter is called the spark coil, and is intended to decrease the sparking on closing circuit. When both are at rest, battery I, has its zinc connected to line through A, and its copper to earth through R*, C I, the lever of key B and key A, which last two are permanently connect- ed. A reversed or spacing current goes to line, without affecting the home relays, since it passes in opposite directions and with equal strength through differentially wound coils. When, however, the key A, is worked alone, it reverses the current and the signal is recorded by the distant relay A. If key B, is worked alone, it breaks connection with copper at the junction of the two battei ies, and makes contact with terminal copper of battery 2, so as to send a zinc current of threefold strength. The distant relay B, records a signal because the current is now strong enough to move it. Relay A, however, is not affected, since the current has not been reversed. When both keys are simultaneously in action, then whenever B, is pressed, although the strength of A, may be increased, since its direction is not changed, the polarized tongue of its relay is un- affected by the movement of B, but any increase of current causes the armature of the distant re- lay of B, to move. This armature is held in position by springs of such a strength as to prevent its motion by a weak current, and being unpolarized, responds to either positive or negative currents. It, there- fore, responds to B, and records a signal. When A, is pressed, it reverses the current, and conse- quently moves the distant relay A, but has no effect on B, since it causes no alternation in the strength of the current. The author has taken the above almost liter- ally from Culley 's " Handbook of Practical Teleg- raphy, ' ' to which the reader is referred for a fuller description and details of apparatus. Tel.] 514 [Tel. Telegraphy, Simplex A system of telegraphy in which a single message only can be sent over the line. Telegraphy, Single-Needle A sys- tem of telegraphy by means of which the of the observer represent the dashes, and move- ments to the left, the dots of the Morse alpha- bet. The single-needle apparatus of Wheatstone and 1 Cooke's system is shown in Figs. 535, and 536. Fig. 535, shows the external appearance, and Fig. Fig. S3S- Single- Needle Telegraphic Apparatus. signals transmitted are received by observing the movements of a vertical needle over a dial. & S3 6. Whcatstone and Cooke's Single-Needle Appa- ratus, Internal Arrangement. Movements of the top of the needle to the right Fig. 537. Wheatstone and Cooke's Single-Needle Ap- paratus. External View. 536, the internal arrangements as seen from the back. An astatic needle is placed inside two coils of insulated wire C C. Only one of these needles N, is vis- ible on the face of the receiving instrument. The current from the line enters at L, passes through the coil C C, and leaves at N. The movements of the needle to the right or the left are ob- tained by changing the direc- tion of the current in the coils C C. This is effected by work- ing the handle when sending, and thus moving the commuta- tor at S, S, and bringing the contact springs resting thereon into different contacts. In the more modern form of single-needle in- strument, shown in Fig. 537, a single magnetic' needle N S, Fig. 538, only is placed in the- coil. This needle is rigidly attached to a light needle a, b, used only as a pointer, and is alone visible in the front of the instrument. The relative dis- position of these needles is shown in Fig. 538. The reversals of the current, required to deflect the needle to the right or left, are obtained by FiS-538. Needle and Pointer. Tel.] 515 [Tel. means of a double key or tapper, shown in Fig. 539- The levers L and E, are connected respectively to line and earth, and, when not in use, rest against C, connected with the po?itive side of the battery; but when de- pressed connect with Z, attached to the negative side of the bat- tery. The depression of L, therefore, sends a negative current into the line and deflects the needle, say, to the left, while the depression of E, sends a positive current into the line and deflects the needle Fig. JJQ. Double to the right. The terms positive Key or Tapper. and negative currents are used in telegraphy to indicate currents whose direction is positive or negative. Telegraphy, Speaking A system for the telegraphic transmission of articulate speech. (See Telephone.} Telegraphy, Step-by-Step A sys- tem of telegraphy in which the signals are registered by the movements of a needle over a dial on which the letters of the alphabet, etc., are marked. Dial telegraphs are especially employed for communication by those who are unable to readily read the Morse characters. The annexed instrument, devised by Breguet, was formerly used on some of the railway sys- tems of France. ' A needle advances over a dial by a step-by-step Fig. j 40. Step-by- Step Wheel. movement in one direction only. The alternate to-and-fro motions of the armature of an electro- magnet are employed to impart a step-by-step mot on to a peculiarly shaped toothed wheel T, T, Fig. 540, through the action of a horizontal arm c, attached thereto, and moving between the two prongs of a fork d, vibrating on a horizontal axis to which is attached a vertical pallet i. The receiving instrument is called the indicator, and consists of a needle attached to the axis of this wheel. The needle moves over the face of Fig. 541. Breguet's Indicator. the dial, shown in Fig. 541, on which are marked the letters of the alphabet and the numerals. The sending instrument is called the manipu* later. It consists of a device for readily sending over the line the number of successive impulses required to move the needle step-by-step from any letter on the indicator te which it may be pointing, to the next it is desired to send. The dial, shown in Fig. 542, is marked on its face with the same characters as the indicator. The edge of the wheel is provided with twenty-six notches in which a pin attached to a movable arm engages. The arm is jointed so that it can be placed in any of the notches on the face of the wheel. Fig. 3.42. Breguet's Manipulator. Below the dial face, and attached to the same axis as the movable arm, is a wheel provided with undulations consisting of thirteen elevations and thirteen depressions. Tel.] 516 [Tel. A lever T, pivoted at a, rests in these undu- lations at its upper end, and plays between two contact points at P and Q. If, now, the dials of the indicator and the man- ipulator both being at O, a movement is given to the arm by the handle M, to any point on the manipulator, there are thus produced the required number of makes and breaks to move the needle of the indicator to the corresponding letter or character. Telegraphy, Submarine A system of telegraphy in which the line wire consists of a submarine cable. In long submarine cables, in order to avoid retardation from the self-induction of the cur- rent, and the static charge arising from the cable acting as a condenser, very small currents are used. To detect these a very sensitive receiving instrument, such as the mirror galvanometer, or the siphon recorder, is employed. (See Galva- nometer, Mirror. Recorder, Siphon.} According to Culley, the retardation in the case of one of the submarine cables between Newfoundland and Ireland, amounts to two- tenths of a second before a signal sent from one end produces any appreciable effect at the other end, while three-tenths of a second are required for the current through the cable to gain its full strength. Telegraphy, Synchronous- M u 1 1 i p 1 e x, Delany's System A system devised by Delany for the simultaneous telegraphic transmission of a number of messages either all in the same direction, or part in one direc- tion and the remainder in the opposite direc- tion. The Delany system embraces the following parts : (i.) A circular table of alternately insulated and grounded contacts at either end of a tele- graphic line. (2.) A synchronized rotating arm or trailing contact, at each end ot the line, driven by a phonic wheel, and maintained in synchronous rotation by means of electric impulses automatic- ally sent out over the main line in either direc- tion, on the failure of the wheel at either end to rotate synchronously with that at the other end. (3.) Transmitting and receiving instruments connecting similar contacts at each end of the main line, and forming practically separate and independent lines for the simultaneous transmis- sion of dispatches over the main line in either direction. The main line is simultaneously connected at both of its ends to corresponding operating in- struments, and transferred from one set of instru- ments to another so rapidly that the operators, either sending or receiving, cannot realize that the line has been disconnected from their instru- ments and given to others, because each of them will always have the line ready for use, even at the highest rate of manipulation, and will, there- fore, to all practical intents and purposes, have at his disposal a private wii e between himself and the operator with whom he is in communica- tion. Therefore, although more than one operator may be spoken of as simultaneously using the line at any given time, yet in reality no two ope- rators are absolutely using it at the same time; but they follow one another at such short in- tervals, and the line is taken from one operator and transferred to another so rapidly, that none of them can at any time tell but that he has the line alone, and that therefore it is practically open for the use of every operator just as if he alone had control of it. There will, therefore, be established, by the use of a single line, as many private and separate lines as there are transferences of the line from the time it is taken from the first operator, and again given back to him. This system has been extended to as many as seventy-two distinct and separate printing cir- cuits, maintained and operated on a single con- necting line wire. The speed at which the circuits may be operated is in the inverse order of the number of circuits organized. The best results, practically, are obtained from six divisions of the contacts in the circle, which gives each operator about 36 con- tacts with the line per second, a speed which ad- mits oi the highest rate of transmission on each of the six circuits. Fig. 543 shows the apparatus at each end of the line, at the stations X and Y. The apparatus at each end is substantially identical. A steel fork a, at each station, is automatically and con- tinuously vibrated by the action of the local bat- tery L, B, and the electro-magnet A, called the vibrator magnet. Platinum contacts x, x 1 , placed on the inner faces of the tines of the fork, make and break contact with delicate contact springs y, y 1 . Tel.] 517 [TeL The fork being mechanically started into a vibratory motion, will automatically make and break its local circuit, and thus send impulses into the fork magnet A, that will continuously maintain the vibrations of the fork, in a well known manner. The making and breaking of the contacts x and y, consequent on the fork's vibration, open and close another local battery placed in a circuit called the motor circuit, in which is also placed an electro-magnet D, the functi -n of which is to maintain the continuous rotation of the trans- mission apparatus C. disc C, is rotated by the electro-magnet D, the trailing contact f, sweeps around the circular , 343- Delany's Synchronous Mutiplex Telegraph. The continuous vibration of the fork makes and breaks the contacts at x and y, and thereby makes and breaks the motor circuit. The alter- nate magnetizations and demagnetizations of the cores of the motor-magnet D, cause the rotation of the transmission apparatus C. The motor magnet and transmission wheel or disc C, provided with projections c, c, is the in- vention of Paul La Cour, and is styled by him a "phonic wheel." The transmission apparatus is illustrated in de- tail in Figs. 544 and 545, and is an exact coun- terpart of the receiving apparatus at the other end of the line. A base plate E, provided with Fig- 544- Tk' Phonic Wheel. binding posts, carries a vertical rotary shaft F. A circular table F 1 , is provided with a series of insulated contacts arranged symmetrically around the axis of rotation of the shaft. A radial arm F J , connected with the shaft F, carries at its outer extremity a trailing contact finger f. As the f'f- 545- Th' Phonic Wheel. table F 1 , and is brought successively into contact with the insulated contact pieces placed on the upper face of the table F 1 . The main line Q, Q, has one of its ends con- nected with the trailing finger f. As the shaft F, rotates, the line is therefore brought into suc- cessive electrical connection with the series of in- sulated contacts in the upper face of the table FI. Any suitable number of insulated contacts may be placed on the circular table F 1 ; sixty are shown in Fig. 546. In practice these contacts are connected in accordance wiih the number of circuits which it is desired to simultaneously maintain on the same wire. In the special case shown in the figure above referred to, it is ar- ranged so that four separate circuits shill be e?tablished on the same line wire. The sixty contacts are placed in six indepen- dent series, numbered from I to 10, consecu- tively. In the arrangement here shown two of the contact pieces in each series of ten are con- nected in the same circuit, and, as there are six series, each of the circuits so connected will have twelve contacts for each rotation of the disc, and twelve electrical impulses, as will be afterwards described. The detailed mechanism, by means of which the separate and independent circuits so obtained are utilized for the transmission and reception of messages, is shown in Fig. 546. R, R 1 , R* and R, are polarized relays; S, S, S and S 3 are ordinary Morse sounders, although in the practice of this invention some improvement has been in- troduced in connection with the receiving instru- ments. The connections with the main and the local batteries M B and L B, are clearly shown in the figure. It will be noticed that the relay R, is connected Tel.] 518 [Tel. with the wire r, and with the contacts I and 5 ; R 1 is connected by r 1 , with the contacts 2 and 6, R*, by the wire r, with the contacts 3 and 7, and R 8 7 by the wire r 3 , with the contacts 4 and 8. Similar instruments and circuits are placed at each end of the line. Without further describing the operation of the instruments shown in the figure, it need only now be borne in mind that the corresponding relays at the distant stations are connected with the corre- spondingly numbered contacts. When, therefore, the trailing contact finger at each station simul- taneously touches the contacts bearing the same number, the corresponding instruments connected Fig. 546. Working and Receiving Currents. with these contacts at each station will be placed in communication over the main line, the trailing contact finger f, completing the connection of the main line with the contact arm in the man- ner already described. Telegraphy, Time A system for the telegraphic transmission of time. A system of time telegraphy includes a master clock, the movements of whose pendulum automati- cally transmit a number of electric impulses to a number of secondary clocks and thus moves them ; or self-winding clocks are employed, which are corrected daily by an impulse sent over the line from a master clock. (See Clock, Electric. ,) Telegraphy, Writing A species of fac-simile telegraphy, by means of which the motions of a pen attached to a transmit- ting instrument so vary the resistance on two lines connected with a receiving instru- ment as to cause the current received thereby to reproduce the motions, on a pen or stylus, which transfers them to a sheet of paper. A system of writing telegraphy consists essentially of transmitting and receiving in- struments connected by a double line wire. The transmitting instrument is shown in Fig. 547- - S4-7- Transmitter of Writing Telegraphy. A stylus or pen resting on a top plate, is con- nected by the rod C, with a series of steel contact springs S, S, secured to the base and placed at right angles to one another. A series of resist- ances R, R, are connected with the lower ends of these contact springs. Two contact bars, B, B, are provided on the side facing the springs with platinum contacts opposite the contacts on the springs. The stylus rod C, is securely fixed to the base, but a spring at the lower end per- mits of its free movement. A pressure block at P, is fastened to the stylus rod, as shown, and in its normal position the pressures are adjusted so that contact is secured with the first spring. A movement of the stylus, as in writing, presses the contact bar against the spring, vary- ing the position and number of contacts, and thereby cutting in or out the resistance necessary to effect the proper movement of the receiving pen.. The receiving instrument is shown in Fig. 548. It consists of two electro-magnets placed at right angles to each other. A double armature sup- Tel.] 519 [Tel. ports the receiving stylus or pen in the manner shown. The variations in the current sent over the line by the varying resistances introduced into the circuit, or cut out or in by the action of the transmitting stylus, causes variations in the position of the double armature, under the vary- ing magnetic attraction of the receiving electro- magnet, and thus causes the receiving pen to correctly reproduce the motions of the trans- mitting pen. Fig. 54.8. Receiver of Writing Telegraph. This system has been operated over a line nearly 500 miles in length, when it successfully reproduced written characters. The author is indebted for the drawings and the general facts to the Electrical Engineer of New York. Tele-Hydro-Barometer, Electric An apparatus for electrically transmitting to, and recording at a distant station the height of water or other liquid. Tele-Manometer, Electric - - A gauge for electrically indicating and record- ing pressure at a distance. The tele-manometer includes a pressure gauge furnished with electric contacts operated by the movements of the needle of the steam gauge, for instance, and indicating and record ing apparatus. An alarm bell is provided to call attention to any rise of the pressure above or its fall below .the given or predetermined limits for which the hands have been set. Telemeter. An apparatus for electrically indicating and recording at a distance the pressure on a gauge, the reading of a ther- mometer, or the indications of similar in- struments. (See Tele-Hydro-Barometer, Electric. Tele-Manometer, Electric. Tele- Thermometer, Electric?) Telephone. To communicate by means of a telephone. Telephone. An apparatus for the electric transmission of articulate speech. The articulating telephone, though first brought into public use by Bell, was invented by Reis, in Germany, in 1 86 1. In America, after very protracted litigation, Bell has been decided legally to be the first inventor, but scientific men very generally recognize the principles of the in- vention to be fully anticipated by the earlier in- struments of Reis. Bell, however, is justly en- titled to the credit of inventing the first really successful telephone. In Bell's magneto-electric telephone, the transmitting and receiving instruments are iden- tical. A coil C, of insulated wire connected with the line, is placed on a core of magnetized steel, mounted opposite the centre of a circular dia- phragm of thin sheet iron, rigidly supported at its edges. In transmitting, the message is spoken into the mouth-piece at one end, as at D, in Fig. 549, and the to and -fro motions thus imparted to the metallic diaphragm attached to the mouth-piece P, produce in- duction currents in the coil C, on the magnet M. (See In- duction, Electro -Dynamic. ) These impulses, passing over the main line E L, Fig. 550, produce similar movements in the diaphragm P', of the receiving instrument, at D', and thus cause it to repro- duce the message, in articu- Telfphant. late sounds, to one listening at the receiving in- strument. A ground circuit is shown in the figure, as usually employed in practice, except for long distance and in large cities. Tel.] 520 [Tel. A* magneto-telephone constitutes in reality a magneto-electric machine, driven or propelled by the voice of the speaker, in which the currents so produced instead of being commuted are em- ployed uncommuted to reproduce the uttered speech. In actual practice the instrument above de- scribed is replaced by the electro-magnetic tele- E a 1_ . sso. Telephone Circuit. phone, in which the to-and-fro motions of the transmitting diaphragm are caused to vary the resistance of a button of carbon^ or a variable con- tact transmitter similar to that employed by Reis in some of his instruments. The variable resistance is placed in the circuit of a battery, so that on speaking into the trans- mitter, electric impulses are sent over the line and are received by a tele- phone with a magnet core provided with a coil in the main-line circuit. The telephone is ar- ranged for actual com- mercial use in the United States in the manner Fig. shown in Fig. 551. Telephone. Bi A term sometimes applied to a double telephone receiver so ar- ranged as to permit of easy application to both ears of the listener at the receiving in- strument. Telephone Cords. (See Cords, Tele- phone^ Telephone, Electro-Capillary A telephone in which the movements of the transmitting diaphragm produce currents by means of variations hi the electromotive forces of the contact surfaces of liquids in capillary tubes. (See Phenomena, Electro- Capillary^) In Breguet's telephone both the transmitting and the receiving instruments are similar in con- Telephone Ap- struction and operate by means of electro-capil- lary phenomena. A vertical capillary tube com- municates at its upper end with an air space below a diaphragm, and at its lower end with a mercury surface on which rests a layer of acidu- lated water. A line wire connects the mercury reservoirs of the transmitting and receiving instruments, the remainder of the circuit being formed by another wire connecting the mercury near the upper parts of the two vertical tubes. The alterations in the contact surfaces at the transmitting end produced by the movements of the diaphragm, cause electric impulses that pro- duce similar movements of the diaphragm at the receiving end. Telephone, Electro-Chemical A name sometimes given to the Edison electro- motographic telephone. (See Telephone, Electro-Motographic?) Telephone, Electro-Motographie A telephone in which the receiver consists of a diaphragm of mica or other elastic material operated on the principle of the electro- motograph. A straight lever, which forms part of the line circuit, is rigidly attached at one end to the centre of the receiving diaphragm, and rests near its other end on the surface of a chalk cylinder moistened with a solution of caustic potash or potassium iodide, maintained in rotation by suit- able mechanical means. Electric impulses being sent into the line by the voice of a speaker talking at a transmitter of ordi- nary construction reduce the friction between the lever and the cylinder, and produce slipping movements of the lever that reproduce articulate speech in the receiving diaphragm. Telephone, Reaction An electro- magnetic telephone in which the currents in- duced in a coil of wire attached to the dia- phragm are passed through the coils of the electro-magnet, and thus react on and strengthen it. Telephone Switch, Automatic (See Switch, Telephone, Automatic.) Telephonic. Pertaining to the telephone. Telephonic Alarm. (See Alarm, Tele- phonic^ Tel.] 521 [Tel. Telephonic Cable. (See Cable, Tele- phonic^) Telephonic Exchange. (See Exchange, Telephonic, System of.) Telephonic Exchange, System of (See Exchange, Telephonic, System of.) Telephonic Joints. (See Joint, Tele- graphic or Telephonic?) Telephonically. In the manner of the telephone. (See Telephoned) Telephoning 1 . Communicating by means of the telephone. Telephote. An apparatus for the tele- graphic transmission of pictures by means of the action of light on selenium. (See Tele- photography^) The telephote is sometimes called the pherope. Telephotography. A system for fac- simile transmission by means of dots and lines transmitted by means of a continuous current whose intensity is varied by a trans- mitting instrument containing a selenium re- sistance. (See Telegraphy, Fac-Simile. Resistance or Cell, Selenium?) The transmitter consists of a dark box mounted on an axis, so as to be capable of a sidewise motion. The picture to be transmitted is thrown continuously on the face of the box by any lantern projection apparatus, and a small opening containing a selenium resistance receives wise continuous current in the circuit of which the selenium resistance is placed. The picture is received at the other end on a sheet of chemically prepared paper moved syn- chronously with the transmitting box. Telescope, Reading A telescope employed in electric measurements for read- ing the deflections of the galvanometer. The image of numbers on an illumined scale is seen in the mirror through the telescope, shown in Fig. 552. Teleseme. A self-registering hotel an- nunciator, by means of which a dial operated in a room indicates on the annunciator the article or service required. Tele-Thermometer, Electric An electric recording thermometer for indicating and recording temperature at a distance. The tele thermometer consists essentially of a transmitter and a receiver. The transmitter consists of a delicate thermometer provided with suitable contacts. The receiver, which is in circuit with the transmitter, has, in some forms, a recording dial on which a continuous record, for a day or week, is made. In cases where it is desired that a given maximum temperature shall not be exceeded, an alarm bell, connected with contacts on the dial face, is rung. Telluric Magnetic Force. (See Force, Magnetic, Telluric.) Telpher Line. (See Line, Telpher) Telpherage. A system for the convey- ance of carriages suspended from electric F'S- S3 2. Reading Telescope. the alternations of light and shade, and transmits the same as variations in the strength of the other- fif. S3 3- Circuit for Telpherage System conductors, and driven by means of electric motors, that take directly from the conductors the current required to energize them. Tem.] 522 [The. Two lines are provided, an tip and a down line, that cross each other at regular intervals. Each line is in segments, and the alternate segments are insulated from each other, but are connected electrically by cross-pieces on the supporting posts. In this way the line shown in Fig. 553 is obtained. The two lines are maintained at a difference of potential by a dynamo-electric machine at D, Fig. 554. As the train at L T, or L' T', is of such a length as to come into contact with two different segments at the same time, it receives a current sufficient to run the motor connected with it, the current being received through a conduc- tor joining a pair of wheels that are insulated from the truck. The general arrangement of the line is shown in the annexed Fig. 554 FiS- S3 4' Circuit/or Telpherage System. Temperature Alarm. (See Alarm, Tem- perature^) Temperature, Effects of, on Electric Ee- sistance (See Resistance, Effect of Heat on Electric) Tempering, Electric A process for temperaing metals in which heat of elec- tric origin is employed instead of ordinary furnace heat. Temporary Intensity of Magnetization. (See Magnetization, Temporary Intensity of.} Tension, Electric A term often loosely applied to signify indifferently surface density, electromotive force, dielectric stress, or difference of potential. This term is now very generally abandoned. Terminal, Cable A water-tight covering provided at the end of a cable to prevent injury to the cable insulation by the moisture of the air. Terminal, Negative The negative pole of a battery or other electric source, or the end of the conductor or wire connected with the positive plate. Terminal, Positive The positive pole of a battery or other electric source, or the end of the conductor or wire connected to the negative plate. Terminals. A name sometimes applied to the poles of a battery or other electric source, or to the ends of the conductors or wires connected thereto. The two terminals are distinguished as the positive and the negative. Their names are un- like those of the battery plates to which they are connected, the positive terminal being con- nected with the negative plate and the negative terminal with the positive plate. Terrestrial Magnetism. (See Magnet" ism, Terrestrial) Testing, Methods of Various methods for determining the values of the current strength in any circuit, the difference of potential, the resistance, the coulombs, the farads, the joules, the watts, etc. (See Measurements, Electric?) The investigation of an apparatus or cir- cuit for the purpose of determining whether it is in standard or working condition. Testing of Joints. (See Joint, Test- ing of.} Testing Pole. (See Pole, Testing) Testing Transformer. (See Trans- former, Testing) Tetanus. Continuous, spasmodic contrac- tion of the muscles. Tetanus, Acoustic Tetanus pro- duced in a muscle by means of alternate currents induced in a coil of wire by a mag- netized steel spring vibrating near the coil with sufficient rapidity to give a musical note. The rapidity of the inductive shock can be de- termined from the pitch of the musical note; hence the use of the term acoustic. Theatrophone. A system of telephonic communication between theatres or operas and subscribers, by means of slot machines. Any person at a cafe, club, restaurant or other public place, by the theatrophone, is automati- cally placed in communication with the theatre by means of a receiving telephone so as to hear The.] 523 [The. the performance by dropping a given piece of money in the slot of the machine. Theodolite, Magnetic An appa- ratus for measuring the declination or varia- tion of the magnetic needle at any place. A divided circle, like that on a theodolite, is supported horizontally. The needle is formed of a tubular magnet, having an achromatic lens at one end and a scale at the focus of the lens at the other end. Theory, Alternation, of Muscular Nerve Current A theory proposed by L. Hermann, in which the currents of nerves or muscular fibres are regarded as a result of their alteration from an original condition. Hermann states: (I.) That protoplasm undergoing partial death at any part, either while dying or by metamor- phosis, becomes negative to the uninjured part. (2.) Protoplasm, when excited at any part, be- comes negative to the unexcited part. (3.) Protoplasm, when partially heated at any part, becomes positive, and, on cooling, negative to the unchanged part. (4. ) Protoplasm is strongly polarizable on its surface, the polarization constantly diminishing with excitement and while dying. According to this theory, passive, uninjured and absolutely fresh tissues are devoid of elec- tric currents. This matter must still be regarded as unsettled. (See Theory, Molecular, of Mzts- fles or Nerve Current.} Theory, Contact, of Yoltaic Cell (See Cell, Voltaic, Contact Theory of.} Theory, Difference A theory as to the cause of the electric currents excited be- tween injured and uninjured protoplasm. Theory, Molecular, of Muscles or Nerve Current A theory proposed by Du Bois Reymond, in which every nerve or mus- cular fibre is regarded as composed of a series of electromotive molecules arranged in series and surrounded by a neutral con- ducting fluid. " The molecules are supposed to have a posi- tive equatorial zone directed towards the surface and two negative polar surfaces directed toward the transverse section. Every fresh transverse section exposes new negative surfaces, and every artificial longitudinal section new positive area." (Landois and Sterling. ) Theory of Electric Displacement. (See Displacement, Electric, Theory of.} Therapeutical Electrization. (See Elec- trization, Therapeutical.) Therapeutic Bath, Electro - (See Bath, Electro-Therapeutic) Therapeutics, Electro, or Electro- Therapy The application of electricity to the curing of disease. (See Biology, Elec- tro) Therapeutist, Electric One skilled in electro-therapy. An electro-medical practitioner. Therapy, Electro - A term some- times used instead of electro-therapeutics. (See Therapeutics, Electro, or Electro- Therapy) Therapy, Magneto Alleged electro- therapeutic effects produced by the move- ments of magnets over the body of the patient. It is asserted by eminent authorities that such effects have an actual existence. They should, however, until more carefully investigated, be accepted with extreme caution. Therm. A heat unit propose.! by the British Association. A therm is the amount of heat required to raise the temperature of one gramme of pure water at the temperature of its maximum density one degree centigrade. (See Calorie) Therniaesthesiometer. An instrument employed in electro-therapeutics for testing the temperature sense in nervous diseases. The thermaesthesiometer consists of two ther- mometers movable on a standard, with flat ves- sels of mercury in order to readily apply them to the skin. The mercury vessel of one of the two thermometers is surrounded by an insulated platinum wire and may be warmed at pleasure by passing a galvanic current through the wire. The two vessels, brought to different tempera- tures, are set on the same part of the skin, one after the other, so as to test the sensibility of the skin for the differences in temperature. Thermal Absorption. (See Absorption, Thermal) The.] 524 [The. Thermal Cautery. (See Cautery, Ther- mal.) Thermal Incandescence. (See Incan- descence, Thermal.) Thermic Balance. (See Balance, Ther- mic, or Bolometer?) Thermo-Battery. (See Battery, Thermo!) Thermo Call. A call operated by means of thermo currents. Thermo-Cell. (See Cell, Thermo-Elec- tric?) Thermo-Electric Battery. (See Battery t Thermo-Electric?) Thermo-Electric Cell. (See Cell, Thermo-Electric.) Thermo-Electric Couple. (See Couple, Thermo-Electric.) Thermo-Electric Diagram. (See Dia- gram, Thermo-Electric.) Thermo-Electric Effect. (See Effect, Thermo-Electric.) Thermo-Electric Inversion. (See In- version, Thermo-Electric.) Thermo-Electric Pile, Differential (See Pile, Thermo, Differential.) Thermo-Electric Pile or Battery. (See Pile, Thermo-Electric.) Thermo-Electric Power. (See Power, Thermo-Electric.) Thermo-Electric Series. (See Series, Thermo-Electric.) Thermo-Electricity. (See Electricity, Thermo?) Thermo-Electrometer. A name some- times, but not happily, applied to an electric thermometer. (See Thermometer, Electric?) Thermo-Electromotive Force. (See Force, Electromotive, Thermo?) Thermolysis. A term applied to the chemical decomposition of a substance by heat. Thermolysis, or dissociation, is an effect pro- duced by an action of heat somewhat similar to the effect of electrolysis, or chemical decomposi- tion produced by the passage of an electric cur- rent. When a chemical substance is heated, the vibration of its molecules is attended by an inter- atomic vibration of its constituent atoms so that a decomposition ensues. If the temperature is not excessive, these liberated atoms recombine with others which they meet. At higher temperatures, however, such recombination is impossible, and a permanent decomposition ensues, called ther- molysis or dissociation. Thermometer, Electric A device for determining the effects of an electric dis- charge by the movements of a liquid column on the expansion of a confined mass of air through which the discharge is passed. Thermometer, Electric Resistance A thermometer the action of which is based on the change in the electric resistance of metallic substances with changes in tem- perature. The electric resistance thermometer is used, among other purposes, for determining the temper- ature of the sea at different depths. Its operation is based on the electric resistance of two perfectly similar coils of insulated wire, enclosed in separate water- tight copper cases. One coil is placed where the temperature is to be determined, and the other in a vessel of water, the temperature of which is altered until the two coils show the same resist- ance, when, of course, the temperature of the distant coil is the same as that of the water sur- rounding the other coil. Thermometer Scale, Centigrade (See Scale, Thermometer, Centigrade?) Thermometer Scale, Fahrenheit (See Scale, Thermometer, Fahrenheit?) Thermophone. Any instrument by means of which sounds are produced by the absorp- tion of radiant energy. (See Photophone.) A telephone has been constructed in which the motions of the receiving diaphragm are effected by the expansions and contractions of a thin me- tallic wire connected to the diaphragm and placed in the circuit of the main line. Thermostat. An instrument for automati- cally maintaining a given temperature by the closing of an electric circuit through the ex- pansion of a solid or liquid. Thermostats are often used in systems of auto- matic fire telegraphy and in systems of automatic temperature regulation in connection with indi- The.] 525 [Tic. A thermo- cating instruments for sounding an alarm or giv- ing notice when the temperature changes. They are operated either on open or closed cir- cuits. Thermostat Alarm. (See Alarm, Ther- mostat.) Thermostat, Closed-Circuit A thermostat maintained normally on a closed circuit. In closed-circuit thermostats, the adjustment for any degree of temperature within a given range is effected by means of a screw. Thermostat, Electro-Pneumatic An instrument for automatically indicating the existence of a given temperature by the closing of an electric circuit on the expansion of a gas. Thermostat, Mercurial stat operating by the ex- pansion of a mercury column. A mercurial thermostat is shown in Fig. 555. One terminal is connected di- rectly with the mercury; the other is placed in the arm to the left. On a cer- tain predetermined tem- perature being reached, the rise of the mercury column completes the circuit and rings an alarm bell. By connecting the thermostat with an annunciator, the particular locality where an excessive temperature has been reached is indicated. Such a system is in use in a well known system of fire alarm. Thermostat, Open-Circuit A ther- mostat maintained normally on an open cir- cuit. In open-circuit thermostats the adjustment for temperature within a given range is effected by varying the distance of the fixed and movable contact points. Thermostatic. Of or pertaining to a ther- mostat. (See Thermostat.) Thompson's Gauss. (See Gauss, S. P. Thompson's.) - SSS- Mercurial Thermostat. Thomson's Gauss. (See Gauss, Sir Wil- liam Thomson's.) Three-Branched Sparks. (See Spark, Three-Branched.) Three-Filament Incandescent Electric Lamp for Multiphase Circuits. (See Lamp, Electric, Incandescent, Three-Filament, for Multiphase Circuits) Three-Way Trolley Frog. (See Frog, Trolley, Three-Way) Three- Wire System. (See System, Three- Wire) Throttling. Choking, or stopping off. Through Circuit (See Circuit. Through) Through Line. (See Line, Through) Throwback Indicator, Electrical (See Indicator, Electric Throwback) Throwback Indicator, Mechanical (See Indicator, Mechanical Throwback) Throw of Needle. (See Needle, Throw of) Thumb-Cock Electric Burner. (See Burner, Thumb-Cock Electric) Thunder. A loud noise accompanying a lightning discharge. Thunder is due to the sudden rush of the sur- rounding air to fill the partially vacuous space accompanying the disruptive discharge of a cloud. This space is caused mainly by the condensation of the vapor formed on the passage of the discharge through drops of rain or moisture in the air, as well as by the expansion of the air itself. Thunder Rod. (See Rod, Thunder) Thunder Storms, Geographical Distribu. tion of (See Storms, Thunder, Geo- graphical Distribution of) Tick, Magnetic A faint metallic click heard on the magnetization and demag- netization of a magnetizable substance. Ticker Serrice, Stock The simul- taneous transmission of stock quotations or other desired information to a number of subscribers. The stock ticker-service includes a central transmitting station connected with a given num- Tic.] 526 [Tis. her of subscribers, each of whom is furnished with a stock ticker. The transmitter at the cen- tral station consists of a keyboard and a cylinder furnished with spiral pins. The spiral pins are connected through a series of pole-changers to separate line wires radiating in all directions from the central office. The connections are such that, a rapid rota- tion being given by means of an electric mo- tor to the cylinder, the impulses sent out by the keyboard are transmitted to each of the separate circuits. Since each of these circuits has a num- ber of ticker printers connected with it, reports of fluctuations in prices are simultaneously printed in hundreds of different offices. Ticker, Stock A form of step-by- step telegraphic instrument employed for au- tomatically sending and recording stock quo- tations to any desired number of subscribers. (See Telegraphy, Step-by- Step.} A form of printing telegraph. Callahan's Printing Telegraph is used as a stock ticker. (See Telegraphy, Printing.) Phelps' Stock Printer is employed extensively as a stock ticker. This form of printing telegraph requires but a single wire, and has a working speed of almost thirty words a minute. A double type-wheel, maintained in motion by clockwork, is stopped at the desired characters by the motion of a polarized relay, working be- tween the poles of two electro -magnets, furnished with a soft iron or non-polarized armature. The release of the armature of the printing mag- net releases a train, and thus insures the impres- sion of the character it is desired to print. The type-wheel is driven by a step-by-step movement obtained by means of rapidly alter- nating pulsations. Although these pass through the coils of the printing magnet, they follow one another too rapidly to charge its coils, so that the armature is unaffected until a pause is made, when, its armature being attracted, it releases the printing mechanism. The message is received on a fillet of paper, fed by a suitable mechanism. Time-Ball, Electric (See Ball, Electric Time.} Time-Constant of Circuit (See Circuit, Time-Constant of.} Time-Constant of Condenser. (See Con- denser, Time-Constant of.) Time-Constant of Electro-Magnet. (See Constant, Time, of Electro-Magnet) Time Cut-Out, Automatic An au- omatic cut-out arranged on a storage bat- tery so as to cut it in or out of the circuit of the charging source at predetermined times. Time-Fall of Electromotive Force of Secondary or Storage Cell During Dis- charge. (See Force, Electromotive, of Sec- ondary or Storage Cell, Time-Fall of.} Time-Lag of Magnetization. (See Mag- netization, Time-Lag of.} Time, Reaction The time required for the effects of an electric current to pass from a nerve to a muscle. Time-Rise of Electromotive Force of Secondary or Storage Cells During Dis- charge. (See Force, Electromotive, of Sec- ondary or Storage Cell, Time-Rise of) Time-Switch. (See Switch, Time.} Time, Telegraphic, Register for Rail- roads (See Register, Time, for Rail- roads^) Time Telegraphy. (See Telegraphy, Time.} Tinned Wire. (See Wire, Tinned) Tinning, Electro Covering a sur- face with a coating of tin by electro-plating. (See Plating, Electro^ Stannic chloride, or the perchloride of tin, dis- solved in water in the proportion of 30 parts of the salt to 1,250 of water, makes a good tinning bath. Tinnitus, Telephone A professional neurosis, or abnormal nervous condition of the auditory apparatus, believed to be caused by the continual use of the telephone. Tips, Polar The free ends of the field magnet pole pieces of a dynamo-electric machine. Tissue, Nerve or Muscular Excitability of Electric stimulation of nervous or muscular tissue. Ton.] 527 [Tor. The general effects of electric stimulation of nervous or muscular tissue may be summarized as follows: ( i . ) Electric stimulation of a motor nerve, pro- duces a contraction of the muscles to which such nerve is distributed. (2.) Electric stimulation of a sensory nerve, produces pain in the parts to which the nerve is distributed. (3.) Electric stimulation of mixed motor and sensory nerves produces both of the effects men- tioned under (i) and (2.) Tongs, Cable Hanger Tongs pro- vided with long handles for the purpose of attaching the hangers of an aerial cable to the suspending wire or rope. Tongs, Discharging A term some- times used for a discharging rod. (See Rod, Discharging.} Tongue, Relay, Bias of A term employed to signify such an adjustment of a polarized relay, that on the cessation of the working current, the relay tongue shall always rest against the insulated contact, and not against the other contact, or vice versa. Sometimes, as in the split-battery duplex, the bias is toward the uninsulated contact. (See Relay > Polarized.} Tool, Lead Scoring A tool for readily scoring the surface of the lead of a lead-covered cable, when the same is to be removed preparatory to making joints. Toothed-Ring Armature. (See Arma- ture, Toothed-Ring^) Top, Induction A top consisting of an iron disc supported on a vertical axis, which, when spun before the poles of a steel magnet, assumes an inclined position, through the influence of the currents induced in the disc. The top maintains the inclined position so long only as the strength of the induced currents is sufficiently great ; that is, while speed of rotation is sufficiently great. Toppler-Holtz Machine. (See Machine, Ttjppler-Holts) Torch, Electric Gaslighting A gaslighting appliance consisting of the com- bination of a portable voltaic battery and a spark or induction coil. The torch is mounted on the end of a rod pro- vided with means for turning on the gas. A key is then touched and the gas lighted by the spark produced by an induction coil or a small electro- static induction machine. Torpedo, Automobile A torpedo which contains in itself the power for its own motion. The moving power may be that derived from compressed air or gas, or from a storage bat- tery contained within the torpedo. An auto mobile torpedo provided with a storage battery and electric motor would then be distinguished from an electrically propelled torpedo, connected by means of cables with a driving dynamo located outside the torpedo on a ship, or on the shore. Torpedo Boat. (See Boat, Torpedo) Torpedo Cable. (See Cable, Torpedo) Torpedo, Drifting A torpedo sus- pended from a float, and connected by means of rope with similar torpedoes, allowed to drift with the current, so as to catch against a vessel. Torpedo, Electric A name some- times given to the electric ray. (See Ray, Electric.} Torpedo, Electric An electrically operated torpedo. This latter usage of the term is the commoner. Torpedo, Halpine-Savage A special form of torpedo, in which electricity is both the propelling and directing power, and in which the electric source furnishing the pro- pelling current is contained within the torpedo. In the Halpine-Savage torpedo, the propelling power is obtained from a storage battery placed within the torpedo. Torpedo, Lay A moving torpedo, in which the moving power is carbonic acid gas, or compressed air, or other similar power not electric, and the guiding power is electric. The Lay torpedo has the form of a cylindrical boat furnished with conical ends. The explosive is placed in the fore part of the torpedo. Flags are Tor.J 528 [Ton. attached to the torpedo, showing the operator the exact course taken by it. The torpedo is started, stopped and steered by means of electric currents sent to the torpedo through an insulated cable connected with the torpedo. Torpedo Nets. (See Nets, Torpedo?) Torpedo, Outrigger A pole or spar torpedo. The torpedo is placed in a metallic case and supported on the end of a spar or outrigger. The spar is depressed until the torpedo is sunk below the water line. The torpedo is fired when its end comes in contact with the side of the enemy's vessel. Torpedo, Sims-Edison A special form of torpedo in which electricity is both the propelling and the directing power, but the electric source is situated outside of the torpedo. The torpedo is propelled by means of an electric motor placed hi the torpedo, and driven by means of an electric current transmitted through a cable connected with the sending station. Torpedo, Spar A torpedo, attached to the end of a spar, and designed to be exploded by percussion against the side of an enemy's vessel, when thrust against the side below the water-line. The spar torpedo is but little used, having been replaced by more efficient forms. Torpedo, Stationary A term some- times employed instead of a submarine mine. (See Mine, Submarine?) A stationary torpedo is so named in order to distinguish it from a torpedo which is moved through the water by any means. (See Torpedo, Towing.} Torpedo, Towing A torpedo ar- ranged to be towed on the surface after a ves- sel and explode when it strikes the side of an enemy's vessel. The torpedo is shaped so that it maintains dur- ing its motion a certain distance from the sides of the towing boat or vessel. Torqne. That moment of the force ap- plied to a dynamo or other machine which turns it or causes its rotation. The mechanical rotary or turning force which acts on the armature of a dynamo- electric machine or motor and causes it to rotate. In the case of the armature of a dynamo- electric machine the torque is equal to the radius of the armature, multiplied by the pull at the circumference, or the radius of fts pulley multiplied by the pull at the circumference of the pulley. A torque is exerted on the shaft of a motor from the electro-magnetic action, or pull at the periphery of the armature. The torque is usually measured in pounds of pull at the end of a radius or arm I foot in length. Torricellian Tacuum. (See Vacuum, Torricellian?) Torsion Balance, Coulomb's (See Balance, Coulomb's Torsion?) Torsion Galvanometer. (See Galvanom- eter, Torsion?) Total Disconnection. (See Disconnec- tion, Total?) Total Earth. (See Earth, Total?) Total Magnetic Induction. (See Induc- tion, Total Magnetic?) Touch, Double A method of mag- netization in which two closely approximated magnet poles are simultaneously drawn from one end of the bar to be magnetized to the other and back again, and this repeated a number of times. Touch, Separate A method of magnetization in which two magnetizing poles are simultaneously applied to the bar to be magnetized and drawn over it in opposite di- rections. (See Magnetization by Touch?) Touch, Single A method of mag- netization in which a single magnetizing bar is drawn from one end to the other of the bar to be magnetized, and returned through the air for the next stroke. (See Magnetization, Methods of.) Tourmaline. A mineral consisting of natural silicates and borates of alumina, lime, iron, etc., possessing pyro-electric properties. (See Electricity, Pyro.) Tow.] 529 [Tra. Tower, Conning A shot-proof tower from which the commander of a turret ship directs the movements of a vessel during action. Tower, Electric A high tower pro- vided for the support of a number of electric arc lamps, employed in systems of general illumination. Tower System of Electric Lighting. The lighting of extended areas by means of arc lights placed on the tops of tall towers. The tower system of electric illumination is only applicable to wide open spaces, since otherwise objectionable shadows are apt to be formed. Towing Torpedo. (See Torpedo, ToW- ing^ Traction, Magnetic The force with which a magnet holds on to or retains its armature, when once attached thereto. Magnetic traction is to be distinguished from magnetic attraction, or the ability of a magnet pole to draw an armature or other magnets to- wards it from, a distance. Train Wire. (See Wire, Train.} Tramway, Electric A railway over which cars are driven by means of elec- tricity. An electric railroad. The term tramway is sometimes applied to roads in cities, as distinguished from inter-urban roads. Transformer. An inverted Ruhmkorff induction coil employed in systems of dis- tribution by means of alternating currents. A transformer is sometimes called a converter. The word transformer is, however, the one most employed. A transformer consists essentially of an indue- tion coil, Fig. 556, in which the primary wire is long and thin, and consequently has many turns, as compared with the secondary wire, S, S, which is short, thick, and has few turns. To prevent heating and loss of energy in con- version, the core of the transformer is thoroughly laminated; to lower the resistance of its mag- netic circuit, the transformer is usually iron-clad. In a system of electrical distribution by means of transformers, alternating currents, of small current strength and comparatively considerable difference of potential, are sent over a line from a distant station, and passing into the primary wire of a number of converters, generally connected to the line in multiple arc, produce, by induction, Fig. 556. Transformer. currents of comparatively great strength and small difference of potential in the secondary wires. Various electro-receptive devices are connected in multiple arc to circuits connected with the sec- ondary wires. This method of distribution greatly reduces the cost of the main conducting wires or leads in all cases where the distance is considerable, since considerable energy may be conveniently sent over a comparatively thin wire, with but a trifling loss, if the difference of potential is sufficiently great. The general arrangement of the converters on the main line, and the connection of the second- ary circuits with the electro-receptive devices in Fig. SS7- Transformer Circuit*. such a system, are shown in Fig. 557. The trans- formers are supported on the line poles, as more Tra.] 530 [Tra. clearly shown in Fig. 558, in which the terminals of the primary and secondary of the converter are readily seen. When the converter is properly constructed, the loss of conversion at full load is but small; that is to say, the number of watts in the secon- dary is very nearly equal to the number in the primary. A current of to amperes, at 2,000 volts, when passed into a converter the number of whose turns in the primary is twenty times the number in its secondary, will produce in its sec- ondary a current whose strength is about twenty times as great, that is, nearly 200 amperes, but whose voltage is only about one-twentieth, or, loo; the watts in the two cases are nearly the same, or theoretically 20,000 watts. The ratio between the windings of the primary and the secondary circuits is called the co-effi- cient of transformation. In general, the shorter the wire on the second- ary, and the smaller its number of turns, the greater is the reduction in the difference of po- tential, and the greater the current produced. The reduction is nearly proportionate to the ratio of the number of windings of the two coils. Fig. 558. Transformer Attached to Poles. Transformer, Closed Iron Circuit A transformer the core of which forms a complete magnetic circuit. These transformers are sometimes called iron- clad transformers. Transformer, Commuting A term sometimes applied to a variety of motor gen- erator in which neither the armature nor the field magnets revolve, the variations in the polarity of the magnetic circuit being obtained by means of special commutators. Transformer, Constant-Current A transformer in which a current of a constant potential in the primary is converted into a current of constant strength in the secondary, despite changes in the load on the secondary. Transformer, Core A transformer in which the primary and secondary wires are wrapped around the outside of a core consisting of a bundle of soft iron wires or plates. A Ruhmkorff coil is a core transformer. Transformer, Efficiency of The ratio between the whole energy supplied in any given time to the primary- circuit of a transformer and that which appears in the form of electric current in the secondary circuit. The energy applied to the primary circuit of a transformer is dissipated: (i.) By eddy currents in the core of the trans- former. (See Currents, Eddy.) (2. ) By hysteresis, or magnetic friction. (See Hysteresis. ) (3.) By heating of the primary circuit. (4.) By heating of the secondary circuit. When a transformer is overloaded, its efficiency decreases. There is a certain range of second- ary resistance and current, within which a trans- former is most advantageously operated. Transformer Guard. (See Guard, Trans- former, Lightning?) Transformer, Hedgehog A name applied to a particular form of open-iron cir- cuit transformer. (See Transformer.} The advantages claimed for the hedgehog trans- former are that it can be made to give a higher all-day efficiency, since it insures a smaller loss from hysteresis in the iron. The efficiency for very small loads, or for no loads is greater than in the closed-circuit transformer. Transformer, Leakage Current of A term sometimes used for the current which escapes from the primary through the dielec~ trie of a transformer to the secondary circuit. The term is a bad one, since the true leakage current would be the current which represents the leakage between the primary or secondary circuit and the ground. Tra.] 531 [Tra. Transformer Lightning- Arrester. (See Arrester, Lightning, Transformer?) Transformer, Multiple Any form of transformer which is connected in multiple to the primary circuit. A multiple or parallel transformer is self-regu- lating under variable loads, provided the electro- motive force in the primary is maintained con- stant. Transformer, Oil A transformer which is immersed in oil in order to insure a high insulation. Transformer, Open-Iron Circuit A transformer the iron of which does not form a complete magnetic circuit, but is formed instead partly of iron and partly of air. Transformer, Pilot A small trans- former, placed at any desired portions of a line in order to determine the drop of poten- tial. The pilot transformer is used in connection with a lamp or other suitable indicating device. Its use is similar to the use of the pilot incandescent lamp. Transformer, Rotary-Current A transformer operated by means of a rotary current. (See Current, Rotating?) The rotary current transformer for a rotary current of three separate alternating currents com- bined, transforms all three currents together. There are 'three cores, connected at one set of ends and at the other to the circumference of an iron ring. Each core contains a primary and secondary wire. Transformer, Rotary-Phase A ro- tary current transformer. (See Transfor- mer, Rotary-Current?) Transformer, Series Transformers which are connected in series with the pri- mary circuit. A series transformer is not as readily made self- regulating under variations in the load as a mul- tiple transformer. If, however, its core is not saturated, and the electromotive force of its secondary is small, it can be made fairly self- regu- lating. Series transformers are used in the Jablochkoff system for feeding arc lamps in the shape of Jablochkoff candles. Transformer, Shell A transformer in which the primary and secondary coils are laid on each other, and the iron core is then wound through and over them so as to en- close all the copper of the primary and secondary circuits within the iron. The iron shell surrounding the copper may consist of the thin plates of iron, built up so as to leave a rectangular space for the introduction of the primary and secondary. Transformer, Step-Down A trans- former in which a small current of compara- tively great difference of potential is con- verted into a large current of comparatively small difference of potential. An inverted Ruhmkorff induction coil. Transformer, Step-Up A trans- former in which a large current of compara- tively small difference of potential is con- verted into a small current of comparatively great difference of potential. The term step-up transformer is used in contra- distinction to the step-down transformer. The old form of Ruhmkorff coil is an example of a step-up transformer. Transformer, Testing- A trans- former employed in any system of distribu- tion for the purposes of testing for grounds, condition of line, drop of potential, etc. Transformer, Welding A trans- former suitable for changing a small electric current of comparatively high difference of potential, into the heavy currents of low difference of potential required for welding purposes. Welding transformers have in general a very low resistance in their secondary coils, and almost invariably consist of a single turn or at the most of a few turns of very stout wire. Transforming Currents. (See Current, Transforming a.) Transforming Down. Transforming by means of a step-down transformer. (See Transformer, Step-Down?) Transforming Station. (See Station, Transforming?) Transforming Up. Transforming by means of a step-up transformer. (See Transformer, Step-Up?) Tra.] 532 [Tra. Transient Currents. (See Currents, Transient^ Transit, Magnetic Variation An apparatus for measuring the declination or variation of the magnetic needle at any place. The variation transit generally consists of an altitude and azimuth instrument, the telescope of which is so arranged as to be readily converted into a microscope. Transition Resistance. (See Resistance, Transition^] Translator, Double-Current A telegraphic translater or repeater designed to operate on double current transmission. Translater, Single-Current A tele- graphic translater or repeater designed to operate a single-current transmission. Translater, Telegraphic A term sometimes applied to a telegraphic repeater. (See Repeaters, Telegraphic^ Translating Device. (See Device, Trans- lating^) Translating Devices, Multiple-Arc-Con- nected (See Devices, Translating, Multiple- Arc-Connected.} Translating Devices, Multiple-Con- nected (See Devices, Translating, Multiple- Connected.) Translating Devices, Multiple-Series- Connected - (See Devices, Translat- ing, Multiple-Series-Connected.} Translating Devices, Series-Connected (See Devices, Translating, Series- Connected.) Translating Devices, Series-Multiple- Connected (See Devices, Translat- ing, Series-Multiple-Connected.) Translucent-Disc Photometer. (See Photometer, Translucent-Disc.) Transmission, Double The simul- taneous sending of two messages ovef a sin- gle wire in opposite directions. (See Teleg- raphy, Duplex, Bridge Method of.) Transmission, Multiple The simul- taneous sending of more than two messages over a single line or conductor. Transmission of Energy. (See Energy, Electric, Transmission of.) Transmitter, Carbon, for Telephones A telephone transmitter consisting of a button of compressible carbon. The sound waves impart to-and-fro movements to the transmitting diaphragm, and this to the carbon button, thus varying its resistance by pres- sure. This button is placed in circuit with the battery and induction coil. (See Telephone.) Transmitter, Double-Current The transmitting instrument employed in systems of telegraphy, by means of which the direc- tion of the currents on the line is alternately changed, according to whether the key rests on its front or on its back stop. Double-current transmitters are used in con- nection with instruments, such as polarized re- lays, which respond to change in the direction of the current, rather than to changes in its in- tensity. Transmitter, Electric A name applied to various electric apparatus employed in telegraphy or telephony to transmit or send the electric impulses over a line wire or con- ductor. The sending instrument as distinguished from the receiving instrument. In most telegraphic systems, the transmitting; instrument consists of various forms of keys for in- terrupting or varying the current. In the tele- phone the transmitter consists of a diaphragm operated by the voice of the speaker. (See Tele- phone.) Transmitter, Water-Jet Telephone A telephone transmitter consisting of a jet of water issuing vertically downwards from a. small orifice. The jet forms a part of the circuit of the re- ceiving telephone. In order to reduce its resist- ance, the water is rendered acid by the addition of sulphuric acid, and a battery of high electro- motive force is employed. Since the jet has a- high resistance, a battery of high resistance can. be used without inconvenience. Tra.] 533 [Tro. Transposing. In a system of telephonic communication a device for avoiding the bad effects of induction by alternately crossing equal lengths of consecutive sections of the line. (See Connection, Telephonic Cross.) Transverse Electromotive Force. (See Force, Electromotive, Transverse.) Treatment, Hydro-Carbon, of Carbons Exposing carbons, while electrically heated to incandescence, to the action of a carbonizing gas, vapor or liquid, for the pur- pose of rendering them more uniformly elec- trically conducting throughout. (See Car- bons, Flashing Process for.) Tree, Parallel, Circuit (See Cir- cuit, Parallel-Tree.) Trembling Bell. (See Bell, Trembling) Trigonometrical. Of or pertaining to trigonometry. (See Trigonometry.) Trigonometrical Function. (See Func- tion, Trigonometrical^) Trigonometrically. In a trigonometrical manner. Trigonometry. That branch of mathe- matical science which treats of the methods of determining the values of the angles and sides of a triangle. There are in every triangle three sides and three angles. If any three of these parts are given, except the three angles, the values of the remaining parts can be determined by means of fff. SS9- Dynamo Brush Trimmer. trigonometry, by what is called the solution of the triangle. (See Function, Trigonometrical.) Trimmer. An employee of an electric light company who renews the carbons in arc lamps. Trimmer, Dynamo Brush A de- vice for insuring rapid and accurate trimming of dynamo brushes. The brush trimmer consists of a knife, placed as shown in Fig. 559 on a rigid support The brushes are placed under a clamp, and against a straight edge, so that a single cut with the knife blade insures a clean and true cut. Trimming. A term sometimes applied to the act of placing the carbons in an electric arc lamp. The phrase, carboning a lamp, would appear to be preferable to trimming a lamp. Triple-Carbon Arc Lamp. (See Lamp t Arc, Triple-Carbon?) Tripod Roof Support. (See Support, Tripod Roof) Trolley. A rolling contact wheel that moves over the overhead lines provided for a line of electric railway cars, and carries off the current required to drive the motor car. Trolley Crossing. A device placed at the crossing of two trolley wires, by which the trolley wheel running on one wire may cross the other. Such a device can also be made to hold the two wires together. Trolley Crossing, Insulated A de- vice used at the crossing of two trolley wires, which insulates the wires from each other, but which permits the trolley wheel of one line to cross the other trolley line. Trolley Cross-Over. (See Cross-Over, Trolley) Trolley, Double The traveling con- ductors, which move over the lines of wire in any system of electric railways that employs two overhead conductors. In one form of double trolley a bar of wood carries two hangers, separated from each other, and furnished with diverging feet, with clips that embrace the two conducting wires. These wires serve also as the track for the two-wheeled trolley. The trolley consists of two plates connected to and insulated from each other under the conductor:-, Tro.] 534 [Tub. and carrying flanged wheels, extending in over the conductors. Swinging from the axles of the poles are arms, which form a bail-like draft loop, with insulated material between their lower ends, and furnish means for connection with the car motor. In order to remove this trolley from the conducting wires, these arms are pressed together at points between two points of hangers, which allows them to pass between the inner ends of the wheel axles. The trolley cannot be removed from the wires except at the end of the track, and it is therefore found in practice to be particularly useful in mines, where, from the nature of the galleries, the trolley wheel is very apt to become detached from the trolley wires. Trolley, Drop The trolley wheel and rod for an electric car which drops away from the wire on slipping from the wire, and is reset upwards through proper elastic press- ure. Trolley Fork. (See Fork, Trolley) Trolley Frog. (See Frog, Trolley) Trolley Frog, Standard (See Frog, Trolley, Standard) Trolley Hanger. (See Hanger, Trolley) Trolley Pole. (See Pole, Trolley) Trolley Section. (See Section, Trolley) Trolley, Single A traveling con- ductor or wheel which moves over a single conductor in a system of electric railways, and takes off the current for driving the elec- tric motor, in connection with an earth or grounded return conductor. Trolley Wheel. (See Wheel, Trolley) Trolley, Wire (See Wire, Trolley) True Contact Force. (See Force, True Contact) True Resistance. (See Resistance, True) Trumpet, Electric An electro- magnetic buzzer, the sound of which is strengthened by means of a resonator in the shape of a trumpet. (See Buzzer, Electric. .Resonator, Electric) The electric trumpet is used to replace electric bells. It gives a louder and more penetrating sound than the electric bell. Trunking Switch Board. (See Board, Switch, Trunking) Tube, Crookes' A tube containing a high vacuum and adapted for showing any of the phenomena of the ultra-gaseous state of matter. (See Matter, Radiant, or Ultra- Gaseous) Tube, Insulating A tube of insu- lating material provided for covering a splice in an insulated conductor. Tube, Mercury Vacuous glass tubes in which a flash of light is produced by the fall of a small quantity of mercury placed in- side it. The light is caused by the electricity produced by the friction of the mercury in falling against the sides of a spiral glass tube placed inside the vacuous tube. Tube, Plucker A modification of a Geissler tube adapted for the study of the stratification of the light, and the peculiar- ities of the space adjoining the negative elec- trode. (See Tubes, Geissler) Tube, Spark A high vacuum tube, across which, when the vacuum is sufficiently high, the spark from an induction coil will not pass. A spark tube, connected with incandescent lamps while undergoing exhaustion, acts as a simple gauge to determine the degree of ex- haustion. When an induction coil discharge ceases either to pass, or to pass freely, the vacuum is considered as sufficient, according to circum- stances. Tube, Stratification An exhausted glass tube, the residual atmosphere of which displays alternate dark and light striae, or stratifications, on the passage through it of an induction coil discharge. (See Discharge, Luminous Effects of) Tubes, Geissler Vacuum tubes of glass containing various gases, liquids or solids, provided with platinum electrodes, passed through and fused into the glass, de- signed to show the various luminous effects Tub.] of electric discharges through gases at com- paratively low pressures. Geissler tubes are made of a great variety of shapes, and often include tubes, spirals, spheres, etc., within other tubes. These enclosed tubes are made either of ordinary glass, or of uranium glass in order to obtain the effects of fluorescence. The vacuum in Geissler tubes is by no means what might be called a high vacuum. Indeed, if the exhaustion of the tube be pushed too far, much of the brilliancy of the luminous effects is lost. Some of the many forms of Geissler tubes are shown in Fig. 560. 535 [Twi. Fig. 360. Geissler Tubes. Tubes of Force. (See Force, Tubes of.) Tubes of Induction. (See Induction, Tubes of.) Tubes, Tacuum Glass tubes, from which the air has been partially exhausted and through which electric discharges are passed for the production of luminous effects. (See Tubes, Geissler^ Tubular Braid. (See Braid, Tubular.} Tumbling Box. (See Box, Tumbling?) Tuning-Fork or Reed Interrupter. (See Interrupter, Tuning-Fork. Interrupter, Reed) Turn, Ampere A single turn or winding in a coil of wire through which one ampere passes. An ampere-turn is sometimes called an ampere- winding. Magneto-motive force in a magnetic circuit is proportioned to the number of ampere- turns linked with it. The practical unit of mag- neto-motive force is J_ X ampere turn = .0796 47f ampere turn. Therefore the magneto-motive force, m. m. f., is found by multiplying the am- pere turns by 4 it or 12.57. The number of amperes multiplied by the number of windings or turns of wire in a coil give the total number of ampdre-turns in the coil. In a coil of fixed dimensions the magnetizing force developed by a given number of ampere-turns remains the same as long as the product of the amperes and the current remains the same. That is to say, the same amount of magnetizing force can be obtained by the use of many windings and a small current, as in shunt dynamos, or by a few turns and a proportionally large current, as in series dynamos. (See Machine, Dynamo-Elec- tric.) Turns, Ampdre, Primary The ampere-turns of the primary of an induction coil. Turns, AmpSre, Secondary - The ampere-turns of the secondary of an induc- tion coil. Turns, Dead The number of revo- lutions a self-exciting dynamo makes before it excites itself. Turns, Dead, of Armature Wire Those turns of the wire on the armature of a dynamo-electric machine which produce no useful electromotive force or resultant current, on the movement of the armature through the magnetic field of the machine. The wire on the inside of a Gramme or ring armature is dead wire, but not dead turns. Turns, Series, of Dynamo-Electric Ma- chines The ampere-turns in the series circuit of a compound-wound dynamo- electric machine. (See Machine, Dynamo- Electric, Compound- Wound?) Turns, Shunt, of Dynamo-Electric Ma- chine The ampere-turns in the shunt circuit of a compound-wound dynamo-elec- tric machine. (See Machine, Dynamo-Elec- tric, Compound- Wound) Turn-Table, Electric A table, suit- able for show windows, revolved around a vertical axis by means of an electric motor. Twig. A sub-branch. (See Branch, Sub.) Twin Wire. (See Wire, Twin.) Twi.] 536 LTJni. Twist in Leads. (See Leads, Armature, Twist in.) Twisted Bunched Cable. (See Cable, Bunched, Twisted) Twisted-Pair Cable. (See Cable, Twisted- Pair.) Twisting Force. (See Force, Twisting.) Two-Fluid Voltaic Cell. (See Cell, Vol- taic, Two-Fluid.) Two-Point Switch. (See Switch, Two- Point) Two, Three, Four, etc., Conductor Cable (See Cable, Two, Three, Four, etc., Conductor?) Two-Way Splice Box. (See Box, Splice, Two- Way.) Two-Way Switch. (See Switch, Two- Way.) Type-Printing Telegraph. (See Teleg- raphy, Printing.) Typewriter, Electric A typewrit- ing machine, in which the keys are intended to make the contacts only of circuits of electro-magnets, by the attraction of the arma- tures of which the movements of the type levers required for the work of printing are effected. Electric typewriters secure a uniformity of im- pression that is impossible to obtain with hand worked machines. They also greatly lessen the mechanical labor of writing. (See Dynamograph.) U. A contraction sometimes used for unit. Ultra-Gaseous Matter. (See Matter, Radiant, or Ultra-Gaseous) Underground Cable. (See Cable, Under- ground) Underground Conductor. (See Con- ductor, Underground.) Undulating Currents. (See Current, Undulating) Undulatory Currents. (See Currents, Undulatory) Undulatory Discharge. (See Discharge, Undulatory) Ungilding Bath. (See Bath, Ungild- *) Unidirectional Discharge. (See Dis- charge, Unidirectional) Unidirectional Leak. (See Leak, Uni- directional) Uniform Density of Field. (See Field, Uniform Density of) Uniform Magnetic Field. (See Field, Magnetic, Uniform) Uniform Magnetic Filament. (See Fila- ment, Uniform Magnetic) Uniform Potential. (See Potential, Uniform) Uniformly Distributed Current. (See Current, Uniformly Distributed) Unipolar Armature. (See Armature, Unipolar) Unipolar-Electric Bath. (See Bath, Uni- polar-Electric) Unipolar Induction. (See Induction, Unipolar) Unit Angle. (See Angle, Unit. Velocity, Angular) Unit Angular Velocity. (See Velocity, Angular) Unit, B. A. A term formerly ap- plied to the British Association unit of re- sistance, or ohm. (See Ohm) Unit-Difference of Potential or Electro- motive Force (See Potential, Unit Difference of) Unit, Magnetic, A A term some- times used for a line of magnetic force, or the amount of magnetism induced in an area of one square centimetre at the centre of a coil having a diameter of 10 centimetres and carrying a current of 7.9578 amperes. Unit, Natural, of Electricity (See Electricity, Natural Unit of) Uni.] 537 [Uni. Unit of Acceleration. (See Acceleration, Unit of.) Unitof Activity. (See Activity, Unit of.) Unit of Current, Absolute (See Current, Absolute Unit of.) Unit of Current, Jacobi's (See Current, Jacobi's Unit of.) Unit of Electrical Supply. (See Supply, Unit of, Electrical) Unit of Electromotive Force, Absolute (See Force, Electromotive, Absolute Unit of.) Unit of Electrostatic Capacity. (See Capacity, Electrostatic, Unit of.) Unit of Heat. (See Heat Unit.) Unit of Inductance. (See Inductance, Unit of) Unit of Mass. (See Mass, Unitof.) Unit of Photometric Intensity. (See Intensity, Photometric, Unit of.) Unit of Power. (See Power, Unit of.) Unit of Pressure, New The Barad. (See Barad.) Unit of Resistance. (See Resistance, Unit of.) Unit of Resistance, Absolute (See Resistance, Absolute Unit of) Unit of Resistance, Jacobi's (See Resistance, Unit of, Jacobi's.) Unit of Resistance, Matthiessen's (.See Resistance, Unit of, Matthiessen's.) Unit of Resistance, Varley's (See Resistance, Unit of, Varley's.) Unit of Telocity, New (See Ve- locity, New Unit of) Unit Quantity of Electricity. (See Elec- tricity, Unit Quantity of.) Unit-Strength of Current. (See Cur- rent, Unit Strength of.) Units, Absolute A system of units based on the centimetre for the unit of length, the gramme for the unit of mass, and the second for the unit of time. These units are more frequently called the centimetre -gramme-second units. Units, Centimetre-Gramme-Second A system of units in which the centimetre is adopted for the unit of length, the gramme for the unit of mass, and the second for unit of time. This is the same as the absolute system of units. Units, C. G. S. - The centimetre- gramme-second units. (See Units, Funda- mental) Units, Circular Units based upon the value of the area of a circle whose diame- ter is unity. The advantages possessed by the circular units of cross-section arise from the fact that in these units the areas are equal to the squares of the diameter. No necessity exists, therefore, for mul- tiplying by .7854. Units, Circular (Cross-Sections), Table of I circular mil = .78540 square mil. " " = .00064514 circular millimetre. " " == .00050669 square millimetre. I square mil = 1.2732 circular mils. " " = .00082141 circular millimetre. I circular millimetre = 1550.1 circular mils. " " = 1217.4 square mils. " = .78540 square milli- metre. I square millimetre .... =1973.6 circular mils. * " =1.2732 circular mil- limetres. If d, is the diameter of a circle, the area in other units is: If d, is in mils, the area in square millimetres. . . . = d X .00050669. d, in millimetres, area in square mils = d*X 1217.4. d, in centimetres, area in square inches = d X 12174. d, in inches, area in square centimetres = d X 5.0669. Uni.J 538 Units, Derived -- Various units ob- tained or derived from the fundamental units of Length, L., Mass, M., and Time, T. The derived units and their dimensions are as follows: Area, L 2 . The square centimetre. Volume, L 3 . The cubic centimetre. Velocity, V. Unit distance traversed in unit time, or V = ^. (i) Acceleration, A. The rate of change which will produce a change of velocity of one centi- metre per second. A = ^. (2) Substituting in equation (2) the value of V, in equation (i), we have L A T L A =T = T" (3) Force, F. The dyne, or the force required to act on unit mass in order to impart to it unit velocity. F = MXA. (4) Substituting the value of A, derived from equa- tion (2), we have Substituting the value of V, derived from equa- tion (i), we have Work or Energy, W. The erg, or the work done in overcoming unit force through unit dis- tance. Power, P. The unit rate of doing work. Units, Dimensions of The values given to the units of length, L ; mass, M, and time, T. (See Units, Derived^ Units, Electro-Magnetic A system of units derived from the C. G. S. units, em- [Uni. ployed in electro-magnetic measurements. (See Units, Centimetre-Gramme-Second.} Units based on the attractions or repul- sions between two unit magnetic poles at unit distance apart. (See Units, Electro- static.') Units, Electro-Magnetic, Dimensions of Current Strength = Intensity of FieldxLength = v/ML T" Quantity = Current X Time= >/M X L . Potential, Difference of Potential, Electromo- tive Force = Resistance = Work Quantity = Electromotive Force L^ Current = T Capacity = Q^tity T. Potential L Units, Electrostatic Units based on the attractions or repulsions of two unit charges of electricity at unit distance apart. Two systems of electric units are derived from the C. G. S. system, viz., the electrostatic and electro-magnetic. These units are based respec- tively on the force exerted between two quanti- ties of electricity and between two magnet poles. The electrostatic units embrace the units of quantity, potential and capacity. No particular names have as yet been adopted for these units. Unit of Quantity. That quantity of electricity which will repel an equal quantity of the same kind of electricity placed at a distance of one cen- timetre from it with the force of one dyne. Electrostatic potential, or power of doing elec- trostatic work, is measured in units of work, or ergs. Unit Difference of Potential. Such a differ- ence of potential between two points as requires the expenditure of one erg of work to bring up a unit of positive electricity from one point to the other against the electric force. Unit of Capacity. Such a capacity of conduc- tor as will take a charge of one unit of electricity when the potential is unity. The ratio between the inductive capacity of a substance and that of air, measured under pre- Uni.] 539 [Uni. cisely similar conditions, is called the specific in- ductive capacity. The specific inductive capacity is obtained by comparing the capacity of a condenser filled with the particular substance and the capacity of the same condenser when filled with air. The spe- cific inductive capacity of air is taken as unity. Units, Electrostatic, Dimensions of Quantity = v/ForceX( Distance) * = N/F X L Current = Q uantit y Potential = Resistance : Quantity Potential -=L Capacity Current Quantity Potential = Specific Inductive Capacity = One Quantity Another Quantity = A Sim ple Ratio or Number. Electromotive Intensity = Force Quantity The fractional and negative exponents used above are merely convenient methods of express- ing the extraction of roots and division respec- tively by the quantity represented by these expo- nents. Units, Fundamental The units of length, time and mass, to which all other quantities can be referred. The unit of length is now generally taken as the centimetre, the unit of time as the second, and the unit of mass as the gramme. These form a system of measurement known as the centimetre- gramme-second system, or the C. G. S. system, or absolute system. (See Units, Derived.} The dimensions of the fundamental units are designated thus: Length = L. Mass =M. Time =T. Units, Heat Units based on the quantity of heat required to raise a given weight or quantity of a substance, generally water, one degree. The principal heat units are the English heat unit, the greater and smaller calorie and the joule. (See Calorie. Joule.) The following table gives the values of some of the prin- cipal heat units : i gram, centigrade, .001 kilogram centigrade, i pound Fahrenheit, 1,047.03 joules. " 773. foot-pounds. " 106.731 kilogram metres. " '55556 pound centigrade. " .25200 kilogram centigrade. " .29084 watt-hours. " .0003953 metric horse-power. " .0003899 horse-power hours, i pound centigrade, 1,884.66 joules. " '1389.6 foot-pounds. " 192.116 kilogram metres. " 1.800 pound Fahrenheit. " -4536 kilogram centigrade. " -5 2 35* watt -hour. " .0007115 metric horse-power hour. " .00070x8 horse-power hour, i kilogram centigrade, 4,154.95 joules. " 3.063-5 foot-pounds. " 423.54 kilogram metres. " 3.9683 pound Fahrenheit. " 2.2046 pound centigrade. " 1-1542 watt-hour. " .001569 metric horse-power hour. " .0015472 horse-power hour. Hering. Units, Magnetic Units based on the force exerted between two magnet poles. Unit strength of a magnetic pole is such a magnetic strength of pole that repels another magnetic pole of equal strength placed at unit distance with unit force, or with the force of one dyne. Magnetic Potential. Is the power of doing work possessed by a magnetic pole. Magnetic potential is measured like electro- static potential in units of work or in ergs. Magnetic Potential, Unit Difference of. Such a difference of magnetic potential between two points that requires the expenditure of one erg of work to bring a magnetic pole of unit strength from one to the other. Unit Intensity of Mngnetic MtM.Such an intensity of magnetic field as acts on a north or south-seeking pole of unit strength with the force of one dyne. Uni,] 540 [Upr. Units, Magnetic, Dimensions of Strength of Pole, or i Quantity of Magnetism J = V Force X (Distance) 2 Magnetic Potential Work Strength of Pole Intensity of Field = Stre n g thof Pole Units, Practical Multiples or frac- tions of the absolute or centimetre-gramme- second units. The practical units have been introduced be- cause the absolute units are either too small or too large for actual use. Electromotive Force. The Volt = 100,000, - ooo C. G. S. or absolute units, that is, io 8 abso- lute units of resistance. (See Volt.) Resistance. The Ohm = 1,000,000,000 abso- lute units of electromotive force, or io 9 absolute units. (See Ohm.) Current. The Ampere = fa absolute unit of current. (See Ampere.) Quantity. The Coulomb = fa absolute unit of quantity, of the electro-magnetic system. (See Coulomb.} Capacity. The Farad = i QQO I QQ ^ ^ abso- lute unit of capacity, or io 9 units of capacity. (See Farad. Henry. Watt. Joule.) Units, Proposed New The follow- ing units and terms have recently been pro- posed by Oliver Heaviside. Some of these have been generally adopted. Conductance. Capacity for conducting elec- tricity. Numerically, the ratio, in absolute measure, ot the current strength to the total electromotive force in a circuit of uniform flow. A quantity with the nature of a slowness or reciprocal to a velocity. The practical unit is called the mho. Conductivity. Conductance per unit volume. Elastance. Capacity of a dielectric for oppos- ing electric charge or displacement. ' ' Numerically, the ratio, in absolute measure, of the difference of potential in an electrostatic cir- cuit to the total charge or displacement therein produced. The reciprocal of permittance and a quantity of the inverse nature of a length." " Elastivity. Elastance per unit volume of di- electric." Impedance. Capacity for opposing the variable flow of electricitv-^ "Numerically, in the absolute measure, the ratio of the total electromotive force to the cur- rent strength at any instant in a circuit of a vari- able flow. A quantity with the nature of a velocity and in any circuit always greater than the resistance." "Inductance. Capacity for magnetic induc- tion." "Numerically, in absolute measure, the num- ber of unit lines of magnetic force linked with a circuit traversed by the unit current strength. Sometimes alluded to as the co-efficient of self in- duction. A quantity of the nature of a length." " Inductivity \ Specific capacity for magnetic induction. 1 ' The numerical ratio of the induction in a medium to the induction producing it." Permittance. Electrostatic capacity. Capa- city of a dielectric for assisting charge or displace- ment. "Numerically, the ratio, in absolute measure, of the total charge or displacement in the electro- static circuit, to the difference of potential pro- ducing it* A quantity with the nature of a length." " Permittivity. The numerical ratio of the permittance of a dielectric to that of air. " Also known as specific inductive capacity." "Reluctance. Capacity for opposing mag- netic induction. "Numerically, the ratio, in absolute measure, of the magneto-motive force in a magnetic cir- cuit to the total induction therein produced. A quantity with the nature of the reciprocal of a length. Sometimes described as magnetic resist- ance." Reluctancy or Reluctivity. Reluctance per unit volume. "Sometimes described as specific magnetic re- sistance. A numeric, the reciprocal of induc- tivity." " Resistance. Capacity for opposing the steady flow of electricity. "Numerically, in absolute measure, the ratio of the total electromotive force to the current strength in a circuit of uniform flow. A quantity with the nature of a velocity. The practical unit is called the ohm." "Resistivity. Resistance per unit volume; sometimes alluded to as specific resistance." Universal Discharger. (See Discharger, Universal.') Upright Galvanometer. (See Galva- nometer, Upright^ Vac.] 541 [Var. T. A contraction sometimes used for volt. T. A contraction sometimes used for ve- locity. T. A contraction sometimes used for vol- ume. V. A. A contraction sometimes used for voltaic alternative. (See Alternatives, Vol- taic^ Vacuum, Absolute A space from which all traces of residual gas have been removed. A term sometimes loosely applied to a par- tial vacuum. It is doubtful whether an absolute vacuum is attainable by any physical means. Vacuum, High A space from which nearly all traces of air or residual gas have been removed. Such a vacuum that the length of the mean free path of the molecules of the residual atmosphere is equal to or exceeds the di- mensions of the containing vessel. (See Layer, Crookes'.) Vacuum, Low Such a vacuum that the mean free path of the molecules of the residual gas is small as compared with the dimensions of the containing vessel. (See Tubes, Geissler.) In a high vacuum groups ot molecules can move across the containing vessel without meet- ing other groups of molecules. In a low vacuum such a group of molecules would be broken up by collision against other groups before reaching the other side of the vessel. Vacuum, Partial A name some- times applied to a low vacuum. (See Vac- uum, Low.) Vacuum, Torricellian The vacuum which exists above the surface of the mercury in a barometer tube or other vessel over thirty inches in vertical height. The Torricellian v icuum is high only when the mercury has been carefully boiled and the tube or other vessel vigorously heated, so as to thor- oughly drive out the moisture and adherent film of air. Vacuum Tubes. (See Tubes, Vacuum.) Valency. The worth or value of a chemi- cal atom as regards its power of displacing other atoms in chemical compounds. (See Atomicity?) The worth or valency of an atom of oxygen is twice as great as that of hydrogen, since one atom of oxygen is able to replace two hydrogen atoms in chemical combinations. Valve, Electric - An electrically controlled or operated valve. In systems of electro-pneumatic signals, gaseous or liquid pressure controlled by electrically oper- ated valves is employed to move signals, ring bells, control water and air valves, or to perform other similar work. Vapor Globe of Incandescent Lamp. (See Globe, Vapor, of Incandescent Lamp.} Variable Inductance. (See Inductance, Variable.) Variable Period of Electric Current (See Current, Variable Period of.) Variable Resistance. (See Resistance, Variable.) Variable Resistance, Automatic (See Resistance, Variable, Automatic.) Variable Resistance, Non-Automatic (See Resistance, Variable, Non-Auto- matic?) Variable State of Charge of Telegraph Line. (See State, Variable, of Charge of Telegraph Line?) Variation, Angle of - The angle which measures the deviation of the magnetic needle to the east or west of the true geo- graphic north. The angle of declination of the magnetic needle. (See Declination, Angle of.) Variation, Annual - An approxi- mately regular variation in the magnetic Tar.] 542 [Vel. needle which occurs at different seasons of the year. Variation Chart or Map. (See Map or Chart, Isogonic.) Variation, Cyclical Magnetic Secu- lar magnetic variations occurring during great cycles of time. (See Variation, Secular. Variation, Magnetic) Yariation, Diurnal An approxi- mately regular variation of the magnetic needle, which occurs at different hours of the day. (See Declination.) Variation, Irregular A variation of the magnetic needle which occurs at ir- regular intervals. (See Declination!) Variation, Magnetic Variations in the value of the magnetic declination, or inclination, that occur simultaneously over all parts of the earth. The term is also applied to the magnetic decli- nation itself. These variations are: (I.) Secular, or those occurring at great cycles of time. (2.) Annual, or those occurring at different seasons of the year. (3.) Diurnal, or those occurring at different hours of the day. (4.) Irregular, or those accompanying mag- netic storms. The first three are periodical ; the last is irregular. (See Declination, Angle of. Chart, Inclination.) Variation, Secular A variation in the magnetic declination which occurs at great cycles or intervals of time. (See Dec- lination) Varieties of Circuits. (See Circuits, Varieties of) Variometer, Magnetic An instru- ment for comparing the horizontal compo- nent of the earth's magnetism in different localities. Varnish, Electric A varnish formed of any good insulating material. Shellac dissolved in alcohol, applied to a thoroughly dried surface and afterwards hard- ened by baking, forms an excellent varnish. Varnish, Stopping-Off A varnish used in electro-plating to cover portions which are not to receive the metallic coat- ing. A good stopping-off varnish is made by mixing together 10 parts of rosin, 6 parts of beeswax, 4 parts of sealing-wax and 3 parts of rouge, dis- solved in turpentine. (See Stopping- Off.) Vat, Depositing The vat in which the process of electro-plating is carried on. (See Plating, Electro) The depositing vat contains the plating liquid, the metallic anode and the object to be plated. Vegetation, Effects of Electricity on Most vegetable fibres contract when an electric current is passed through them while on the living plant. Some experiments appear to show that electric charges and currents hasten the germination and growth of certain plants. Other experiments seem to show that under certain circumstances electric currents retard plant growth. The di- rection of the currents is probably of main im- portance. Yelochneter. Any apparatus for measur- ing the speed of a machine. Velocity, Angular The velocity of a body moving in a circular path, measured, not as usual, by the length of its path divided by the time, but with reference to the angle it subtends and to the length of the radius. Unit angle is that angle subtended by a part of the circumference equal to the length of the radius, or 57 degrees 17 minutes 44 seconds .8 nearly . (Daniell. ) Unit angular velocity is the velocity under which a particle moving in a circular path, whose radius equals unity, would traverse unit angle in unit time. Velocity, New Unit of - The kine, (See Kine.) Velocity of Discharge. (See Discharge, Velocity of) Velocity Ratio. (See Ratio, Velocity.) Yen.] Ventilation of Armature. (See Arma- ture, Ventilation of.) Vernier. A device for the more accurate measurement of small differences of length than can be detected by the eye alone, by means of the direct reading of the position of a mark on a sliding scale. The sliding scale is called the vernier. There are a variety of vernier scales in use. Vertical Component of Earth's Magnet- ism. (See Component, Vertical, of Earth's Magnetism?) Vertical Electrostatic Voltmeter. (See Voltmeter, Vertical, Electrostatic!) Verticity, Poles of, Magnetic The earth's magnetic poles, as determined by means of the dipping needle. The point of the north where the angle of dip is 90 degrees. (See Map or Chart, Inclination. ) Vibrating. Moving to-and-fro. Vibrating Bell. (See Bell, Vibrating) Vibrating Contact. (See Contact, Vibrat- ing) Vibration. A to-and-fro motion of the particles of an elastic medium. (See Wave.) Vibration or Wave, Amplitude of The ratio that exists in a wave between the degree of condensation and rarefaction of the medium in which the wave is propa- gated. The amplitude of a wave is dependent on the amount of energy charged on the medium in which the vibration or wave is produced. A vibration or wave is a to-and-fro motion pro- duced in an elastic material or medium by the action of energy thereon. Sound, light and heat are subjectively effects produced by the action of vibrations or waves, which in the case of sound are set up in the air, and, in that of light and heat, in a highly tenuous medium called the lumi- niferous ether. Objectively they are the waves themselves. As the amplitude of a sound wave increases, the loudness or intensity of the sound increases. As the amplitude of the ether wave increases, the brilliancy of the light or the intensity of the light or heat increases. [Tib. Let A C, Fig. 561 represent an elastic cord or string tightly stretched between A and C. If the string be plucked by the finger, it will move to-and-fro, as shown by the dotted lines. Each to-and-fro motion is called a vibration. The Fig. S6l. Amplitude of Wave. vertical distance B D, or B E, represents the amplitude of the vibration, and the sound pro- duced is louder, the greater the amount of energy with which the string has been plucked, or, in other words, the greater the value of B D, or BE. Vibrations assume various forms in solid or fluid media, but in all cases the amplitude will increase with the increase in the energy that causes the vibration. Vibration Period. (See Period, Vibra- tion!) Vibration, Period of - The time occupied in executing one complete vibration or motion to-and-fro. Vibration, Phase of The position of the particles in motion in a wave or vibra- tion at any instant of time during the wave period, as compared with a zero line, or a line passing through their mean or middle position. Vibrations, Isochronous Vibra- tions which perform their to-and-fro motions on either side of the position of rest in equal times. The vibrations of a pendulum are practically isochronous, no matter what the amplitude of the swing may be, that is, whether the pendulum swings through a large arc or a small arc, pro- vided this arc be not very great All vibrations that produce musical sounds may be regarded as isochronous; that is, in any case, the time required to complete a to-and-fro motion is the same at the beginning when the sound is loud, as at the end, when it is faint. Vibrations, Sympathetic - Vibra- tions set up in bodies by waves of exactly the same wave rate as those produced by the vibrating body. The pitch or tone of the note produced by the body set into sympathetic vibration, is exactly the Tib.] 544 [Vol. same as the pitch or tone of the exciting waves or vibrations. Hertz's experiments show that sympathetic vi- brations are excited by electro-magnetic waves- (See Electricity, Hertz's Theory of Electro-Mag- netic Radiations or Waves.) Yibrations, Sympathetic, Electrical Vibrations set up in circuits, by the effect of pulses in neighboring circuits, that are of exactly the same mean length. Vibrations, Synchronous Vibra- tions that are performed not only in the same time as one another, but which pass through the same portions of their to-and-fro move- ment at the same time. Vibrator, Electro-Magnetic - A lever, or arm, automatically moved to-and- fro by the alternate attractions of an electro- magnet and an opposing spring, or by the successive action of two electro-magnets. In either case the movement of the lever is utilized to permit the action of first one and then the other device. Automatic or trembling bells are operated by means of an electro magnetic vibrator. Villari Critical Point. A term proposed by Sir William Thomson for that strength of magnetic field at which the reversal of the effects of tension occurs. Both magnetic susceptibility and permeability are affected by mechanical stress, vibration and changes of temperature. In a weak magnetic field the susceptibility of iron wire is increased by longitudinal tension, while in a strong field it may be decreased. The particular strength of field at which the reversal occurs is called the Villari critical point. Viscosity, Magnetic - That prop- erty of iron or other paramagnetic substance in virtue of which a certain time is required before a given magnetizing force can pro- duce its effects. (See Hysteresis, Viscous?) Viscous Hysteresis. (See Hysteresis, Viscous?) Vis-Viva. The energy stored in a moving body, and therefore the measure of the amount of work that must be performed in order to bring a moving body to rest. If M, is the mass and V, the velocity The Vis- Viva = MY. 8 2 Vitreous Electricity. (See Electricity, Vitreous?) Vitrite. An insulating substance. Volatilization, Electric A term sometimes used instead of electric evapora- tion. (See Evaporation, Electric?) Volcanic Lightning. (See Lightning, Volcanic?) Volt. The practical unit of electro- motive force. Such an electromotive force as is induced in a conductor which cuts lines of magnetic force at the rate of 100,000,000 per sec. Such an electromotive force as would cause a current of one ampere to flow against the resistance of one ohm. Such an electromotive force as would charge a condenser of the capacity of one farad with a quantity of electricity equal to one coulomb. io s absolute electro-magnetic units of elec- tromotive force. Volt-Ammeter. A wattmeter. A variety of galvanometer capable of di- rectly measuring the product of the difference of potential and the amperes. (See Watt- meter.} Volt AmpSre. A watt. (See Watt?) Volt-Coulomb. The unit of electric work. The joule. (See Joule.} Volt, Mega One million volts. Volt, Micro The one-millionth of a volt. Voltage. This term is now very com- monly used for either the electromotive force or difference of potential of any part of a circuit as determined by the reading of a voltmeter placed in that part of the circuit. Voltage, Terminal - The electro- motive force expressed in volts of a dynamo or other electric source, as indicated by a voltmeter placed across its terminals. The terminal voltage is greater than that on the leads or conductors at some distance from Vol.] 545 the source and less than that generated by the source. There is an exception to this general statement in the case of certain leads connected with an a'ternating dynamo- electric machine. (See Ef- fect , Ferra nti.) Voltaic Arc. (See Arc, Voltaic) Voltaic Battery. (See Battery, Voltaic) Voltaic Battery Indicator. (See Indica- tor, Voltaic Battery.} Voltaic Battery Protector. (See Pro- tector, Voltaic Battery) Voltaic Cell. (See Cell, Voltaic) Voltaic Cell, Bichromate - (See Cell, Voltaic, Bichromate) Voltaic Cell, Bunsen's (See Cell, Voltaic, Sunsen's.) Voltaic Cell, Callaud's (See Cell, Voltaic, Callaud's.) Voltaic Cell, Capacity of Polarization of (See Cell, Voltaic, Capacity of Polar- ization of,) Voltaic Cell, Closed-Circuit - (See Cell, Voltaic, Closed-Circuit.) Voltaic Cell, Contact Theory of (See Cell, Voltaic, Com act Theory of) Voltaic Cell, Creeping of - (See Cell, Voltaic, Creeping in) Voltaic Cell, Daniell's (See Cell, Voltaic, Darnell's) Voltaic Cell, Double-Fluid - (See Cell, Voltaic, Double-Fluid) Voltaic Cell, Dry (See Cell, Vol- taic, Dry) Voltaic Cell, Gravity (See Cell, Voltaic, Gravity) Voltaic Cell, GrenSt - (See Cell, Voltaic, Grenet) Voltaic Cell, Grove - (See Cell, Vol- taic, Grove) Voltaic Cell, Leclanchg (See Cell, Voltaic, Leclanche) Voltaic Cell, Local Action of (See Action, Local, of Voltaic Cell) Voltaic Cell, Meidinger -- (See Cell, Voltaic, Meidinger) Voltaic Cell, Negative Plate of -- (See Plate, Negative, of Voltaic Cell) Voltaic Cell, Open-Circuit -- (See Cell, Voltaic, Open-Circuit) Voltaic Cell, Poggendorff -- (See Cell, Voltaic, Poggendorff) Voltaic Cell, Polarization of (See Cell, Voltaic, Polarization of) Voltaic Cell, Positive Plate of -- (See Plate, Positive, of Voltaic Cell) Voltaic Cell, Siemens-Halske -- (See Cell, Voltaic, Siemens-Halske) Voltaic Cell, Simple - (See Cell, Voltaic, Simple) Voltaic Cell, Single-Fluid - (See Cell, Voltaic, Single-Fluid) Voltaic Cell, Since --- (See Cell, Vol- taic, Smee) Voltaic Cell, Standard (See Cell, Voltaic, Standard) Voltaic Cell, Standard, Clark's - (See Cell, Voltaic, Standard, Clark's) Voltaic Cell, Standard, Clark's, Ray- leigh's Form of (See Cell, Voltaic, Standard, Rayleigh's Form of Clark's) Voltaic Cell, Standard, Fleming's (See Cell, Voltaic, Standard, Fleming's) Voltaic Cell, Standard, Lodge's (See Cell, Voltaic, Standard, Lodge's) Voltaic Cell, Standard, Sir Win. Thom- son's (See Cell, Voltaic, Standard, Sir William Thomson's) Voltaic Cell, Standardizing - (See Cell, Voltaic, Standardizing a) Voltaic Cell, Two-Fluid (See Cell, Voltaic, Two-Fluid.) Voltaic Cell, Water - (See Cell, Voltaic, Water) Voltaic Cell, Zinc-Carbon - (See Cell, Voltaic, Zinc-Carbon) Voltaic Cell, Zinc-Copper - (See Cell, Voltaic, Zinc-Copper) Voltaic Circle. (See Circle, Voltaic) Vol.] 546 [Yol. Toltaic Circuit. (See Circuit, Voltaic} Yoltaic Couple. (See Couple, Voltaic.} Toltaic Effect. (See Effect. Voltaic.} Toltaic Electricity. (See Electricity, Voltaic.} Toltaic Element. (See Element, Vol- taic} Toltaic or Current Induction. (See In- duction, Voltaic} Toltameter. An electrolytic cell em- ployed for measuring the quantity of the electric current passing through it by the amount of chemical decomposition effected in a given time. Various electrolytes are employed in voltam- eters, such as aqueous solutions of sulphuric acid, copper sulphate, or other metallic salts. In the sulphuric acid voltameter shown in Fig. 562, the 1 attery terminals are connected with pla- tinum electrodes, immersed in water slightly acidu- lated with sulphuric acid, and placed inside glass tubes, also filled with acidulated water. On the passage of the current hydrogen appears at the kathode, and oxygen at the anode, in nearly the proportion of two volumes to one. (See Ozone.'] Fig.jbs. A Sulphuric Acid Voltameter. In the case of water containing sulphuric acid (hydrogen sulphate") the decomposition would ap- pear to be that of the sulphuric acid rather than that of the water. The reaction is as follows: H 2 S0 4 =H, +S0 4 . The hydrogen appears at the electro negative terminal or kathode. The SO 4 appears at the electro positive terminal or anode, but combines with one molecule of water, thus, SO 4 -J- H 2 O = H a SO 4 -|- O, gaseous oxygen being driven off at the anode. Voltameters are not as well suited as galva- nometers for the measurement of electric currents, because a certain electromotive force must be reached before electrolysis is effected. The voltameter in reality measures the cou- lombs, and, therefore, is valuable as a current measurer only when the current is constant. Coulomb-meter would, therefore, be the pref- erable term. Then, again, time is required to produce the results, and considerable difficulty is experienced in maintaining the current strength constant, either on account of variations in the electro- motive force of the source, or of variations in the resistance of the voltameter. Toltameter, Copper A voltameter in which the quantity of the current passing is determined by the weight of copper de- posited. A current, the strength of which is constant, is passed through the voltameter for a given time. The kathode, preferably of platinum, is thor- oughly cleaned and dried with a current of heated air and accurately weighed before and after. The current strength is then deduced from the increase in weight and the time. A galvanometer is kept in the circuit of the battery and voltameter. If a Daniell battery is used, it should be kept on closed -circuit through a resistance for some lime before use, in order to insure normal current. It will be noticed that the indications of this voltameter are based on the gain in weight of the kathode. The loss in weight of the anode is mis- leading, owing to secondary chemical action and disintegration. Toltameter, Gas A term sometimes used for volume voltameter. (See Voltam- eter, Volume} Toltameter, Siemens' Differential A form of voltameter employed by Sir Wil- liam Siemens for determining the resistance of the platinum spiral used in his electric pyrom- eter. (See Pyrometer, Siemens' Electric} Two separate voltameter tubes, provided with platinum electrodes and filled with dilute sulphu- ric acid, are provided with carefully graduated tubes to determine the volume of the decomposed gases. (See Voltameter, Volume.} A current from a battery is divided by a suit- able commutator into two circuits connected re- spectively with the two voltameter tubes. In one of these circuits a known resistance is placed, in the other the resistance to be measured, i. e. , the platinum coil used in the electric pyrometer. Yol.] 547 [VoL Yoltameter, Silver A voltameter in which the quantity of the current passing is determined by the weight of silver de- posited. A solution of silver nitrate is used as the elec- trolytic liquid. When the current to be measured is strong the strength of the silver nitrate solution is made stronger. Voltameter, Volume A voltameter in which the quantity of the current passing is determined by the volume of the gases evolved. In some forms of volume voltameter in which dilute sulphuric acid is electrolyzed, both the hydrogen and the oxygen are measured, either separately or together. In one form of volume voltameter the hydrogen only is collected, and thus the error in volum- -etric determinations arising from the decrease in volume from the formation of ozone is avoided. The evolved oxygen is isolated from the hydrogen by placing a porous jar between the electrodes. The negative electrode, is formed of platinum fused in the tube, which, for ease of connec- tion, is partially filled with mercury. The graduated glass tube, in which the hy- drogen is collected, is maintained at a nearly con- stant temperature by means of a water column. A thermometer is provided for corrections of volume as affected by temperature. The voltameter contains dilute sulphuric acid, about 30 per cent, of acid. Voltameter, Weight A voltameter in which the quantity of the current passing is determined by the difference in the weight of the instrument after the circuit has passed for a given time. A weight voltameter consists essentially of platinum electrodes and some means for thor- oughly drying the evolved gases. A vessel filled with pumice stone moistened with sulphuric acid, or a chloride of calcium tube, may be used for this purpose. The voltameter is carefully weighed before and after the decomposition. The differ- ence in weight gives the weight of the sulphuric acid decomposed. Voltametric Law. (See Law, Voltamet- .rzc.} Voltmeter. An instrument used for meas- uring difference of potential. (See Galva- nometer. Potential, Difference of. Volt.) A voltmeter may be constructed on the principle of a galvanometer, in which case it differs from an ammeter, or ampere meter, which measures the current, principally in that the resistance of its coils is greater, and that in an ampere meter the coils are placed in the circuit, while in a volt- meter they are placed as a shunt to the circuit. The difference of potential is determined from the reading of a voltmeter, by the fact that accord- ing to Ohm's law, the product of the current and the resistance is equal to the electromotive force, E as C = - from which we obtain C X R = E. JX In the ordinary operation of a voltmeter, the action of the current in passing through a coil of insulated wire is to produce a magnetic field, which causes the deflection of a magnetic needle. Since the resistance of the voltmeter is constant, the current passing, and hence the deflection of the needle, will vary with the value of E. The magnetic field produced by the current deflects the magnetic needle against the action of another field, which may be either the earth's field, or an artificial field produced by a permanent or an electro-magnet. Or, it may deflect it against the action of a spring, or against the force of gravity acting on a weight. There thus arise varieties of voltmeters, such as permanent-magnet voltmeters, spring voltmeters, and gravity voltmeters. Or, the current produced by a given difference of potential may be used to heat a wire, and the value of the potential difference determined .by the movement of a needle by the consequent expansion of a wire. Cardew's voltmeter operates on this principle. (See Voltmeter, Cardew's..) Or, the potential difference to be measured may be utilized to charge a readily movable needle, and thus produce electrostatic attractions and repulsions. This form of instrument is in reality a form of electrometer. (See Electrometer, Quadrant. Attraction, Electrostatic. ) Voltmeter, Cardew's A form of voltmeter in which the potential difference is measured by the amount of expansion caused by the heat of a current passing through a fixed resistance. The current produced by the difference of potential to be measured is passed through a high Vol.] 548 [VoU resistance wire of platinum silver, the expansion of which is caused to move a needle across a graduated arc. The wire is thin and therefore quickly acquires the temperature due to the current. The Cardew voltmeter possesses an advantage of being independent of changes of temperature. It is also capable of being used to measure the potential difference of alternating currents. Voltmeter, Closed-Circuit A volt- meter in which the points of the circuit, be- tween which the potential difference is to be measured, are connected with a closed coil or circuit, and which gives indications by means of the current so produced in said circuit. All galvanometer-voltmeters are of the closed- circuited type. The Weston standard voltmeter shown in Fig. 563 is a closed-circuit voltmeter. ton Standard Voltmete Voltmeter, Electro-Magnetic A form of voltmeter in which the difference of potential is measured by the movement of a magnetic needle in the field of an electro- magnet. (See Voltmeter?) Voltmeter, Gravity A form of volt- meter in which the potential difference is measured by the movement of a magnetic needle against the pull of a weight. Sir William Thomson's balance instruments are used as gravity voltmeters. (See Voltmeter ) Voltmeter, Magnetic-Vane A volt- meter in which the potential difference is measured by the repulsion exerted between a fixed and a movable vane of soft iron placed within the field of the magnetizing coil. A pointer, fixed to the moving vane, serves to measure the amount of the repulsion, and conse- quently the potential difference producing the magnetizing current. The moving vane moves under the magnetic repulsion against the action of a spring. Discs of copper for damping the movements f the movable vane, are placed be- fore and behind it. Voltmeter, Multi-Cellular Electrostatic An electrostatic voltmeter in which a series of fixed and movable plates are used instead of the single pair employed in the quadrant electrometer. The movable pairs of plates are connected to a movable axis and placed vertically above one another. To the top of the axis is fixed a light aluminium needle or pointer, which moves over a. graduated scale. A series of fixed plates, suita- bly supported and insulated from the ground, alternate with the needle plates. Voltmeter, Open-Circuit A volt- meter in which the points of the circuit where potential difference is to be measured are connected with an open circuit and give in- dications by means of the charges so pro- duced. Electrometer-voltmeters are of the open-cir- cuited fype. Voltmeter, Permanent Magnet A form of voltmeter in which the difference of potential is measured by the movement of a magnetic needle under the combined action of a coil and a permanent magnet, against the pull of a spring. (See Voltmeter^ Voltmeter, Redncteur or Resistance for (See Reducteur or Resistance for Voltmeter^ Voltmeter, Vertical Electrostatic - A form of voltmeter the needle of which moves in a vertical instead of in a horizontal plane. The construction of the vertical electrostatic voltmeter is, in general, similar to that of the quadrant electrometer. (See Electrometer, Quad- rant.} Vol.] 549 [Wat. The fixed and movable sectors, the pointer and the graduated scale, however, are in vertical in- stead of horizontal plai.es. Fig. 564.. Vertical tdectro*tntic I oltmeter. The general arrangement of the vertical elec- trostatic voltmeter will be readily understood by an inspection of Fig. 564. Volume Toltameter. (See Voltameter, Volume?) Yortex Atom. (See Atom, Vortex) Vortex Cylinder. (See Cylinder, Vor- tex) Vortex-Ring Field. (See Field, Vortex- Ring^ Yulcabeston. An insulating substance composed of asbestos and rubber. Vulcanite. A variety of vulcanized rub- ber extensively used in the construction of electric apparatus. Vulcanite is sometimes called ebonite from its black color. It is also sometimes called hard rubber. Though an excellent insulator, vulcanite will lose its insulating properties by condensing a film of moisture on its surface. This can be best re- moved by the careful application of heat. The surface is very liable to become covered by a film of sulphuric acid, due to the gradual oxi- dation of the sulphur. Mere friction will not re- move this film, but it may be removed by wash- ing with distilled water. A thick coating of var- nish will obviate this last defect. Vulcanized Fibre. (See Fibre, Vulcan- ized) W. A contraction watt. W. A contraction work. contraction sometimes used for sometimes used for sometimes used for removing magnetism from W. A weight. Wall Plug. (See Plug, Wall) Wall Socket. (See Socket, Wall) Ward. A term proposed by James Thom- son for a line and direction in a line. Sir William Thomson thus defines the ward of magnetization : ' ' The ward in which the magnet- izing force urges a portion of the ideal northern magnetic matter or northern polarity." Waring Anti-Induction Cable. (See Cable, Anti-Induction, Waring) Waste Field. (See Field, Magnetic, Waste) Watches, Demagnetization of Pro- Flf. S&S' Wright's Demagnetization Affaratut. The demagnetization of watches can be readily effected by a method proposed by J. J. Wright. Wat.] 550 [Wat. The watch is held by its chain and slowly lowered to the bottom of a hollow conical coil of wire, and then slowly withdrawn from the coil. The wire is wound on the coil, as shown in Fig. 565, in the shape of a cone, viz.: with a single turn at the top, and gradually increasing in number of turns towards the bottom. The conical coil is connected with a source of rapidly alternating currents. As the watch is lowered into the coil, it gradu- ally becomes more and more powerfully magnet ized with alternately opposite polarities, thus completely removing any polarity it previously possessed. As it is now slowly raised from out the hollow cone, this magnetization becomes less and less, until, if removed from the conical coil while high above its apex, all sensible traces of magnetism will have disappeared. Watchman's Electric Register. (See Register, Watchman s Electric?) Water Battery. (See Battery, Water.) Water-Dropping Accumulator. (See Ac- cumulator, Water-Dropping?) Water, Electrolysis of The de- composition of water by the passage through it of an electric current. Water does not appear to conduct electricity when pure; it is therefore not quite certain that pure water can be electrolytically decomposed. The addition of a small quantity of sulphuric acid, or of a metallic salt, however, renders its electrolysis readily accomplished. (See Vol- tameter. ) In the opinion of most, it is the sulphuric acid that is decomposed rather than the water. Water Horse-Power. The Indian Gov- ernment's term for horse-power developed by falling water. The estimate is made by the following simple rule : 15 cubic feet of water falling per second through i foot equals I horse-power. Water-Jet Telephone Transmitter. (See Transmitter, Water-Jet Telephoned) Water - Level Alarm. (See Alarm, Water or Liquid Level?) Water-Proof Wire. (See Wire, Water- Proof.} Water Pyrometer. (See Pyrometer, .Siemens' Water.} Water Rheostat. (See Rheostat, Water?) Water Voltaic Cell. (See Cell, Voltaic, Water?) Watt. The unit of electric power. The volt-ampere. The power developed when 44.25 foot- pounds of work are done per minute, or -7375 foot-pounds per second. The y^ ff of a horse-power. There are three equations which give the value of the watts, viz. : (I.) C E The watts. (2.) C 2 R = The watts. (3.) !* = The watts. Where C = the current in amperes ; E = the electromotive force in volts, and R = the resist- ance in ohms. (See Energy, Electric.} Watt Arc. (See Arc, Watt.} Watt Generator. (See Generator, Watt) Watt-Hour. A unit of electric work. A term employed to indicate the expendi- ture of an electrical power of one watt, for an hour. Watt-Hour, Kilo - The Board of Trade unit of work equal to an output of one kilo-watt for one hour. Watt, Kilo One thousand watts. A unit of power sometimes used in stating the output of a dynamo. A dynamo of 20 units, or a 2O-unit machine, is one capable of giving an output of 20 kilo- watts. Watt-Meter. A galvanometer by means of which the simultaneous measurement of the difference of potential and the current passing is rendered possible. The watt-meter consists of two coils of insu- lated wire, one coarse and the other fine, placed at right angles to each other as in the ohm-meter, only, instead of the currents acting on a sus- pended magnetic needle, they act on each other as in the electro-dynamometer. Watt-Minute. A unit of electric work. An expenditure of electric power of one watt for one minute. Watt-Second. A unit of electric work. An expenditure of electric power of one watt for one second. Web.] 551 [Wav. Wave. A disturbance in an elastic me- dium that is periodic both in space and time. Wave, Electric An electric disturb- ance in an elastic medium that is periodic both in space and time. (See Oscillations, Electric.} Waves, Amplitude of The ampli- tude of a vibration. (See Vibration or }Vave, Amplitude of.] Waves, Displacement Waves pro- duced in the ether of dielectrics by means of electric displacement. The electric stress applied to a dielectric to pro- duce electric displacement soon strains it to its utmost and no further displacement can occur until the direction of the electric power is re- versed. A rapidly intermittent current therefore can pass through a dielectric and thus produce a series of displacement waves. Dielectrics, therefore, may be considered as pervious or transparent to rapidly intermittent or reversed periodic currents, but opaque or imper- vious to continuous currents. A condenser inter- polated in a telephone circuit does not prevent tele- phonic communication, though it does effectually stop all continuous currents. Waves, Electro-Magnetic - Waves in the ether that are given off from a circuit through which an oscillating discharge is passing, or from a magnetic circuit under- going variations in magnetic intensity. Waves, Electro-Magnetic, Interference of Interference effects similar to those produced in the case of waves of light, ob- served in the case of electro-magnetic radi- ations, or waves, in which one system of waves, retarded a half wave length behind another system of equal wave length and am- plitude, results in a complete loss of motion of the particles of the ether they tend to simultaneously affect. In order that complete interference may take place, it is necessary (i.) That the two waves, or system of waves, must meet in opposite phases. That is, that one be retarded back of the other one-half a wave length, or some odd number of half wave lengths. (2.) That the waves simultaneously affect the same particles of ether in which they are mov- ing. (3.) That the energy charged on the ether in the shape of waves of electro-magnetic radiation, must be equal in the case of each system of waves. (4.) That the two systems of waves must have the same wave length. These conditions, it will be seen, are exactly the same as in the case of the interference of light. It will, of course, be readily understood that if electro- magnetic radiations can produce the effect of resonance, they must also necessarily produce interference effects. Waves, Electro-Magnetic, Reflection of Reflection of electro-magnetic waves similar to the reflection of waves of light. In his experiments on electro- magnetic radia- tions, Dr. Hertz shows that true reflection of electro- magnetic waves occurs from the surfaces of certain substances placed in the path of the waves. In some experiments made in a large room, Dr. Hertz obtained undoubted indications of re- flection of electro-magnetic waves from the walls of the room. W r aves of Condensation and Rarefaction. The alternate spheres of condensed and rarefied air by means of which sound is transmitted. (See Waves, Sound.) Waves, Sound Waves produced in air or other elastic media by the vibrations of a sonorous body. (See Sound.) Way Line. (See Line, Way.) Weather Cross. (See Cross, Weather.) Weber. A term formerly employed for the unit of electric current, and replaced by ampere. (See Ampere?) The term weber was originally used to express a quantity of electricity equal to what is now called one coulomb, and a current designated by one weber per second. It was, however, used finally as a unit of current. Weber. A term proposed by Clausius and Siemens for a magnetic pole of unit strength, but not adopted. This same term was also employed to desig- nate the unit strength of current, now replaced by the term ampere. Web.] 552 [Wei. Weber's Theory of Diamagnetism. (See Diamagnetism, Weber s Theoty of.} Weight, Atomic - The relative weights of the atoms of elementary sub- stances. Since the atoms are assumed to be indivisible, they must unite or combine as wholes and not as parts. Although we cannot determine exactly the actual weights of the different elementary atoms, yet we can determine their relative weights by ascertaining the smallest proportions in which any two elements that combine atom for atom will unite with each other. Such numbers will represent the relative weights of the atoms as compared w th hydrogen. Weight Voltameter. (See Voltameter , Weight.) Weights and Measures, Metric System of A system of weights and measures adopted by almost all civilized nations except English-speaking, and by the scientific world generally. For measures of length, the one ten-millionth part of the quadrant of a meridian of the earth is taken as the unit of length. This unit of length is called a metre, and various subdivisions and multiples of its length are made on the decimal system. For a system of weights, the weight of one cubic centimetre of pure water at 39 2 degrees Fahr., the temperature of the maximum density of water, is taken as the unit of weight. This is called a gramme, and various multiples and sub- divisions of this unit are made on the decimal system. The following table of French measures and their corresponding English values are taken from Deschanel's " Elementary Treatise on Natural Philosophy ": Length. I millimetre = .03937 inch, or about ^ inch. I centimetre = -3937 inch. I decimetre = 3.937 inches. I metre = 39.37 inches = 3.281 feet = 1.0936 yard. I kilometre = 1093.6 yards, or about mile. Deschanel gives the length of the meter as equal to 39.370432 inches. U. S. Coast Survey Bull No. 9 of 1889, gives value of meter = 39.36980 inches. Therefore, 39.37 is probably as accurate as any other figure. Area. I square millimetre "= .00155 square inch. I square centimetre = .155 square inch. I square decimetre = 15.5 square inches. I square metre = 1550 square inches = 10.764 square feet = 1.196 square yards. Volume. I cubic millimetre = .000061 cubic inch. I cubic centimetre = .061025 cubic inch. i decimetre = 61.0254 cubic inches. Cubic metre = 61025 cubic inches = 35.3156 cubic feet = 1.308 cubic yards. The litre (used for liquids) is the same as the cubic decimetre, and is equal to 1.7617 pint, or .22021 gallon. Mass and Weight. I milligramme = .01543 grain. I gramme = 15.432 grains. I kilogramme = 15432.3 grains = 2.205 pounds avoirdupois. More accurately, the kilogramme is 2.20462125 pounds. Miscellaneous. i gramme per square centimetre = 2.0481 pounds per square foot. i kilogramme per square centimetre = 14.223 pounds per square inch. i kilogram me tre = 7.2331 foot-pounds. i force de cheval -.= 75 kilogrammetres per second, or 542^ foot pounds per second, nearly, whereas I horse-power (English) = 550 foot- pounds per second. Conversion of English into French measures ; Length. i inch = 2.54 centimetres, nearly. I foot = 30.48 centimetres, nearly. I yard = 91.44 centimetres, nearly. I statute mile = 160933 centimetres, nearly. More accurately, I inch = 2.5399772 centi- metres. Area. I square inch =6.45 square centimetres, nearly. I square foot = 929 square centimetres, nearly. I square yard = 8361 square centimetres, nearly. i square mile = 2.59 X IO 1 square centimetres, nearly. Volume. I cubic inch = 16.39 cubic centimetres, nearly. i cubic foot = 283 1 6 cubic centimetres, nearly- Wei.] I cubic yard = 764535 cubic centimetres, nearly. I gallon = 4541 cubic centimetres, nearly. Mass. I grain = .0648 gramme, nearly. I ounce avoirdupois = 28.35 grammes, nearly. I pound avoirdupois = 453. 6 grammes, nearly. I ton = 1.016 X io 6 grammes, nearly. More accurately, I pound avoirdupois = 453.59265 grammes. Velocity. i mile per hour = 44.704 centimetres per second. i kilometre per hour = 27. 7 centimetres per second. Density. I pound per cubic foot = .016019 gramme per cubic centimetre. 62.4 pounds per cubic foot = I gramme per cubic centimetre. Force (assuming g = 981). Weight of I grain = 63.57 dynes, nearly. " I ounce avoirdupois = 2.78 X io< dynes, nearly. " I pound avoirdupois = 4.45 X io 5 dynes, nearly. " i ton 9.97 X io 8 dynes, nearly. " I gramme = 981 dynes, nearly. " I kilogramme = 9.81 X io 5 dynes, nearly. Work (assuming g = 981). i foot-pound = 1.356 X io 7 ergs, nearly. I kilogrammetre = 9.81 x io 7 ergs, nearly. Work in a second by one theoretical "horse- power" = 7.46 X io 9 ergs, nearly. Stress (assuming g = 981). I pound per square foot = 479 dynes per square centimetre, nearly. i pound per square inch = 6.9 X io 1 dynes per centimetre, nearly. I kilogramme per square centimetre = 9.81 X lo^ dynes per square centimetre, nearly. 760 millimetres of mercury at o degree C. = 1.014 X IO" 7 dynes per square centimetre, nearly. 30 inches of mercury at o degree C. = 1.163 X io" dynes per square centimetre, nearly. Welding, Electric Effecting the welding union of metals by means of heat of electric origin. In the process of Elihu Thomson, the metals [Wei. are heated to electric incandescence by currents obtained from transformers, and are subsequently pressed or hammered together. Fig. 566, shows the Thomson apparatus for the direct system of electric welding. The dynamo is combined with the welding apparatus. The armature contains two separate windings; one of fine wire, in series with the field magnet coils, and another of very low resistance, being formed of all shaped bar of copper. No commutation is used, the alternating currents being well adapted for heating purposes. The terminals of the dynamo are, therefore directly connected to the clamps that hold the bar to the welder. Fig- 5 6 7. shows the apparatus for the Thomson Indirect System of Electric Welding. This sys- tem is applicable to heavy work, and to cases where more than one welding machine is operated by the current from a single dynamo. In this case a high tension current is converted Fig. j(>6. The Thomson Direct Welder. into the large welding current employed, by means of a suitably proportioned transformer. The welding process is the same in either sys- tem, and consists essentially in leading the weld- ing current into the pieces to be united through their points of junction when brought into firm end contact. As the current is led across the junction the temperature rises sufficiently to soften the metal, when the pieces are firmly pressed to- gether by the motion of the clamps or holders. In the process of Benardos and Olzewski, the heat of the voltaic arc is employed for a some- what similar purpose, but by a different process. In the Thomson system of electric welding alternating currents are employed. They are either supplied by an alternating current dynamo or by a transformer. The process of welding is substantially as fol- Wei.] 554 [Win. lows, viz. : the welding junctions are made slightly convex, so as to touch in but one part of their opposing faces. They are made to touch near their centres and the welding heat is first reached near their points of junction. Pressure is then applied by means of a screw, lever or hydraulic pressure until all the surfaces are at the welding temperature. This operation requires in practice but a few seconds for small work, and at the most but a fig- S&7- The Thomson Indirect Welder. few minutes for larger work. The heating is practically local, extending in most cases a dis- tance equal to about the diameter of the weld. For the purpose of control'.ing the electro- motive force, and thus adapting the same welder to different classes of work, when a transformor is used, a second transformer provided with a mov- able core is placed in series with the first. A number of coils of insulated wire are placed in a segment- of a split-ring laminated-core. These may be connected in series or in multiple by a switch. An iron armature placed within the split ring encloses the annular core and acts as the low-resistance secondary. When this is placed so as to embrace the primary coils, the difference of potential will be different than if moved to one side or the other of the ring. Welding Transformer. (See Trans- former, Welding?) Wheatstone's Electric Balance. (See Balance, Wheatstone's Electric.} Wheatstone's Electric Bridge. (See Bridge, Wheatstone's Electric) Wheel, Barlow's or Sturgeon's A wheel or disc of metal capable of rotation on a horizontal axis, that is set into rotation when placed between the poles of magnets and traversed by a current of electricity from the centre to the circumference. Wheel, Phonic A wheel maintained in synchronous rotation by means of timed electric impulses sent over a line, and em- ployed in Delany's synchronous multiplex telegraphic system. The phonic wheel was invented by La Cour, but was first put into successful operation in multiplex telegraphy by Delany in his system of synchronous multiplex telegraphy. (See Telegraphy, Synchron- ous Multiplex, Delany' 's System.) Delany ob- tains the exact synchronism of the phonic wheel by means of a series of correcting electric impulses, automatically sent over the line on the failure of the phonic wheel at either end of the line to ex- actly synchronize with that at the other end. Wheel, Reaction, Electric A wheel driven by the reaction of a convective dis- charge. (See Flyer, Electric.} Wheel, Trolley A metallic wheel connected with the trolley pole and moved over the trolley wire on the motion of the car over the tracks, for the purpose of taking the current from the trolley wire by means of rolling contact therewith. Whirl, Electric A term employed to indicate the circular direction of the lines of magnetic force surrounding a conductor conveying an electric current. (See Field, Electro-Magnetic.} This is more correctly called a magnetic whirl. (See Whirl, Magnetic.} Whirl, Expanding Magnetic One of the magnetic whirls which are sent out from a conductor through which a current of gradually increasing strength is passing, or from a magnet whose magnetism is increas- ing. The=e magnetic whirls, according to Hertz r move outward through free ether with the velo- city of light. Whirl, Magnetic The lines of mag- netic force which surround the circuit of the conductor conveying an electric current. Whistle, Steam, Automatic Electric A steam whistle, employed on foggy days in some systems of railway signals, when the Whi.] 555 [Wir. visual signals cannot be seen, in which the passage of the steam through the whistle is automatically obtained by the closing of an electric contact, or the passage of the loco- motive over a certain part of the track. White Heat (See Heat, White) White Hot. (See Hot, White.} Wimshurst Electrical Machine. (See Machine, Wimshurst Electrical.) Wind, Electric The convection stream of air particles produced at the ex- tremities of points attached to the surface of charged, insulated conductors. (See Con- vection, Electric. Flyer, Electric.) Windage of Dynamo. A term proposed for the air gap between the armature and the pole pieces of a dynamo. This term is not much used. Winders, Telegraphic Paper Ap- paratus for winding or coiling the paper fillets used on telegraphic registers. When moved by means of a spring they are generally styled automatic winders. Winding, Ampere A single wind- ing or turn through which one ampere passes. Ampere-winding is used in the same significa- tion as ampere-turn. (See Turn, Ampere.) Winding, Bifllar A winding of a coil of wire in which, instead of winding the wire in one continuous length, it is doubled on itself and then wound. This method is employed in resistance coils, so as to avoid the induction effects. (See Coil y Resistance.) Winding, Compound, of Dynamo-Electric Machine A method of winding in which shunt and series coils are placed on the field magnets. (See Machine, Dynamo- Electric, Compound- Wound.) Winding, Series A winding of a djnamo-electric machine in which a sin- gle set of magnetizing coils are placed on the field magnets, and connected in series with the armature and the external circuit. (See Machine, Dynamo-Electric, Series- Wound.) Window-Tube Insulation. (See Insula- tor, Window- Tube.) Wipe Spark. (See Spark, Wipe.) Wiping Contact (See Contact, Wiping.) Wire, Air-Line That portion of a circuit which is formed by air-strung wires, in contradistinction to the portion which passes through underground or submarine cables. Wire, Binding, for Telegraph Lines The wire used for securing lines of wire conductors to the insulators. The line wire rests against the insulators at as small an area of contact as possible, generally only a mere edge. In order to attach the wire to the insulator, and protect the wire from chaf- ing, it is secured to the insulator by binding with wire. Wire, Block A line or wire em- ployed in a block system for railroads, con- necting a block tower with the next tower on each side of it. (See Railroads, Slock System for.) Wire, Braided A conducting wire covered with a braiding, as distinguished ff om a wire that is merely wrapped with insulating material. Cotton or silk is used for braiding. The cov- ering is often coated by a layer of some insu- lating gum or varnish dissolved in a rapidly drying liquid. It is sometimes covered with melted paraffme. . fig. J6S. Braided 1 1 ', A copper wire covered with insulating material and then braided is shown in Fig. 568. Wire, Calling A wire employed in a telegraphic or telephonic system, by means of which a subscriber communicates with the central office, or one central office communi- cates with another. This wire is termed the calling wire in order to distinguish from the wire actually used for talking or telegraphing. Wire, Condiictibility and Sizes of For tables giving the resistance, size, weight per foot, etc., of wire according to some of the principal wire gauges see pages 254 and 256. Wir.] 556 [Wir. Wire, Copper, Hard-Drawn Copper wire that is drawn three, or four times after annealing. The drawing subsequent to annealing renders the wire hard and elastic, with but a trifling de- crease in its conductivity. A hard- drawn wire, } of course, possesses greater limits of elasticity than soft-drawn wire, and, therefore, in the case of air lines, permits of the use of a longer distance between adjacent poles. Wire, Copper, Soft-Drawn Copper wire that is softened by annealing after drawing. (See Wire, Copper, Hard- Drawn.) Wire, Dead, of Armature That part of the wire on the armature of a dynamo which produces no electromotive force or resultant current. It is called dead because it does not move through the field of the machine. Wire, Duplex An insulated con- ductor containing two separate parallel wires. Wire, Earth-Grounded - A wire one terminal of which is grounded or put to earth, so that the earth forms a part of the circuit in which the wire is placed. Wire, Feeding A term sometimes applied to the wire or lead of a multiple cir- cuit which feeds the main. In a system of electric railroads the feeding wires feed the trolley \vin.s. Wire Finder. (See Finder, Wire) Wire, Fuse A readily fusible wire employed in a safety catch to open the cir- cuit when the current is excessive. (See Catch, Safety?) Wire Gauge, Vernier (See Gauge, Wire, Micrometer^) Wire, Grounded (See Ground or Earth.} Wire, House In a system of in- :andescent electric lighting any conductor that is connected with a service conductor and leads to the meter in the house. Wire, Insulated Wire covered with any insulating material. Cotton and silk are generally employed for in- sulating purposes, either alone, or in connection with various gums, resins, or other materials, which are rendered plastic by heat, but which solidify on cooling. India rubber, caoutchouc, and various mixtures and compounds are also em- ployed for the same purpose. For most of the purposes of line wires, high in- sulating powers, combined with a low specific inductive capacity, are required in the insulating materials. For overhead wires a waterproof covering is necessary. In the neighborhood of combustible matenals, some fireproof covering is desirable. Wire, Lead A lead fuse wire. Wire, Line In telegraphy the wire that connects the different stations with one another. In bell and annunciator circuits, the term line wire is sometimes applied to all circuits other than the main line. In arc light circuits the term line wire is applied to the entire metallic circuit, io which the lamps are connected in series. Wire, Main The principal wire. In any system of bell circuit*, the main wire is the wire which runs from one pole of the battery to one of the springs of all the pushes, in distinc- tion from the line wires, or the rest of the wires in the battery circuit. Wire, Message A line or wire em- ployed in a block system for railroads, ex- tending along the road and used for local traffic or business. (See Railroads, Block System for.) Wire, Negative A term sometimes applied to that wire of a parallel circuit which is connected to the negative pole of a source. Wire, Neutral The middle wire of a three-wire system of electric distribution. Wire, Omnibus An omnibus bar. (See Bars, Omnibus.) A bus bar or wire. (See Wires, Bus.) Wire, Paraffined Wire wrapped or braided with some textile material and after- wards coated with paraffine. The term paraffined wire is sometimes limited to a wrapped wire that is afterwards paraffine coated. Wir.] 557 [Wir. Wire, Positive The wire or con- ductor connected to the positive pole or ter- minal of any electric source. Wire, Potentiometer The wire of a potentiometer which has been calibrated in order to measure the drop of potential in any circuit. (See Potentiometer.) Wire, Return - The wire or con- ductor by means of which the current returns to the electric source after having passed through the electro-receptive devices. (See Sources, Electric. Device, Electro-Recep- tive^) Wire, Shade Guard (See Guard, Wire Shade.} Wire, Slide A wire of uniform diameter employed in Wheatstone's electric bridge for the proportionate arms of the bridge. A sliding contact key moves over the slide wire and determines the length of the arms. Some forms of bridges have a double or a triple slide wire. (See Bridge, Electric, Slide-Form of.) Wire, Span The wire employed in systems of electric railways for holding the trolley wire in place. The span-wire is used when the poles are erected on both sides of the street or road-bed, and the trolley wire, suitably insulated from the span wire, is suspended therefrom. Wire, Suspending, of Aerial Cable The wire from which an aerial cable is strung or suspended. In case the aerial cable is unusually heavy the suspending wire is replaced by a wire rope. (See Cable, Aerial.) Wire, Taped - A conducting wire covered with an insulating material in the shape of tape. A wire covered with an insulating material and subsequently taped is shown in Fig. 569. Fig. j6g. Taped Wire. Wire, Tinned Copper wire covered with a coating of tin prior to its being insu- lated. The coating of tin is for the purpose of insur- ing greater ease in soldering. It is also useful in case vulcanized rubber is used for the insulator, to prevent the sulphur from attacking the copper. Wire, To To fix or place the con- ductors or mains for any electric circuit. Wire, Train - A line of wire em- ployed in a block system for railroads, con- nected with the general dispatcher's office, and used for sending train orders only. (See Railroads, Block System for.) Wire, Trolley The wire over which the trolley passes in a system of electric rail- ways, and from which the current is taken to drive the motors on the cars. A bare conductor or wire, supported over- head on suitable hangers and provided for transmitting current by the trolley to the motor connected with the car on the passage of the trolley wheel over its surface. (See Wheel, Trolley.) Trolley wires, being necessarily bare, are carefully insulated at their points of attachment to all supports. Wire, Trolley, Continuous A trol- ley wire or conductor employed in overhead dependent systems of electric railways. (See Railroads, Electric, Dependent System of Motive Power for.) Wire, Trolley, Sectional or Divided A trolley wire or conductor for systems of electric railroads in which the wire is divided into a number of separate sections that are suitably connected with the generating dyna- mo by means of feeder wires. (See Rail- roads, Electric, Dependent System of Motive Power for.) Wire, Trunk A main line or wire, extending between two distant stations, such as between two large cities, and provided solely for communication between them, not being tapped at intermediate points. Wire, Twin A conductor, consist- ing of two separately insulated wires, bound together by an additional insulating covering. Wire, Water-Proof A wire pro- tected from the weather by a coating of any waterproof material. Wir.J 558 [Wuv Wire, Wrapped Wire that is insu- lated by placing strands of some insulating material, like cotton, parallel to its length, and then wrapping a number of strands around the wire. The wrapped wire is afterwards either coated with paraffine or other insulator, or is used with- out such coating. Wires, Bus A term sometimes used for omnibus bars or wires. The wires which receive the full current generated by the electric source, and carry it to the feeders. The bus-wires collect the current from all the sources, hence the name. Wires, Breaking-Weight of The weight required to be hung at the end of a wire in order to break it. Ordinary copper wire will break at about 17 tons to the square inch of area of cross section. Common wrought iron breaks at 25 tons to the square inch. These figures are to be regarded as approximate only, since almost inappreciable differences in the physical condition of metals, as well as slight variations in their chemical com- position, often produce marked differences in their breaking weights. Wires, Cross (See Cross, Electric) Wires, Crossing A device employed in telegraphic circuits whereby a faulty con- ductor is cut out of the circuit of a telegraph line by crossing over to a neighboring, less used, line. To cut out a faulty section of wire in any cir- cuit, such as C D, in the circuit A B C D E, Fig. 570, a cross-connection is mide to a line X Y, running near it, and which may be temporarily thrown out of use. By this means the interrup- tion of an important circuit may be repaired. A B C D E X } * Y' Fig. S?o. Crossing Wires. Wires, Dead Disused and aban- doned electric wires. The term dead is often applied to a wire through which no current is passing. The term, however, is more properly applied to a wire formerly employed, but subsequently abandoned. Dead wires in the neighborhood of active wire? are a constant menace to life and property, and should invariably be carefully removed. It is often a matter of considerable importance to be able to.determine whether or not a current is passing through a wire. When the wire is not enclosed in a moulding, or fastened against a wall, this can readily be ascertained by bringing a small compass needle near the wire, when it will tend to set itself across the wire. The term dead wire, as will be seen, is used in two distinct senses. Wires, Lead ing- In The wires or conductors which lead the current through (into and out of) an electric lamp. The term leading -in wires is generally applied to incandescent electric lamps, Geissler or Crookes tubes, and to various other apparatus. Wires, Leading-Up - Wires em- ployed for raising an aerial cable to the cable hangers. Wires, Omnibus A term sometimes used for bus wires. (See Wires, Bus.} Wires or Conductors, Continuous Wires or conductors free from joints. Wires or conductors without soldered or twisted joints or without any joints whatso- ever. Wires, the entire lengths of which have been taken from the hitherto uncut coil of wire from the draw plate. Strictly speaking, any metallic circuit consists of a continuous wire, whether in one piece or in several sections or pieces. The preferable term would appear to be unjointed wires or conductors. Wires, Phantom A term applied to the additional circuits or wires obtained in any single wire or conductor by the use of some multiplex telegraphic system. (See Telegraphy, Multiplex. Telegraphy, Syn- chronous-Multiplex, Delatiys System.) Wires, Pilot In a system of incan- descent lighting, where a comparatively low potential is employed on the mains, thin wires leading directly from the generating station to different parts of the mains, in order ta determine the differences of potential at such points. Wir.] 559 [Wor. Pilot wires indicate on a voltmeter the differ- ence of potential at the various points. The pilot wires extend to the various seats of supply, and so give instant warning of any change in the value of the potential. Wires, Pressure In a system of incandescent electric lighting, wires or con- ductors, series-connected with the junction boxes, and employed in connection with suit- able voltmeters, to indicate the pressure at the junction boxes. The pressure wires are sometimes called the pilot wires. Wires, Tap The wires or conduc- tors used to carry the current from the feed- ers or mains at the pole to a near point on the trolley wire. Wiring. Collectively the wires or con- ducting circuits used in any system of electric distribution. Wiring. Placing or establishing the wires or conductors for any electric circuit. Wiring, Case Placing or establish- ing electric conductors or wires that are held in place on the walls or ceiling of a room, by means of continuous cleats. Wiring, Cleat Placing or estab- lishing electric conductors or wires that are held in place on the walls or ceiling of a room by means of suitably shaped insulating cleats. Wiring, Inside The conductors that, in a system of incandescent electric lighting, lead to the interior of the house or area to be lighted. Wiring, Moulding Electric con- ductors or wires that are held in place on the walls or ceiling of a room by means of suit- ably shaped mouldings. Work. The product of the force by the distance through which the force acts. A force whose intensity is equal to one pound acting through the distance of one foot, does an amount of work equal to one foot-pound. Work is to be distinguished from the more gen- eral term energy. Work, Electric The joule. (See Joule.} The product of the volts by the coulombs. I joule = 10,000,000 ergs, or .73732 foot-pounds. " =i volt-coulomb. " =i watt for I second. Work, Electric, Unit of The volt- coulomb or joule. (See Volt-Coulomb. Joule.) Work, Unit of - The erg. . The amount of work done when a force of one dyne acts through the distance of one centimetre. (See Erg.) Raising one gramme against gravity, through the distance of one centimetre, requires an amount of work equal to 980 ergs. Work, Units of Various units em- ployed for the measurement of work. The following table of Units of Work is taken from Hering's work on Dynamo-Electric Ma- chines : WORK. erg = I dyne-centimetre. " = .0000001 joule. gramme-centimetre . . = 981.00 ergs. " .. = .00001 kilogr. -metre. foot-grain I joule, or i volt-cou-] lomb, or I watt I during every second ! or I volt-ampere f during every! second . . '937 5 ergs. f 10,000,000 ergs, .737324 foot pound, .101937 kilogram - metre, .0013592 metric horse- power for one second. I volt ampere during | _ .0013406 horse-power every second ...... ) for one second. " =.0009551 pound- " Fah., heat unit. " = .0005306 pound- Centig., heat unit. " = .0002407 kilogr.- Centig., heat unit. = .0002778 watt-hour. = 13562600 ergs. = 1.35626 joules. =. 13825 kilogr. metre. =.0018434 metric horse-power for e second. =.00181818 horse- power for one second. I foot-pound WorJ 5i i foot-pound = .0012953 pound- Fah., heat unit . " = .0007196 pound - Centig., heat unit. " = .0003264 kilogr.- Centig., heat unit. " = .0003767 watt-hour. I kilogram-metre = 98100000 ergs. = 9.81000 joules. " = 7.233 14 foot-pounds. " = .01333 metric horse- power for one second. " =.013151 horsepower for one second. " = .009369 pound-Fah., heat unit. " =.005205 pound- Centig., heat unit. " ==.002361 kilogr.- Centig., heat unit. " = .002725 watt-hour. i watt-hour = 3600 joules. " = 2654.4 foot-pounds. " =366.97 kilogram. metres. " ' =3-4383 pound-Fah., heat units. " = 1.9102 pound- Centig., heat units. " =.8664 kilogr.- Centig., heat units. " =.0013592 metric horse power-hour. " =.0013406 horse. power-hour. I metric h. -p. -hour . . . . = 2648700 joules. " . . . . = 1952940 foot-pounds. ' =270000 kilogram- metres. ' . . . . = 2529.7 pound-Fah., heat units. ' .... = 1405.4 pound- Centig., heat units. " = 637. 5 kilogr. -Centig., heat units. " = 735-75 watt-hours. * = .98634 horse-power- hour. i horse-power-hour = 2685400 joules. " .... = 1980000 foot- pounds. " =273740 kilogram- L>Vur. i horse-power-hour. . . . = 2564.8 pound-Fah., heat units. " .... = 1424.9 pound- Centig. , heat units. = 646.31 kilogr.- Cen tig., heat units. ' = 745.941 watt-hours. " . . . . = 1.01385 metric horse- power-hour. HEAT. I gram-Centig = .001 kilogram-Centi- grade. I pound-Fahr = 1047.03 joules. " = 772 foot-pounds. " = 106.731 kilogram- metres. " =.55556 pound-Centi- grade. " =.25200 kilogram- Centigrade " = .29084 watt-hour. " = -0003953 metric horse power-hour. " =.0003899 horse- power hour. i pound-Centig = 1884.66 joules. " = 1389.6 foot-pounds. " =192.116 kilogram- metres. " = 1.8000 pound- Fahrenheit. " = .4536 kilogram-Centi- grade. " = .52352 watt-hours. " =.0007115 metric horse-power-hour. " =.0007018 horse- power-hour. I kilogram-Centig = 4154-95 joules. " = 3063. 5 foot-pounds. " =423.54 kilogram- metres. < =3.9683 pound- Fahrenheit. " =2.2046 pound-Centi- grade. " = 1.1542 watt hours. " = .001569 metric horse- power-hour. " = .0015472 horse- power-hour. Working, Direct The transmis- Wor,] sion of signals over a telegraph line with- out the use of relays or repeaters. Working, Multiple, of a Dynamo-Elec- tric Machine A term sometimes used for the parallel working of dynamo-electric machines. (See Working, Parallel, of Dy- namorElectric Machines.} Working, Parallel, of Dynamo-Electric Machines The operation of working several dynamo-electric machines as a single source, by connecting them with one another in parallel or multiple arc. The effect of parallel working is to reduce the internal resistance of the dynamo. If a current be required in a circuit at an electro- motive force equal only to that of a single machine, and the requirements of the circuit are equal to the output of more than a single dynamo, a num- ber of dynamos must then be coupled in mul- tiple. Working, Reverse-Current A term sometimes used in telegraphy for a method of working by means of a double current in place of a single current. The double-current system of working was de- vised by Varley to permit Morse characters to be sent rapidly through underground conductors. In order to avoid the retardation due to induction, the current was reversed between each signal. This reversion in the conductor hastened the dis- charge of the conductor. 561 [Yok. Working, Series, of Dynamo-Electric Machines Such a coupling of several dynamo-electric machines as will deliver the current supplied by them in series. As in all series connections of sources, there re- sults an electromotive force equal to the sum of the electromotive forces of the different dynamos. Worming, Cable A central core of hemp or jute around which are wrapped the several separate conductors of a cable con- taining more than a single separate conduc- tor. Wood's Button Repeater. (See Repeat- ers, Telegraphic} Wrapped Wire.-(See Wire, Wrapped.} Writing, Electrolytic Imprinting written characters on cloths, or other textile fabrics, by the electrolytic decomposition of a dyeing substance with which they are im- pregnated. The cloths, etc., to be written on, are impreg- nated with an aniline salt, and placed on an insu- lated metallic plate next to the salt, which is con- r.ected to one pole of an electric source. The other pole is connected to a carbon electrode, which is used as the writing stylus or pencil. By suitably connecting the terminals the writing is obtained in color on a white ground, or in white on a colored ground. (See Dyeing, Electric.) Writing Telegraphy. (See Telegraphy, Writing.} Y-Shaped Sparks. (See Spark, Y-Shaped} Yale-Lock-Switch Burglar Alarm. (See Alarm, Yale-Lock-Switch Burglar} Yoke, Multiple-Brush - A term sometimes applied to multiple brush rocker of a dynamo or motor. (See Rocker, Mul- tiple-Pair Brush.} Yoke, Multiple-Pair Brush A device for holding a number of pairs of brushes of a dynamo-electric machine in such a manner that they can be readily moved or rotated on the commutator cylinder. The brushes are placed side by side on the com- mutator cylinder. In such cases the several pairs of brushes are so arranged that they can be thrown off or out of contact with the commutator cylinder while cleaning the cylinder, without stop- ping the machine. Yoke, Single-Brush A -term some- times used for single-brush rocker. (See Rocker, Single-Brush.} Yok.] 562 [Zoil. Yoke, Single-Pair A single-brush rocker. (See Rocker, Single-Brush?) Yoke, Single-Pair Brnsh A device for holding a single pair of collecting brushes of a dynamo-electric machine in such a way that they can be readily moved or rotated on the commutator cylinder. Yoked-Horseshoe Electro-Magnet. (See Magnet, Electro, Yoked-Horseshoe.} Z. -A symbol sometimes used in electro- therapeutics for contraction. The use of Z, is for the purpose of avoiding the letter C, which has already been used for cur- rent or ampere in Ohm's law. Increasing strengths of contraction are represented by Z', Z", Z'". Z. A symbol for electro-chemical equiva- lent. Zero, False -A zero taken midway between any two equal and opposite deflec- tions of a measuring instrument. Zero, Inferred A zero deduced or inferred from the deflection produced by a charge that is to be measured by comparison with the value of the deflection by means of a known charge in an electrical measuring instrument. An inferred zero is usually completely off the scale, hence its name. It does not actually exist. Zero Methods. (See Method, Null or Zero} Zero Potential. (See Potential, Zero.) Zero, Shifting A zero that changes or shifts in position ; a polar zero in a measur- ing instrument. Zigzag Electro-Magnet. (See Magnet, Electro, Zigzag.} Zigzag Electromotive Force. (See Force, Electromotive, Zigzag.) Zigzag Lightning. (See Lightning, Zig- zag.) Zinc, Amalgamation of The cov- ering or amalgamation of zinc with a layer of mercury. To amalgamate a plate of zinc, its surface is first thoroughly cleaned by immersing the plate in dilute sulphuric acid of about I part of acid to 10 or 12 parts of water. A few drops of mercury are then rubbed over its surface, thus coating it with a bright metallic film of zinc amalgam. Care must be taken not to use too much mercury, since the zinc plate would thus be rendered brittle. Zinc-Carbon Yoltaic Cell. (See Cell, Voltaic, Zinc-Carbon.}. Zinc-Copper Yoltaic Cell. (See Cell, Voltaic, Zinc-Copper} Zinc, Crow-Foot A crow-foot- shaped zinc used in the gravity voltaic cell. (See Cell, Voltaic, Gravity.) The term "crow-foot " refers to the shape of the claws. It is hardly a happy term. Zinc-Lead Yoltaic Cell. (See Cell, Vol- taic, Zinc-Lead.) Zinc Sender. (See Sender, Zinc.) Zincode of Yoltaic Cell. A term for- merly employed to indicate the zinc terminal or electrode of a voltaic cell. The negative electrode or kathode are prefer- able terms. Zone, Anelectrotonic A name sometimes given to the polar zone. (See Zone, Polar.) Zone, Kathelectrotonic A name sometimes given to the peripolar zone. (See Zone, Peripolar.) Zone, Peripolar A term proposed by De Watteville for the zone or region sur- rounding the polar zone on the body of a patient undergoing electro-therapeutic treatment. Zone, Polar A term proposed by De Watteville for the zone or region surround- ing the therapeutic electrode applied to the human body for electric treatment. THE FIRST SYSTEMATIC TREATISE ON THE ELECTRIC RAILWAY. THE "ELECTRIC RAILWAY IN THEORV 7*ND PRACTICE. By O. T, CROSBY AND DR. LOUIS BELL. Covering the Genera/ Principles of Design, Construction and Operation. OCTAVO, 400 PAGES AND j 79 ILLUS- TRATIONS, PRICE, 2.50 TABLE OK CONTENTS : Chapter I. General Electrical Theory. II. Prime Movers. III. Motors and Car Equipment IV. The Line. V. Track, Car Houses. Snow Machines. VI. The Station. VII. The Efficiency of Electric Traction. VIII. Storage Battery Traction. IX. Mis- cellaneous Methods of Electric Traction. X. High Speed Service. XI. Commercial Con- siderations. XII. His- torical Notes. O. T. CROSBY. APPENDICES : Appendix A. Electric Railway vs. Telephone Decisions. B. Instructions to Linemen. C. Engineer's Log Book. D. Classification of Expenditures of Electric Street Rail- ways. E. Concerning Lightning Protection, by Prof. Elihu Thomson. In this important new hook just issued will be found a full discussion of the principles, apparatus and methods of construction employed in electric railroading. As will DR . LOUIS BELL. be seen from the table of contents, it treats all departments of the subject as comprehensively as is practicable in a volume of reasonable size. The illus- trations have been prepared especially for it, and manv of them are entirely new. To Electric Railway Managers, Superintendents, Electricians and Operators, this volume is invaluable, while no one interested in the modern applications of electricity will want to be without it. The necessity for such a book has been keenly felt. Copies of The Electric Railway in Theory and Practice, or of any other Electrical work published, will be mailed to any address, POSTAGE PREPAID, on receipt of price. Address THE W. J.JOHNSTON COMPANY, Ltd. TIJVIES BUIUDIN, NEW YORK. FIRST AMERICAN BOOK ON ELECTRIC MOTORS. THE ELECTRIC MOTOR ITS KRRL.ICHTIONS. By T. C. MARTIN and Jos. WETZLEB. With an Appendix on the Development of the Electric Motor since 1888. By DR. Louis BELL. This is the first American Book on Electric Motors, and the only one in any language dealing exclu- sively and lully with the modern Electric Motor in all its various practical applications. CONTENTS. Chapter i. Elementary Considerations ii. Early Motors and Experiments in Europe iii. Early Motors and Experiments in America iv. The Electrical Transmission of Power v. The Modern Electric Railway and Tramway in Europe vi. The Modern Electric Railway and Street Car Line in America vii. The use of Storage Batteries with Electric Motors for Street Rys " viii. The Industrial Application of Electric Motors in Europe. Chapter ix. The Industrial Application of PAGE. 125 Electric Moiors in America " X. Electric Motors in Marine and Aerial Navigation 137 xi. Telpherage 143 " |xii. Latest American Motors and Motor Systems 152 xiii. Latest American Motors and Motor Systems Con 196 " xiv. Latest European Motors and Motor Systems 246 xv. Alternating Current Motors 255 " xvi. Thermo-Magnetic Motors 272. Appendix. The Development of the Electric Motor since 1888 27? 315 Pages* 353 Illustrations. Price, $3.00. The W.J. JOHNSTON CO., Id. 167-176 Times Building, New York. THE LEADING AMERICAN BOOK ON DYNAMOS. Principles of Dynamo-Electric Machines, And Practical Directions for Designing and Constructing Dynamos, With an Appendix containing several articles on allied subjects and a table of equivalents of units of measurement. By CARL HERING. CONTENTS. Chapter I., Review of Electrical Units and Fundamental Laws; Chapter II., Fundamental Principles of Dynamos and Motors; Chapter HI. , Magnetism and Electromagnetic Induction; Chapter IV., Generation of Electromotive Force in Dynamos; Chapter V , Armatures; Chapter VI., Calculation of Armatures; Chapter VII., FieM Magnet Frames; Chapter VIII., Field Masrnet Coils; Chapter IX., Regulation of Machines; Chap- ter X., Examining Machines; Appendix I , Practical Deductions from the Franklin Institute Tests of Dynamos; Appendix II., The So-called " Dead Wire" on Gramme Armatures; Appendix III., Explorations of Magnetic Fields surrounding Dynamos; Appendix IV., Systemsof Cylinder-Armature Windings; Appendix IV., Systems of Cylinder-Armature Windings; Appendix V.. Equivalents of Units of Measurements (Table). American electricians have long felt the need of a work of this nature, written in plain and simple lan- guage by a man thoroughly familiar with all types of generating apparatus. The book is copiously illus- trated, printed on an extra good quality of paper, and substantially bound. Cloth, 279 Pages. 59 Illustrations. Price, $2.5O Copies of the above, or of any other electrical book or books published, will be promptly mailed to any address in the world, POSTAGE PREPAID, on receipt of price. Address : The W. J. JOHNSTON CO., Li, Times Building, New York. Complete Rules for the Safe Installation of Electrical Plants. FOR THE USE OP ENGINEERS AND ARCHITECTS By E. A. MERRILL. The author has drawn up a set of specifications covering the various classes of lighting installations, which may serve as forms for any special type or character of plant, and which are at the same time full enough to cover the ordinary installation of electrical apparatus and electric light wiring. The book will prove especially useful to architects and engineers who desire a full knowledge of the necessary requirements of the various classes of electrical in- stallations in order to meet the demands of the insurance inspectors and the conditions of safety. THE LATEST RULES ARE GIVEN OF THE (1) National Electric Light Association. (2) National Board of Fire Underwriters. (3) New England Insurance Exchange. OTHER CONTENTS: Specifications for the Installation of Electric Lighting Plants. General Specifications. Installation of Dynamos and Switchboards. Alternate Current Converter System, Constant Potential. General Specifications for Alternate or Direct Current Dynamos for Parallel System of Distribu- tion. Arc Dynamos. Fixtures, etc. Interior Wiring. Two- Wire, Direct or Alternating Current System. Three- Wire Sj'stem. Three- Wire System Adapted to Two- Wire System. Arc System. Conduit System, Two- Wire. Interior Wiring for Central Station Plants. Pole Lines. Low Potential, Direct Current, Two or Three- Wire. Alternating System. Street Lighting Circuits. Specifications for Steam Plant. Bound in Cloth. Price, l ^? $1.5O. Copies of MERRILL'S ELECTRIC LIGHTING SPECIFICATIONS, or of any other Electrical book or books published, will be mailed to any address in the \vorld, postage pre- paid, on receipt of the price. Address: The W. J. JOHNSTON COMPANY, Ld, Times Build'g, NEW YORK. RECORD OF AN ACTIVE FIELD OF DEVELOPMENT. RECENT PROGRESS IN ELECTRIC RAILWAYS. By Carl Hering. Compiled and Condensed from Current Electrical Literature. About 400 pages and 120 Illustrations. Cloth, Price $1.00. The volume of electrical literature has now assumed such proper tions that it is impossible to keep abreast of it, much less to make such records or abstracts as would be of use for future reference. To meet the demand of those interested in the progress of Electric Rail- ways, and who have felt the want of a general index to recently pub- lished matter on this subject, this compilation has been prepared. The book contains a classified summary of the recent literature on this active and promising branch of electrical progress and descriptions of new apparatus and devices of interest to the technical reader. CONTB NXS. Chapter I. Historical. Chapter II. Development and Statistics. Chapter III. Construction and Operation. Chapter IV. Cost of Construction and Operation. Chapter V. Overhead Wire Surface Roads. Chapter VI. Conduit and Surface Conductor Roads. Chapter VII. Storage Rattery Roads. Chapter VIII. Under- ground Tunnel Roads. Chapter IX. High Speed In- terurban Railroads. Chapter X. miscellaneous Systems. Chapter XI. Generators, motors ana Trucks. Chap- ter XII. Accessories. CARL BERING. TESLA'S LONDON LECTURE. EXPERIMENTS WITH ALTERNATE CURRENTS Of High Potential and High Frequency. By NIKOLA TESLA. 156 Pages, with Portrait and 35 Illustrations. Cloth, $1.00. This book gives in full Mr. Tesla's important lecture before the LONDON INSTITUTION OF ELECTRICAL ENGINEERS, which embodies the results of years of patient study and investigation on Mr. Tesla's part of the phenomena of ALTERNATING CURRENTS or ENORMOUSLY HIGH FREQUENCY AND ELECTROMOTIVE FORCE. Every Electrician, Electrical Engineer or Student of Electrical Phenomena who makes any pretensions to thorough acquaintance with recent progress in this important field of research which Mr. Tesla has so ably developed must read and reread this lecture. The book is well illustrated with 35 cuts of Mr. Tesla's experimental apparatus, and contains in addition a biographical sketch, accompanied by a full-page portrait, which forms a fitting frontispiece to a lecture which created such widespread interest. Copies of the above or of any other Electrical Books published, will be promptly mailed to ANY ADDRESS on receipt of price. Address NIKOLA TESLA. TheWJ. JOHNSTON CO., Limited. Times Building, New York. A BOOK FOR EVERY DEALER AND EVERY BDYER. ELECTRICAL^STREET RAILWAY DIRECTORY. Published Annually. -:- Price, in Cloth, THIS BOOK CONTAINS: A LIST OF CENTRAL ELECTRIC LIGHT AND POWER STATIONS, with the Number of Lights in Use, Electric Power Supplied, Capital Paid in. Name of System Name of Managing Official, Superintendent, Purchasing Agent, Electrician, and other particulars. A LIST OF ISOLATED ELECTRIC LIGHT PLANTS, with Name of Electrician, Purchasing Agent, Engineer, System and Size of Plant, and other particulars. A LIST OF STREET RAILWAY COMPANIES, with Length of Road, Number of Cars, Car Miles Run, Capital Paid in. Managing Official, Superinten- dent, Purchasing Agent, System Electric, Horse or Cable and other particulars. A LIST OF EVERY MANUFACTURER AND SUPPLY DEALER connected with the Electrical or Street Railway Industry. A special effort is made to have this Directory the most complete, the most reliable and the most yaluafole of any work of the kind issued. Its pages are full of interest not only to every dealer in Electrical and Street Railway Apparatus, Machinery and Supplies, and every manufacturer who wishes to reach those engaged in this large, important and growing industry, but to the purchasers of Electrical Apparatus and Supplies and to all in any way interested in the progress and development of either the Electrical or the Street Railway business. Copies of Johnston's Electrical and Street Railway Directory, or of any other Electrical or Street Railway books, will be mailed to any address in the world, postage prepaid, on receipt of the price. Address : THE W. J. JOHNSTON COMPANY, Ltd., 167-176 Times Building, NEW YORK. AUTHORIZED AMERICAN EDITION. By PROF. SILVANUS P. THOMPSON, D.SC., B.A., M.I.E.E. A full theoretical and practical account of the properties and peculiarities of electromagnets: together with complete instructions for desi&iiing magnets to serve any specific purpose. Published with the express consent and careful revision of the author. Cloth, 280 Pages. 75 Illustrations. Price $1.OO. LECTURE I. Introductory ; Historical Sketch ; Generalities Concern- ing Electromagnets ; Typical Forms ; Polarity; Uses in General ; The properties of Iron ; Methods of Measuring Permeability; Traction Meth- ods; Curves of Magnetisation and Permeability ; The Law of the Elec- tromagnet; Hysteresis; Fallacies and Facts about Electromagnets. LECTURE II.^General Principles of Design and Construction; Prin- ciple of the Magnetic Circuit. LECTURE III. Special Designs; Winding of the Copper; Windings for Constant Pressure and for Constant Current; Miscellaneous Rules about Winding; Specifications for Electromagnets; Amateur Rules about Resistance of Electromagnet and Battery; Forms of Electromag- nets; Effect of Size of Coils; Effect of Position of Coils; Effect of Shape of Section; Effect of Distance between Poles; Researches of Prof. Hughes ; Position and Form of Armature ; Pole-Pieces on Horseshoe Magnets ; Contrast between Electromagnets and Permanent Magnets; Electromagnets for Maximum Traction; Electromagnets for Maxi- mum Range of Attraction ; Electromagnets of Minimum Weight ; A useful Guiding Principle ; Electromagnets for Use with Alternating Currents; Electromagnets for Quickest Action; Connecting Coils for Quickest Action; Battery Grouping for Quickest Action; Snort Cores vs. Long Cores. PROP. SILVANUS P. THOMPSON. LECTURE IV. Electromagnetism and Electromagnetic Mechanism. THE ONLY BOOK TREATING OP THIS SUBJECT EXCLUSIVELY. TJ By WM. MAVER, Jr., and MINOR M. DAVIS. With Chapters on The Dynamo-Electric Machine In Relation to the Quadruples The Practical Working of the Quadruples. Telegraph Repeaters and the Wheatstone Automatic Telegraph. By WM. MAVER, Jr. CONTENTS. The Quadruples. Development of the Quadruples. Introduction and Esplanatory. The Transmitter, Rheostat and the Condenser. Stearns Duplex. Instruments of the Polar Duplex. The Polar Duplex. The Dynamo-Electric Machine in relation to the Quadruples. The Practical Working of the Quadruples. Telegraph Repeaters. The Wheatstone Automatic Telegraph. This book is written in plain, simple and explicit language, and is within the ready comprehension of all. The illustrations are numerous, and with their aid the readers can at once grasp, mentally, the operation of the Quadruples. The book is handsomely printed on fine paper and substantially bound. Every Telegrapher and every Electrician should have a copy. Cloth, 126 Pages. 63 Illustrations. Price, $1.50. THE TELEPHONE MAN'S TEXT BOOK. PRACTICAL INFORMATION FOR TELEPHONISTS. By T. D. LOCK-WOOD, Electrician, American Bell Telephone Company. Historical Sketch of Electricity from 600 B. C. to 1882 A. D. Facts and Figures about the Speaking Telephone. How to Build a Short Telegraph or Telephone Line. The Eartb and Its Relation to Telephonic Systems of Communication. The Magneto-Telephone What it is, How it is Made, and How it Should be Handled. The Blake Transmitter. Disturbances Experienced on Telephone Lines. The Telephone Switch-Board. A Chronological Sketch of the Magneto-Bell, and How to Become Acquainted with it. Telephone Transmitter Batteries. Lightning Its Action ui>on Telephone Apparatus How to Prevent or Reduce Troubles Arising Therefrom. The Telephone Inspector. The Telephone Inspector His Daily Work. The Inspector on Detective Duty. The Daily Routine of the Telephone Inspector Individual Calls for Telephone Lines. Telephone Wires versus Electric Light Wires. Electric Bell Construction, Part I. Electric Bell Construction, Part H. Housetop Lines, Pole Lines and Aerial Cables. Anticipations of Great Discoveries and Inventions. 12mo. 192 Pages; Cloth. Price, $1.00. Copies of the above books, or of any other electrical book or books published, will be promptly mailed to any address in the world, postage prepaid, on receipt of price. Address : THE W. J. JOHNSTON CO., Lim., TIMES BUILDING, N. Y. T. D. LOCKWOOD. RECOMMENDED BY THE ELECTRICAL WORLD FOR SPECIAL READING. We are often asked by those who desire to inform themselves in regard to electrical matters to recommend to them a course of reading or book on particular subjects or in relation to certain special departments of electrical application. The following list will, we trust, meet the requirements of most of those who desire such information. "With scarcely an. exception, the books mentioned are substantially bound in cloth and copiously illustrated. (A.) PRINCIPLES AND THEORY OF ELECTRICITY AND MAGNETISM. (1.) An Elementary Course. Atkinson's Elements of Static Electricity, with a full description of the H&tz and TSpler Machines $1.50 Atkinson's Elements of Dynamic Electricity and Magnetism 2.00 Ayrton's Practical Electricity for First Year Students 2.50 Electrician Primers, vol. I, Theory, $1.00; vol. II, Practice 1 .00 Fleming's Short Lectures to Electrical Artisans 1.60 Houston's Dictionary of Electrical Words, Terms and Phrases. Second edition, entirely re- written, containing about 5,000 distinct titles, 570 illustrations and 562 double column pages. 8vo. 5.00 Jenkln's Electricity and Magnetism, with an Appendix on the Telephone and Microphone 1.60 Kennelly & "Wilkinson's Practical Notes for Electrical Students 2.50 Maycock's First Book of Electricity and Magnetism 0. 60 Thompson's Elementary Lessons in Electricity and Magnetism 1.25 Thompson's Lectures on the Electromagnet 1.00 (2.) An Advanced Course. Cummlng's Introduction to the Theory of Electricity $2.25 Mintage's Introduction to the Mathematical Theory of Electricity and Magnetism 1 .90 Ewing's Magnetism of Iron and other Metals (new) 4 00 Fleming's Alternate Current Transformer in Theory and Practice. 3 vols., second vol. in press. 8.00 Faraday's Experimental Researches in Electricity. 8 vols 20.00 Houston's Dictionary of Electrical Words, Terms and Phrases, second edition, entirely re- written, containing about 5,000 distinct titles, 570 illustrations and 562 double column pages. 8vo. . 6.00 Lodge's Modern Views of Electricity 8.00 Mascart & Jou bert's Treatise on Electricity and Magnetism. 2 vols Maxwell's Treatise on Electricity and Magnetism. 2vols. New edition Thompson's Electromagnet and Electromagnetic Mechanisms . Watson dc Burbury's Mathematical Theory of Electricity and Magnetism. 2 vols (B.) PRACTICAL APPLICATIONS OF ELECTRICITY AND MAGNETISM. (1 ) General Trea*lse. Electricity in Daily Life WOO Hospitaller's Modern Applications of Electricity 2 vols Houston's Dictionary of Electrical Words, Terms and Phrases, second edition, entirely re- written, containing about 5,000 distinct titles, 570 illustrations and 562 double column pages. 8vo. Gulllemln's Electricity and Magnetism Sllngo A: Brooker'a Electrical Engineering for Electric Light Artisans and Students Trevert's Electricity and Its Recent Applications \Vrmell's Electricity in the Service of Man (2.) Special Treatises. (a.) Electric Lighting. PRICE. Alglave & Bonlard's Electric Light: Its History, Production and Application 5.0O Atkinson's Elements of Electric Lighting 1 . 50 Day's Electric Light Arithmetic 0.40 Desmond's Electricity for Engineers 2.50 Dredge's Electric Illumination. Vol. I., $15., Vol. n 7.50 Cordon's Decorative Electricity 3.75 Houston's Dictionary of Electrical Words, Terms and Phrases, second edition, entirely re-writ- ten, containing about 5,000 distinct titles, 570 illustrations and 562 double column pages. 8vo. . . 5.00 Latimer's Incandescent Electric Lighting . 0.50 Merrill's Electric Lighting Specifications, for the use of Engineers and Architects 1 . 50 Russell's Electric Light Cables 1.50 Urquhart's Electric Light : Its Production and use 3.00 Urquhart's Electric Light Fitting , 2.00 Ob.) The Electric Motor. Badt's Electric Transmission Hand-book 1.00 Hot tone's Electro-motors ; How Made and How Used .50 Crosby & Bell's Electric Railway in Theory and Practice 2.60 Hering's Recent Progress in Electric Railways 1 .00 Houston's Dictionary of Electric Words, Terms and Phrases, second edition, entirely re-written, containing about 5,000 distinct titles, 570 illustrations and 562 double column pages. 8vo 5 00 Kapp's Electric Transmission of Energy 3.00 Martin & Wetzler's Electric Motor and Its Applications ; with an Appendix by Dr. Louis Bell. 3.00 Urquhart's Electro-motors 3.00 (C.) Telegraphy. Abernethy's Commercial and Railway Telegraphy 2.00 Houston's Dictionary of Electrical Words, Tcrmsand Phrases, second edition, entirely re-written, containing about 5,000 distinct titles, 570 illustrations and 562 double column pages. 8vo 5 .00 Lockwood's Electricity, Magnetism, and Electric Telegraphy 2.50 Maver & Davis' Quadruplex, with Chapters on Telegraph Repeaters and the Wheatstone Automatic Telegraph 1 .50 Pope's Modern Practice of the Electric Telegraph 1.50 Preece & Siverwright's Telegraphy 1.75 Prescott's Electricity and the Electric Telegraph. T\vo vols 7.00 Plum's Military Telegraph During Our Civil War. Two vols 6.00 Reid's Telegraph in America 5.00 (d.) The Telephone. Du Moncel's Telephone, The Microphone and the Phonograph 1 .25 Houston's Dictionary of Electrical Words, Terms and Phrases, second edition, entirely re-written containing about 5,000 distinct titles, 570 illustrations and 562 double column pages. 8vo 5.00 Lock wood's Practical Information for Telephonists 1 .00 Poole's Practical Telephone Hand-book 1 .25 Preece & Maler's Telephone 4.00 Prescott's Bell's Electric Speaking Telephone : 6.00 (e.) Electro-Metallurgy Bonney's Electro-platers' Hand-book. . 1-20 Gore's Art of Electrolytic Separation of Metals, etc 3.50 Gore's Theory and Practice of Electro-deposition 0.80 Houston's Dictionary of Electrical Words, Terms and Phrases, second edition, entirely re-written, containing about 5,000 distinct titles, 570 illustrations and 562 double column pages. 8vo 5.00 Urquhart's Electrotyping 2.00 AVahl's Galvanoplastic Manipulation 7.50 Watt's Electro-deposition 8.60 (f.) Batteries. Carhart's Primary Batteries 1-50 Gladstone & Tribe's Chemistry of Secondary Batteries of Plante and Faure 1.00 Houston's Dictionary of Electrical Words,Terms and Phrases, second edition, entirely re-written, containing about 5, 000 distinct titles, 570 illustrations and 562 double column pages. 8vo 5.00 Niaudet's Elementary Treatise on Electric Batteries 2 - ^ TVlblett's Secondary Batteries Reynier's Voltaic Accumulator .......' Salomons' Electric Light Installation and the Management of Accumulators! ......... "^\...[ (g.) The Dynamo. Badt's Dynamo Tenders' Hand-book. . . $1.00 Bott one's Dynamo : How Made and How Used Croft's How to Make a Dynamo Heriug's Principles of Dynamo Electric Machines " " 2 50 Thompson's Dynamo Electric Machinery. New. Fourth edition. Revised. Re-written" ...'. 0.00 Walker's Practical Dynamo Building for Amateurs .80 (h.) Alternating Currents. Blakesley's Papers on Alternating Currents of Electricity. Reprinting Dewiiioiid's Electricity for Engineers g.50 Fleming's Alternate Current Transformer in Theory and Practice 8.00 Houston's Dictionary of Electrical Words, Terms and Phrases, second edition, entirely re- written, containing about 5,000 distinct titles, 570 illustrations and 562 double-column pages. 8vo 5.00 (C.) ELECTRICAL TESTING AND MEASUREMENT. Ayrton's Practical Electricity $2.50 Gray's Absolute Measurement in Electricity and Magnetism 1.85 Herlng's Table of Equivalents of Units of Measurement 0.50 Houston's Dictionary of Electrical Words, Termsand Phrases, second edition, entirely re- written, containing about 5,000 distinct titles, 570 illustrations and 56'J double-column pages. 8vo 5. 00 K.empc's Hand-book of Electrical Testing 6.00 E. ock. wood's Electrical Measurement and the Galvanometer 1.60 Swinburne's Practical Electrical Measurement . . 1 . 75 Webb's Testing of Insulated Wires and Cables 1 .00 (D.) MISCELLANEOUS. Allsop's Practical Electric Bell Fitting $1.28 Atkinson's Elements of Static Electricity 1.80 Gray's Electrical Influence Machines 1.75 Houston's Dictionary of Electrical Words, Terms and Phrases, second edition, entirely re- written, containingabout5,000distincttitles,570illustrationsand5e2doublecolumn pages. 8vo. 8.00 HerliiK's Universal Wiring Computer 1 .00 Tesla's Experiments with Alternate Currents of High Potential and High Frequency - 1 .00 (E.) BOOKS FOR THE NON-TECHX1CAL READER. Benjamin's Age of Electricity $2.00 Gulllemln's Electricity and Magnetism 8.00 Hosplt aller's Modern Applications of Electricity. Two vols 8.00 Houston's Dictionary of Electrical Words, Terms and Phrases, second edition, entirely re- written, containingabout5,000 distinct titles, 570 illustrations and562 doublecolumn pages. 8vo. 6.00 Reid's Telegraph in America 5.00 Worinell's Electricity in the Service of Man .00 (F.) HISTORICAL WORKS. Alglave & Boulard's Electric Light $5.00 Dredge's Electric Illumination. Vol. I, $15.00, vol.11 Fanie's History of Telegraphy to 1837 Martin & Wctzler's Electric Motor and Its Applications Pope's Evolution of the Electric Incandescent Lamp Prescott's Telephone Reid's Telegraph in America Thompson's Dynamo Electric Machine-y. New. Fourth edition. Revised. Re-written Thompson's Philipp Reis, Inventor of the Telephone 8.00 Copies of any of the books mentioned above, or of any other electrical books published, will be mailed, POSTAGE PREPAID, to any address in the world on receipt of the price. Address : THE W. J. JOHNSTON COMPANY, LIMITED 167-176 TIMES BUILDING, NEW YORK. THE PIONEER ELECTRICAL JOURNAL OF AMERICA. HANDSOMELY AND PROFUSELY ILLUSTRATED, IS PUBLISHED EVERY SATURDAY BY THE W. J. JOHNSTON COMPANY, Ltd. ESTABLISHED 1874. INCORPORATED 1889. Telephone Call: CORTLANDT 924. Cable Address: "ELECTRICAL," NEW YORK. Publication Offices : 167-176 TIMES BUILDING, HEW YORK. 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