m mm fill 1 Iw LIBRARY library UNIVERSITY OF CALIFORNIA. MAY 5 1894 ' '*<> x--, /x -, No<5electricity, from the Greek words electron and odos. An electrolyte is a compound decomposable by the electric force, and the term electrolysis means the act of such decomposition. 36. Give some simple directions for the care of batteries. The Daniell, gravity, Grove, and Leclanche batteries, being types of all the principal batteries in use, will alone be noticed here. The Daniell Battery. Use the best quality of copper sulphate procurable. Never use powdered sulphate, as it soon cakes and then dissolves too slowly to be of much use. Never use porous cups after they are cracked or any way damaged, or let the zinc touch the porous cup. If the zinc is used inside the porous cup, VOLTAIC ELECTRICITY. 33 let it be suspended, so that it will not touch the bottom of the cup. The zinc solution is at its best when it is half satu- rated. When it is stronger than that point of satura- tion, a portion should be drawn off and the cell filled up with water. At least once in two months a Dan- iell battery should be thoroughly cleaned, the plates scraped, and any copper found attached to the porous cup scraped off. The copper solution, if clean, may all be restored, but half the zinc solution will usually be sufficient. The following hints may be given on the maintenance of the gravity battery : After setting up, if the battery is weak connect the poles by a wire for a day or two ; this will tend to sepa- rate the solutions and to concentrate the zinc sulphate solution. Keep the level of the water at least a quarter of an inch above the zinc. Avoid shaking the solutions. Keep the line between the copper and zinc solutions as sharp as possible. If the blue is too low draw off a little of the upper solution with a syringe, and replace it with pure water ; then leave the battery circuit open when not being used. If the blue gets too high put the battery on short cir- cuit when not in use. If a froth generates on the surface remove it with a piece of wood or a brush. If the zincs become very dirty take them out, scrape and wash them. Jars should never touch each other. Shelves should not be allowed to become dirty. Generally speaking, if the blue rises too high the resistance in the circuit is too great for the battery. Be sure that the covering of the insulated wire leading up from the copper plate is perfect ; and in setting up a battery never use old material, unless it is in every re- spect good. The Grove Battery. The zincs of this and all other 34 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. acid batteries should be kept well amalgamated in order to prevent local action. Grove batteries should be taken apart every night ; one-tenth of fresh nitric acid should be added every morning, and the dilute sulphuric acid renewed twice a week. Use great care in handling the acids, as they are very corrosive. Place the zincs every night in water weakly acidulated with sulphuric acid. The Leclanche Battery. Never let the outside solu- tion rise above the shoulder of the jar. When setting up the battery pour a little water in the porous cup. The sal-ammoniac solution should be saturated, but too much sal-ammoniac ought not to be put into the jar at once, as it is apt to cake instead of dissolving. When the solution becomes too weak, crystals of oxychloride of zinc form on the zinc and weaken the action of the battery. Watch the connecting wires carefully, as they are liable to be eaten through by the free ammonia gene- rated in the battery. If the battery is weak, and no cause is apparent, test each cell separately, and, when the defective cell is found and examined, probably a salt of lead will be found between the lead cap and the carbon plate, partially insulating it. Renew the water in the outside vessel when necessary, at the same time adding a little sal-ammoniac. If by accident the Leclanche cell be left on closed cir- cuit and run down, its strength may be to a certain extent renewed by soaking the porous cups in water or dilute muriatic acid and giving the battery a con- siderable rest. Rolled zinc should be used in preference to cast, as it is purer and more economical in the end. The following hints are applicable to all batteries : Insulate each cell perfectly, and keep the shelves on which they stand clean and dry. Keep all points of contact and all connections clean and bright. No leak- age or creeping of liquids from the cells should be al- VOLTAIC ELECTEICITY. 35 lowed, and as soon as any such thing shows itself it should be wiped away with a damp cloth. To prevent siich action the edges of the outside vessel should be dipped in melted paraffine. The temperature of a battery room should not be too warm, or the liquids will evapo- rate ; nor too cool, or they will los power. Solutions should always be renewed before they are exhausted, and the batteries periodically examined, so that any defect will be located and removed before causing any radical trouble. Every connection must be made tight and kept free from oxide. 37. Hoiv is the presence of iron in sulphate of copper detected $ The suspected crystals must be dissolved in water, and liquid ammonia added to the solution. This will at first precipitate both copper and iron, and the solution will appear very cloudy. More ammonia is then to be added, when the copper will be redissolved, forming a bright blue solution, and the iron, if present, will fall to the bottom in the form of a brown powder. CHAPTER III. THEEMO-ELECTEICITY. 38. What is thermo-electricity f Thermo-electricity is the name given to that branch of the science of electricity which relates to the production of electric currents by the agency of heat. The term literally means heat-derived electricity. Professor Seebeck, of Berlin, in 1823 discovered that if two bars of any two metals, especially bismuth and antimony, be soldered together at one end, and have their other ends connected with one another by a wirg, so as to form a complete circuit, on the application of heat to the point where the metals are soldered a por- tion of the applied heat is absorbed and disappears, and an electric current is developed in its stead. Fig. 14. Electricity produced by Heat. All metals, and many other conductors of electricity, are capable of producing thermo-electric currents, and they are all classed either as thermo-electro-positive or thermo-electro-negative bodies. The former class com- prises those conductors in which the current proceeds from the colder to the warmer portion ; and the latter THERMO-ELECTRICITY. 37 We take a bar of Fig. 15. Thermo-electric Battery, with Galvanometer. includes those in which the current proceeds in the opposite direction. Bismuth may be regarded as the representative of the former class, and antimony as that of the latter. In ex- periments in this science, therefore, these metals are most frequently used. For example bismuth, and solder or braze, one end of it to one end of a bar of an- timony, then attach a galvanometer by wires to the free ends of the two bars, so that the circuit is completed from the bismuth to the antimony by soldering ; then from the other end of the antimony to one terminal of the galvanometer, and from the other terminal of the galvanometer to the free end of the bismuth. If we then heat the junction of the two bars we shall see the needle deflect, the current proceeding from the bismuth through the heated point to the antimony, thence through the gal- vanometer and back to the bismuth. Some metals when thus united are found to produce a current in one direc- tion when the junction is moderately heated, but when the heat is increased the direction of the current is reversed. 39. What is a thermo-electric battery 1 When only one bar of each of the metals employ- ed is used the arrangement is called a thermo-electric pair. A number of these thermo-electric pairs may be joined in series, just as a number of voltaic cells are joined together for the for- mation of a voltaic battery, joined the entire series is Tigs. 16 and 17. Nobili's Thermo-electric Battery. When the pairs are so called a thermo-electric battery, and its electro -motive 88 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. force is equal to the sum of the electro-motive forces of all the pairs added together. To make such a battery, suppose we have six bars of bismuth and the same number of antimony, each bar being three inches long, three-quarters of an inch wide, and one-fourth of an inch thick. Arrange them alternately, so that if the first bar is bismuth the last will be antimony. The bars must then be soldered together at each end, the sec ond, antimony, being, for instance, at one end soldered to the first bar and at the other end soldered to the third ; the third, in its turn, having its other end spidered to the fourth, and so on. The two terminal bars will, of course, have one end unattached. These free ends rep- resent the poles of the battery. To set the battery in operation all the junc- tions on one side must be heated, while all those on the other side must be kept cold. While the arrangement described represents the principle of the thermo- battery there are many varieties, modifications, and improvements. One of the first thermo-bat- teries was invented by Melloni in 1834. He made what he called a thermo-multiplier. It consisted of about fifty little bars of antimony and bismuth enclosed in a brass cylinder, the whole arrangement being but two and a half inches long and about half an inch in diameter. The termi- nal bars were connected by wires to a delicate gal- vanometer. This contrivance was so sensitive to slight changes in temperature that when the hand was brought near to one end of the instrument the current generated was sufficient to move the needle several degrees. Two Fig. 18. The Thermo-electric Multiplier for Mea- suring Heat. THERMO-ELECTRICITY. 39 of the most efficient thermo-electric batteries are those of Noe, of Vienna, and Clarnond, of Paris ; the former being more speedily excited and giving a powerful current, and the latter being very strongly constructed. To sum up : A thermo-electric battery may be briefly defined as a device which transforms heat into elec- tricity. 40. Has the thermo-electric battery ever been employed for practical purposes f Yes, it has been applied to several purposes. Mel- loni, at a very early date, used the thermo-pile, previ- ously described as having been constructed by him, to measure small differences in temperature. Clamond's battery has been quite extensively experimented with in England for working telegraph circuits. It was expect- ed that the thermo-electric pile, in diamond' s improved form, would, on account of its low resistance, be useful as a universal battery that is, one from which many circuits are worked ; and at one time five thermo-batter- ies were used to work no less than ninety separate circuits from the London post-office. Each of these cir- cuits was less than one hundred miles in length. All the thermo-batteries, however, ultimately failed by the burning out of the insulating material between the several layers of bars. This is probably not a fault which will prevent the thermo-pile from being eventually used. But the most important application of the thermo- electric battery has hitherto been to furnish a current for the electro-deposition of metals, or, to use more fa- miliar terms, for electro-plating. It was first so used in 1843 by Moses Poole, and patented, but did not then come into general use. Thermo-electricity has, however, been more or less employed since that time for plating, and, since the invention of Clamond, has done efficient work. Clamond's thermo-electric battery is now in use in various plating establishments in Birmingham, Lon- don, and Sheffield, arid it is said that a machine of one 40 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. hundred bars, with a consumption of eight to nine feet of gas, deposits an ounce of silver per hour. These batteries have experienced such important im- provements of late years that it is believed they will soon be utilized with great advantage. Dept.Mech.Bng. CHAPTER IY. EARTH-CURRENTS AND EARTH-BATTERIES. 41. What are earth-currents f They are currents which are always flowing through telegraphic lines, and which depend for their existence on a .difference of potential between the two points of the earth at which the line is terminated. They are, therefore, currents flowing from one part of the earth to another, which, being of course subject to the ordinary laws of electricity, and finding another path . open to them at the ground-plate where they enter, divide there, part of the current taking the wire route to the distant point, the other part taking the route through the earth. They vary in strength at different periods in the day and year, and sometimes are so strong as to render the working of a line difficult. They are then called electric storms. Sometimes they flow in one direction, sometimes in the other, and in any case are very unwelcome visitors in telegraph lines. They are particularly frequent on long cables, and en- danger the safety of the cable. They also render test- ing with the galvanometer very uncertain and incorrect. 42. How may the effects of earth-currents on telegraph lines be obviated 1 On ordinary telegraph lines this may be done in two ways : The first mode may be adopted when two wires run parallel to each other ; it consists in abandoning the use of the ground-wires at the terminal offices, and looping the wires, so as to form a metallic circuit. In practice, if the wires are looped together at but one end the result is satisfactory. 41 42 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. The second method may be used where there are not two wires parallel to each other, and is effected by re- moving the ground-wire at one end of the line and lengthening the circuit by connecting another line run- ning in another direction to it, so that if a straight line were drawn connecting the two end offices it would be out of the direction of the earth- current prevailing at the time. In the case of submarine cables of considerable length the same result is effected by the use of condensers, which are interposed between the ends of the cable and the ground. 43. Are there any other currents which appear on telegraph lines without apparent cause 1 Yes. If the earth-plates of a circuit are of different metals a permanent current will be set up, varying in strength according to the metals used. For example, if a copper plate be buried in the earth at one end of the line, and a zinc plate at the other, the current will be comparatively powerful. If one earth-plate be of lead and the other of iron, the current will not be as strong as that developed by the copper and zinc, but it will still be quite perceptible. This may readily occur, and to the inexperienced electrician sometimes proves very puzzling. If, for in- stance, the wire be grounded on an iron gas- pipe at one end of the line and on a lead water-pipe at the other, and a current appears, as under the circumstances it surely will, it needs some experience to determine its origin. When suspected one ground or the other must be changed until no current passes. This current has been utilized under the name of the earth-battery current. It was used by Gauss in Ger- many at an early date, was subsequently employed by Bain to work electric clocks, and in 1846 was used by Steinheil on a Bavarian telegraph line twenty miles long. For telegraphs, however, it has not attained any re- markable degree of success. CHAPTER Y. MAGNETISM ELECTRO-MAGNETISM AND ELECTRO- MAGNETS. 44. What is magnetism*} It is the name given to the science which treats of the peculiar properties of attraction, repulsion, polarity, and the development of magnetism in other magnetic bodies by induction, which are possessed, under certain condi- tions, by iron and some of its compounds, and in inferior degree by nickel. The metals cobalt, chromium, and manganese also possess magnetic properties to a limited extent. The term is also employed to denote the cause of mag- netic phenomena. The name is generally supposed to be derived from Magnesia, a place in Asia Minor, where the natural magnet was originally found by the Greeks. The existence of magnetism is noticed in very ancient Chinese, Greek, and Roman manuscripts. 45. Wliat is a magnet ? A body which exhibits magnetic properties is called a magnet. The name is usually confined to the ferrous substances mentioned above (44) ; but all conductors of electricity are capable of showing similar effects while conveying a current. 46. What is a natural magnet f The natural magnet, often also called the loadstone, is an ore of iron, called by chemists ferrosoferric oxide. It is known by the symbol F 3 O 4 , and is by minera- logists termed magnetite. It is generally met with in small pieces, but sometimes occurs of quite a large size. It is composed of about seventy-three parts iron and 43 44 ELECTEICITY, MAGNETISM, AND TELEGRAPHY. twenty-seven oxygen. First found in Magnesia, in Asia, it has since been procured from many other places, and at the present time the most powerful natural magnets are found in Siberia and in the Harz Mountains of Ger- many. The natural magnet has been known in almost every country from the earliest ages, and in nearly every lan- guage the name given to it is based on its supposed partiality for iron. The English name loadstone is de- rived from the Saxon word Icedan (to lead), a name sug- gested by observation of its directive power. . The attractive force of the natural magnet is not great in proportion to that exhibited by artificial magnets, as it is very seldom that a piece is met with that will sus- tain its own weight. 47. What is an artificial magnet ? It is a body possessing all the properties of the natu- ral magnet, these properties having been imparted to it by artificial means. If a bar of hard steel is repeatedly rubbed from end to end by a magnet, the steel receives all the magnetic properties. Or if such a bar is placed within a helix of insulated wire, and a current of elec- tricity passed through the helix, the bar becomes mag- netic. A piece of steel thus acted upon is an artifi- cial magnet. The property which magnets have of imparting mag- netism to steel is extremely valuable, as steel can be easily shaped into any required form, and utilized in many ways and for many purposes that a natural mag- net could not be applied to. 48. What are the characteristic properties of magnets ? First, Attraction. This property resides principally in two opposite points. These points are called poles. When either pole of a magnet is brought near to a piece of iron a mutual attraction takes place between them. The reason is that the iron also becomes magnetized by its proximity to the magnet, the part which is nearest to either pole of the magnet acquiring an opposite polar- ELECTRO-MAGNETISM AND ELECTRO-MAGNETS. 45 ity to it, causing the iron to attract the magnet with a force equal to that with which the magnet attracts the iron. Thus it will be seen that the attraction which a magnet appar- ently has for iron is really an attrac- tion for the opposite pole of another magnet, as graphically shown in Figure 19. Second, Repulsion. This is seen in the action of two magnets upon each other. If two magnets are suspended so that they can move freely in an horizontal plane, and their similar poles are placed close together, they will be observed to repel each other and turn round until their opposite poles are in juxtaposition. Or if, as in Figure 20, one of the magnets, s n, is sus- pended, and the second, ET S, is brought close to it, the north pole of one being- pre- sented to the north pole of the other, a quick re- pulsion takes place ; the same occurring also if two south poles are brought together. Thus the two magnetisms in this have a resemblance to the two electricities : like poles repel ; opposite poles attract. Third, T7ie power of de- veloping magnetism in iron or steel by induction. Fig. so.-Mutuai Action of Magnetic Poles, whenever magnetic prop. erties are developed in bodies not previously possessed of them, the process is called magnetic induction ; and Fig. 19. 46 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. for sucli development it is not necessary that the body shall be brought into actual contact with the magnet. By bringing a magnet near to iron or steel the latter bodies are rendered magnetic by induction ; are then capable of attracting iron, and themselves possess the power of communicating the properties to other pieces of iron. This is especially the case with soft iron, and it is only while the iron remains in the vicinity of the magnet that it retains these qualities. As soon as the magnet is withdrawn, the iron loses its induced powers. With steel and hardened iron the case is different. When iron is hardened magnetism is induced more slowly, and is more slowly parted with ; and when magnetism is induced in hardened steel it re- quires, as it were, to be rubbed in. When once thoroughly magnetized the piece of steel is a permanent magnet. Fourth, Polarity. If a magnet is suspended so as to move freely in a horizontal direction it will always come to rest with the same pole pointing to the north, as in Figure 21. This property is called polarity, or directive force, and is familiarly illustrated by the ordinary compass. If the magnet is suspended so as to move freely in a vertical plane, it will be found to have the power of inclining itself to the horizon at various angles, ac- cording to the locality. This power is called the dip of the magnet. North of the equator the ex- tremity that points to the north Fig. 21. Directive Action of the Earth. (Jjpg . south of the equator the other end dips. The dip varies with the latitude. Near the equator the needle lies nearly level, while near the north and south poles it verges on an upright position. ELECTRO- MAGNETISM AND ELECTRO-MAGNETS. 47 In the latitude of New York the angle of dip is about seventy degrees. 49. What are the poles of a magnet ? The extremities of a magnet, where its magnetic powers most clearly manifest themselves. In a bar magnet the poles are found very nearly at the ends. The earth is itself a magnet, and has north and south magnetic poles. The pole which in any magnet points to the north is called the north pole, and the other is called the south pole. Any two north poles repel each other, as do also any two south poles ; but any north pole attracts any south pole, and vice versa. The poles of the magnet are shown in Figure 22, in which iron filings are seen to accumulate at both ends of the bar, while the middle does not attract them at all. Hence the di- rective power Of Fig. 22.-The Magnet. the magnet. The north pole of the earth attracts the opposing pole of the magnet, which, strictly speaking, should therefore be called the south pole; but it has long been customary in English-speaking countries to call the pole pointing to the north the north pole, hence it would now tend to create confusion if the practice were changed. If a magnet be broken in two each piece becomes a complete magnet, with north and south poles. It has been found desirable for practical purposes to distinguish the two poles by marking one of them usually the extremity which points northward with a small file-cut. Another method is to color the north pole blue and the south pole red. 50. Wfiat is a permanent magnet ? As previously noticed, steel (which is a compound of iron with carbon), while it acquires magnetism with difficulty, retains its magnetism more or less perma- 48 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. nently, after the withdrawal of the inducing magnet. This difficulty in the reception of magnetism, and the permanency with which, when once acquired by steel, it is retained, is called coercive force. On account of the latter property a magnet formed of hard steel is called a permanent magnet. Permanent magnets may be of any required form, but for general purposes only two styles are made namely, bar and liorseslioe magnets. 51. Describe the bar, horseshoe, and compound magnets. A bar magnet is an artificial permanent magnet in the form of a straight bar The magnetic needles used in telegraph instruments and compasses are delicate bar magnets. A magnet which is bent in such a manner as to bring its two ends, or poles, near each other, so that they can be connected by a short, straight piece of iron, is called a horseshoe magnet. Magnets for general use are most frequently made in this form, because it is then easier to bring both poles into play upon the same object. The short piece of iron spoken of as being used to connect the poles of a horseshoe magnet should be of soft iron. It is called an armature, or keeper, and when the magnet is not being used, the armature, to prevent the loss of power, should be constantly kept across its poles. A compound magnet consists of two or more bar or horseshoe permanent magnets, placed side by side and fastened, together, with their similar poles in contact. They are arranged in this way for the purpose of in- creasing the magnetic power. Although a compound magnet is stronger than any of its component magnets, it is very much weaker than the sum of the strengths of all the magnets, were they used separately. This is because the similar poles of all of them, being laid close to one another, have^a tendency to react on each other, and, to a certain extent, induce an opposite polarity in the contiguous magnets. ELECTRO-MAGNETISM AND ELECTRO-MAGNETS. 49 52. Describe the process of magnetizing steel for the forma- tion of permanent magnets. There are several different methods of magnetizing steel bars, needles, and horseshoes, among which may be noted the following as the most important and the most generally used. Small needles can be magnetized by merely placing them across the poles of a permanent magnet for a short time. One of the simplest ways to magnetize a steel bar is to place the middle of the bar on one of the poles of a strong bar or horseshoe magnet, and draw one end of it over the pole a number of times, never failing to draw it from the middle to the end ; then turn the bar end for end and repeat the process, drawing the other end over the other pole of the permanent magnet. The end that has been drawn over the north pole of the permanent magnet will possess south polarity, and the other will possess north polarity. A horseshoe can be magnetized by drawing it over the two poles of a permanent or electro magnet in such a w~ay that both halves of the horseshoe pass at the same time over the poles to which they are applied. If it is thick it should be turned over, and the process repeated on the opposite side. But of all the modes practised the most efficient is the use of the electric current. A helix is prepared, con- sisting of a number of layers of insulated wire. It has a small central opening, and when a steel bar is placed in- side the opening, and a strong current passed through the helix, the bar is strongly magnetized. 53. What is the meaning of the term "magnetic field" t The presence of a magnet always modifies in some way its immediate neighborhood, so that pieces of iron and steel brought into the proximity of the magnet acquire magnetic properties by induction ; and any other magnet placed there shows at once that it experiences a pecu- liar force. This locality immediately surrounding the magnet is called the magnetic field, and the term literally means 50 ELECTRICITY, the extent of space surrounding the poles of a magnet in which the magnetic forces may be recognized. 54. WJiat is diamagnetism ? In 1845 Faraday demonstrated the magnetic condi- tion of all matter, and showed that all bodies divided themselves into great classes the one attracted, the other repelled by the poles of a magnet. As the force producing the former result is called magnetism, he gave to the force causing the repulsion the name dia- magnetism, or cross-magnetism. And any substance which, when delicately suspended between the poles of a magnet, instead of settling across from pole to pole, arranges itself transversely to that position, so that it points in the same direction as the magnet and is re- pelled by both poles alike, is called a diamagnetic body. The bodies which most strongly exhibit this force are bismuth, antimony, and zinc. But the force of diamag- netism is, at its best, much feebler than that of ordinary magnetism, as bismuth, which is of all substances the most strongly repelled, is still repulsed with a force so much less than that exerted in the attraction of iron as to bear no comparison to it. 55. What is the nature of the relation between electricity and magnetism, and by whom was this relation discovered 1 The discovery of the relationship between electricity and magnetism was an ob- ject eagerly desired and sought for by the electri- cians and scientists of the last century, but for such a protracted period without result that it was doubted, and by some even denied, that any such relationship existed. But in the year 1820 Hans Christian Oersted, professor of natural phil- osophy at Copenhagen, announced his discovery that if a wire conveying an electric current be placed horizontally ELECTKO-MAGNETISM AND ELECTRO- MAGNETS. 51 above a magnetic needle, and parallel to it, the needle is deflected, as represented in Figure 23, and tends to place itself at right angles with the conducting wire, the end of the magnet nearest the positive pole of the battery de- flecting eastward. If the conducting wire be similarly placed under the needle all the effects are the same, except that they are in an opposite direction. This relationship, described in plain language, consists literally in the fact that a wire electrified by a constant source or stream of electricity becomes practically a magnet (or, to speak more correctly, a straight current produces in a wire a magnetic field, in which the lines of force are circles concentric with the wire), and dis- turbs the magnetic field of the earth' s magnetism, con- sequently tending to deflect a magnetic needle, pivot- ed within the sphere of its influence, from its position pointing north and south. The fact of the deflection of the magnetic needle, when placed near a wire conveying a current, had been previously discovered and announced as early as 1802 by an Italian philosopher, Gian Domenico Romagnesi, of Trent ; but owing to the limited publicity he gave to his discovery, and to the unprepared condition of the Scientific world at that time, it attracted no notiqe un- til rediscovered by Oersted. From the foregoing facts, when announced by Oersted, Ampere, of France, made the deduction that "magnet- ism is the circulation of currents of electricity at right angles to the axis joining the poles of the magnet." Arago (also a French scientist) shortly after showed that every conductor of electricity, while conveying a current, becomes possessed of magnetic powers, and in the same year discovered that current electricity would magnetize small pieces of iron and steel ; and he accom- plished this by placing them in a glass tube and wind- ing a wire, which connected the two poles of the battery, round the tube. Sir Humphry Davy, of England, like- 52 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. wise in 1820 found that sewing-needles could be mag- netized by merely rubbing them across a wire convey- ing electricity. From this time electrical discovery has been rapid and progressive. The two forces are so intimately connected that by many scientists they are considered to be only different manifestations of the same agency, the motion of a magnet always producing electricity, and the transfer of electricity as uniformly producing magnetism. 56. What is electro-magnetism $ It is that department of electrical science which re- lates to the development of magnetism and the deflection of magnetic needles by means of electrical currents. 57. What is an electro-magnet ? A helix of wire conveying a current of electricity has magnetic properties. If such a spiral be made of insu- lated wire and wound on a bar of soft iron the iron be- comes magnetized and its force is added to that of the coil. The combination of the coil and the iron together is called an electro-magnet. Electro-magnets may be made of any form, but the most common forms are the bar, in which the poles are as far apart as possible, and the TiorsesJwe, in which the poles are as close to- gether as possible. For practical purposes they are made by winding covered copper wire on two bobbins or spools, a a', pass- ing soft iron cores, c c', through them, fixing the two soft-iron cores on a connecting-piece or yoke, 5, also of I , soft iron, and connecting the two spirals together in such a manner that if the cores were straightened out into one bar the wire would be coiled in the same direction from one end to the other. The ends of the cores are called the poles of the elec- tro-magnet. An electro-magnet has, as long as the current flows Dept. Mech. Bng-. ELECTRO-MAGNETISM AND ELECTRO-MAGNETS. 53 in the coils, all the properties of a permanent magnet, and can be made to possess much greater power than Si permanent magnet of the same size. The magnetic force developed in any electro-magnet is dependent on the strength of current, the number of turns the wire takes round the core, and the size of the iron core itself. The first electro-magnet was made in 1825 by Stur- geon, but a practical and useful one was not produced until 1830, when Professor Henry constructed the first magnetic spool or bobbin ever produced, by winding in- sulated wire round a soft-iron core, and by so doing ex- alted the power of the electro-magnet in an astonishing degree. 58. What is residual magnetism ? We have seen that when a piece of soft iron is brought near to a magnet it becomes magnetized by induction, and that when removed from the influence of the mag- net it loses all trace of its induced magnetism. This is also the case with electro-magnets. When a current is conveyed through the coil of the electro-magnet the soft-iron core is strongly magnetized ; and when the circuit is broken, or from any cause the current ceases to flow, demagnetization instantly takes place. It is this property that makes the electro-magnet so valuable and so universally useful. It must be observed, how- ever, that this complete demagnetization is dependent on the quality and softness of the iron. If it is not very soft and pure, or, in the case of an electro-magnet, if the armature is allowed to touch the poles, a certain amount of magnetism remains in the iron, and is called residual magnetism. Hence the iron used should be of the softest and purest kind, old Swedish iron being pre- ferable. 59. In making calculations on the strength of electro-magnets is the resistance of the battery to be taken into consideration ? In short circuits, where the resistance is proportion- ately large to the resistance of the rest of the circuit, it should be. For example, in a local circuit of a Morse 54 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. sounder there is practically no resistance outside of the sounder-coil, except the battery. It is obvious, then, that it must be considered and the coil made equal to it. But when the battery of a very long external cir- cuit is in question it is not necessary to include the re- sistance of the battery with that of the circuit, because, though large, it is yet, in proportion to the rest of the circuit, very small, and to simplify the calculation it is usually ignored. 60. Has the length of the iron core any effect on the working of an electro -magnet ? Yes. Electro-magnets with short cores charge and discharge more rapidly than those with long ones. Ad- vantage of this fact has been taken in telegraphy, and all the later forms of relay have short cores. A magnet also works quicker when charged by a battery of many cells than when few are used. When strength rather than speed of action is required it is well to employ magnets with long cores, because the convolutions of wire can then be increased in number without decreas- ing their distance from the core, by adding a great num- ber of layers of wire. 61. What proportion should the resistance of an electro-mag- net bear to the resistance of the other component parts of the circuit '! It is one of the laws of electro-magnetism that with any given battery the greatest magnetic force is obtain- ed when the resistance of the coils of the electro-mag- net or magnets is equal to the resistance of the other portions of the circuit that is, of the ba.tteries and con- ducting wires. This law holds good practically on short and local circuits ; but on long telegraphic circuits it is only applicable when they are perfectly insulated. It is, therefore, usual in telegraphic practice to make the total resistance of the electro-magnets considerably less than that of the line, when in good order, so that in bad weather the best results may be obtained. To illustrate : It is required to ring a bell over a copper ELECTRO-MAGNETISM AND ELECTRO-MAGNETS. 55 wire one hundred feet long, with two cells of Leclanche battery. What should be the resistance of the bell-mag- net to obtain the greatest magnetic power? The Le- clanche cell has an internal resistance of about one ohm; therefore two cells would have a resistance of two oh ms, and in this case the conductor, on account of its short- ness, may be ignored. The resistance of the bell-magnet need be only two ohms to obtain the best result. The consideration of wire comes in here. Although we have decided that the resistance of the coils should be two ohms, it is still possible to err in the size of wire em- ployed ; therefore after ascertaining, by the relative re- sistances of the circuit and the rule already given, what the resistance of the electro-magnet should be, we must take care not to use wire that is too fine, or we shall reach the required resistance before the core is suffi- ciently covered to give much magnetic effect, as with very fine wire it takes very few convolutions to give a resistance of two ohms. It is essential not to use wire that is too coarse, as in that case we have to wind so many layers that, except in the first one or two layers, the convolutions are so far away from the core as to lose their influence on it. Wire should always be chosen, therefore, for winding electro- magnets that will reach the required resistance before the last convolution attains a distance of half an inch from the core. Between half an inch and three-eighths from the core is the best distance for the last layer of wire. We will now suppose a line half a mile long, built of No. 9 iron wire, with two bell -magnets in circuit, and a battery of ten cells. The battery resistance is ten ohms, the line resistance about eight ohms ; total resist- ance of line and battery is, then, eighteen ohms. The sum of the electro-magnets should then, likewise, be eighteen ohms, or nine ohms each, to obtain the great- est magnetizing power from the given battery of ten cells. TJ5I7BRSIT7)) 56 ELECTKICITY, MAGNETISM, AKD TELEGRAPH Y. 62. In constructing an electro-magnet for a very short cir- cuit ivhat kind of wire should be used, and why ? We have seen that the resistance of the electro-mag- net coil should be equal to that of the other portions of the circuit. It is, therefore, apparent that to accom- plish this in a very short circuit it is necessary to em- ploy a comparatively short, coarse wire short, because even a very small addition would increase the resistance of the circuit out of all proportion ; thick, because the current is not greatly enfeebled by its use, while the number of convolutions it allows of are sufficient to effect a strong magnetization. In short, we use a com- paratively thick wire because it is necessary to get the greatest magnetic effect without the weakening of the current consequent on the use of a thin wire, which necessarily is of high resistance. 63. How should an electro-magnet be made for a very long circuit, or a circuit of very high resistance, and why ? For a long circuit, such as that of a telegraph line, or a circuit which has a high resistance outside of the coil for instance, in the battery the magnet must be wound with a very fine, small wire of great length, which will allow of a great number of convolutions being wound over the core without exceeding the distance at which they cease to increase its magnetism. The reason of this is that in a very long circuit, like a telegraph line, or in a circuit of very high resistance, the current is neces- sarily very weak and i'eeble, even though the battery be composed of a large number of cells. The coil is, there- fore, made of fine wire, so that a great many convolu- tions can be used, each one adding its own influence to the combined magnetic effect, while its own resistance (which, considered by itself, is great) is yet so small in proportion to the entire circuit that it does not decrease the strength to any great extent. The rule relating to the proper proportion of the electro-magnet to the circuit holds good in this case. For example, we have a line, two hundred miles long, of ELECTRO-MAGNETISM AND ELECTRO-MAGNETS. 57 "No. 9 wire, and a battery of eighty Callaud cells. We are to have five relays. What should be the resistance of each of those relays ? " We call the line- wire resistance 16 ohms per mile ; then for 200 miles the line resistance will be 3,200 ohms. Calling the battery resistance 3 ohms per cell, the resistance of the entire battery will be 240 ohms, giving as the total resistance of line and battery 3,440 ohms. Then, following the rule already given, we must make the total resistance of the electro-magnets 3,440 ohms also. This divided by 5, for the number of mag- nets, gives as the resistance of each magnet 688 ohms. In practice, however, as has already been observed, it is well to keep the magnet resistance less than that of the line and battery, to allow for variations in resistance due to weather. Moreover, in this country, for unifor- mity, the resistance of the majority of relays used is made very much the same for comparatively long and short circuits. "The condensed reason, then, why we use fine wire and a great deal of it for circuits of high resistance, is that the high resistance of the circuit greatly enfeebles the current, and we must use fine wire to make the best of the remaining strength of the current by a greatly- increased number of convolutions." 64. When we require an electro-magnet for long lines, or for circuits of great resistance, why do we call for one of high re- sistance f Is high resistance advantageous ? No. Resistance, considered by itself, is a positive dis- advantage, because every additional unit of resistance added to the circuit tends to further enfeeble the cur- rent. But, as already stated, to make the most of the existing current we require many turns of wire, and the resistance is a necessary but unwelcome adjunct. If we could obtain the convolutions without the resistance it would be so much the better, but that is impossible ; and it has been found convenient to designate magnets 58 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. intended to work on long lines as high-resistance mag- nets not because it is in virtue of their high resistance that they work better, but simply because they necessa- rily have a high resistance, and to denominate them as such is an easy way to distinguish them. CHAPTER VI. MAGNETO-ELECTRICITY, AND MAGNETO AND DYNAMO- ELECTRIC MACHINES. 65. What is magneto-electricity? It is the name given to electric currents which are developed by the relative movements of magnets and wires. For example, if a magnet and a coil of insulated wire are caused to alternately approach and recede from each other rapidly, momentary currents are induced in the coil, which are alternately opposed to each other in direction. The process of developing magneto-electri- city, as already stated (see answer 18), is called mag- neto-electric induction. It is one of Faraday's most important discoveries. Fig. 25. Magneto-Electric Induction. While experimenting in the year 1831, he ascertained that by inserting the end of a permanent magnet into the middle of a coil of wire to which no battery was 60 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. attached a current of electricity was produced, whose direction depended upon the pole of the magnet inserted and the direction in which the coil was wound. By in- serting the other end of the magnet a current in the opposite direction was produced. In the same year he produced a spark, a, &, by pulling an armature, s (covered with a coil of insulated wire, n\ Fig. 26. The Electric Spark obtained from a Magnet. from the poles, N, S, of a magnet (Figure 26), and also obtained magneto-electric currents by rotating a copper plate between the poles of a magnet, and by sliding a coil of insulated copper wire upon a bar magnet. We see, therefore, that by the mere motion of a magnet in near proximity to a conductor, or of a conductor in the immediate vicinity of a magnet, without any battery, dynamic electricity may be produced. In the next year, 1832, the first magneto-machine was invented, and elec- tricity generated in this manner is now one of the most important agents in the useful arts, and is for many pur- poses to be preferred to that produced by voltaic bat- teries. MAGNETO-ELECTRICITY, ETC. 61 66. What are the principal applications of magneto-electri- city ? It has been extensively applied in ways too numerous to recapitulate. The following are, however, a few of its most important applications : Magneto- currents generated by small machines are frequently used for medical purposes, and have also been much employed in the experimental room and laboratory for chemical and physiological reactions. It is now almost universally used in the production of the electric light, and was first employed for that ob- ject by F. H. Holmes, who showed a machine for the purpose in the International Exhibition of 1862, since which time whenever the electric light has been profita- bly used, its currents have been generated by magneto- machines. For blasting, and the explosion of mines and sub- marine charges, it has proved a very valuable agent, Professor Wheatstone having devised an ingenious ap- paratus for the ignition of fuses. It has the power of igniting from two to twenty-five fuses simultane- ously. The application of magneto-electricity to electro-plat- ing was an event of importance in the history of that art. It was first so applied in 1842, and the machine then introduced was used for many years, but has now been superseded by newer and more improved arrange- ments, such as the Gramme, Weston, or Siemens and Alteneck machines. One of the most important applications of magneto- electricity is to telegraphy. Gauss and Weber, in 1833, moved their telegraph needle by magneto-electricity, which was the first employment of Faraday's discovery in such service. Subsequently Steinheil in 1837, and Wheatstone in 1840, made great improvements in apparatus ; and at the present time Wheatstone' s alphabetical telegraph is almost exclusively employed on country lines in Eng- 62 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. land, while the magneto-pointer telegraph of Siemens and Halske holds its own as a private-line instrument in Russia and Germany. In our own country the mag- neto-printers of G. L. Anders are well and favorably known. The magneto- current has been more extensively em-- ployed during the last few years than ever before, owing to the extraordinary number of magneto-bells manufac- tured and introduced as telephone signals. The tele- phone itself is also an important application of magneto- electricity, which will be more fully considered here- after. A few years since an attempt was made by J. B. Fuller, of Brooklyn, N. Y., to work the Morse telegraph lines of the Western Union Telegraph Company by means of a dynamo- electric machine. On account of the high speed necessary at that time to produce a uniform current this experiment was unsuccessful and was soon abandoned. In 1880 Stephen D. Field, of New York, renewed the experiment with improved apparatus and with a dif- ferent arrangement of circuits. He used three ma- chines, two of which had their armature coils in the circuits to be operated, while the third machine served to energize the field magnets of the first two. These later experiences have realized such a saving in the cost of electric power as to encourage high hopes of the profitable substitution at an early day of machine currents for voltaic electricity at many of the principal telegraph offices. 67. Has the magneto-electric system of developing electricity any advantages over the voltaic-battery method ? If so, describe some of them. For certain purposes it has decided advantages, some of which may be enumerated as follows : On comparatively short telegraph lines, such as pri- vate and municipal telegraphs, it is far superior to the battery system, inasmuch as although the first cost of MAGNETO-ELECTRICITY, ETC. 63 the machine is greater, there is practically no outlay for its management and maintenance, while the expense and annoyance inseparable from the' maintenance of batter- ies are totally dispensed with. It has also been ascertained, in the practical working of magneto-telegraphs, that they will work satisfactorily over a heavy escape that renders a line worked by bat- teries totally inoperative. In the production of the electric light the magneto- machine presents great advantages on the score of econ- omy and convenience, It has also been the most valu- able agent in bringing the cost of the light within com- mercial requirements. The chief objection to the use of the electric light was formerly the enormous expense necessarily contingent on the continued use of large voltaic batteries, and the consumption of zinc anfl. other materials essential to keep them in good working order. The introduction of the magneto-machine in 1862 by Holmes, and the successive improvements that have since been effected by Wilde, Siemens, Wheatstone, Ladd, Gramme, Weston, and others, have completely obviated this objection and made the electric light an ordinary illuminator, known and valued by many, in- stead of being, as formerly, a cabinet curiosity, only within the grasp of the professional electrician. These machines have also, with excellent results, been applied to electro-plating and electrotyping, and for that service are now being universally preferred to batteries, with the same advantages as in their application to lighting. This application of magneto-electricity was first made in 1842 by J. S. Woolrich, who took out a patent for the use of a magneto-electric machine in elec- tro-plating. The modern machines of Wilde, Gramme, Siemens and Alteneck, and Weston have, however, en- tirely superseded the Woolrich machine, and are now, in some of their multitudinous types, constantly used. The first Gramme machine used for this purpose ran 64 five years without repairs or outlay, except the cost of oil for lubrication. But since the general introduction of the telephone magneto-electricity may be said to have found its appro- priate sphere. Merely mentioning the telephone itself, in which the magneto currents may be said to be invol- untarily generated, it was early seen that some signal was necessary to attract the attention of the distant telephone operator ; and the application, in a branch circuit, of the magneto-electric generative apparatus, in combination with the special polarized armature invent- ed by Thomas A. Watson, answered the purpose so ad- mirably that it is still used substantially in the same manner as at first. Many thousands of these bells are now in use, and will be fully described in their place. The use of the magneto-bell for a signal hds also the advantage of being able to ring over long or short lines indifferently, and in large offices the economy in maintenance, and the valuable space saved which would otherwise be devoted to large batteries, is such a consideration as to render the magneto system the only one now regarded as worth a second thought. 68. What is a magneto-electric machine ? A magneto- electric machine may be briefly defined as an apparatus whereby motion is by means of magnetism transformed into electricity. Such machines are made in many different forms, and the modifications of the machine are almost as numerous as are those of the vol- taic battery. Nearly all may, however, be comprehend- ed in three classes : First. Those in which the working current is gene- rated by the movement of coils of wire in the vicinity of permanent magnets. Second. Those in which a comparatively small perma- nent magnet and armature are made to generate a cur- rent which is merely made use of to excite a very large electro-magnet. This is then used to induce a second MAGNETO-ELECTEICITY, ETC. 65 current, which can be as much stronger than the first as the electro -magnet is more powerful than the permanent magnet. Third. Those in which the small amount of residual magnetism always present in electro-magnets is utilized to generate a current, which is first used to increase the magnetism of its inducing magnet and thereby its own strength. When the current reaches the required point of strength, in some of the machines of this class, a por- tion is shunted off for use, while another portion is di- rected continuously through the coils of the inducing magnet, thereby maintaining its magnetism. In other machines the whole of the current generated in the armature-coil is led through the magnet-coil be- fore passing out to the external circuit. Each of these three classes may be again subdivided into machines furnishing alternating and machines fur- nishing direct or continuous currents. 69. Describe a machine of the first class mentioned. This class of machine is the simplest of any, and for a long time was the universal type of all magneto-ma- k t Fig. 27. chines in use. It is shown in Figure 27. A pair of coils, c d, of insulated wire, connected together in the 66 ELECTRICITY, MAGNETISM, AND TELEGKAPHY. same way as electro-magnets, contain soft-iron cores, aft, united by a soft- iron yoke-piece, X ; these are fixed on. a horizontal axis, S, which may be revolved rapidly by means of a cord passing over a multiply ing- wheel, W, f and a pulley on the axis S, in front of the poles of ^a permanent magnet or series of magnets, M. The rapid alternate approach and retreat of the coils through the magnetic field of the permanent magnet induces cur- rents in each coil, which, by means of a circuit-breaker, 7c i, dipping into a mercury bath having two chambers, I ra, insulated from one another, are made intermittent, and thus shocks may be received from the handle-con- ductors, H H. Dispensing with the circuit-breaker, the currents may be led off by suitable conductors. For some purposes, such as ringing bells, these reversed currents are used just as they come from the machine ; but if the current is required to be continuous and to flow in the same direction constantly, as it necessarily must for many purposes, an arrangement called a pole-changer or com- mutator is attached to the axis of rotation and to the terminals of the coils, which brings both currents into the line in the same direction. The commutator, one _ -^ form of which is re- \^) presented in Figure 28, is an attachment on the armature-shaft, by which the two leading- out wires are reversed at the same instant that the cur- rents are ; so that, on the well-known principle that two negatives are equivalent to an affirmative, the current reversal does not become apparent. The above remarks do not refer to machines working upon the principle of the Gramme machine, since such machines originate a constant current in one direction. Machines of the class just described may, and now Q MAGNETO-ELECTRICITY, ETC. 67 often are, provided with a Siemens armature instead of the two helices fixed upon the soft-iron cores and yoke- piece. 70. What was the first important advance made in magneto- machines after the invention of those already described ? The invention of the Siemens armature. It was pro- posed in 1857 by Dr. Werner Siemens, and consists of a 2 Fig. 29. cylindrical piece of soft iron hollowed out at two sides for the reception of insulated wire wound longitudinally or parallel to its axis. This armature is shown in Figure 29 ; No. 1 represent- ing a side view, No. 2 the coiled armature, and 3 an end view thereof. In No. 1 G shows the hollowed sides before winding. In No. 2 L L is the commutator ; H H brass bands which bind securely the bands of covered wire ; 1 1 are the axles on which the armature revolves, and K a pulley for a driving-belt. This ar- mature is fixed on bearings in a magnetic cylinder formed by the extension of the poles of the permanent or electro magnet, which are joined together by brass or copper strips. The Siemens armature is rapidly revolved within this chamber, and from its position directly between the poles of the magnet, where the magnetic field is much more intense than in that occupied by the old form of armature, much more powerful currents are produced. The terminals of the wire wound round the armature are led out of the chamber and convey the current to its desired destination. 68 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 71. Describe a machine of the second class which illustrates the second great improvement. The machine which may be regarded as the type of the second class is that of Henry Wilde, of Man- chester, England, who discovered that if the current produced by the revolving armature of a permanent magnet was made to flow through the coils of an elec- tro-magnet, a degree of magnetism much stronger than that of the original magnet, was produced by revolving the armature sufficiently fast. Having made this discovery, it then occurred to him that an electro-magnet so excited might be used to evolve a proportionately large amount of electricity. Making a machine embodying the principle, he discov- ered that such was the case. The following is a descrip- tion of the Wilde machine, as patented by him in 1867 : A very large electro-magnet, A B, of the horseshoe pattern, forms the lower and much larger part of the machine, and is fixed with its poles downward ; the yoke-piece joining the two electro-magnet cores is util- ized as a base whereon to place a series of permanent magnets, M, also having their poles downward. The permanent magnets are much smaller than the electro-magnet. Both magnets are provided with Sie- mens armatures, which are rapidly revolved simulta- neously by the same power. The armatures rotate in what is called the magnet-cylinder. This, in the upper cylinder, is formed by masses or pole-pieces of iron, m n> and in the lower by similar pole-pieces, T, attached to the poles of the magnet, and kept separate from each other by brass or copper plates, o and i ; these are bored to make a cylindrical cavity. The upper armature is rotated with a velocity of about twenty-four hundred revolutions per minute, and the current thereby obtained is directed, after passing through a commutator, to binding-screws, p and Fig. 80. The electro-magnet, M, is placed upright ; its armature is furnished with a long lever, L, and at the end of the lever is fastened a steel point, or style, p, which may be adjusted up or down by a set-screw. The strip of paper passes through the guide, g, and be- tween the grooved rollers. The steel point is adjusted immediately under the groove in the upper roller, and is on the under side of the passing paper. A spring retracts the armature when no current is pass- ing, just as in the relay or sounder. Every time the re- lay points are closed the register armature is attracted, OFFICE WIRES, FITTINGS, ETC. 217 and as the armature end of the lever goes down the style (being on the other side of the pivots, which are support- ed by set-screws) goes up, a mark is made upon the paper by the point, corresponding in length to the dura- tion of the passage of the current. The magnet is wound with silk-covered copper wire of No. 23 or 24 gauge, and is ordinarily of about four ohms resistance. Two large cells of gravity battery ought to work it well. Main-line registers are sometimes employed for lines not exceeding in length twenty or thirty miles. They must, of course, be wound with much finer wire. The register is not at present used to any great extent in America, having been superseded by the more simple sounder. In small country offices it may, however, be seen in all its glory. Had it remained in universal use it would probably by this time have developed into the ink- writing instrument, which is much used in Europe. The connections are made exactly the same as those of the sounder. 197. It is required to connect a sounder and register ivith a three-point switch, so that either can be worked by the relay ; how is it done $ We will suppose the relay, register, and sounder to be already fixed upon the table and the local battery set up. Connect one pole of the battery to one of the relay local connections, and the other relay binding-screw to the lever - point of the switch. Attach one of the other points of the switch to a register binding- post, the other to a sounder binding- post. Then run a wire from the other register-post to the remaining sounder- post, and from there to the other pole of the battery, and it is done. To work the register the switch must Fig. 81. 218 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. be turned to one point ; to work the sounder, to the other. This is shown in diagram by Figure 81. 198. What are repeaters ? Repeaters are peculiar arrangements of instruments and wires whereby the relay, sounder, or register of one circuit is caused to open and close another circuit, thus repeating or duplicating the signals sent on the first cir- cuit, by the hand of the operator working a Morse key, on to the second circuit by the upward and downward movements of the instrument armature-lever, in the same way that a relay closes the local circuit of a sound er or register. The earliest ones were so arranged that but one side had facilities to repeat ; and if the receiving operator desired to break he was dependent on the at- tendant at the station where the repeater was located to turn a switch whereby the repeating devices were trans- ferred to his circuit. This had obvious disadvantages, and many automatic repeaters have been invented which do not need the services of an attendant, as by their use either side can send, either circuit repeating into ike other at will. Repeaters are used to connect two cir- cuits together to work through which are ordinarily operated separately ; and by their use direct communica- tion has been had from Heart' s Content, Newf oundland, to San Francisco. They are also often used for connect- ing branch lines with a main line. The first repeater was used for this purpose, and was designed and put into operation at Auburn, N". Y., to repeat press news from that office to Ithaca. 199. WJiat are the repeaters which up to the present time have been invented ? The first was the one previously alluded to, and is universally known as the button-repeater. It was planned by Merritt L. Wood in September, 1846. The next was the open-circuit repeater of Charles S. Bulk- ley, devised in 1848, which enabled messages to be sent direct between New York and New Orleans Farmer Dept. Meek, OFFICE WIKES, FITTINGS, ETC. and Woodman in 1856 invented the first automatic closed circuit repeater, while after this in rapid succes- sion came the automatic repeaters of Hicks who has invented no fewer than three different forms of re- peaters Clark, Milliken, Toye, Gray, Haskins, Bun- nell, and Gerritt Smith. The last one produced was that of Catlin. All of these have their special virtues, and have each been more or less used, but only a few of them are now in operation. 200. State ivhich repeaters are now most frequently used. Wood's button-repeater, though the oldest, is still much used on account of its simplicity and the readi- ness with which it is constructed by amateurs or in offices without special facilities. It is simply a switch which is capable of being placed in either of three posi- tions. In one of these positions each line is connected, through a ground-switch, with a common ground- wire. In a second position the armature-lever of each of the sounders is interposed in the circuit of the other line so as to operate as an electro-magnetic key. The third posi- tion is but the second reversed. It needs an attendant all the time, as it can only be worked from one direction. When the receiving operator wishes to break he opens his key or makes dots, and the attendant, seeing that the sounders are not working together, turns the button, permitting the receiver to become in his turn the sender. When it is desired to work the two lines through as one it is only necessary to throw off the ground-switch. The connections are clearly shown in Figure 82. M, M' are the relays of the two circuits, S S' their sounders, B and B' the main batteries, 4 the ground- switch, E and W the east and west line- wires. When the lever, L, is in the position shown the wires are arranged as two independent circuits. To make a continuous through circuit the lever, L, is left untouched, but the ground switch, 4, is thrown off. To arrange the two circuits for repeating, the ground- switch, 4, is closed, and the lever, Z/, placed either on the plates 2 2 or 3 3. In the 220 ELECTRICITY, MAGNETISM, AND TELEGKAPHY. Fig. 82. former position the eastern line repeats into the west- ern, and in the latter position the western re- peats into the eastern circuit. The automa- tic repeaters which are now most generally used are those of Milliken y Toye, Bunnell, and Haskins. The chief aim of all of them is to give the power of break- ing, sending, and receiving to each circuit alike, and the great difficulty in the way has been to keep the arma- ture of the relay of the receiving wire quiescent, and at the same time have it so arranged that it would promptly come into action when a break was made. This has, however, been successfully accomplished in many ways.* An operator sending through a repeater must send firmly and heavily, and make long dots and correspond- ingly long dashes, because the lever of the repeating instrument requires an appreciable amount of time to make its stroke, and each repeater on a single line of communication shortens the current still more. For this reason the repeater-levers must be adjusted to a short a stroke as possible. 201. Was there not a very simple repeater devised by Edison f Yes. It is described in Pope's " Modern Practice of * A full description of nearly all the repeaters that are, or have been, in use can be found in Davis and Rae's invaluable " Hand-book of Diagrams and Connections." OFFICE WIKES, FITTINGS, ETC. 221 WEST EAST the Electric Telegraph," and also in the " Hand-book of Diagrams and Connections " already referred to, and is shown in diagram by Figure 83. It is a very conve- nient button-re- peater, has been found serviceable, and can be fitted up very quickly, as it needs no apparatus except the regular relays and sounders and a common two- point ground- switch. To set it up, the line, say from the west, is connected first with its own relay, M ; thence it passes to the point 3 of the ground-switch, and through the local points of the opposite relay to the main battery, E, and ground, G. The other line is simi- larly connected ; the main post of the ground- switch, S, is then connected with one pole of the local battery, E'. The other pole of the local battery connects with the sounder, L, passing from the second binding-screw of the sounder to the wire 1, which connects the two sets of re- lay-points with the ground. The sounder and local bat- tery form a portion of both local and main circuits. When the button-switch is turned on to the point which touches the eastern circuit the eastern circuit repeats into the western, while the western relay works the sounder, and vice versa. Fig. 83. CHAPTER XY. ADJUSTMENT AND CAKE OF TELEGRAPH INSTRUMENTS, 202. What is usually meant by the "adjustment" of a re- lay? The adjustment of a relay means the adjustment of its vibrating armature, both as regards its distance from the magnet- cores and the space through which it vibrates, or the length of its vibration. The first ad- justment is regulated by the screw working the retract- ing spring of the armature, by the screw working the advance or withdrawal of the magnet, and by the front limit-screw, which also forms the contact-point of the local circuit. The latter adjustment is made by the two limit or set screws, between which the lever plays. Ordinarily a relay should work well when adjusted as follows : With key open, or instruments cut out, fix the front limit-screw so that a moderately thick piece of letter-paper can be inserted between the armature and magnet-cores. Then screw up the back limit- screw till it is as close as possible, leaving an almost imperceptible movement to the lever. Then screw up the magnet until it is less than a sixteenth of an inch, place the instrument in circuit, and turn up the retracting spring. If the armature now sticks to the magnets turn up the spring still more ; and if, when it is turned up pretty high, the action of the magnet is still too strong, the magnet must be withdrawn a little. We have seen operators who uniformly work with a slack retracting spring and magnet turned away back ; but this is against common sense, for, to get the full ADJUSTMENT AND CAKE OF INSTRUMENTS. 223 benefit of the line current and to make the relay work quick and sharp, it is obvious that the magnet should be as close to the armature as it can be without sticking, so that it may advance sharply when the circuit is closed ; and also that the spring should be adjusted high, so that the armature shall fall back promptly when the circuit is broken. Correct adjustment is one of the never-failing signs of a good operator, and it often, especially in wet weather and on way wires, demands great skill and attention. 203. Why is it that the adjustment of the relay is very diffi- cult on some lines in wet weather ? Because in wet weather the escape of current from the line at each insulator (which even in the best-in- sulated lines is always present in some slight degree) is greatly increased and varies frequently, rendering the magnetism of the relay correspondingly uneven, being now stronger and again weaker. This is especially the case in lines where the insula- tion is defective to commence with, and on some long way circuits it has often occurred that during a rain- storm it has been totally impossible to work the wire at all, or only in sections of a few miles in length. The condition of the telegraph lines of America has been so much improved during the last ten years that such cases have now happily become rare. 204. Why is it that during wet weather on badly working wires the relay often remains still when a distant station is sending, and why is it necessary to adjust high in order to get such stations ? This is chiefly noticed on lines where the battery is divided, part of it being at one end and part at the other. As most of them are so arranged, it is a very frequent occurrence on lines of any great length. It is caused by the escape from the insulators which are between the station working and the station where the relay fails to respond. This becomes so considerable, by the aid of the wet insulators and poles, as to act the 224 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. same as if an average country ground-wire were put on ; and the current from the nearer main battery (if both batteries are equal in size) now has a circuit from the ground at the terminal station where it is located, over the line through the relays which remain still, to the escape arising from the united effect of leakage at a great many insulators at once ; and the current in this artificial circuit produces sufficient magnetism in the re- lays to hold the armatures forward when the adjusting spring is at its usual tension, even when the current from the more ojistant battery is interrupted and the line opened by the key which is being worked at the distant station. This phenomenon can occur in either direction when a battery is placed at both ends, but only in one direction when the battery is at but one end of the line; for it is obvious that if a circuit have a battery at only one end, any office, by opening a key, cuts off the current from the entire line beyond it, and the armatures of all the relays beyond must, in conse- quence, fall back. Sometimes, therefore, in hard-work- ing lines, where there is much escape during a rain-storm, the battery is taken off one end. When a relay, at its ordinary adjustment, refuses to respond to the signalling of a distant station, the spring must be adjusted higher, so as to put a greater strain on the armature, in order that it may overcome the attraction of the magnetism due to the escape. It will then respond to the breaks of the distant station. If the escape be still felt the magnet must be withdrawn a little by the back screw. 205. What is the best method of adjusting on a hard-work- ing line in wet weather f The best general way to adjust, both in wet and dry weather, is the common-sense method, which is as follows : The limit set-screws should be so adjusted that when the armature is attracted it will almost touch the mag- net-core, allowing just space enough to insert a piece of stout writing-paper between. This done, adjust the ADJUSTMENT AND CARE OF INSTRUMENTS. 225 back limit-screw up so close as to allow of the least possible motion necessary to open the local circuit. Screw up the back adjustment till the magnet is quite close to the armature ; still, however, being careful that they do not touch. This is so that all the current on the line may be utilized on the magnet. Then screw the adjusting spring up till the tension is quite strong, thus giving the armature all the chance possible to fall back every time the main circuit is opened. If breaks still do not show clear on the sounder or register, the magnet must now be screwed back a little. We may suppose the relay to be adjusted to be located at a station fifty miles from one terminal or repeating office and two hundred miles from the other. In such a case it is probable that the greater part of the business will be to and from the former ; and the best plan will be to keep the instrument so adjusted that the sending of the near repeating office conies light yet perfectly distinguishable. The call from that office, and all between it and the receiving 'station, may then be readily heard, while the heavy sending of the other terminal station and other distant stations have also a good chance to be heard. In any case, however, before opening the key in bad weather the adjustment should be pulled up, so that, if any distant station is using the line, its sending may be made manifest as the tension of the spring is increased. 206. Why does a key sometimes stick, and what should be done to remedy a sticking key ? When a key, on rising, does not break the circuit it is said to " stick." This sticking is generally caused by its platinum contacts becoming gradually burned and made rough by the repeated action of the spark which appears every time the circuit is broken, or by very small specks of metallic dust, which collect round the anvil and points. Sometimes it is occasioned by spongy or soft platinum having been used as the material for the contacts. This fuses to a certain degree every time 226 the key is opened. In either case a partial and imper- fect connection is produced between the two parts of the key, which should be completely insulated from one another when the key is opened. When sticking occurs it can usually be remedied by rubbing the points with fine emery-paper. If that does not cure it a fine file may be very carefully employed, but only until a new surface is made. Frequent use of the file should, however, be avoided. An inexperienced operator is often liable to mistake other troubles for a sticking key. Dirty relay-points will, for example, so far as the register or sounder is concerned, act in precisely the same manner, and must also be cleaned with fine emery or sand paper. Loose pivot- screws will often make trouble with a key, and should not be tolerated ; the pivot-screws should always be kept as tight as is consistent with a free and easy movement of the key. If a key has soft or spongy points there is no radical cure until the points are renewed. In such a case the only way to make the key work at all is to give the lever considerable play when work- ing it, and to clean the points frequently. Keys with soft points are now happily rare. 207. What precautions are necessary to get good work from a sounder ? First and foremost, the sounder magnet helix should have about the same resistance as the local battery. If the battery consists of two cells of the gravity form, the sounder coils should have a resistance of about four ohms. The sounder has three adjustments : one by which the play of the armature-lever is regulated, one by which the distance of the armature from the magnet- cores is regulated, and one determining the degree of tension of the retracting spring. To adjust a sounder the armature-lever is first made ADJUSTMENT AND CARE OF INSTRUMENTS. 227 to work easily and yet snugly upon its pivots, which are then locked by their set-nuts. Then the armature is fixed by the screw so that a piece of thick writing-paper can be passed between the core and the armature. The screw regulating the stroke is then brought to a suitable distance to give the proper length of stroke, after which the retracting spring is screwed up, so that when the circuit opens the lever is pulled sharply back against its back limit- screw. If it now sticks when working, the spring must be tightened ; if the spring is already tight the front limit- screw may be screwed up a little, thus bringing the armature to a point farther from the core. When a sounder gives a satisfactory sound it should be let alone. A sounder should always be screwed down to the table, which then forms a sounding-board. If a sounder has always worked well, but at length commences to stick, the adjustments should all be in- spected to see if they are tight ; if they are, the defect is probably due to residual magnetism in the cores, which may be measurably rectified by reversing the wires. Care must be taken not to break or bend the fine magnet-wires in cleaning or dusting the instrument. 208. How should a register be managed 1 The adjustments already described as belonging to the sounder are all of them in the register also. Be- sides these we find others viz., that by which the rollers which draw the paper along are regulated, and the adjustment of the stylus, or pen. The length of stroke, distance from cores, and tension of retracting spring are adjusted exactly in the same way as in the sounder. To fix the pen-point correctly, first adjust the arma- ture, screwing it to the proper distance from the core, then hold it there by closing the local circuit, at the same time letting the register run, and screw up the 228 ELECTRICITY, MAGNETISM, AND TELEGKAPHY. pen-point until it makes a mark on the paper which is plainly seen, then tighten up the set-nut. The mark should only be deep enough to be distinct. The limit-screw regulating the stroke must allow the pen to just clear the paper when the circuit opens. If the paper runs crooked one end of the rollers presses tighter than the other, and the end that carries the paper fastest must be unscrewed a little. When the armature clips or sticks the relay needs adjusting. The lever should never be allowed to work loose in its pivots, as that would cause irregular dashes, sometimes too deep, and at other times not deep enough. The paper guides must be just wide enough to allow the paper to pass through easily. If the register-lever does not respond to the movements of the relay there is some defect in the local circuit very likely a loose con- nection, a weak battery, or dirty relay-points. A register should be kept clean, but never taken to pieces out of curiosity ; ninety -.nine troubles out of a hundred met with by young operators are due to un- necessary tinkering with the instruments. 209. When and how should a ground-wire at a ivay-station be used ? A ground- wire should be used on a telegraph line only when the circuit is found to be open. It should then be used first as a testing wire, to ascertain on which side the line is open, and afterward put on, and left on, at the side of the instruments on which the trouble is found to be. When used as a testing ground it must be touched to both of the leading-in wires. If when touching either side it cailses the relay to attract its armature, that is the side on which the trouble is, and that is the side on which it must be temporarily left ; thus cutting that station in on the unbroken frag- ment of the line to the terminal station. When the line is in working order the ground- wire should be left untouched. It is too much the practice among operators at w r ay-offices to put on the ground- ADJUSTMENT AND CAKE OF INSTRUMENTS. 229 wire for any or no cause, but it is a habit that cannot be too strongly reprehended. 210. Give some hints on the general care of a way telegraph station. Operators at way telegraph stations are frequently young and inexperienced. A few general hints may, therefore, not be out of place here. After lightning-storms the arrester should always be examined to see if any damage to it has ensued. If so it should be fixed at once. If that kind of lightning- arrester is used in which a thin sheet of paper separates the ground from the line plate, the paper ought to be renewed, whether damage is apparent or not. In bad weather the relay -spring should always be pulled up before the key is opened, to ascertain whether ;any one is using the line. The motion of the relay armature-lever should be kept as small as possible, and the local points of the relay kept clean. The armatures, both of the relay and sounder, or register, must never be suffered to touch the cores of the magnet. Every binding-screw about the office ought to be tried occasionally to see if it is tight, as the good working of the entire line often depends on this. Every loose connection introduces a high resistance into the circuit of which it forms a part. When the instruments are working satisfactorily they should be left strictly untouched. If the instrument table be covered with an oil-cloth, a space should in all cases be cut clear for the key, so that the latter will rest on the table. Many escapes have been traced to an oil-cloth table-cover. All pivots should be just tight enough to prevent lateral play. This applies both to keys and sounders, or registers. If an ordinary Daniell battery with porous cups be used for a local, it should be cleaned at least once a month. The zinc should not be allowed to touch the 230 ELECTKICITY, MAGNETISM, AND TELEGRAPHY. bottom of the porous cup. In cleaning such a battery, half of the clear liquid may be poured from the porous cup, and, after the cup is emptied and cleaned, poured back to form the zinc solution. If all the liquid is emptied it will be some time before the battery works up to its full strength again. If a gravity battery be used the cleaning does not need to be nearly so frequent. CHAPTER XYI. CIRCUIT FAULTS AND THEIR LOCALIZATION. 211. What are the faults most likely to occur on a Morse telegraph line, and how are they most frequently caused $ Open wire or complete disconnection, partial or oc- casional disconnection, dead earth, swinging or occa- sional earth, escapes, crosses, swinging crosses, wea- ther-crosses, and defective ground at the terminals. Complete disconnection, familiarly called a u break," occurs when the circuit is open at any point, and till repaired puts an entire stop to communication. It may be caused in a variety of ways. The terminal ground- wire may be broken or cut, the battery may be defective, a key may be, and often is, left open, the line- wire may be broken this may occur in many ways or a wire may be accidentally pulled out of a binding- post in a station. Partial disconnection occurs when the resistance of a circuit is greatly increased, and is also caused in a va- riety of ways. A rusty or otherwise bad joint on the line -wire, a wire loose in a screw- post, an imperfect terminal ground- wire, or a very bad main battery will cause this trouble ; and it manifests itself by causing the instruments in circuit to work in a feeble and irregu- lar manner. Dead earth, in American phraseology, is called a " ground." It occurs when the line at any point touches the earth, or some good conductor in contact with the earth. When the resistance of such a fault is very low indeed it practically divides the line in two parts, each terminal station working on its own battery to the fault. 231 232 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. If only one station has a main battery the relays be- tween that station and the fault will work stronger than usual, because the total resistance of the circuit is de- creased ; while the instruments beyond the fault will be apparently out of circuit, and will act as if the line were open. If there is a battery at both ends the stations on each side of the ground will be able to work, but those on one side will be unable to communicate with those on the other. This trouble may be caused by contact with a wire running to earth, or by the line- wire lying across a tree or roof ; but is oftenest caused by operators in way-offices, who attach a ground- wire to the line for no sufficient reason, and forget to remove it. A swinging or occasional earth is of the same charac- ter as the preceding fault, with the exception that in- stead of being a permanent interruption it comes on only at more or less regular, intervals. It is a serious fault, and often difficult of localization, as such a ground fre- quently does not stay in long enough to enable it to be tested. It is usually caused by the line-wire swinging, under the influence of the wind, against some conducting substance in contact with the earth, such as a guy-wire. An escape is also of the same general character as a ground. The difference is only one of degree ; for while, in the case of a dead ground, nearly all the working current leaves the line at the fault, only a portion does so in the case of an escape. It is, in fact, simply a branch circuit of comparatively low resistance, by which a certain portion of the current of electricity escapes or leaks to the earth at the wrong place, thus weakening the line current beyond the fault, and strengthening it between the main battery and the fault. It is caused by defective insulation of the line, instruments, or battery, or by contact with an imperfect conductor, such, for ex- ample, as a tree. A cross occurs when two wires come into contact, and is generally caused by the wind or by swaying branches of trees. When two wires are crossed a message sent on CIRCUIT FAULTS AND THEIR LOCALIZATION. 233 one is repeated on the other, so that neither one can be worked without interfering with the other. In such cases the means adopted is to open one wire on each side of the cross until the cross can be cleared. A swinging or intermittent cross occurs where one or more wires are too slack between the poles or supports, so that they are often blown one against the other. This trouble is an annoying one, as it is very difficult to locate, for tlie same reason as that given in describing the intermittent ground. It is of frequent occurrence among the short house-top lines of cities. A weather -cross sometimes occurs in wet weather from defective insulation. In such cases the moisture on the insulators and cross-arms enables the electricity to escape or leak from one wire to another. The evil effect of this trouble is much lessened by earth- wiring the poles. Defective ground terminals act as if all the wires run- ning to ground at the same place were crossed together. It is frequently caused by the severance of a gas-pipe which is used for the common earth connection. It is also sometimes caused by such a pipe being an imper- fect conductor, or by the connection of the wire to the pipe being imperfectly made. 212. How does a disconnection, or break, make itself appa- rent, and how is it to be tested for $ If the line is broken at any point the armatures of all the relays at once fall back, and no work can be done until the line is repaired. If the trouble is caused by an open key the operator at that station will probably sooner or later discover it and close it. But if the line- wire is broken at any point a lineman will have to be sent out as soon as the trouble is located between two stations. As soon as the circuit is discovered to be open the operator at each way-station should connect his ground- wire first with one side of the instrument and then with the other. If connecting it on either side closes the 234 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. circuit it shows that the trouble is on that side, because on such connection the break is cut off and the line virtually terminated at the ground- wire, cutting the instruments in. In Figure 84, which represents a line with*four sta- D Fig/84. tions, A, B, C, and D, the wire is supposed to be broken at F. When B and C attach their ground- wires, as shown and described, it will be seen that two distinct circuits are formed : A then being able to work with B, and C with D. The fault is thus shown to be between B and C. / If the application of the ground- wire fails to close the circuit on either side, the trouble is either in the office, or the ground-wire that the operator is testing with is defective, or some other office has already closed the circuit by the connection of a ground- wire. Hence an operator should always, after testing with the ground- wire, make sure by a careful search that the trouble is not in his own office. As soon as any office discovers on which side the line is open its duty is to report the facts to the remaining terminal station, and from it receive instructions whether or not to keep the ground- wire on. Failing such instruc- tions, a good plan is, if there are many stations between the way and terminal station on the complete side, to keep the ground on and frequently remove it tempo- rarily to see if the circuit has closed ; but if the said way-station is near to the terminal station on the side which is unbroken, it is better to keep the ground off, because the greater number of stations are beyond ; and CIRCUIT FAULTS AKD THEIR LOCALIZATION. 235 when any one of the way-stations has a message to send it can then connect a ground- wire and send it. A break is often tested for with a galvanometer, the general principle of such a test being the comparison of the known insulation resistance when the line is com- plete with the insulation resistance from the terminal stations to the broken ends. It is, of course, a matter of absolute necessity to test for a break in a submarine cable in this or in a similar manner. 213. What method may be adopted on short city lines of special systems, such as American District or stock-printer lines $ The quickest and most satisfactory way is to put on to the broken line a battery of sufficient strength, and then have an inspector or lineman go from station to sta- tion, grounding each instrument for an instant as he goes along, until he reaches an instrument which, when grounded on the side away from the office, does not work, or on which, if a light battery is used, he can taste nothing. He has then passed the break, and, retracing his steps to the last station, he there attaches a ground, leaving it connected until the break thus located be- tween two stations can be repaired. 214. What are the effects of an intermittent disconnection, and how may such a trouble be located 1 An intermittent disconnection is frequently by inspec- tors and linemen called a swinging break. It often oc- curs from a loose connection, a hook-joint which is al- ternately tightened and loosened by the wind, or, in the case of covered wire, it may be caused by the conductor being broken inside the covering. On ordinary lines it will occasionally make itself apparent by the sound of a dot on the sounder, and it sometimes proves very annoy- ing to operators by opening the circuit for an instant while a message is being sent. On printing circuits it shows by the instruments missing a beat, and then " thro wing out," causing the printed slip to write nonsense, while on District circuits and the like a long 236 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. dash is produced on the register-tape and the bell rings. The most satisfactory way, and the only method to be depended on, for the location of a trouble of this charac- ter, is to cross-connect the defective wire with another at an intermediate station. This method may be adopted on either long or short lines, and is as follows : It is better, for the sake of celerity, to make two cross-con- nections at once. For example, we will suppose two parallel lines, No. 1 and No. 2, both running into sta- tions A, B, C, and D, and that No. 1 has an intermittent break. At the point where the wires leave station A interchange them so that No. 1 inside the office connects with No. 2 outside, and vice versa. Duplicate the change also at station C. No. 1 is then temporarily No. 1 from its initial ground at A to the window, No. 2 from there to the switch at station C, and again No. 1 from C to the terminal ground. No. 2 is, of course, correspondingly changed. Suppose now the fault is between B and C on No. 1 ; the trouble will be found to have moved over to No. 2 at the terminal stations A and D, because that portion of No. 1 in which the fault is located has by cross-connection been transferred to No. 2 circuit. When this is ascertained the w^ires at the distant sta- tion C may be straightened and the cross-connection changed to station B. Supposing still that the fault is between B and C, it will, the next time it comes in, be found to have changed back to No. 1, because that sec- tion of line has been transferred back again to No. 1. Now, when thus located between two stations, it can generally be easily found by a lineman. If it is, how- ever, still troublesome, and cannot be found, the lineman will have to cross-connect between stations. 215. How should a partial disconnection causing an ex- tremely high resistance be tested for ? The method of cross-connection described in the an- swer immediately prior to this is the most satisfactory course to pursue when only the ordinary telegraph in- CIKCUIT FAULTS AND THEIK LOCALIZATION. 237 struments are at hand. If, however, a good galvano- meter and rheostat can be readily obtained, a quicker way is to employ them, especially if the fault is con- stant. It will be of great assistance to the tester, in this operation, if the resistance of the line at ordinary times is known ; but even if it is not it can usually be calcu- lated. First measure the suspected line, and see what the resistance is with the fault in ; then have a good ground put on about half way to the terminal, and measure again. If the high resistance is still in take off the ground and attach it nearer, and measuTe again ; if, on the contrary, by grounding the first time the high re- sistance is taken out, the trouble is beyond, and the ground must be attached at a more distant point. By continuing the measurements the trouble can soon be localized between two stations. 216. How should a ground or dead earth be tested for ? The method in general use is to call up all the sta- tions, one after another, and see what ones can be raised. If, for instance, a line has twenty stations and the most distant one that can be raised is the tenth, the presump- tion is that the ground is beyond that station. This is used where there is only one wire. If there are two or more wires the testing office can call the way -offices in rotation on No. 2 and direct them to open No. 1. So long as the opening is not perceptible at the testing sta- tion the ground is between the station opening the key and the testing station ; but as soon as the opening of the key at a station is perceived at the testing station the ground is passed and is then beyond the station opening. If a galvanometer is used and the normal re- sistance of the line is known, the distance of the ground from the testing station can usually be calculated from the measured resistance with the fault in. A dead ground is very often caused by lightning burning out the paper between the plates or fusing the points of a lightning-arrester. On a very short line having many stations or instruments, such as a stock-printer line, the 238 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. quickest plan to locate a ground is to go from station to station. The instruments on the battery side of the ground will be observed to work stronger than usual, while those beyond the ground will work much weaker or not at all. 217. How does an escape manifest itself, and how is it to be tested for ? An escape is manifested much in the same manner as a ground, but its effects are not so pronounced. Stations on different sides of an escape, under ordinary condi- tions have to adjust high to work with each other. It is sometimes found advisable to take off the battery from one end of the line, and let the magnetism in the relay at the receiving end be produced entirely by the influ- ence of the battery of the sending end ; because even though a portion of the current from that battery is lost at the escape, the portion which does arrive at the re- ceiving station beyond the escape is necessarily affected by the key of the sender, since whenever that key is opened all the current is taken from the line. When this is done, however, the receiver must not break, as if he did it would not be noticed by the sender, the circuit being, in any event, partially completed by the escape. Figure 85 represents a line with a main battery, E, at D *+-\ + 5~E .1 Fig. 85. each terminal station, and a fault, consisting of an es- cape, F, between the two stations B and C ; the terminal stations are indicated by the letters A and D. To test for this escape the stations of the faulty wire must be called up, one after another, either by means of a second wire or by the faulty wire itself, and told to open key for a minute or so. When the stations beyond CIKCUIT FAULTS AND THEIE LOCALIZATION. 239 the escape open a current will be still on the line from the testing station to the escape, and will affect the relay of the tester ; but as soon as the first station on the test- ing- office side of the escape opens the current will cease and the tester's relay will fall back. Thus, in the figure, supposing A to be the testing station, when C opens key there is still a current on the line from the battery E through the escape to ground ; but when B opens there is no current, showing the escape to be between B and C. 218. How is a cross or contact between two wires to be local- ized ? When a cross occurs between two wires it is obvious that the two wires will be reduced to one, if one of them is opened on both sides of the cross, or if one is opened on one side of the cross and the other on the other side of the cross. Therefore to test for a cross, say between two wires, No. 1 and No. 2, the most distant station that can be raised must be called up and instructed to open one wire No. 1, for example and make dots on the other. The testing office will open No. 2, and if the dots of the distant station come on No. 1 at the testing sta- tion the wires are obviously crossed. Now instruct the distant station to leave No. 1 open ; then call up the next distant station, direct it to open No. 1 and send dots on No. 2, opening No. 2 at your own station. If the cross is still between the testing office and the dis- tant station the dots will still come on No. 1 ; but if the cross is between the station now sending dots and the preceding one both wires will now be open at the test- ing station. The cross is thus readily located. The test- ing operator or circuit manager must call up and test with station after station in regular succession until the cross is located. 219. How must an intermittent ground or cross be tested /or? The only reliable way to test for and locate an inter- mittent ground is to cross-connect the faulty wire with a perfect one and wait until the next time the fault NIVERSITY 240 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. shows, observing then whether it is transferred to the second wire with the cross-connected section of line, the whole process being in every respect similar to that of testing for an intermittent disconnection described in question 214. The same remarks apply generally to intermittent troubles of any character. 220, How does a weather-cross affect telegraph lines, and how and ivhen must it be tested for ? A so-called weather-cross shows a similar effect on a line of telegraph to that caused by a cross, but in a much less degree. It must be tested for in the same way, and the testing must be done while the wet weather contin- ues, as it is only then that such a fault is sufficiently apparent to be tested for. 221. When a defective ground connection is suspected how may it be tested for and discovered V When such a fault is suspected it may often be found by searching, without testing at all. If it cannot be readily found or proved to exist by search, it can be tested for by several methods. The first is : If more than two lines run to the same earth, first take off all the lines except two, then open one of these two and put a considerable battery on the other. If the ground is very defective a large share of the current will leak past it and make itself manifest to the taste at the end of the opened wire. A second way is given by Haskins, and is as follows: " Connect a wire to .the suspected ground wire between the battery terminal and ground, or, if you have no battery, to the ground -wire between the last instrument and the ground ; connect the other end of the wire to a galvanometer, connecting the other post of your galvanometer to a good earth. If the ground is really defective the current will divide where the second wire is attached and will go to ground through the galvanometer, deflecting the needle." Haskins also gives the following method of measuring the resistance of the defective ground : Measure any two lines to earth. CIRCUIT FAULTS AND THEIK LOCALIZATION. 241 through the suspected wire, then disconnect the two wires from the ground, connect them in metallic circuit, and measure the loop so made. If the sum of the two resistances measured to ground exceed the resistance of the metallic loop, then the excess, divided by two, will give the resistance of the defective ground. Dept. Mech CHAPTER XVII. MULTIPLE TELEGRAPHS. 222. What is meant by the term multiple telegraph ? The term embraces all the various methods of simul- taneously sending two or more communications or mes- sages, either in the same direction or in opposite direc- tions, over a single line. It includes the duplex, quad- ruplex, the various multiplex methods which have been introduced or projected within the last ten years, and the harmonic systems of telegraphy, introduced by Yar- ley, Gray, Lacour, and others. 223. What is the duplex f It is simply an ordinary telegraph, so constructed and arranged that two communications may at the same time be transmitted intelligently over the same wire. Usage has applied the name only to systems wherein the two communications are transmitted in opposite directions. There are two conditions necessary in duplex tele- graphy namely, the relay of either station must not respond to its own key, while it must readily respond to those currents transmitted by the key at the distant sta- tion, and the currents so coming in at either end from the distant station must always have an uninterrupted path to the ground. Many inventions have been pro- duced in duplex telegraphy, but the greater number of those in use at the present time operate on the differ- ential principle, in which the outgoing current divides, one part passing through one coil of a differential relay to ground through a rheostat, and operating to hold the armature still, the other part going through the other MULTIPLE TELEGRAPHS. 243 coil of the relay to the line to operate the relay at the distant station. A differential relay is one which is wound with two separate coils in different directions. The effect when a current is passed through it is that the current from the home battery is equal in both coils, and, they being wound in different and opposite directions, the magnetic effect caused by the current in one direc- tion in the relay will be neutralized by the current in the other direction, and so the effect of the outgoing current will be nothing ; but when the current in the coil leading to line is reinforced by a current from the distant sta- tion, it overbalances the current in the other coil and gives the signal. The only other popular and much- used system of duplex is what is known as the bridge duplex. In it the receiving instrument is placed in the cross -wire of a Wheatstone bridge, and the connections are arranged in accordance with that well-known prin- ciple. The success of both the differential and bridge duplexes is due to the improvements made by Mr. Joseph B. Stearns. 224. Give a brief history of the duplex, naming its successive improvers and inventors. The first to broach the idea of using one wire for the simultaneous transmission of two messages was Mr. Moses G. Farmer about 1852. Dr. Gintl, director of the Austrian State Telegraphs, was, however, in 1853 inventor of a practical duplex system, which was the parent stem of the present differential systems. He used a differen- tial relay, of which one coil was traversed by the line current, and the other by the current of a local equating battery of opposite polarity, the combined effect being to hold the armature of the home relay still, and thus subject to the action of the current coming from the dis- tant station. It was very rudimentary, and was in rapid succession followed by the duplex systems and improve- ments of Frischen in 1854 ; Gintl, in a chemical duplex, which was practically operated in 1854 between Vienna and Linz; Nystrom, of Sweden, in 1856, whose princi- 244 ELECTEICITY, MAGNETISM, AND TELEGRAPHY. pal improvement was to maintain the connection between the line and earth always unbroken by means of a cir- cuit-preserving key ; Mr. W. H. Preece, of England, in 1855 and 1856 ; Siemens and Halske's two-relay method ; Zur Nedden in 1855, and Farmer in 1858. All of these different improvements, however, fell flat, chiefly because the time for them had not arrived, and the science of telegraphy was not developed to such an extent as to require a satisfactory system of duplex telegraphy. Hence all these methods were looked upon merely as electrical curiosities. In 1863 the interest in this branch of telegraphy seemed to revive, and Maron, a Prussian telegraph inspector, effected another improvement by which the receiving instrument was placed where it would not be acted upon by outgoing currents. Fris- chen also, in 1863, improved his former method. In 1868 Mr. Joseph B. Stearns, of Boston, commenced a series of experiments with the duplex of Siemens and Halske, and was soon so successful that duplex telegraphy, which had now become a necessity, was roused from the torpor which had .hitherto crippled it, and was rapidly brought into general use. He applied a transmitter in a local circuit instead -of the old key, and caused it to make the contact of the battery with the line before the interruption of the contact between the line and the ground. He made this transmitter act also as a sounder, so that the -American operator, accustomed to hear his own sending, could be thus accommodated. He subse- quently connected a condenser to the rheostat, forming an artificial line, and thus balanced the static charge which came from the line when the line was changed from bat- tery to ground. Mr. Stearns also introduced his trans- mitter and condenser into the bridge system, where the receiving instrument is placed in the cross-wire of a sys- tem of circuits and resistances, arranged at each station on the plan of the well-known Wheatstone bridge. The receiving instrument is thus placed beyond the range of electrical impulses originating at its own station, while MULTIPLE TELEGRAPHS. 245 free to respond to those caused by the distant station. This is widely used and known universally as the bridge duplex. The success of Mr. Stearns spurred up many inventors, and duplex telegraphs, each having features more or less meritorious, were brought out by the follow- ing well-known electricians : Gerritt Smith ; Vaes, of Rotterdam ; G. K. Winter, of India ; George D' Inf re- ville, J. C. Wilson, C. H. Haskins, T. A. Edison, and others. Duplex telegraphs are still being produced, although the quadruplex has greatly diminished their importance. 225. Give a short description of the entire principle of the Stearns differential duplex. The differential relay, as heretofore explained, is a re- lay the magnets of which are wound with two separate wires of equal length and size, and consequently of equal resistance. Such a relay is employed ; and the wire from the main battery, which is controlled by the transmitter, is connected with the leading-in wire of one coil, and with the leading-out wire of the other coil, so that when by the action of the transmitter the battery is thrown on to the main wire of the relay, the current circulates round the soft-iron core in both directions at once, and the magnetic result in the core is consequently nothing, so long as the home current only is employed. One of the wires leading from this relay is now connected to the line- wire, and the outer end of the other is con- nected to a rheostat or resistance-coil of approximately the same resistance as the line. It will be observed, therefore, that the respective differential circuits of the relay are both extended, the one through a long line to earth, the other through a resistance to earth. It was one of the old difficulties that when the contact of the line to earth was interrupted a momentary break occurred before contact with the battery was made ; Mr. Stearns so arranged his transmitter that the contact of the battery was made before that of the line with the earth was broken, much as Nystrom had done in 1856. 246 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. The transmitter is operated by a local circuit and an ordinary Morse key, and its entire office is to alternately pat the line to battery and ground.* It was found that when the battery was connected to the line, the line became statically charged, and when it was put to earth this charge returned through the relay, causing it to give a "kick." Stearns saw that all the conditions of a line of telegraph were not fulfilled by his balancing resistance-coil, and he accordingly devised the attachment of a condenser around the rheostat or resist- ance-coil which formed the artificial or balancing line. This added the missing feature, electro-static capacity, with the result that when the line was charged the con- denser connected to the artificial line was also charged, and when the line discharged through one wire of the relay the condenser discharged through the opposite wire, thus balanc- ing the forces and neutralizing the "kick." Figure 86 is a theoretical dia- gram of one sta- tion, arranged for duplex transmis- sion, with the local connections omit- ted. T is the trans- mitter, operated by a local battery and key, K, and con- necting with the relay, R ; this is wound differentially, the wire leading from the transmitter dividing at the point H, one division traversing the relay in one direc- tion and leading to line B, and the other passing through the relay in the opposite direction, and through a wire, A, and rheostat, X, to ground. The transmitter is also grounded by a wire extending from its lever to the Fig. 86. * The invention of the transmitter is now ascribed to Farmer. MULTIPLE TELEGRAPHS. 247 ground- wire. The condenser, I, is shown connected as a shunt to the rheostat, and is united on one side to the wire A at a point between the relay and rheostat, and on the other side to earth. The differential relay, being, as we have described, ir- responsive to the impulses of the transmitter at its own station, yields readily to those sent from the distant sta- tion, because the currents passing through the line-coil of the relay are reinforced by the current coming from the distant point, and thereby predominate over that part of the current which passes through the artificial line ; magnetism in the relay -core ensues, and the signals are produced. 226. Give a general description of the bridge duplex. The bridge duplex is simply an arrangement of cir- cuits, in which the receiving relay is placed in the cross- wire of a Wheatstone bridge or balance. It is well known that the Wheatstone bridge is usually repre- sented by a diamond- shaped parallelogram, with two of the opposite corners connected respectively to the two opposite poles of a battery ; the other two opposite corners being connected by a cross-wire having a gal- vanometer in circuit. In such an arrangement of circuits no current passes through the cross-wire, provided the resistances of the opposite circuits on each side are either equal, or are in the same ratio, one to the other. It is, of course, immaterial what form the arrangement of the circuits really is in, if the connections are sub- stantially as indicated here. The foregoing principle is utilized in the bridge du- plex. Figure 87 shows in diagram the theoretical ar- rangement of the bridge duplex. The battery is con- nected through the transmitter, K (which in practice is similar to that of the differential duplex), to the point, H, where the circuits diverge to form the arms of the bridge ; between this point and the cross-wire, on each side, are placed adjustable resistances, A and B, thus forming the first two arms of the bridge ; the line L to 248 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. the distant station, and there to earth, is the third arm, while a rheostat, R, looped by a condenser, C, is the fourth arm. The relay, M, is placed in the cross or bridge wire. Y and W are small resistances placed in the cir- cuit to prevent any short-circuiting of the battery, and also to avoid variation of resistance when the line is changed from battery to ground, or mce versa. The four resistances are adjusted to a suitable ratio, so that the relay does not respond at all to the outgoing current, while it must respond to the incoming current, since a certain portion of that current must necessarily pass through it to earth. The condenser in this system is adopted for the same reason as in the differential sys- tem namely, to counteract the effect of the electro-static discharge from the line by a similar one in the opposite direction from the condenser. The great advantage of the bridge is that it can be readily used with any character of apparatus, from a relay to a Thomson galvanometer. It is also less likely to suffer injury from lightning than is the differential. Ordinarily for long circuits the differential is to be MULTIPLE TELEGRAPHS. 249 preferred, because with a given amount of battery a stronger working current and a greater magnetic force is developed in the receiving instrument. 227. What has been done towards duplicate transmission in the same direction 1 The first attempts in this direction were made in 1855 by Dr. J. B. Stark, of Vienna, and by Siemens, of Ger- many ; these were shortly after succeeded by Kramer, and subsequently by several others. None of these sys- tems was ever brought to practical application, although all were most ingenious and beautiful. A description of the method of Stark will suffice, as showing the general tendency of all. Two keys are, of course, required at the sending station, and two receiving relays at the receiving station. Four conditions are therefore to be provided for namely, 1st, when No. 1 key is closed and the other open ; 2d, both keys closed ; 3d, No. 2 key open and No. 1 closed ; and, 4th, both keys open. Dr. Stark accomplished this by sending with key No. 1 a comparatively weak current, and with No. 2 key a stronger current, while when both keys were closed the combined currents were sent ; finally, when both keys were open no current was on the line. He ar- ranged at the receiving station two relays, so constructed that when the weaker current was sent one relay would respond, and when the key sending the stronger current was depressed the other relay would respond ; while w r hen both keys were operated both relays would re- spond. This was effected by adjusting the relay work- ing with the strong current with a retracting spring of high tension, so that its armature would not move with the weaker current. When, however, the other key was depressed, the armature of the relay moved, and not only closed the circuit of its own register or sounder, but also closed the circuit of another or auxiliary bat- tery, causing a current to circulate round the coils of the first relay which is differential but in an opposite direc- tion to that of the line current; the armature of that 250 ELECTKICITY, MAGNETISM, AND TELEGRAPHY. relay is thus held quiescent. When both keys are ope- rated the current passing through the coils of the first relay, or that responding to the weak current, is strong enough to overcome the local current in its other coil, arid it also responds. Serious difficulties developed themselves in this system, as in others of the same class ; and not until the practi- cal introduction of the Stearns improvements on the du- plex was this idea made thoroughly practical. 228. What is the quadruplex ? The quadruplex is the name given to the apparatus and method whereby four messages may be transmitted upon one wire simultaneously, two in one direction and two in the other. 229. How far back does the idea of a quadruplex date, and to whom is its first conception due ? It dates back to 1855, when Stark, while experiment- ing on the problem of double transmission in the same direction, saw that upon the successful solution of that problem depended that of the greater problem of quad- ruplex telegraphy. His description of his proposed method of simultaneous transmission in the same direc- tion concludes with the following memorable words : " With the method of double transmission in the same direction we may also combine that of counter or oppo- site transmission ; and hence arises the possibility of simultaneously exchanging four messages upon one wire between two stations, which will, however, hardly find any application in practice." Dr. J. Bosscha, Jr., of Leyden, also, about the same time foresaw the ulti- mate result of a successful system of double trans- mission in the same direction, and in a paper read before the Royal Academy of Sciences in Holland, in 1855, after describing his own method for the accomplishment of that feat, he proceeded to outline a method of achiev- ing the greater result. He simply proposed to add to his own system the duplex of Siemens and Halske, or of Frischen. It is very evident, therefore, that both of MULTIPLE TELEGKAPHS. 251 these inventors recognized the fact that quadruplex tele- graphy depended entirely upon a successful system for double transmission in the same direction. 230. What is the origin and principle of the American quad- ruplex $ It originated in experiments made in 1874 by Thomas A. Edison, in association with George B. Fresco tt, with a- view of improving the Stearns duplex. While engaged in this work Mr. Edison devised a new method of double transmission in the same direction, which was more practical than any of its predecessors, and at the same time differed essentially from them. His method was, like the discovery of America, simple enough when known, and consisted in combining the system of tele- graphy known as the double-current system, wherein the telegraphic signals are transmitted by rapidly re- versing the poles of a battery which is always kept on the line, so that the current is constantly alternating in direction from positive to negative, and vice versa, with the single- current system, wherein transmission is ac- complished by breaking and closing of the circuit, but in this case the current is simply made to increase and decrease. Th*us two distinct qualities of electricity > direction or polarity, and strength, are utilized, and an entirely new method of double transmission in the same direction was the result. As foreseen by Stark and Bosscha, it was now an easy matter to apply to this new method the Stearns duplex, or indeed any other practical duplex ; which was accordingly done, giving to the world the far-famed quadruplex. It was ascertained by practical experiment that the bridge duplex was better adapted to the conditions necessary for success than the differential, and the bridge was therefore employed with the earlier com- bined systems. In practice two transmitting instru- ments were set up at each end of the line, both worked by an ordinary Morse key, opening and closing a local battery circuit. One transmitter, the one nearer to the 252 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. line, operated simply as a pole-changer without regard to the strength of battery used. The other operated, when depressed, to add to the ordinary battery about three times as many cells as it would usually have, so as to increase the strength of current correspondingly, irre- spective of the polarity. A certain amount of battery was to be always in circuit. These transmitters were placed in the circuit of the wire leading from the battery to the bridge. In the cross- wire of the bridge, at each end of the line, were placed two relays : one a polarized relay, responding only to the sending of transmitter No. 1 at the opposite end, or the pole -changer ; and the other a relay with a neutral or non-magnetic armature, which responded only to the sending of the transmitter JN"o. 2, which increased or decreased the battery. By the use of this apparatus it was made possible to send two messages from each terminal station at the same time, and consequently to receive at both stations an equal number. An old annoyance, however, showed itself here. The moment of change of polarity, when the polarized relay was being operated, would affect the neutral relay, causing it, if occurring at the same time that the neutral armature was attracted, to make a false break. To remedy this defect Edison caused the armature-lever of his neutral relay to make contact on its back limit- stop, closing a local circuit which included an electro- magnet. This electro-magnet in turn closes the sounder circuit by making contact on its back stop. By thus interposing a local circuit the interval of non-magne- tism was made too brief to affect the sounder. He also incorporated an additional electro-magnet and a condenser, looping a rheostat placed in the bridge- wire, to overcome the effects of the static discharge upon the neutral relay. These devices were, how- ever, cumbersome, and not always effectual, and, though the quadruplex was at this time a tolerable success, it left much room for improvement by subse- quent inventors. MULTIPLE TELEGRAPHS. 253 231. What changes and improvements have been made in the quadruplex since its introduction $ The changes in the working arrangement of the quad- ruplex have been numerous and important ; and although many of them have been the result of careful and pains- taking thought and exhaustive experiment, curiously enough, at the present time, after a fair trial of the nu- merous modifications, the entire system in its essential features is much the same as when first made public. The improvements referred to were, of course, made with a view of simplifying the apparatus and arrange- ment, and of obviating certain faults which had showed themselves. In place of the bridge it was found possi- ble to substitute the differential- circuit arrangement. A compact double-current transmitter was devised, and certain receiving instruments were brought into use, which, while comprising features of great novelty and ingenuity, unfortunately introduced the element of com- plication. The new double -current transmitters have been made extremely simple, and yet capable of the most accurate adjustments, so that the current of one polarity does not cease till that of the opposite polarity commences to flow, while at the same time the time that the battery is placed on short circuit is reduced to an infinitesimal period. The receiving relays were, as already indicated, some- what complicated, a polarized relay replacing the neu- tral relay of Edison. This was so arranged with contact- levers that at all times when the entire force of the batteries was on the line its local circuit was opened, because the armature was either drawn to its full ex- tent in one direction or the other, in either case open- ing the local circuit. When, however, the battery cur- rent on the line was decreased or withdrawn by the de- pression of the proper key, the armature, not being so forcibly attracted, would stay in the centre, being held there by its contact-levers, at the same time closing the sounder circuit. The other relay was, of course, 254 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. also polarized, and responded to the movements of the double-current transmitter only, closing its local sounder circuit only when its armature was drawn to one particular side by a current of definite direction, whether that current be strong or weak. Thus both re- lays were by this plan polarized, one closing its local circuit when drawn to one side and opening it when drawn to the other side, and the other closing its cir- cuit only when a weak current was on the line, and breaking it the moment a strong current was trans- mitted. The principal defect in the original quadru- plex namely, that of allowing the neutral relay to make a false break at the moment when the direction of the current changed was thus overcome. Subsequently it was ascertained that a small neutral relay with short cores was capable of being reversed with sufficient rapidity to answer every requirement, and such a relay was then made to replace the double-tongued polarized relay, thus bringing the quadruplex back almost to its original form. The usual arrangement of the quadruplex as now operated includes the neutral relay, and has a con- denser between the main and artificial line. The differ- ential system is also preserved. In New York dynamo-electric currents are used ; and in conjunction with them it has been found necessary to employ an entirely novel key system, the ordinary quadruplex key system not being suitable. Probably the longest circuit in the world working quadruplex all the way through is that between New York and North Sydney, C. B., via Worcester, Port- land, and Bangor ; a repeater being in circuit at the latter place, the entire distance being about twelve hun- dred miles, and the line built of No. 4 galvanized iron wire. 232. What is the electro-harmonic system of telegraphy ? It is a telegraphic system based upon the facts that musical tones produced by the vibration of an electro- MULTIPLE TELEGRAPHS. 255 toine or circuit-breaker may be transmitted through, a telegraphic circuit, and reproduced at the other end of the line in tones of like pitch, by the vibrations of suit- able armatures ; and that by employing a set of circuit interrupters or changers, each acting by rapid vibration to produce a distinct musical tone of a pitch different from the others, and transmitting the said tones, suc- cessively or simultaneously, over a single circuit com- mon to all the circuit-breakers, and through a series of electro-magnets fitted, instead of armatures, with steel ribbons rigidly fixed at one end and provided with turning- screws at the other, so as to give them the proper tension, each of these ribbons being tuned to give out the same note as its corresponding circuit inter- rupters, each receiver will analyze the tones transmitted through it, pick out its own, and allow the others to pass without interference or interruption to their re- spective receivers. The method of applying this system to telegraphy is well explained in an article prepared under the super- vision of Mr. Gray (who has been the chief inventor in this application of electricity) for the New York Review of the Telegraph and Telephone, and also in a lecture delivered before the New York Electrical Society, April 6, 1883, and subsequently published in the New York Operator. The following description is chiefly drawn from these sources : A battery, P 15 P 2 , P 3 , P 4 , Figure 88, united on one side to the ground, sends in line L an electric current which, at the receiving station, crosses seriatim a certain num- ber of electro- magnets four, for example, E,, E a , E 3 , E 4 . Before these latter are placed the reeds B ir B a , B 3 , B 4 , and, under the influence of the variations of the intensity of the current, each electro-magnet puts in vibration, like the diaphragm of the telephone, a corresponding reed, Further, the four reeds, fixed permanently at one of their extremities, are regulated in such a way as to 256 ELECTRICITY, MAGNETISM, AND TELEGRAPHY, give in vibrating four entirely distinct tones ; conse- quently each of them is only affected by the vibrations of the current when these variations are in accord with the number of vibrations which correspond to it. On the other side the battery of the sender is divided into four groups, and upon each of these groups is dis- posed a derived circuit, including a vibrating reed and a Fig. 88. key for making and breaking the contact. There are thus four vibrating reeds, vibrators Y 15 V a , Y 8 , V 4 , and four contacts, C,, C 2 , C 3 , C 4 . Each time that one of the vibrators touches its contact the circuit from the corre- sponding battery is shut off and the current is dimin- ished ; when the circuit is again cut on the current re- sumes its first intensity, but the vibrators set in action, each by a special magneto-electric system, are constantly driven by a determinate vibratory movement, and the number of vibrations of each of them is the same as that of one of the reeds of the receiving apparatus ; that is to say, that V, will have a number of vibrations equal to that of the tone which gives B,, Y 2 the number of vibra- tions corresponding to the tones of B 2 , etc. Each vibra- MULTIPLE TELEGRAPHY. 257 tor will determine then in the current very rapid vibra- tions, and will produce a series of electric waves in relation with the number of vibrations which it effects. All the vibrators being in action at the same time, there will pass, consequently, in the line four series of distinct electric waves ; and each of these series of waves find- ing at the receiving station a reed in harmony with it, under its influence all the reeds, B n B 2 , B 3 , and B 4 , will enter into vibrations. If now one of the vibrators is stopped the series of electric waves which correspond with it would be sup- pressed, and the corresponding reed ceases to vibrate. If two, three, or four of the vibrators are stopped the arrest of two, three, or four of the reeds will be effected. These arrests will be heard at the receiving station ; and, by making short and long stops, a sort of Morse alpha- bet can be arranged to transmit simultaneously four different despatches. What we have said represents, in short, the harmonic system of transmission invented by Mr. Gray ; but it is evident that in practice special arrangements must necessarily be taken to assure good results. We wish now to indicate these arrangements, after having de- scribed in detail the different apparatus employed. We will describe, in the first place, the receiving ap- paratus, and will indicate how, in the place of producing signals by means of stops in the sound of the receivers, these stops are transformed into electric contacts sus- ceptible of producing ordinary electrical signals. The receiver, with its local sounder, battery, and con- nections, is represented in Figure 89. To the left of the vibrating end of the reed is a supporting piece holding a small bent lever, called a rider, which is nearly balanced at A, and having its bent end resting lightly on the reed at E. The local circuit, starting from the battery, B, travels through the sounder, C, enters the reed at D, the rider through the contact-points. E, and the wire again at A, thence back to the other pole of battery B. When 258 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. the reed is in vibration the local circuit is virtually broken at E by the rider being kicked off, and so much resistance put in at that point by reason of the very im- perfect contact. The instant the reed comes to rest the adjusting spring pulls the rider down and closes the local circuit. Consequently, when at the transmitting station all the vibrators act upon the battery, all the sounder circuits are opened. If, on the contrary, one of the vibrators Fig. 89. stops, the sounder circuit of the corresponding reed is closed. The arrest of a vibrator then acts on its corre- sponding sounder as that of a Morse key would act, in- serted with it, in the circuit of a battery. The vibrator is represented by Figure 90. The electro - magnets, A and B, have respectively one and thirty ohms resistance. The current of the battery, passing through the coils of the two electro-magnets, magnetizes them simultaneously, but on account of the greater number of convolutions the electro-magnet A is the stronger. It thus attracts the steel tongue which hangs from a fixed point between the magnet-cores. This tongue then makes contact by means of the spring D with the point C, establishing a shunt circuit round the magnet A, MULTIPLE TELEGRAPHY. 259 round which the current may now pass. The electro- magnet B becomes consequently stronger, and in its turn attracts the tongue until the spring F makes con- tact with the screw E. The contact D being broken anew, the electro -magnet A again attracts the steel tongue, and thus rapid motion is maintained. The tongue is then maintained in vibration, which is regu- Fig. 90. lated according to its fundamental tone. The contact F represents one of the contacts indicated in Figure 88 by the letters C 15 C 3 , C 3 , and C 4 . In the disposition of Figure 88, when the vibrator is in action by the operation of the battery which corre- sponds to it, it enfeebles this part of the battery in a proportion of about sixty per cent. When the vibrator Is stopped its group of battery resumes all its force, and will tend to increase the intensity of the current in the line. With four vibrators, several among them be- ing liable to be stopped at the same time, the changes of 260 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. intensity would be very considerable and would injure the results derived from the system. In order that this latter effect may not take place it is necessary, at the same time that a vibrator be stopped, to suppress from the circuit the sixty per cent, of the group of the corre- sponding battery, in order to produce on the general cur- rent the same effect as the vibrator when it was in action. To attain this result Mr. Gray, instead of stopping the vibrator by opening the local circuit, which is the idea Fig. 91. ' which presents itself naturally to the mind, produces this arrest by the aid of a special disposition called, the transmitter, and represented by Figure 91. The princi- pal part of this disposition is a lever of brass, A. It is terminated at one end in the form of a T. A spring, R, insulated by a piece of ebonite, is placed on the upper part of a lever, and a second spring, r, is in communica- tion with the lower part. These two springs impinge at their extremities upon a branch of the T when they are not removed from it by one or other of the regulating faces, B and S. An electro-magnet, moved by the local battery, p, and a key, #, is placed above the armature of the lever. MULTIPLE TELEGEAPHY. 261 One of the extremities of the main battery is in com- munication with the axis, O, of the lever, the other with the vibrator and also with the adjoining instrument ; the spring R is united to the line ; the face S communi- cates with the contact, C, to the vibrator. Finally, face B is in relation with a point of the battery dividing this battery into two parts, which should be in ratio of sixty to forty. In the position indicated by the figure the negative pole of the battery communicates with the line by the lever, A, and the spring, R ; the positive pole communi- cates with the adjoining instrument. The contact, C, is thus in relation with the negative pole of the battery. Then happens the arrangement shown in Figure 88, and the movements of the vibrating tongue act upon the battery to produce an undulatory current and to weak- en this group about sixty per cent. It is so when the key, #, remains open ; but when this key is closed the lever is attracted by the magnet, the spring r abandons the face S, and the spring R, is supported upon the con- tact B, but ceases to touch the T of the lever. The portion of the battery to the left of B is then ex- cluded from the circuit, and it is only the portion at the right, or forty per cent, of the battery, which sends its current one way in the line by B and R, and the other way in the other adjoining transmitters by m. The sum total of the current has not changed, and the closing of 7c has the effect simply of suppressing the series of elec- trical waves corresponding to the vibrator, V, and conse- quently of stopping the corresponding vibrating reed. It might be asked why the depression of the lever, A, is accomplished by the aid of a local circuit instead of being depressed directly. The reason for this is in the fact that the pressure of the hand would be very unsteady and the contacts would be irregular ; with the attraction of an electro-magnet, however, on the other hand, the force producing the depression is always the -same. If now the instruments are connected up in the 262 ELECTRICITY, MAGNETISM, A1STD TELEGRAPHY. manner described, we have the general plan shown in Figure 92. This part constitutes the Harmonic system, properly so called. Ifc perm its the trans- mission of four de- spatches simulta- neously in a sin- gle direction that is to say, from the transmitting sta- tion to the receiv- ing station ; but it is necessary that the employees at the receiving sta- tion be able to^ communicate with those at the trans- mitting station, in order to be able to respond to the calls or to make correc- tions. As shown in Fig- ure 92, a differ- ential relay is used at the sending sta- tion and a plain relay at the receiv- ing station,, each having a condenser in a shunt circuit around it to permit the vibrations, to pass without be- ing retarded or interfered with by the charging and dis- charging of the magnets. The compound transmitter at the receiving station will need some explanation. The MULTIPLE TELEGRAPHY. 263 two springs, S s, are both insulated from the lever by ebonite and connected together ; the upper branch of the T is insulated from the spring S at E, and the lower spring, s, is insulated from the point c at e. The upper point C is connected directly to ground. R and K/ are adjustable resistances. R" is the artificial circuit or equating resistance. When all are sending from the sending station, the current, after passing through the tone and simple relays, reaches ground through R' ; that is to say, the circuit in its normal state has the artificial resistance of R' constantly interposed. When it is necessary to break, which is done by operating the compound transmitter by one of the keys, the resis- tance R' is thrown out of circuit and the current on the line is augmented in proportion to the amount of resistance contained in R 7 , which has been thrown from the circuit. The increased line current then divides at D, part of it going through the relays and the transmit- ter to ground from the point C, and part of it through R, the transmitter, and the point C. The resistance R is adjusted to shunt off part of the increased line current, and so maintain an unvarying strength through the re- lays regardless of the position of the transmitter lever. This decrease of resistance, however, throws the line out of balance and operates the relay IN" at the sending sta- tion, where the signals transmitted by any one of the breaking keys are reproduced. We thus have a sixth transmission in a direction opposite to the other five, and in practice the sixth side is used for breaking and other service work. As will be seen by reference to Figure 10, each receiving operator has a breaking key, and all of these work the compound transmitter, which operates the relay N at the distant station. This relay in turn controls as many sounders in its local circuit as there are sending operators. The sections are numbered in regular order from one to five at each end. When, for instance, No. 2 receiver wishes to break No. 2 sender, he simply makes the figure 2 on his key, which is heard 264 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. on all the sounders at the other end, but only No. 2 sender stops work to get his break. Two or three hours' practice enables any operator to become accustomed to this method. Condensers are placed in derived circuit upon each resistance. They have the effect of compensating the extra currents which are produced in the coils of the re- sistance, and which retard the undulatory currents ; in fact, they play the same role as in the Ruhmkoiif or Ritchie ' induction-coils. In Figure 92 the four groups of the battery are repre- sented as being equal. In practice they are not so. All the groups are divided by the line running to the con- tact surface B, in two parts, which stand to each other in the ratio of sixty to forty ; but the absolute value of all the groups is not the same. The reason for this is in the fact, demonstrated by experience, that four pulsa- tory currents, produced by the action of four vibrators, are not produced with equal facility. The electro- motive force necessary for their production is not the same for all ; hence the necessity for making the groups of different value. The Harmonic system of Mr. Gray has been experi- mented with in this country from the 22d of November, 1880, to the 22d of January, 1881, upon the lines of the Western Union between New York and Boston, over a distance of 240 miles. The trial was made under un- favorable circumstances, for the line employed was in the vicinity of other lines upon which nine quadruplex circuits were working, and the currents of these instru- ments created difficulties in the way of induction in the neighboring wires, by reason of the employment of strong batteries and frequent changing of the poles of the battery. In one of the experiments five employees have transmitted, in the space of nine hours, 2,124 de- spatches, or 236 despatches in all per hour, or 47 de- spatches per operator per hour. Another time four employees, chosen among the best, transmitted, in five MULTIPLE TELEGRAPHY. 265 hours, 1,184 despatches, or 59 per employee per hour. After these experiments, the franchises required by a company which is occupied with the construction of special lines to operate in competition with the exist- ing telegraph companies in this country, were acquired. .The Duplex, or Way Harmonic, which is a modification of the system which we have just described, is already employed on several railroads. At least five experimenters worked in the line of Har- monic telegraphy during the years between 1870 and 1876 inclusive viz., Varley of London, La Cour of Copen- hagen, Gray of Chicago, Bell of Boston, and Edison of New York. And, although Mr. Varley was the earliest in the field, Mr. Gray has done so much to develop Har- monic telegraphy, and make it not only practicable but also practical, that it seems but fair to award him the greatest share of the credit.* * Since the above was written the Harmonic system has successfully been operated over the low-resistance compound wire of the Postal Tele- graph Company between New York and Chicago, a distance of one thousand and twenty miles, without the intervention of repeaters. CHAPTER XVIII. MISCELLANEOUS APPLICATIONS OF ELECTKICITY ELEC- TRIC LIGHTING. 233. To what useful arts, besides telegraphy, has electricity been applied 1 It is impossible in a work of this general nature to enumerate all the useful applications of electricity ; its principal applications are, however, the following : elec- tric lighting, electro-plating, electro-typing, bell-ringing and signalling, telephony, medical applications, or thera- peutics, clocks, blasting, and gas-lighting. 234. What is the electric light, and under what divisions may electric lights be classed f By the electric light is meant any light produced by the action of electricity, and all such lights up to the present time may be regarded as belonging to the fol- lowing divisions : arc lights, incandescent lights, and semi-incandescent lights. The so-called electric candles are, properly speaking, but a special variety of the arc. 235. What is the arc light ? It is the extremely brilliant light produced when the two conductors leading from the poles of a powerful source of elec- tricity are brought together so as to complete the circuit, and then slightly separated. It is, as shown in Figures 93 and 94, of curved form when produced in the open air, by means of horizontal elec- trodes, and is for that reason originally called an arc. The more powerful the source the greater may be the length or span of the arc, and the more intense and bril- MISCELLANEOUS APPLICATIONS OF ELECTRICITY. 267 liant the light emitted by it. If the two severed ends of the circuit are made of carbon, and pointed, the effect is materially augmented. The arc is supposed to originate in the passage between the electrodes of the self-in- duced extra current, which attempts to leap from one carbon to another, and in doing so volatilizes a small amount of carbon. The carbon vapor thus produced has a very high resistance, and, while capable of conducting the current, becomes heated by its passage, the carbon points also growing hot. Numerous small particles of carbon are then thrown from one pole of the arc to the other, and during their transit become incandescent, thus aiding in the illumination. The direction in which the particles move is dependent upon the direction of the current ; that is, from the electrode or conductor leading from the positive, to that leading from the nega- tive pole. The positive terminal of an arc light is much hotter than the negative, and is consumed much faster. When enclosed in a vacuum, the consumption of both elec- trodes is much less rapid than when the arc is exposed to the air. For illuminating purposes the electrodes are nearly always made of carbon. The color of the luminous axe depends on the material of the electrodes ; for example, carbon produces a white, copper or silver a green, and sodium a blue light. The electricity traverses the arc, which is, therefore, a part of the circuit. The arc was first produced by Sir Humphry Davy, by means of large voltaic batteries, from which the name voltaic arc, often applied to it, is derived. The following lines are transcribed from the work of Professor Silvanus P. Thompson: "The resistance of the arc may vary, according to circumstances, from five- tenths of an ohm to nearly one hundred ohms. To pro- duce an electric light satisfactorily, a minimum electro- motive force of forty to fifty volts is necessary ; and as the current must be at least from five to ten amperes, it 268 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. is clear that the internal resistance of the battery or generator must be kept small. With weaker currents, or smaller electro-motive forces, it is impracticable to maintain a steady arc. Therefore the internal resis- tance of the ordinary Daniell or Leclanche batteries is too great to admit of their use in producing the electric light. A battery of forty to sixty Grove cells will an- swer the purpose, but will only work well for two or three hours. Had no other method of producing current electricity been discovered, the art of electric lighting would still have been only an electrical curiosity ; but the nume- rous forms of dynamo- electric machines recently in- vented have made the production of the electric light comparatively cheap, and have given the art a great impetus. It will be readily seen, however, that to ap- ply the name voltaic arc to an electric arc produced by electricity evolved by a machine is a palpable incon- gruity. In Davy's experiments, about the beginning of the present century, he produced a light with an arc four inches long, in the open air, by using a battery of some two thousand cells. 236. What is an electric-arc lamp ? An electric-arc lamp, frequently called a regulator, is a device or apparatus constructed for the purpose of maintaining the electrodes of the arc at their proper dis- tance from one another. Such a contrivance becomes necessary, because the carbons are continually burning away, and if some means were not adopted for carry- ing them forward, and keeping them at the proper dis- tance apart, the light would soon be extinguished. Much ingenuity has been displayed in the construc- tion of these lamps and regulators, and many extraor- dinary arrangements have been devised, only a few of which have survived and gone into extensive use. " In some of these the carbons are attached to guides actuated by trains of wheels, which push them forward at the necessary speed. The wheels are put in action or MISCELLANEOUS APPLICATIONS OF ELECTRICITY. 269 stopped, as the case may be, by means of electro-mag- nets forming part of the electric circuit of the lamp. Most of these electric lamps are arranged so that when the lamp, from any cause, goes out, the carbons are brought into contact for an instant, and as soon as the Fig. 95. current is thus re-established the carbons are drawn back to the required distance." * The movement which is most frequently used in America is one wherein the attraction of a solenoid, acting upon a movable iron core, regulates the dis- tance between the carbons. Such a lamp is that of C. F. Brush, which is shown in. Figure 95, and which, be- * " Electric Light," by A. Bromley Holmes. 270 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. sides being capable of regulating the distance between the carbons, automatically short-circuits, or cuts itself out, when defective, thus permitting the current to flow, as it were, round the lamp in the main circuit. As this lamp is quite extensively used, its operation will be fully described. The circuits are shown in the diagram, Figure 96 ; the lower carbon, K', is fixed, and the upper one, K, is at- tached to a metallic rod which, by means of a washer clutch, W, is connected with an armature carried by a Fig. 9o. pair of plungers, arranged to slide in and out of a pair of solenoids, or helices of covered wire, H H. These solenoids are wound in multiple arc with two wires, which are wound oppositely with respect to one another. The first of these wires is in direct circuit with the arc, and consists of a few layers of coarse wire, through which the main portion of the current operating the lamp passes to the rod of the upper carbon. The up- per carbon falls by the action of gravity against the lower carbon, and when the two carbons are together the cur- rent passes on from the upper to the lower, and thence out. MISCELLANEOUS APPLICATIONS OF ELECTRICITY. 271 Entering the lamp at the binding-post X, the path of the circuits, which are three in number, are as follows : The circuit through the lamp carbons is from the point 1, by the parallel wires 2, constituting the coarse- wire helix round the solenoids, H, and by the wire 5 to the carbon-holder, N, and thus through the arc to the terminal, Y, and on to the next lamp. The second cir- cuit is composed of much finer wire, and, branching from the main line at the point 1, passes by the parallel wires 3 through the solenoids, being in practice wound over the layers of coarse wire ; issuing from thence by the wires 4, it is led round the electro-magnet, E, and out to the binding- post Y by the wire 6. Thus the fine wire forms a secondary circuit of high resistance through the lamp, which circuit is indepen- dent of the arc between the carbons, and is always closed. It follows from the difference in direction of the current in the two helices, that the fine-wire helix will con- stantly tend to neutralize the magnetism produced by the coarse- wire or principal helix. The number of con- volutions of the fine- wire helix and its resistance are so proportioned to the number of convolutions in the prin- cipal helix, and its resistance together with that of the normal voltaic arc, that the magnetizing power of the latter shall be much greater than that of the former. Notwithstanding the small amount of current which passes through the fine-wire helix (about one per cent, of the whole current), its magnetic power is very consid- erable owing to its great number of convolutions. Now, when the arc of any lamp becomes too long the resistance of its main circuit is thereby increased and more current is sent through the secondary or fine- wire coil ; the magnetizing power of the solenoid, of course, being thereby weakened, allowing the carbons to ap- proach. On the other hand, if the arc becomes too short its resistance is reduced, less current goes through the fine-wire helix, and the magnetic strength of the sole- noids are correspondingly increased. The plungers are 272 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. sucked into them, carrying the armature, H, and lifting one end of the ring-clutch, W, and the upper carbon- holder with it, and thus the arc is maintained. In prac- tice the resistance of the fine-wire helix or helices in each lamp is rather more than 450 ohms, while the re- sistance of the coarse wire, various connections, carbons, and voltaic arc, in each lamp used with the sixteen-light machine, is about 4.5 ohms. Hence not more than \ per cent, of the whole current is diverted from the arc. The resistance of the coarse-wire helix, carbons (copper- coated), connections, etc., in each lamp is very small. To determine this resistance 16 lamps were connected in series in the usual manner, about 200 feet of No. 10 cop- per circuit wire being used. Full-length carbons were then placed in the lamps, and the upper and lower car- bon of each lamp were connected by means of a strip of sheet copper wired to each carbon. The resistance of the whole set was then measured and .found to be 2.10 ohms, showing a resistance for each lamp with its car- bons of 0.131 ohm. This is 2.91 per cent, of the whole resistance of the lamp when in operation. To this loss must be added the 1 per cent, due to that amount of current diverted from the arc by the fine-wire regulating helix, making a total loss of 3.91 per cent. The remain- ing 96.09 per cent, of the whole energy absorbed in each lamp appears in the arc between its carbons. The third branch circuit through the lamp is only completed when the resistance in the arc becomes abnormally great, or when the arc from any reason fails. It constitutes the short-circuiting or cut-out device, and is operated by the electro-magnet, E. The core of this magnet is surrounded by two coils just like the solenoids, but, unlike them, its coils are both wound in the same direction. The fine-wire coil, as already de- scribed, is a continuation of the fine-wire solenoid helix. The thick- wire coil, which is only brought into action when the lamp is to be cut out, starts from the stud, M', passes round the core, and then unites with the terminal MISCELLANEOUS APPLICATIONS OF ELECTRICITY. 273 wire 6 of the fine coil, passing out to Y. The armature, B, of the electro-magnet, E, connects by a suitable wire, 7 R, with the screw-post, X. The armature-lever of the electro-magnet is suitably pivoted, and is united by the wire R, which may be made of any required resistance, to the incoming line- wire before it reaches the solenoids. If now the arc fails or if its resistance is excessively increased, a large pro- portion of the current goes through the fine wire of the electro-magnet, which thus becomes more strongly mag- netic, and strong enough to attract its armature. The armature, being attracted, closes the circuit of the thick wire. If the trouble in the arc is permanent the short circuit is now maintained through the thick wire cutting the arc completely out. If, on the contrary, it was merely caused by the undue length of the arc, as soon as the short circuit is made through the thick wire of the electro-magnet the solenoids lose their power, the upper carbon falls on the lower one, the electro-magnet in its turn is short-circuited, the solenoids resume their power, and the light is reinstated by reason of the car- bons taking their proper distance apart. The entire series of operations, though taking a long time to de- scribe, are the work of an instant, so that the light, though subject to continuous regulation, is practically maintained without any cessation, except when com- pletely disabled ; when it is immediately short-circuited. The lamp thus described, and all of the types treated of in the above explanation, are of course adapted only for the production of the arc light, and where other va- rieties of electric light are required other forms of lamp become necessary. 237. What is meant by the incandescent electric light ? The incandescent light is that produced by the pas- sage of a strong current of electricity through an im- perfect conductor or a conductor of high resistance. It is based upon the principle that when such a cur- rent is passed through such a conductor the substance 274 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. of the conductor becomes heated ; and if it be attenu- ated as, for example, in the case of a piece of fine wire or a thin carbon pencil or filament after a certain de- gree of heat is reached, say above two thousand degrees Fahrenheit, it glows with light, the brilliancy of the light depending upon the strength of the current. Lighting by incandescence has ever been a favorite idea of inventors and experimentalists in electric lighting, but only within the last few years can it be said to have achieved any important success. Contrary to the gene- ral opinion, this idea is by no means new, since as early as 1845 an American inventor named Starr patented in England a lamp which is shown in Figure 97, and which was intended to operate on this principle. This lamp consisted of a conducting wire, D, sealed into one end of a glass Torricellian vacuum-tube, and connecting with a carbon rod, A, whose lower extremity is in contact with a second conductor, C, which rests in the quicksilver. A non-conducting bar, B, car- ries brackets in which the carbons are sup- ported. The subject, after temporary re- vivals in 1850 and 1852, dropped out of sight, chiefly on account of the lack of an economical generator of electricity ; but in 1873 was again taken up by Lodyguine, a Russian inventor. Since then it has assumed a steadily in- creasing importance, Edison, Weston, Max- im, Sawyer, and Bernstein working upon it in America, and Swan and Lane-Fox in England. Considerable success has attended their efforts, and one of the most, perhaps tlie most important installation, is that of Mr. Edison, who, after many months of patient and con- tinuous labor, has succeeded in illuminating a number Fig. 97. MISCELLANEOUS APPLICATIONS OF ELECTRICITY. 275 of business places and houses throughout an extensive district in New York City from a single central lighting station. After many experiments with iridium and platinum, or alloys combining or containing these metals, all the in- ventors ultimately have decided that carbon is the only suitable known substance to maintain in the incandescent state as an illuminator. Experience has also demon- strated that some method of protecting the light-giving part from the oxygen of the atmo- sphere is necessary, the carbon other- wise being rapidly consumed. For this reason Edison, Swan, Lane-Fox, Weston, Maxim, and Bernstein use lamps in which the deleterious action of the oxygen is prevented by enclosing the incandescing conductor in vacuo ; while Sawyer encloses his carbons in globes filled with nitrogen. 238. What are the distinctive features of the different incandescent electric lamps ? The Edison lamp, as now made, has for a light-producing part a carbonized filament of bamboo. This is enclosed in an exhausted glass globe, and by means of fine platinum wires is con- nected to a screw and sole-plate, which, when screwed on to a bracket or stand, make contact with the two external conducting wires. In the construction of these carbon filaments Mr. Edison made many ex- periments to ascertain the best material to be employed, and, after carbonizing a large number of vegetable fibres and tissues, arrived at the conclusion that certain kinds of bamboo presented the greatest advantages, both for facility of manipulation and for uniformity of structure. The shape of the carbon filament used in this lamp is that of an inverted U, as shown in Figure 98. Fig. 98. 276 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. The Swan lamp- carbon is formed of cotton thread converted by treatment with sulphuric acid into a parchment- like material, and carbonized. The finished carbon is looped with a double turn at the top, as in Figure 99. The ends of the strip are thicker than the middle, and are joined to the conducting wires by metal clamps. The Lane-Fox lamp is represented by Figure 100, ',9. Fig. 100. . and in it the carbon filament is made from the fibres i of Italian grass, or bass-broom. A peculiar method of carbonizing is involved in its preparation. Figure 101 shows the Maxim lamp, which is distin- guished by an incandescing carbon made from card- board and shaped like the letter M. The light giving conductor in the Bernstein lamp con- sists of a hollow cylinder of carbon supported at each end in a carbon socket. MISCELLANEOUS APPLICATIONS OF ELECTRICITY, 277 The Weston lamp is similar in appearance to the Maxim, but the filament is made of non-fibrous cellu- lose, which is afterward carbonized. This material is extremely tough and elastic, and has a high resistance. 239. How is the illuminating power of a light generally expressed 1 The standard unit of measure- ment of light in this country and England is a sperm candle burn- ing approximately one hundred and twenty grains of spermaceti per hour. In France the carcel lamp is the unit ; this lamp burns forty-two grammes, or six hundred and forty -eight grains, per hour. In Germany the unit is a paraffine candle of which six iveigh five hundred grammes ; one carcel is equal to about seven and one-half of these candles. All of these standards are crude ap- proximations, and it has been suggested among other plans that the unit should be derived from the area of floor which any light is capable of illuminating. 240. What is meant by the term electric candlel The electric candle is really nothing more than a pecu- liar arc lamp reduced to its simplest form. It consists of a pair of small carbon-rods placed parallel to each other, with a thin strip of plaster-of-Paris or fine clay between them as an insulator. This being in the shape of a candle, together with the fact that the light com- mences at the free ends and burns downward as the carbons consume away from one end, like the wick and combustible material of a candle, account for the name. The candle is the invention of a Russian engineer, M. Jablochkoff, and was patented by him in March, 1876. 278 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. Its use dispensed with the cumbrous and complicated lamps and regulators then in use, and gave an impetus to electric lighting which is still felt. The sticks of car- bon which constitute the candle are only about one- sixth of an inch in diameter and from nine to ten inches in length, although they have been made as short as six and a half inches. The shorter ones only burn one hour. When the current of electricity passes, an arc of light is maintained across the 'top of the carbons, which are gradually consumed as an ordinary candle is, together with the insulating material. The circuit before the current passes is completed, and the candle lighted by laying a small piece of graphite or black lead across the top of the carbon sticks. The currents em- ployed are of an alternating character, so as to consume both of the carbon sticks equally fast. These candles are more used in France than elsewhere, although they have been employed to a considerable extent in London. Four candles are usually placed in an opalescent glass globe, and an automatic arrangement provided to switch the current from one candle to the next as each burns down. The electric candle has been much improved by the well-known electrician and inventor, Mr. Henry Wilde, of Manchester. He remarked the small part apparent- ly taken by the insulating material, and diminished that material by discontinuing the plaster- of -Paris and mere- ly coating the carbons with a hydrate of lime. No dif- ference in the operation of the candle being observed, he went a step farther and arranged the carbons without any insulator or separating medium at all, finding the light to be absolutely improved thereby. He further observed that even when the circuit was completed at the bottom or lower end of a pair of carbons, the arc or light would immediately ascend to the points. He next arranged an automatic lighting device by making one of the carbon-holders with a hinge at the bottom, and con- tinuing it horizontally in the form of a right-angled lever,. MISCELLANEOUS APPLICATIONS OF ELECTRICITY. 279 the horizontal part serving as the armature of an electro- magnet, the helices of which are included in the light- ing circuit. By its weight the carbon, and its holder, which is hinged, lean against the fixed carbon as long as no current is flowing ; but as soon as a current com- mences to flow, the circuit being completed at the point where the carbons touch one another, the electro-mag- net is charged, attracts the armature, and draws the hinged carbon-holder to an upright position, and so brings the carbons to the requisite distance from one another. 241. WJiat are semi-incandescent electric lights ? These, which are also sometimes called incandescence- arc lamps, are constructed either by arranging a carbon rod to press against a block of carbon, or by having two carbon electrodes, with a piece of refractory non-conduct- ing material, such as marble, interposed between them. In the first case the light is produced by the passage of the current through a rod of carbon, which, at the end that presses against the block, is so small that its extremity becomes heated nearly to whiteness. Also, when the pressure is very slight, small arcs are developed at the point of contact, which aid in produc- ing the light. Of this category are the lamps of Regnier, Werder- mann, and Varley. In Werdermann's lamp a rod of carbon is forced up- wards by the action of a weight against a rounded block of carbon; the rod becomes incandescent at its extre- mity, gives a strong light, and is gradually consumed. Varley' s lamp is one of the earliest of this class, and consists of a disc of carbon with bevelled edge, on which rests the extremity of a carbon pencil mounted at the lower end of a pivoted lever. Regnier' s lamp is an improvement on the foregoing, and comprises a rod and a disc of carbon ; the rod as it falls imparts motion to the disc, which is thus caused to revolve, and con- tinually presents fresh points of contact. 280 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. In the second case the light results from the passage of the electricity over the surface of the block of marble, or other analogous substance, which is between the car- bon electrodes. This, by the intense heat, is made in- candescent, and its incandescence adds to the light of the arc between the electrodes. The most familiar lamp of this class is called the Sun Lamp (Lampe Soleil). This light is very steady, is of a golden hue, and has an advantage in the stored-up heat in the incandescent block, which, if the current weakens momentarily for example, by reason of a slackened driving-belt is suffi- cient to supply the deficiency for a short time. It is said, however, to be very wasteful of power. The earliest worker in both of these classes was W. E. Staite, of London, who, between the years 1846 and 1849, took out several patents in England for different plans of electrical illumination. Dept. Meeh, Eng*. CHAPTER XIX. ELECTED- METALLURGY. 242. What is electro-metallurgy f It is the art which governs the electro-deposition of metals upon any surface prepared to receive them, from a metallic solution. It is based upon the observed fact that a current of electricity passed through such a solu- tion tends to decompose it into its constituents water and the metal held in solution ; depositing the latter, as before stated, upon any prepared surface. The two great divisions of electro-metallurgy are electro-plating and electro- typing. 243. What is electro-plating * It is that division of the art of electro-metallic deposi- tion which treats of depositing a permanent coating of metal by means of electricity. Although we are accus- tomed to *speak of electro-plating only when referring to the deposition of silver and gold, we may with per- fect correctness apply the term to any other metal also. To electro-plate is to provide a chemically clean me- tallic surface, to immerse that surface in a metallic solu- tion, and by means of electricity to cause the metal contained in the solution to be deposited upon the im- mersed surface in such a manner that it may perma- nently incorporate itself with the original surface ; and so, whatever may be the material of which the original surface is composed, after plating it will appear like whatever metal is deposited on it, whether that metal be silver, gold, copper, nickel, or anything else. As already indicated, the article to be plated must be chemically clean. The source of electricity employed may be either a voltaic battery or a dynamo-electric 881 282 ELECTKICITY, MAGNETISM, AND TELEGRAPHY. machine. If tlie plating establishment is a commercial one or doing business on a large scale, a machine is de- cidedly to be preferred. For experimental work a bat- tery is the most convenient. For most work of the ordinary character, either in copper, silver, or nickel, the large Sniee battery is most universally useful. The Daniell battery may be used for small current work, such as gilding ; and the carbon battery can be profit- ably employed where a strong current is required, as in depositing brass or iron. The process is represented in Figure 102, where O is Fig. 102. the depositing battery, C the vessel containing the solu- tion, D a metallic rod connected with the positive pole, having a plate of metal suspended from it and dipping into the liquid ; B is another rod, connected with the negative pole of the battery, and from which the articles to be plated are suspended. These articles are thus made the negative pole of the battery, and the metal plate suspended from D becomes the positive pole. The dynamo-electric machine has within the last ten years to a great extent superseded the batteries in fac- tories, and the forms of machine favored are chiefly those of Gramme and Weston, but any dynamo machine of small internal resistance, furnishing constant currents of non-alternating direction, may be successfully used. Electro-plating is one of the most useful of arts, and ELECTRO-METALLURGY. 283 serves either to protect a valuable surface, or to beautify a surface, or ornament and give an appearance of value to articles of ordinary character. 244. What is electro-typing ? By electro-typing is meant the production of copies in metal of any object by means of the action of electricity. It differs from electro-plating in that the metal deposited on the article subjected to the process is not intended to remain permanently, but merely, as it were, to form itself upon, and assume the shape of, that article. While the electrical features are the same as in electro-plating, and while the art is dependent upon exactly the same principle, the technical details are completely dissimilar, since in the former art all the skill of the operator is directed to the establishment of a permanent adherent coating of metal, while in electro-typing his efforts are oppositely directed, and all the details of the process must be arranged to admit of a ready separation of the deposited metal from the original article. 245. Give a brief outline of the art of electro -typing. This art was first introduced as early as 1838 by Pro- fessor Jacobi, of St. Petersburg, in a paper communi- cated by him to the Academy of Sciences of that city, in which he explained a process of producing copies of engraved plates by means of electricit}^ Almost at the same time Mr. Thomas Spencer, of Liver- pool, made public a series of experiments in which he had been engaged on the same subject; while nearly sim- ultaneously a printer named Jordan described similar experiments which he had made about the same time. In this, as in other great discoveries, it thus appears that several experimentalists were close to each other on the same track at once ; but Spencer was by far the most painstaking of the three, and demonstrated its practical value. The entire process is founded upon a very simple prin- ciplenamely, that certain metals can be deposited from a solution of their salts by the passage through that so- 284 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. Fig. 103. lution of a current of electricity. The primitive methods adopted in the early days of the art are now obsolete, except as used by amateurs ; nevertheless, as they em- body the above principle as well as the most recent modes can do, and also possess the cardinal virtue of simplicity, they are here noticed. A modification of the Daniell battery, such as is shown in Figure 103, was generally used, consisting of a glazed earthenware or glass cell containing a solution of sulphate of copper, kept at the proper strength by ex- tra crystals on a shelf. A porous cup con- taining dilute sulphuric acid stood in the jar. holding an amalgamated zinc rod. The object to be copied, or electro-typed, whether a coin, medal, a seal, or other article, was attached by a copper wire to the zinc of the battery and suspended in the solution. This object thus formed the ne- gative plate of the voltaic cell, and an electrical current passed from the zinc, through the two liquids and the porous cup, to the object to be copied, and back to the zinc rod through the wire, completing the circuit. When the circuit was closed the zinc dissolved and formed its sulphate; the copper solution was also de- composed and its copper deposited on the object to be copied. Any part not required to be copied was coated with varnish or some other non-conductor. The deposit was separated from the object when sufficiently thick, and found to be an exact fac-simile of the original article. Such is the art of electro-typing in its crudest me- thods, but substantially identical in every essential fea- ture to the same art as practised with every modern appliance. If the model be not a conductor it becomes necessary to coat the surface to be copied with some me- tallic powder (black-lead is generally used), applied over the surface with a fine brush. It is evident that by this ELECTRO-METALLURGY. 285 device we are enabled to use as models plaster-of -Paris, wax, gutta-percha, or any fusible or plastic substance. It was early discovered that the use of a separate bat- tery, as shown in Figure 104, was a great improvement ; when this was used a batli of the solution of the metal to be deposited was prepared, and the copper plate of the battery connected with a second copperplate sus- pended in the solution, while the articles to be copied were also suspended in the solution and united by a wire Fig. 104. to the zinc plate of the battery. When so disposed the suspended copper plate dissolves, adding copper to the solution as fast as it is abstracted from it by deposition on the articles to be copied. As in the sister process of electro-plating, the use as a generator of the dynamo- electric machine has greatly advanced of late years, and it is now employed in all large establishments. The electro-typing process finds many uses : it is uni- versally employed to produce copper duplicates of wood engravings, and set-up type is often thus copied ; sta- tuettes, medals, and coins can be thus reproduced without limit, and many electro-type copies are fully as beautiful as the originals. CHAPTER XX. ELECTRIC BELLS. 246. How is electricity made to ring bells ? Practically in the same way in which it is made to operate a telegraph. An electro -magnet is. fitted with an armature; that arma- ture is pivoted, and its lever extended to the necessary length and furnished at its free end with a bell-ham- mer, which, when the electro-magnet is excit- ed and the armature consequently attracted, strikes upon a gong Fig> 105- with more or less force. This is shown by the engraving, Figure 105. There are several ways in which electricity may be utilized for this purpose. The method already described may be varied by so disposing the several parts that the armature and hammer are attracted away from the gong when the electro-magnet is charged by the closing of the circuit, while when the circuit is again broken the hammer, being retracted by a spring, strikes the gong. Sometimes the bell is so constructed as to ring when the direction of the current is reversed, and the bell is then called a polarized bell. At other times, when a heavy stroke is required, while the power exerted by the current is but feeble, the hammer is impelled by a weight or spring acting through a train of clock-work, the electricity in such cases merely act- ELECTRIC BELLS. 287 ing as a controller to release and detain the clock- work. 247. What is a single-stroke electric belli It is a bell comprising an electro-magnet, an armature operated by the same, and a hammer extending from the armature, which may be arranged to strike its gong a single stroke or tap at the moment either of breaking or making the circuit ; of changing the direction of the current ; or both ; at the will of the manipulator. The name single-stroke is colloquially applied to such a bell in contradistinction to a bell giving a continuous ring. 248. What is a vibrating or trembling electric bell ? It is an electric bell which, in addition to the ele- ments possessed by the single- stroke bell, has some device adapted to alternately allow the electricity to I>ass through the electro- magnet helices and shut it off from them, so that as soon as the hammer is so far drawn up as to strike the bell it is drawn back again once more to be attracted, and again withdrawn, and so on as long as the circuit is kept closed at the point of manipulation ; that is, if a bell of this character be placed in the circuit of a battery, the said circuit also passing through a key which is normally open, when the circuit is closed by pressing the key, the magnet will become charged and will attract the armature, and the bell-hammer attached to the armature will com- mence to alternately strike the bell and withdraw from it, and continue so to do until the key is once more opened. This kind of bell usually is arranged by leading the circuit of the bell-magnet through the armature-lever itself, and from it to the back limit-stop, thence to the binding-post ; thus when the armature is attracted under the influence of the current, it has only time to strike the gong before the circuit is broken by the withdrawal of the lever from the back limit, and it is compelled to recede. The lever is usually furnished 288 ELECTRICITY, MAGNETISM, AKD TELEGRAPH Y. with a platinized spring, which improves the contact, and at the same time gives the armature an im- pulse and prevents it from breaking the circuit prematurely. Figure 106 repre- sents one of the most frequent forms of the vibrating bell. There are several other ways of constructing vibrating bells, but the foregoing is for ordinary use the best way. 249. How is a polarized bell constructed ? Quite a variety of polarized bells are made, and used for special purposes. Two, however, are sufficient to exemp- lify the principle. The first, and until the days of the telephone the most usual form, has substantially the same construction as a Siemens polarized relay (Q. 192). A base of hard steel is made in the shape of a right angle ; on the horizontal or flat side of the steel base an electro-magnet is transversely placed, so that if the end of the flat side is of north polarity the same polarity is by induction continued through the electro-magnet, and both of its poles become north poles. The other end of the angular steel magnet is, of course, a south pole, and is forked ; one end of a slender rod of iron is pivoted in this fork, and the other extends outwardly until its end rests between the two extremities of the electro- magnet, which are fitted with adjustable pole- pieces. As shown in Figure 107, which represents a modifi- cation of this type of polarized bell, an extension-rod provided with a hammer is attached to the end of the iron rod which serves as an armature, and in its range a bell is placed. When the electric impulses sent from a magneto-generator, or a battery and pole-changer, are passed through the coils of the bell-magnet, the arma- ture vibrates from side to side and rings the bell. Such a bell, though strong and reliable where com- paratively slow alternations of current are sent, is rather ELECTRIC BELLS. 289 sluggish, in its action when the alternations of direc- tion are very rapid. This fact led to the introduction Fig. 107. of the second form of polarized bell, which is now to be described. This is the form so familiar to us in the regulation telephone bell-box. In this bell, as in the one already described, an electro-magnet is fixed upon one end of a permanent magnet, while near, but not neces- sarily attached to the other end of the permanent mag- net, a soft-iron armature is pivoted by its centre, and arries by a light metal rod the bell-hammer. The per- manent magnet is Fig.ioa in shape like a bar magnet, with each end bent for about an inch at right angles to itself ; one of these bent ends is placed behind the heel-piece of the electro-magnet, and the other be- hind the centre of the pivoted armature. Two gongs are arranged in front, between Fig. 108. 290 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. which the bell-hammer vibrates, striking each alter- nately. When an electric pulsation of positive direc- tion is sent through the coils of the electro- magnet the armature swings over to one side, and when a pulsation of negative direction is sent it swings over again to the other side. Figure 108 represents the working parts of a bell of this character. Rapidly alternating electrical currents, generated either by a magneto-machine or by a battery having: a pole-changer in circuit, are used to operate these bells, and in practice a generating magnet and coil is attached to each one, and placed in the same case, immediately below the bell, so that each instrument possesses not only the power of ringing but also that of operating other bells. 250. How must the apparatus and wires be arranged for a simple bell circuit, where one bell is to be rung from but one point, and tvhat apparatus is required ? All that is required is one bell, one press-button, or key, as much battery as may be found necessary (for any distance short of fifty feet one cell of Leclanche will do),. and enough wire for about twice the distance between the button and the bell. To set up the apparatus, screw up the bell to a support where it is wanted, then mea- sure off the wire, taking care to have the pieces long enough. Find a place for the battery and set that up ; then attach to the terminal screws of the press-button two wires, one extending to the bell, and the other to- the battery ; having attached them to the press-button, screw up the button in its place and put on its cover. In Figure 109 the connections are clearly shown, H indicating the bell-hammer, E the electro-magnet, C the automatic circuit-breaking points, P the press-button, and B the battery. Figure 110 shows a vertical section of the press-button, which clearly explains its operation. One of the press-button wires is connected with one of the bell binding- screws, and the other to one pole of the battery. A third wire must now be made to unite the ELECTRIC BELLS. 291 remaining bell terminal to the other battery pole ; this done, the construction is complete. The circuit may now, referring to the figure, be readily traced : com- mencing at the positive pole of the battery, and fol- lowing the arrows, the circuit is first to the press-button, where it is ordinarily open, then to one of the bell ter- minals, through the bell-magnet to the armature-lever, through the lever to the points C, then to the outgoing terminal, and thence back to the negative pole of the battery. For good work the wires must be well insulated by being covered with cotton, or, if they are to rest in damp places, with kerite or india-rubber ; of course, before Fig. 109. Fig. 110. making connections, the ends of the wire must be care- fully stripped for about an inch and a half. The wires should be nea.tly tacked to the walls, or otherwise secured. More than one wire must never be placed under one staple, and the entire work must be made as neat as possible. It is just as easy to make a hand- some job as an unsightly one. This is the simplest plan for a signal-bell circuit, and may readily be constructed by any one. 292 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 251. How may electric bells be operated by a pull, similar to the ordinary mechanical door-bell ? By using a pull circuit-closer, like that shown in Figure 111, instead of a press-button. As shown, the circuit-closer consists in a pair of springs, B B, mounted on a block of non-conducting! material, like hard rubber, and connected respectively! with the bell and battery wires, but not touching one' another when in a state of rest. A hole is bored through the insulating block, and a rod ending at the inside in a metal disc, C, and surrounded by a helical spring, is passed through, and fitted at its outside end with the flange and knob, P. The helical spring serves to keep the disc, C, away from the ends of the flat contact- springs, B, and also to draw in the knob after it is pulled out to close the circuit. When the knob is pulled the helical spring is compressed, and the disc, C, makes contact with both of the flat springs, B, thus closing the circuit. The pull circuit-closer is well adapted for use in connection with door-bells. 252. How may we arrange a circuit to ring a single bell from two or more separate points ? Such an arrangement may be easily understood by reference to the engraving, Figure 112. Setting up the bell and battery as before, connect one pole of the battery with one of the bell binding-screws by a wire; then run a wire from the other battery pole past and near to all the press-buttons, at the points from which it is desired to ring, terminating at the most distant press- button, to which the end of the wire, after being bared, is attached. At each of the intermediate buttons branch wires are extended from this battery wire in the follow- ing manner : At the nearest point of the battery wire to each of the buttons strip its covering from it for a space of about an inch, and scrape the wire thus bared ELECTRIC BELLS. 293 PARLOR till it is bright ; the wire at these points then presents the appearance in- dicated at A, Figure 114. Then bare about three inches of the ends of the proper number of branch wires, and wind the bared ends round the stripped portions of the bat- tery wire, as at B, Figure 114 ; this, especially if solder- ed, makes a good splice. The free ends of the branch wires, after being bared, are attached each to one screw of their respective press-buttons, which may be at any dis- tance from the UMMUUL ma ^ n battery wire. In some cases two of the buttons may be very near together ; the branch may then be connected to the main line in the manner represented in ^ Figure 113 ; c c /J being the main \ N=^SS?SS5SS^M V wire, d the branch to one of the buttons, and e the branch to the other. At this point in con- struction we have a battery wire extending by branches to each press-button. Finally, as in the figure, a simi- KITCHEN Fig. 112. Fig. 113. 294 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. Fig. 114. lar main wire is run from the remaining bell terminal to the most distant button, I | branching to the intermedi- ate ones, precisely the same way as is done in the bat- tery wire. It is obvious now that a bell circuit nor- mally open is constructed, which is capable of being closed at any of the buttons. 253. Hoiv must the wires be arranged to ring two bells from a single button or circuit-closer 1 The apparatus required is a battery, a press or pull button, or key, and the two bells which are to be rung. These may, if required, be in different rooms. The arrangement is indicated in diagram by Figure 115. One of the battery wires runs directly to one of the Fig. 115. press-button screws, and the other battery wire is ex- tended to one binding-screw of each of the bells, as shown. A third wire is led from the other push-button screw, and branches to the remaining binding-screw of each bell. When the button is pressed the current divides between the two bells, and thus they are both rung. Another way to do this is to provide but one vi- brating bell, allowing the other bell to be a single-stroke bell ; they must, when this plan is adopted, be arranged in series, or directly after one another in circuit, and the second, although in itself a single-stroke bell, will vi- brate in unison or harmony with the intermissions of the current produced by the vibrator. In either of the ELECTRIC BELLS. 295 rabove ways several bells may be operated from one button or circuit-closer with one battery. 254. Describe a plan whereby an answering press-button may be combined with each of a series of bells, so that a re- sponsive ring may be sent. Such a device is shown by the diagram in Figure 116. The same battery is made to serve for the ringing in both directions. One pole of the battery, B, has a wire leading past all the bells, &, to the most distant one, brandling to one terminal of each bell in passing. Call this wire No. 1. From the other pole of the battery a wire is led which branches in two direc- tions. One branch leads to a press-button, P, the other to the response bell, R. From the other screw of the press-button a wire, 2, is led to the most distant bell, branch- ing to each bell en route in the same manner as No. 1. Now run a third wire, No. 3, from the remaining terminal of the response bell, E, to a point near to the most distant bell, &, there con- necting it to one screw of the answering button, P, the other screw of the same button being con- nected by a short wire to main wire, No. 1. In raRniiH R V( B \ ^S P Fig - 116 - like manner from No. 1, near each of the bells, , short 296 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 255. Describe the circuit wires are run to the answering buttons, P, which by their other screws are connected with the response wire, No. 3. By this arrangement a pressure of the button, P, will simultaneously ring all of the bells, b; and when any of the buttons, P, are pressed, the bell, R, will be rung. connections of a bell line of two stations, each of the said sta- tions being capable of signal- ling the other. This arrangement will be understood by reference to Figure 117. The line at each terminal station con- nects with the key, K, which by its own resili- ency presses against its back stop or contact, b y this in turn being connect- ed by insulated wire with one of the bell terminals, the other -being attached to a ground or return wire. When the line is at rest its condition is as shown in the engraving; the key at both stations being elevated, and the bells being both maintain- ed in the main-line circuit. The anvil or front contact of the key at each station connects by means of a wire with a battery, D, the opposite pole of the bat- ^f tery being permanently united with the ground or return wire. When either key is pressed the distant bell will be rung. ELECTRIC BELLS. 297 256. What kind of bell signals are or have been employed on telephone lines $ A great variety have from time to time been employed. Small, single-stroke bells were at first much, used, and in their operation a steady battery was kept on the line, and the signals were given by breaking and closing the circuit a given number of times. Magneto-bells are more universally employed at present than any other, because they are much cleaner, more economical in the end, more easily managed, and very rarely get out of order. 257. What is a magneto-bell? A magneto-bell is a polarized relay, having its arma- ture extended into a hammer which vibrates between two bells. It takes its name from the fact of its being operated by the electric pulsations produced by the rotation of coils of wire across the field of force of a magnet. 258. What is an individual signal-bell ? Described in general terms, it is a bell which, when placed in series with other bells in an electric circuit, is so arranged as to ring when desired, to the exclusion of the others. That is, if, for example, six stations were placed on one circuit, any one of the six may be signal- led without ringing the remainder of the bells in the cir- cuit. These bells are usually adapted to be rung ex- clusively from the central station ; but some varieties are capable of ringing any station from any other station. 259. Upon what principle are individual signals constructed ? Many different principles of action are embodied in these bells. A large number of them are operated by successive pulsations of electricity, which, when sent over the line, work/ a ratchet-wheel, either positively or by controlling the escapement of a clock-train. This ratchet-wheel, at a certain definite time or place, differ- ing at each station, either brings into activity an extra electro-magnet, which works the bell-hammer, or al- 298 ELECTRICITY, MAGNETISM, AND TELEGKAPHY. lows the bell-hammer to reach the bell at the required station ; the bells at the other stations having their electro-magnets cut out of circuit or their hammers me- chanically controlled. When brought to the ringing- point, bells of the step-by-step class are frequently caused to ring by sending a current of different cha- racter from that used to work the step-by-step motion. Other kinds of individual signals are worked by a clock- train, which at definite times introduces the different magneto-bell magnets into the circuit. In such appa- ratus the clock-work is tripped by an electric current sent from the central station, and rotates, bringing into circuit the different bells one after another. Still an- other kind is the harmonic ; these have armatures poised or tuned differently at each station in circuit. A trans- mitting instrument is placed at the central station, and provided with a circuit-breaker. The armature of the transmitter is adjustable in length, and when set in motion, only that circuit bell which corresponds in its rate of vibration to the rate of vibration of the circuit- breaker will ring. CHAPTER XXI. THE TELEPHONE. 260. What is the electric telephone ? The idea expressed in the word telephone is the trans- mission of sound to a distance, and hence any instrument capable of such transmission is properly termed a tele- phone. The electric telephone, however, does not ac- tually transmit sound, but is simply an instrument by which, through the agency of electricity and a conduct- ing medium therefor, sounds of any kind, including articulate speech, when produced at any point or place, may be simultaneously reproduced at any other place at a distance therefrom. 261. What is the magneto-telephone* It is a telephone in which, when used as a transmit- ter, the vibrations of a metallic diaphragm, when sounds are uttered in its vicinity, cause variations of intensity in the field of force of a magnet, whereby electrical cur- rents corresponding in character and form to the origi- nal sounds are produced in a helix of insulated wire surrounding the pole or poles of the magnet ; these tra- verse a line- wire in the circuit of which the helix is in- cluded ; and in which, when used as a receiver, the said currents circulating in the helix vary the strength of the magnet, which consequently attracts its diaphragm with varying strength, permitting it in turn to vibrate, and, bji the movement in the air so caused, to reproduce similar sounds to those transmitted. The magneto-tele- phone is now used almost exclusively as a receiver, since it has been long known that battery telephones are much more powerful transmitters. It consists of a magnet, 300 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. which may be either an electro or a permanent magnet. On one end of this magnet, or of a soft-iron core affixed thereto, is placed a coil or helix of fine, silk- covered wire, while stretched immediately in front of this core and coil is an elastic disc or diaphragm of thin sheet- iron, held to its frame by being compressed at its edges between the case and its cap or ear-piece. Some of the lines of force of the magnet pass through the coil, and others through the iron disc. Thus the plate is attract- ed towards the magnet with a constant force when the instrument is quiescent. When, however, a constantly varying electric current is passed through the coil, in either direction, the strength of the magnet is momen- tarily either increased or diminished, the attraction between it and the diaphragm varying accordingly. When the current in the coils is in such a direction as to reinforce the magnet the diaphragm is attracted more strongly than before, while if it is in the opposite direc- tion it is attracted less strongly. Now, as these varia- tions in the strength of the current are controlled by the action of the distant transmitter, they are in exact ac- cordance with the movements of its diaphragm, and thus the diaphragm of the receiving telephone is caused to vibrate also in accordance with the transmitter, and reproduces the sound. 262. Can the magneto-telephone, just described, transmit arti- culate speech, or is it restricted to its reproduction % It transmits speech quite distinctly ; indeed, for some time after its invention it was used for this purpose quite as much as for a receiver. It is one of the dis- tinctive features of the magneto-telephone that it may be so used. When acting as a transmitting telephone the operation of the instrument, depending ur^on the principles of magneto-electric induction, is as follows : The voice of the speaker throws the air into vibrations ; these, acting on the diaphragm, cause it also to vibrate ; every vibration of the diaphragm alters the magnetism of the inducing magnet, and at every change in the mag- THE TELEPHONE. 301 netic strength a transitory current is produced in the coil. Since the coil is in the line circuit, these transitory currents pass over the line and through the distant coil also. There they affect the magnetism of the receiving instrument in a similar way ; and the diaphragm of the said receiving instrument, being thus attracted with Fig. 118. Fig 119. varying degrees of strength, repeats or reproduces the motions of the transmitting diaphragm, and the speech uttered in the mouth-piece of the sending telephone is thus duplicated by the receiver. 263. Is the magneto-telephone restricted to any particular form? No ; it may and has been made in many forms. The 302 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. standard form, which, is that adopted by the American Bell Telephone Company, is shown in Figure 118, while Figure 119 is a vertical section of the same, showing the internal construction. It consists of a case of ebonite or hard rubber, containing a compound bar-magnet made of four separate bars of steel (each one separately mag- netized), laid together in pairs with similar poles to- gether. By this construction it is found that the mag- netism is more permanent than if a single bar were used. At each end, between the two pairs, is placed a soft- iron core or pole- piece. The shorter one is placed at the end intended for the handle, and a screw passes into it from the outside of the case and aids in holding the parts together ; the long- er pole piece is placed at the dia- phragm end. The helix, which is formed of very fine silk- covered wire, surrounds this longer core, and ordinarily has a re- sistance of about seventy-five ohms ; its terminal wires are extended through the case beside the magnet, and are soldered to two binding- screws at the end of the handle. Stretched in front of the pole-piece is the dia- phragm, which is simply a thin, round iron plate, such as is used by photographers in the preparation of ferro- types. This is clamped at its edges between the end of the case and the cap which forms the ear-piece, and is thus maintained in close proximity to the magnet-core, Fig. 120. THE TELEPHONE. 303 which, however, it is never allowed to touch. This instru- ment is almost universally used in America. Another form which has been used considerably is that of the "Pony Crown," of which Figure 120 shows a sectional, and Figure 121 a perspective, view. The "Crown Telephone," represented in perspective by Figure 122, has also been used to some extent. The telephone designed by M. Clement Ader is one of the handsomest forms, and is used in France. It is Fig. 121. Fig. 122. shown in sectional elevation in Figure 123, while Figure 124 is a plan view of the magnetic cores and helices, with their enclosing cup, the diaphragm being removed, and Figure 125 a side elevation of the in- strument. In this telephone A is the magnet, which is made cir- cular. The pole-pieces are of rectangular form, and are surrounded by small helices or spools, B B, which in practice are connected with the binding-screws, N N, and by their means included in the line circuit. A cup of non- magnetic metal, O, is fastened to the magnet, and surrounds both helices, forming an interior space, across which, and passing close over the cores, is the dia- 304 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. phragm, M. A cap, C, fitted with, a flaring ear-piece, E, surmounts the instrument. The peculiar feature of the Ader telephone is what the inventor calls a rein- forcer. This is a mass of iron, X, enclosed in the cap, C, and lying within the field of force of the magnet, A, and said to aid and reinforce the magnet in its action on the diaphragm, and thus to cause the diaphragm to vi- brate more energetically than it otherwise would, and to give out louder articulations. Very satisfactory re- sults have been obtained from this instrument. It is useless to attempt a description of the num- Fig. 123. Fig. 124. Fig. 125. berless forms of magneto-telephones which have been produced, the instrument being apparently capable of indefinite variation in form, but of very little variation in principle. 264. What is a battery telephone transmitter % It is an instrument adapted for the transmission of articulate speech, in which the operating electrical cur- rents, instead of being actually produced by the vibra- tions of a diaphragm in proximity to a magnet, as are those of the magneto-telephone, are developed by a vol- taic battery, and the vibrations of the diaphragm under the influence of the voice operate merely to control the THE TELEPHONE. 305 currents so produced. Battery telephones have been commonly arranged in two classes viz., those like the typical Edison telephone, in which varying degrees of pressure are brought to bear upon certain semi-conduct- ing substances included in the battery circuit, whereby the particles of such substances are brought into vary- ing degrees of intimacy, their resistance varying in a corresponding degree and in proportion to the amount of pressure to which they are subjected ; and those which are also technically and popularly called micro- phones, in which two points or electrodes of the circuit are brought more or less closely together in such a man- ner that the slightest shake or vibration greatly affects the amount of the resistance at the point of contact, and thus, of course, throughout the circuit. 265. How do such instruments operate when used to transmit articulate speech ? In those of the former type a diaphragm is mounted in a frame, just as in the Bell telephone, and is arranged to press with a light but steady initial pressure against a little button of prepared carbon or lampblack which is placed in the circuit. The resistance of finely-di- vided carbon has been by some supposed to diminish greatly under pressure ; but the real cause of the ap- parent diminution is now thought to be, as before in- dicated, the closer intimacy into which the finely-di- vided particles are brought. However that may be, when the diaphragm is spoken against it vibrates, and presses with varying degrees of strength against the lampblack button, causing its resistance correspond- ingly to vary ; and as the electro-motive force is sup- posed to be constant, the strength of the current in the circuit varies inversely with the resistance of the but- ton. When the resistance of the button is greatest the strength of current is least, and when the resistance of the button is at its minimum the current strength is at its greatest. The best authorities no longer think that in the transmitter the resistance of the substance of the 306 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. Fig. 126. carbon is susceptible of variation, but believe that such, variation is due, as we have already stated, to the vary- ing degree of con- tact between the multitude of par- ti c 1 e s composing the mass. The Edison trans- mitter, which is the best-known instru- ment of the forego- ing class, is shown in Figures 126, 127, and 128 ; Figure 126 being a vertical section of the trans- mitter, Figure 127 a perspective view, and Figure 128 a view of the entire instrument mounted on a jointed arm and fitted on a desk-stand, with bell-call, and automatic switch operating by the removal and replacement of the receiving telephone to change the line from its normal route through the signal- bell to the branch leading through the telephone. Figures 127 and 128 require no explana- tion. In Figure 126, which shows the transmitter in sec- tion, the button of prepared carbon is compressed between two metal surfaces, and the initial pressure is given by a screw, which is capable of adjustment from the rear. The diaphragm presses upon a protuberance of the upper metal plate, and when spoken against varies the contact between the metal plates and the button. One THE TELEPHONE. 307 of the circuit- wires is attached to the upper metal plate, and the other to the metal casing. The well-known Blake transmitter may be taken as the type of the second variety. Figure 129 represents the external appearance of this instrument as usually constructed. The operative parts consist of a diaphragm loosely sup- Fig. 128. ported in a frame and clamped thereto, while suspend- ed from one of its edges are two flat springs ; the nearest one to the diaphragm is the lightest of the two, and at its extremity carries a little stud of platinum, which at one side touches the diaphragm, and at the other a little disc of hard carbon with a highly polished face ; the carbon disc is carried on the lower end of the other and heavier spring. The two springs are relatively so adjusted that when they both from any reason are forced 308 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. away from the diaphragm , the platinum point has a tendency to follow the carbon disc for at least a short distance, usually about three-eighths of an inch. The springs are insulated from one another, and the only connection between them is at the point of contact between the platinum and the carbon. Figure 130 shows a sectional elevation of the working parts of the transmitter. The. two springs are carried upon the same adjust- ing lever, F, this being suspend- ed from the frame, B, by a stiff flat spring, and being ad- justable by the screw, G. This adjustment reg- ulates the ini- tial pressure of the carbon and platinum elec- trode, and also the pressure of both against the diaphragm, D. Figure 131 is a representation of the instrument with the door open and all parts in their proper position. The diaphragm, which is insulated from the iron frame by an encircling band of india-rubber, is on one side clamped to its frame by the brass clamp, h, and is at the other furnished with a damping spring, K, by which undue vibrations are checked. The front of the case is fitted with a mouth-piece; and in one corner of the case, as shown in Figure 131, the induction-coil stands. Connections are arranged where- by the two springs and the electrodes they carry, to- Fig. 129 THE TELEPHONE. 309 gether with the primary circuit of the induction-coil, are placed in a battery circuit. These circuit con- nections are represented in Figure 132. A, B, C, and D are binding screws, A and B for the battery-wires and C and D for the line-wires. Entering at A, the circuit of the battery proceeds by the wire S to the hinge H, and by the wire M to the platinum electrode through the spring, I ; from thence it continues to the carbon button, J, and by the spring thereof to the metal adjusting-lever, K, and by means of the screw, 0, to the frame, V. A wire, L, unites this frame to the lower hinge, G, and from thence another wire, P, leads to the primary coil, F, and out to the battery return by wire Y and screw B. The line- wires, or line and ground wires, are simply attached to the binding-screws C and D, which by the wires X and W lead through the secondary coil, E. In this diagram N re- presents the diaphragm. When in the operation of this transmitter the diaphragm is spoken to, the contact resistance of the platinum and carbon electrodes is varied, and the resistance of the circuit, and the strength of the current flowing therein, are correspondingly varied. The essential difference between the action of the bat- tery and magneto telephones, when the latter is used as a transmitter, is that in the battery transmitter the electrical undulations are produced by varying the resistance, and in the magneto by varying the elec- tro-motive force. 266. What is the reason that an induction-coil is used in connection with battery transmitters 1 It is found to be an advantage to use an induction-coil, 310 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. and to place the microphonic contact, or the variable re- sistance, in its primary circuit, connecting the termi- nals of the secondary circuit of the coil with and in the line circuit, because although the said resistance is ca- pable of, and actually passes through, great variations when actuated by the vibrations of the diaphragm, the extreme variation between the highest and lowest points is but an inconsiderable factor in a long-line cir- cuit, whereas the same variation in a short local circuit is proportionately great. Therefore by placing the THE TELEPHONE. 311 variable resistance in the short circuit of a primary coil, where a comparatively small change in the total resistance in the circuit would cause a great difference in the strength of current ; and by causing the second- ary coil to be a part of the line circuit, we produce in the secondary coil, and hence in the line of which it forms a part, induced currents, having as wide Fig. 132. a range of variation in the line circuit which they traverse as the battery currents which induce them have in the primary coil and circuit ; and they thus act with equal vigor upon the diaphragms of all receiving telephones in the main circuit, irrespective of the vary- ing distances at which they may be placed. 267. What other types of transmitting telephone are used* There are but two other forms of transmitter that have been employed to any extent. These will be now described. The first is the Crossley transmitter, which is repre- sented by Figure 133, and consists of a number of varia- 312 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. ble contacts, which may be partly in series and partly in multiple arc. As usually constructed, these contacts Fig. 133. are produced by arranging on a wooden diaphragm, which may or may not be furnished on the reverse side with a mouth-piece, a compound microphone, consisting Fig. 134. of four carbon pencils resting loosely at their ends in carbon socket-blocks of the form shown. The circuit- wires are attached to two of the opposing socket-blocks. THE TELEPHONE. 313 The microphone in practice is worked with a battery and fitted with an induction-coil, precisely as in the Blake and Edison transmitters. The entire apparatus is set up for work in the form represented in Figure 134. The apparatus is mainly enclosed in a compact box, on which is fixed the call-bell, IS", a calling-key, E, be- ing placed on the front of the box, and the usual au- tomatic switch, adapted to operate as a rest for the tele- phone, at the end opposite to the bell. The second form is one wherein suitable conducting material in a finely-divided condition or in the form of a coarse powder is enclosed between two conducting surfaces in a battery circuit, the strength of current being varied by the change of position in the particles of the powder. The principal type of this instrument is that invented by the Rev. Henry Hunnings, and of which Fig- ure 135 is a representation. A metal plate, B, of any desir- ed thickness, is placed in a re- cess cut into a suitable block, D, and connected with a bind- ing-screw terminal, E ; stretched over this, and held in place by a ring, F, or in other suitable way, is a very thin diaphragm of metal, A (platinum foil is generally used), which is ar- ranged at such a distance from the first plate as to form a shal- low intervening space. The thin diaphragm is connected with the second binding- screw, and the intervening space is nearly fill- ed with loose, finely-divided con- Fi e- 135 - ducting material, C, oven-made coke being found to 314 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. give good results. The instrument, when in use, may be connected directly in the line circuit, a battery also being included therein, its great initial resistance rendering the use of an induction-coil unnecessary. Of course this transmitter is not restricted to any special form. In practice a suitable handle is usually added for con- venience. Both Crossley's and Runnings' transmitters, though differing materially in detail from one another and from transmitters of the Blake and Edison types, yet operate on the broad .principle of varying the strength of a battery current by varying the resistance of the circuit at one or more points in the said circuit. 268. What is Dolbear's receiving telephone ? It is a receiver in which the vibrating plate is operated by the variation of a static charge of electricity instead of by the variation of magnetism produced by a varying current. The instrument in its simplest form is shown in sec- tion in the figure, and consists of two metallic discs, C and D, about two inches in diameter, so mounted as not to be in metallic contact. This is effected by separating them at the edges by a flange of hard rubber, which forms a part of the enclosing case. The mouth -piece is screwed down over one of the plates, and a handle over the other. Through the middle of the handle a screw is sunk, which touches the back plate and serves to adjust its flexibil- ity. The back plate is thus fastened both at the middle and at the edges, and therefore Fig - 136> cannot vibrate, while the front plate, being fastened only at the edge, is free to vibrate. THE TELEPHONE. 315 A screw-post, A, is attached to each plate, by which the instrument may be attached to the line-wires or to the line and ground. It is quite feasible, however, to connect but one of the plates to a binding-screw termi- nal, for attachment to the line- wire only, and to unite the other plate to a metal ring or plate on the knob which must be touched by the person using the instru- ment. A large induction-coil is essential in connection with the transmitter when this receiver is used, and any microphonic transmitter will answer. 269. Why is it usual to place the receiving telephone, when not in use, upon a hook or yoke at the end of a lever- switch 1 Upon the introduction of the telephone as an instru- ment of electrical communication it was found that it could not be depended upon to speak loud enough to announce when a message was to be sent, and thus it became requisite to place at each station an electric bell, by means of which a signal might be given from the dis- tant station whenever it became desirable to attract at- tention. It was also found to be advantageous for many reasons to keep the telephone helices out of the line circuit, except during the act of conversation. A switch which should be able at any desired moment to cut the bell-magnet out from the line, and introduce the telephone into the line circuit, and vice versa, thus became an essential. A button- switch was first used for this purpose, but the attendant or user frequently for- got to replace the switch, so as to restore the signal-bell to the circuit when conversation was finished. This led to the device of a lever-switch which should be operated by the weight of the telephone ; and the fact that when the telephone was laid down the hook or yoke was the most natural place for any one to leave it, was relied upon to furnish a constant and sufficient reminder for persons so to place it, and thus make the required cir- cuit change automatically, or without any positive act of their own being necessary. 316 ELECTRICITY, MAGNETISM, AND TELEGrKAPHY. Line & d a 270. How is the automatic switch generally constructed ? A bar of metal, terminating at one end in a hook or yoke adapted for the support of a telephone, is pivoted in the bell-box, so that the end for the telephone sup- port projects some distance on the outside through a slot. This bar is permanently attached to the line-wire, and when the weight of the telephone is on the bar it is brought into contact with a flat metal spring which is united by a wire to the bell- magnet, and thence to earth. When the weight is taken from the end of the bar the outer end of the bar is drawn upward by a spring, and makes contact with another spring united with a wire leading to the telephones, and thence to the earth. The connections are shown in the dia- gram, Figure 137. 271. In an ordinary magneto-bell box what other office is ordi- narily performed by the automatic switch ? Since the general introduction of the battery transmit- ter, in addition to the work of trans- ferring the main- line connection from the signal-bell to the telephone branch, the auto- Fig - 138 - matic switch-lever is so arranged as to close the local battery circuit of the transmitter when the telephone THE TELEPHONE. 317 is taken from its support. Owing to the general use of open-circuit batteries for this work such a contrivance is necessary. For convenience and compactness the battery circuit is led into the bell-box, and terminates therein in two flat springs, which, when the telephone rests upon its lever, have no communication with one another. Leaving the carbon pole of the battery, a wire may be led to the transmitter ; there the circuit is through the contact points and the primary circuit of the induction-coil ; from the transmitter it goes to the bell-box to one of the flat springs, while a wire from the other spring connects with the other pole of the battery. The act of removing the telephone from its place of rest, and the consequent recoil of the switch- lever, is made to interpose a metallic connecting piece between the two flat springs, and so the circuit is closed. CHAPTER XXII. ELECTKO-THEKAPEUTICS. 272. What is meant by the compound term "electro-physi- ology " ? Electro-physiology is tliat branch of electrical science which treats of animal electricity and its laws ; and also of the phenomena produced by the action of electricity upon the skin, muscles, and other organs of living be- ings when in a natural or healthy condition. 273. What effects may be produced in the body by the appli- cation of electricity ? When a current from a battery of considerable elec- tro-motive force is passed through the human body it produces a disagreeable tingling or burning sensation at the points at which it enters and leaves the body. A sudden and strong current of short duration, such as would be produced by the discharge of a Leyden jar, when sent through the body, produces what is gene- rally known as an electric sliock. The disturbance caused in the animal system by such shocks can be made so great as to produce severe illness, or even death. Deaths by lightning are due sometimes to the sudden discharge of electricity from the body, which has been inductively charged by the clouds, and sometimes to the direct stroke. The passage through the body of a rapid succession of magneto-currents, or of currents from an induction-coil, produces a species of temporary paralysis or numbness, so that a person grasping the electrodes connected with a source of electricity cannot let them go, but is con- strained to convulsively hold them until the cessation of the currents. 318 ELECTRO-THERAPEUTICS. 319 That many modifications may be made in the condi- tion of an animal body by electricity is very evident from the contraction of muscles and nerves when sub- jected to its action ; and also from the fact that the fluids of the body are all compounds of several ele- ments, and hence are all capable of electrolysis. 274. What is the meaning of the words therapeutics and elec- tro-therapeutics f Therapeutics is the name of the science of healing. Electro- therapeutics is the branch of electrical science that treats of the study of electricity in its relation to disease and as applied to the healing or alleviation of disease. It is a very old idea; indeed, the remedial powers of electricity are referred to by Pliny. Only quite recently, however, has it advanced to the dignity of a science, and its practical history may be traced from the year 1743, when Kruger d' Helmstadt suggested that frictional electricity might be made serviceable in the practice of medicine. From that time until the dis- covery of the voltaic battery, fifty-six years later, fric- tional electricity was considerably used as a remedial agent, with varying success. In 1799 the voltaic battery was first constructed. This gave new life to electro-the- rapeutics, and rapidly superseded the use of frictional electricity ; and voltaic currents yet subserve valuable purposes in this department, and are extending their usefulness continually. Another advance was made in 1832, when Neef, of Frankfort, commenced to use the rapidly alternating currents of magneto-electricity in the treatment of diseases. For a long time, however, electrical treatment was regarded as a species of quack- ery, but is now fully recognized as a valuable element in the healing art. Both battery and magneto currents are at the present time extensively employed in electro- therapeutics. 275. What are the names applied by the medical profession to the three forms of electricity we have referred to ? The first, frictional electricity, is often denominated 320 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. Frariklinic, because of the large share borne by Frank- lin in its application to medicine. The second form is generally called Galvanic, and its application is called ''electrization by galvanization," because Galvani, the Italian physician, by his researches brought the subject prominently before the scientific world, which publicity resulted in the conception and construction of the bat- tery by Volta. The third form is by the medical pro- fession called Faradic electricity, because Faraday was the discoverer of magneto-currents and the method of producing them. t 276. What instrumentalities are principally employed in elec- tro-therapeutical applications ? The direct current of a battery is sometimes employed through the intervention of a coil, which is composed of wire varying in thickness at different parts of its length, and furnished with a switch, by which more or less of the coil may be placed in circuit ; a circuit- breaker is also provided, by which, if desirable, a suc- cession of shocks may be produced. Frequently a com- plete induction-coil is employed, in which case the elec- trodes of the secondary coil are applied to the patient. Magneto-electric machines are also extensively used for medical purposes, and are very convenient for the ap- plication of rapidly recurring pulsations of alternating direction. 277. WJiat is meant by electro-surgery f It is a branch of electro-therapeutics which exclu- sively treats of the application of electricity to such diseases which are commonly known as surgical. In addition to the ordinary methods of application by passing electricity through the body or portions of the body, it includes two other methods i.e., galvano-cau- tery and electrolysis, which two are peculiar to it. Electro- surgery as a special branch dates back only as far as 1825, but is, perhaps, now the most valuable feature in the entire field of electro-therapeutics. Galvano-cautery means the practice of burning or ELECTKO-THERAPEUTICS. 321 searing by a wire of high electrical resistance, heated by the passage of electricity through it. This method is often used in the removal of tumors and cancers. Electrolysis, which implies the art or process of de- composing a compound substance by electricity, is chiefly applied to the decomposition of morbid growths, or to organs affected by chronic inflammation, by means of some form of needle electrodes, which are inserted in the diseased part. 278. What is the approximate electrical resistance of the hu- man body 1 The resistance, in ohms, of the human body averages about as follows : From one hand to the other, through the body, hands dry, over ten thousand ohms ; same with hands wet, six thousand ohms. From mouth to hand, hands dry, eight thousand ohms ; same with hands wet, five thousand ohms. These results were deduced from measurements made of eight persons by Professor A. E. Dolbear. of Tufts College, Somerville, Mass. 279. What is an electrical probe ? The electrical explorer, or .probe, is a little instru- ment employed to ascertain the presence and location of metallic bodies in wounds. It is in shape much like the Edison electric pen> and consists of a slender rod or sound, which encloses two conducting wires or needles, insulated from one another, and covered entirely by a non-conducting substance. The points are uncovered, and the other or outer end of the sound supports in a convenient stand a little vi- brator, or trembling electro-magnet. One of the probe conductors is attached to the electro-magnet, and the other by a flexible cord to the battery direct ; the other pole of the battery is connected with the second magnet- wire. When the circuit is closed by the contact of the two probe-points upon a metal surface for example, a leaden bullet the battery current traverses the magnet, causing the armature to tremble. The depth at which 322 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. the bullet lies is simultaneously made known by the ex- tent of insertion. The first electric exploration of wounds occurred in 1863, and was conducted substantially upon the above principle ; instead, however, of the vibrating magnet a galvanometer was used as an indicator. CHAPTER XXIII. OTHER APPLICATIONS OF ELECTRICITY: ELECTRIC CLOCKS TIME-BALLS ALARMS BLASTING TRANSMISSION OF POWER ELECTRICAL STORAGE. 280. What are electric clocks ? They are clocks which are either driven or controlled by electricity. In clocks which are driven by electricity the ordinary use of a spring or weight is dispensed with ; and instead of using the pendulum to retard and regulate the motion, it is employed to propel the hands, being itself attracted alternately from side to side. The second class of electric clocks is that in which a clock of otherwise ordinary character, driven by weight, controls or governs by electricity a number of subordinate clocks. A clock of the former class consists, usually, simply of a pair of hands adapted to rotate round a dial, and placed on the axis of a ratchet-wheel, which, by means of an electro-magnet, armature, and pawls, is caused to advance one tooth with every two swings of the pen- dulum. Clocks of the second class, on the contrary, are gene- rally constructed with a regular train of clock-work, the escapement of which is alternately released and retained by an electro -magnet, which is charged and discharged by the action of the controlling clock, which makes and breaks the circuit of the said electro-magnet. 281. When and by whom were electric clocks of the first variety invented ? The clock in which electricity supplies the actual motive power was first suggested by Alexander Bain in 324 ELECTRICITY, MAGNETISM, AND TELEGRAPHY, the year 1840. In the next year, 1841, he, in conjunction with a Mr. Barwise, obtained a patent for the application of electricity to the regulation and movement of clocks. The patent specified for its principal object the move- ment of several clocks by currents of electricity, trans- mitted at regular intervals by the agency of a clock of ordinary character, which, of course, indicates the second system we have spoken of ; and it is probable that Mr. Bain would have succeeded better had he carried out that system. But by a subsequent improvement each clock was made to move independently by electricity, and this method was at that time regarded as a much more perfect invention. The arrangement by which this is accomplished will be understood by reference to the annexed figure. The pendulum- bob, A, consists of a hollow coil of covered copper wire, and is suspended from the rod B, the wires, e d, from the ends of the coil, being carried up the pendu- lum-rod, and at the upper end thereof maintained in metallic con- nection with two springs from which the rod hangs. A brass tube, C, about two inches in diam- eter, passes through the coil, there being sufficient space left for the coil to move backward and for- ward without touching. Within this tube, and on each side of it, are placed permanent bar mag- nets, with their similar poles, n n', j)resented towards one another at a distance of about four inches apart. When an electric current passes through the coil, A, it instantly becomes magnetic ; the end towards the right, we will suppose, having, a south polarity, and that towards the left a north polarity. The coil is conse- quently attracted towards the right, and is repelled by OTHER APPLICATIONS OF ELECTRICITY. 325 the magnets on the left, as the pendulum swings in that direction. Before arriving at the end of its vibration the connec- tion with the battery is broken by the action of the pendulum ; the magnetic property of the coil instantly ceases, and it descends by the force of gravity. On as- cending the other arc of its vibration, contact is made with the battery, and a current is sent through the coil, but in the reverse direction ; so that the left hand of the coil has south polarity given to it, and the right becomes the north pole. By this reversal of the "current the coil is impelled towards the left, and the vibrations of the pendulum are thus maintained for an indefinite time. A light frame attached to the upper end of the pendulum- rod carries springs which connect with the coil- wires, e d, and make and break the battery contacts, and reverse the direction of the current through the coil. Fig, 140 shows the mode in which the vibrations of the pendulum are made to propel the hands. An electro- magnet, A, is fixed on the top of the clock, and the current is sent through the coil on each vibration of the pendu- lum. Upon each electri- cal pulsation the magnet attracts the armature, B, to which the pawl, D, is attached, and this, engaging with the teeth of the ratchet-wheel, E, advances it one tooth. The wheel is prevented from falling jDack by the retaining pawl, L. By this arrangement the ratchet-wheel is advanced one tooth by two swings of the pendulum. Thus when the wheel contains thirty teeth, and the pendulum vibrates once a second, the wheel will make one complete revolution 326 ELECTRICITY, MAGNETISH, AND TELEGRAPHY. every minute. That wheel will, therefore, constitute the seconds-wheel of the clock, and the minute and hour hands may be moved by it in the same manner as in ordinary clocks. Mr. Bain worked these clocks by means of an earth battery consisting of a large plate of zinc and a quantity of coke buried in moist ground. They did not work very satisfactorily, chiefly, no doubt, because of the unstable nature of the battery. 282. How may clocks of the character described above be governed by a central clock, and by whom was such a method devised $ As we have seen, Mr. Bain described such a system in his patent of 1841. Wheatstone, however, is generally regarded as the first person to conceive the idea of a number of clocks governed or controlled by a central clock. His ideas were greatly improved by Mr. R. L. Jones, an English railroad man, and Mr. Ritchie, of Edinburgh. Clocks operated upon this general plan have had considerable success, and are largely used in connection with observatories and many other large establishments. Mr. Jones used clocks made on the Bain principle. The standard or governing clock is the only one provided with a circuit breaker or changer, and its pendulum is not under electrical control. In short, it is of the usual construction, except that it is made to operate a circuit- breaker. The pendulums of the copying clocks have no break, as the primary pendulum performs the circuit-breaking function for all. The clocks are, therefore, necessarily maintained to- gether. The pendulums are not entrusted completely to the stimulus of the electricity, but are moved by their own weights, so that even if their- supply of electricity should fail they would go on for a time without it. There is no conflict between the two controlling forces of electricity and gravity, and by this system, therefore, OTHER APPLICATIONS OF ELECTRICITY. 327 copying clocks of little value may be made as perfect as the most costly observatory clock. 283. How are clocks of the second variety to be operated, and by whom were, they first arranged f As already indicated, these clocks may have a regular train of mechanism, and may be operated, as shown in the annexed figure, by an electro- magnetic escapement. One pendulum may serve any number of clocks. At Fig. 141. each clock is an electro-magnet, B, the armature of which is a permanent bar magnet, N" S, carrying an es- capeinent, D, which works into an escapement-wheel, E, and thus either positively propels the clock or regulates its movements. The pendulum may be placed in one of the clocks, and by dropping its points, A, into the mer- cury-cups, m', alternately, continually reverses the cur- rent of the battery, Z C, through the escapement magnet, B. Any number of these magnets may be worked in series by a proper proportionment of the battery. The first introduction of this principle into electric horology was made by a Mr. Shepherd, of London, who exhibited the arrangement publicly at the International Exhibition of 1851. 328 ELECTRICITY, MAGNETISM, AND TELEGKAPHY. 284. How may time-balls and time-guns be operated 1 They are operated by being electrically connected, with a clock which is arranged to complete a circuit by means of con- tact-springs, and thus at any pre- determined time attract the arma- ture of an electro-magnet and re- lease a trigger, which permits the ball to drop or fires the gun. The method will be understood on an examination of the annexed figure, 142. A time-ball is usually a large wicker globe covered with painted canvas or flannel ; this is fixed to a piston which falls down into a bell- mouthed tube just air-tight enough for the air to act as an elastic cush- ion. It is hauled up by hand a few minutes before the time at which it is to be dropped. 285. How can ordinary clocks be made to ring bells at any desired time ? There are several ways of doing this. One of the easiest is to place on the arbor of the hour-hand a cir- cuit-wheel of non-conducting mate- rial having a small piece of metal let in at one point of its periphery and extending through to the metal of the arbor, so as to be electrically connected with the frame and works of the clock. The wheel is made to fit, by friction only, upon the arbor, and is just tight enough to prevent slipping, while it is sufficiently loose to be easily moved round for setting at any desired point. A flat spring is attach- ed to an insulated base and made to press lightly on the edge of the circuit-wheel ; it is connected with one pole of a battery. The metal part of the circuit -wheel, by means of the frame and clock-work and a connecting Fig. 142. OTHEE APPLICATIONS OF ELECTRICITY. 329 wire, is united to one binding-screw of the alarm-bell, and the other screw of the bell to the second pole of the battery. When, by the movement of the clock, the spring is brought into contact with the metal piece on the edge of the circuit-wheel, the circuit is closed and the bell rings until the metal has passed from under the spring. The wheel, being only attached to the arbor by friction, is easily readjusted. Sometimes an arrangement like the above is unsatis- factory, because the wheel, being on the hour-hand arbor, rings the bell too long ; when such is the case a second circuit-closer is attached to the arbor of the minute-hand, which closes the battery circuit at that point once an hour. But as the circuit is also open on the hour-hand wheel, the bell cannot ring ; therefore only when both circuit-closers close at the same time can the bell ring, and only for the length of time that the wheel on the minute-hand arbor takes to pass its spring, which time can be made very short. Another way is to insert one or more metal points in the face or dial of the clock, connecting all the points to one of the bell and battery wires, and then to arrange a trailing spring to travel round, attached by friction to the hour-hand arbor, and connected with the other bat- tery wire ; a little switch is provided in each of the wires leading from the metal points to their main con- necting wire, and the switch of the point at which the bell is desired to ring is closed. 286. What are the principal methods of blasting by electricity f Passing a spark discharge, produced either from a frictional machine or a Euhmkorff or Ritchie coil, through a fuse of fulminating powder, which in its deflagration kindles the larger charge of gunpowder or other explosive, is one very general method. Another way frequently adopted is to arrange a fuse in which a very fine platinum wire is joined in circuit with a pair of stout conducting wires leading from a battery. This wire becomes heated when the current 330 flows, and, being laid amidst an easily combustible siib- stance, the latter is ignited and sets fire to the charge. 287. Describe more particularly how frictional or high-tension electricity, such as that developed by the frictional machine or induction-coil, is used to explode charges. A fuse is made, consisting of a hollow rod of gutta- percha or some other suitable non-conductor, and in this are placed two insulated wires with their ends bared; one of these wires enters the non-conducting rod at one end, and the other wire enters the other end, so that their bared ends tend to meet one another. These ends are not permitted to touch, but remain a little distance apart ; they are, however, connected by a layer of the fulminating material or mixture, which is preferably a composition of sub- sulphide of copper, sub- phosphide of copper, and chlorate of potash. A fuse has been employed which is based upon the action which india-rubber has upon copper. It has been as- certained that when copper wire is insulated with vul- canized india-rubber its surface becomes covered, after a ]apse of some months, with a layer of sulphide of copper, which is capable of conducting electricity. The fuse is ingeniously formed by removing a portion of the covering from a loop of such wire, as in Figure 143, and then cutting away a very small piece of the wire. Fig. 143. A and B represent the wires leading from the source of the electricity, and the current, interrupted by the space between the points a and 5, takes the route by means of the sulphide of copper which coats the inner surface of the covering, igniting it, and with it any inflammable OTHER APPLICATIONS OF ELECTRICITY. 331 substance, like gunpowder or gun-cotton, which may be placed in the cavity. If the exploding is done by an electric machine it is better to first charge a condenser by means of the ma- chine, and then discharge the condenser through the fuse. In addition to the sources of electricity which have been already mentioned i.e., the electric machine and induction-coil a magneto-electric machine is fre- quently used ; while if the fuse employed is composed of the three ingredients first described it is quite possi- ble to explode it even with a battery current. 288. Describe more particularly how electricity generated by a battery or dynamo-electric machine is used in blasting. The battery or dynamo-machine being provided, wires are led from its poles to the different points at which the explosions are to be produced. At these points the large wire, which is insulated, is cut, and a small piece of very fine platinum wire stretched between the two ends of the break. As many of these platinum joints as are desired are in this way placed in the circuit. The fuse is caused to surround the fine ware, which should be coated with fulminate of mercury. Upon closing the circuit of the battery or ma- chine the fine wires are heat- ed to redness by the passing electricity, and explode their charges. In the accom- panying figure the circuits are represented as being arranged Fig. 144. to operate the exploder from a safe distance. The fuse, being hidden in a hole drilled in the rocks, is connected 332 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. by wires, a ~b, with a battery, B, the circuit of this battery passing also through the contact-points of the relay, R. The relay electro-magnet is in the circuit of the battery L, by means of the wires x y, and when the main circuit is closed by the depression of the key, #, the relay armature is attracted, the local points come together, the local circuit is closed, and the charge is fired. The battery B and relay, R, are, of course, placed in a protected position. 289. What advantage has the second plan over the first ? It has two advantages : first, that the condition of the conductors may be tested after they are laid, from time to time, as frequently as may be desirable, by feeble currents which will not heat the platinum wires to any great extent ; and, second, that several insulated con- ductors may be laid in one cable without interfering with each other, which cannot be done when a fuse is fired from a condenser discharge, owing to the powerful currents induced in the adjacent wires, which would fire the fuses attached to all the wires whenever an electri- cal current or impulse was passed along a single wire. 290. Has electricity been applied to the production of motion f Yes ; the idea of a moving force derived from electri- city, and especially through the medium of electro-mag- netism, was one of the earliest in the history of electri- cal science. Numberless attempts have been made to embody the idea in a practical form ; nearly all of them, up to the year 1872, being based upon one principle namely, the instantaneous production and destruction of force either by making and breaking the circuit of a battery which includes one or more electro magnets, or by re- versing continuously the currents in the circuit and through the electro-magnets. One of the earliest electro-motors of which we have any knowledge is that of Professor Jacobi, who in 1834, under the auspices of the Russian government, constructed an electro-magnetic engine of considerable OTHER APPLICATIONS OF ELECTRICITY. 333 power. This was fitted in a boat 28 feet long, 7j- wide, and drawing 2f feet of water. The boat moved, when propelled by the engine, at a rate of four or five miles per hour. A battery of sixty -four cells was used to excite the engine. Some years later an electric engine was built by a Mr. Davidson, in Scotland, and tried on the Edinburgh and Glasgow Railway, but no great power was developed by it. One reason why these engines developed so little power is the very limited sphere of magnetic attrac- tion, and in order to overcome this disadvantage engines with axial magnets, or suck- ing-coils, were devised. In these a core of soft iron is drawn alternately into and out of a hollow coil as the circuit is made arid broken, and the reciprocating recti- linear motion thus produced is transformed into a regu- lar circular or rotary motion by a connecting-rod, a crank, and a fly-wheel. Our own Fig. 145. countryman, Charles Graf- ton Page, contrived a great many such engines ; and one of the simplest is shown in the engraving, Figure 145. M. Froment, of France, has made one of the best of this class of motors. Figure 146 represents this ma- chine. It is made on the same principle as those already described that is, the successive break and make of the current through the several electro-magnets. These magnets, A, B, C, and D, are four in number, and are fastened on an iron frame, X. A drum carrying eight soft-iron armatures, M M, rotates between the electro- magnets. The battery current enters at the screw-post, K, passes through the machine, and leaves at the sec- ond terminal, H. The current is broken, and each 334 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. magnet neutralized, just as the armature comes oppo- site to its poles ; the magnetic power being restored at the moment when each armature has passed one-half the distance which separates each electro-magnet from the next. These changes are made by a suitable circuit- breaker arranged on the metal arc, O. In the figure this Fig. 146. motor is represented as supplying power to turn a small mill. 291. Have such electro-magnetic motors been practically suc- cessful ? No ; several reasons have prevented this. In the first place, it is a physical impossibility for power derived from the consumption of zinc and acids in a voltaic bat- OTHER APPLICATIONS OF ELECTRICITY. 335 tery to compete economically with power derived from the consumption of coal to produce steam. The con- sumption of the metal at the circuit-breaking points is also very rapid, necessitating close attention and militat- ing against satisfactory work. Moreover, the power in such engines operates under great disadvantages, and the transformation of electro-magnetism into mechani- cal energy is attended with great loss, chiefly owing, as before indicated, to the fact of the rapid diminution of the attractive power of the magnet as the armature re- cedes from it, the said attraction varying inversely as the square of the distance. Some years since the late Dr. Joule published his bril- liant researches, in which he showed that the potential energy of zinc was so much lower than that of coal that it was impossible that a motor driven by the consump- tion of the former substance could ever successfully compete with steam, except in certain special cases where the power required is very light. 292. On what principle may practical electro-motors be con- structed 1 The only practical electro-motor known, and one which promises at no distant date to be eminently use- ful, is the dynamo- electric machine when made opera- tive by passing a current into it from some external source. It was not known until about the year 1872 that the action of the dynamo- electric machine was reversible, and that it could be used interchangeably as a machine to develop electricity or as a machine to transform electricity into motion. M. Gramme early discovered that his machine could be so utilized; and it is said that the late eminent philo- sopher, mathematician, and electrician, Professor J. Clerk Maxwell, was so impressed with the far-reaching im- portance of this discovery that when asked what he regarded as the greatest discovery of the nineteenth century, he replied without hesitation, "The reversi- bility of the Gramme machine." 336 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 293. How are dynamo-electric machines arranged to operate as motors, and how may power by their agency be transmitted ? Power from any convenient source, such as a steam- engine or water-wheel, is caused to drive one dynamo- electric machine, a belt being carried from the motor to the armature-pulley of the machine, and the armature is thus rotated. The rotation of the armature between the magnet-poles develops electric currents in its coils, which, if led away by conducting wires connecting at their distant extremities with the terminals of a second dynamo- electric machine, cause the armature of the second machine to rotate rapidly in the opposite di- rection to that of the first ; a pulley may be placed on the armature shaft of the second machine, to which a belt is attached to convey the power thus reproduced wherever it is wanted. The first machine thus generates the current, which is utilized in imparting motion to the second machine. The work done by the original power is in the first machine transformed into electricity, and can then be conveyed or transferred by conducting wires to the dif- ferent points where it is required ; arriving at such points, it is passed through the armature and field-mag- net coils of other machines, causing the armatures to ro- tate and to reconvert the electricity into motive power, which by any well-known means may then accomplish its work. As much as sixty per cent, of the original power has in this manner been experimentally reclaimed under favorable circumstances-, or, in other words, the pulley of the second machine has been known to exercise a power equal to sixty per cent, of the original power re- quired to work the armature of the first or generating machine. Practically this percentage is higher than can ordi- narily be expected ; for inasmuch as the armatures of all magneto or dynamo-electric machines generate cur- rents when rotated, there can be no exception in this OTHER APPLICATIONS OF ELECTRICITY. 337 case, and as soon as the armature of the second machine commences to revolve it sets up a current opposite in direction and consequently tending to weaken the origi- nal current and to reduce its power on the second arma- ture materially. 294. Has electrical power so transmitted been utilized to any great extent ? If so, where and how ? The general utilization of this important application of electricity is still in the future. It has, however, been extensively illustrated upon the lecture platform, and was also practically illustrated in France in 1879, when two French engineers ploughed a field by power electrically transmitted. A double-ended plough was used, so that it might go either backward or forward without turning, like a ferryboat. This plough was pulled across the field from side to side by a pair of dy- namo-electric machines, one on each side. Both of the machines were driven alternately by electric currents supplied alternately to each by a third machine located upon the road a few hundred yards away, to which motion was given by a steam-engine placed near it. One of the most interesting and important features of the subject of electro- motion is the bearing which it has upon the railway problem. In all probability the present century will see a large proportion of the steam- locomotives of the present day superseded by dynamo- electric locomotives. The idea of applying electro-mo- tors to railways appears to have originated with Dr. Werner Siemens in 1867, although not until some years later did he find an opportunity to experiment practi- cally upon the subject. The first practical demonstra- tion of the idea was a small railway constructed by Dr. Siemens and exhibited in Berlin in 1879. This railway was circular and had a total length of about three hun- dred and fifty yards. The currents, from low-tension dynamo-machines, were transmitted along the rails and supplied to an electro-motor on the first car of the train by means of frictional contacts, such as metal brushes 338 ELECTKICITY, MAGNETISM, AND TELEGRAPHY. depending from the motor terminals and bearing upon the rails. This experimental railway was succeeded by a second, which was built by Siemens and Halske, and which was opened for business in 1881. This railway was first built from Berlin to Lichterfelde, but has since been extended to Potsdam, a distance of seventeen miles, and is now in process of a still further extension to Steg- litz. It works very successfully. It was found, in the light of experience gained by the Berlin railway, that instead of having a special locomotive it was better to attach a smaller motor to each car, which is now done. Mr. Thomas A. Edison has also constructed an electric railway upon similar principles at Menlo Park, New Jersey, which he has operated for some time. It is stated that he has achieved a speed of thirty miles per hour. The latest experiments in the electrical transmission of power were made by M. Marcel Deprez quite recently in the workshops of the Northern Railway at Paris. These experiments consisted in the transmission of six horse-power over a line of wire twelve and a half miles long, ma Bourget, and of ten horse-power over a twenty- two-mile line ma Sevran Livry. It is stated that the re- sults were a reclamation of one -half the original power in both cases. The data of the shorter-line experiment were as fol- lows : Resistance of the telegraph-wire, 160 ohms. Generator. Resistance of inducing armatures, 20 ohms. Resistance of field-magnet helices, 36 ohms. Number of revolutions per minute, 650. Strength of current, 2.1 amperes. Receiver. Resistance of armature-coils, 50 ohms. Resistance of field-magnets, 33 ohms. OTHER APPLICATIONS OF ELECTRICITY. 339 Number of revolutions per minute, 313. Resistance of the total circuit, 299 ohms. Useful work measured on the brake, per second, 156 kilogramme tres. The measurements of the electro-motive force and the mechanical work expended are not given. No satis- factory opinion can be based upon the above data as to the economy of the work done, especially as it has been ascertained that instead of working the generating ma- chine from an independent source of power which could be measured by a dynamometer, the power was taken from a countershaft in the shops, so that the horse- power expended could not be measured. Moreover, the generating and reproducing machines were placed very near to one another, and, though connected on one side by the line-wire 12J miles long, were connected for the return circuit simply by an insulated wire of a few yards in length. Therefore this was not a satis- factory practical test; and although the newspaper re- ports were very flattering indeed, and although the friends of M. Deprez claimed a return of 50 per cent., it is not easy to see how such conclusions can be arrived at from the incomplete data given. These experiments were not the first made by Marcel Deprez. In October, 1882, he transmitted power with a certain degree of success between Munich and Mies- bach, a distance of a little over 31 miles. At that time it was broadly stated by the friends of M. Deprez that 60 per cent, of the power expended was reclaimed ; but the certificate of the Munich Electro-Technical Com- mittee gives no more than 38.9 per cent., even this being a liberal estimate. In this case also, although the re- turn of horse-power is stated at 0.25, no mention is made of the power expended. It thus appears that the only practical knowledge gained from these tests is the knowledge that it is pos- sible to transmit to a distance of at least thirty miles 340 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. the force of a certain number of horse-power over an ordinary telegraph-wire and by means of dynamo- electric machines. 295. What are secondary batteries ? Secondary batteries, frequently but erroneously called accumulators of electricity, are batteries which origi- nally have no electro- motive force of their own, but are capable of being acted upon by an external source of electricity in such a manner that they acquire the power to give out an electric current opposite in di- rection to that of the external source by which they were treated. Secondary cells consist of two plates, of identical material or character, immersed in some suit- able liquid, such as water. Normally such a cell can have no electro-motive force, because as the plates are alike and immersed in the same liquid there is no difference of potential between them, and consequently no E. M. F. and no tendency to set up a current of electricity. But if we connect such a cell in circuit with an active voltaic battery or a dynamo-electric ma- chine, or, in fact, with any other generator of strong and constant direct currents, a result occurs which we may regard as the storage of electrical energy. It has been found that if the immersed plates are made of lead the secondary effects are more powerful and lasting than if other metals are used ; therefore it has become customary to employ leaden plates in these batteries. Moreover, since it is well known that acidulated water has a much higher conductivity than pure water, and also aids the action of the charging current, it is usually employed as the liquid in which the plates are im- mersed. When the cell of leaden plates immersed in water acidulated with sulphuric acid is subjected to the action of the charging source, that plate which is connected with its positive pole, or, in other words, that plate of the secondary cell at which the current from the charging source enters, becomes covered with a spongy brown surface of peroxide of lead, while the OTHER APPLICATIONS OF ELECTEICITY. 341 other plate is deoxidized by the liberation of hydrogen from the dilute acid. When the leaden plates arrive at this condition the battery is said to be charged, and tends to furnish an electrical current, as already stated, in opposition to that of the charging current. If the original generator is now removed, and the wires lead- ing from the two electrodes of the secondary cell are connected together by a conducting wire, so as to form a closed circuit, it will be found that a current of elec- tricity will pass through it from the peroxidized plate to the other, the bright or deoxidized plate becom- ing gradually oxidized, and the oxidized surface of the other becoming gradually reduced to a less oxidized con- dition ; and the current will continue to flow until the two leaden plates are again brought to a similar con- dition. This identical phenomenon operates in nearly all voltaic batteries to coat their own plates with the gases oxygen and hydrogen, and is called ' ' polarization of plates." 296. Give a short account of the history of the secondary cell. The history of the secondary cell dates from the year 1801. Gautherot, in that year, found that the wires of platinum or of silver, w^hich had been employed as elec- trodes of a voltaic battery in the decomposition of salt water, acquired, and retained after they were discon- nected from the battery, the power of yielding a tran- sient current ; this was, of course, due to polarization. In 1803 a philosopher of Jena, Bitter by name, observed the same phenomenon, using wires of gold ; and, attach- ing some importance thereto, constructed the first sec- ondary pile, which, like the pile of Volta, was an actual pile of discs, consisting of alternating discs of copper and moistened card, piled one upon another, and moist- ened with a solution of salt or sal-ammoniac. It was found that this pile, after being connected for some time. in the circuit of an ordinary voltaic battery, received a charge which was capable of giving a con- siderable shock. Hitter, however, did not succeed in 342 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. discovering the underlying principle of this phenome- non, and the only result accruing from his experiments seems to have been that they attracted the attention of other experimenters. In 1842 Professor Grove con- structed his gas-battery, which was a true secondary battery, in which the secondary currents were produced by the recombination of oxygen and hydrogen, previ- ously separated, by electricity derived from an external source. M. Gaston Plante, as early as 1859, followed up these researches by vigorous and persevering experi- ments, and succeeded in producing a really valuable and practical secondary battery, which has been utilized for a variety of purposes : it has been made to produce light ; it has been extensively employed in galvano-cau- tery and other surgical applications, in telegraphy, and even as a propelling power for velocipedes and pleasure- boats. Undoubtedly the present state of the electrical storage of energy, and our present knowledge of second- ary cells, 'is due more to M. Plante than to any other person. No advance was made upon the battery of Plante until quite recently. In the spring of 1881 it was announced that "a box of electric energy equiva- lent to nearly a million foot-pounds" had been trans- ported from Paris to Scotland in perfect safety. This statement was soon after confirmed by Sir William Thomson, to whom the box was consigned, and at the time attracted considerable attention. It was subse- quently ascertained that this box was really an im- proved secondary battery, constructed upon the plan of M. Camille Faure, who in 1880 conceived the idea of giving to the two plates of the cell to be constructed a preliminary coating of red lead, which rendered them much easier of reduction to the necessary condition for speedy charging. By M. Faure' s improvement the time spent in the formation of the cell was reduced from months to days. The ultimate result is .the same as in the Plante cell namely, the development, upon leaden plates immersed in acidulated w^ater, of a coat- OTHER APPLICATIONS OF ELECTRICITY. 343 ing of peroxide of lead, which may easily and quickly be reduced to the loosely crystalline metallic condition. By the process of "formation," in which the current from a dynamo-electric machine is sent through the secondary cells for several days without intermission, the coating of red lead is on one plate transformed gradually to a spongy metallic state, and on the other to a spongy surface of peroxide of lead. . Since the improvement of M. Faure was made pub- lic many modifications of his process, as also innumer- able alternative methods of achieving the same result, have been introduced. It may be here stated that an important part of Faure' s process was the protection of the red-lead coating of the plates by means of en- velopes of flannel or felt ; and that the great majority of his successors present no other novelty than to dis- pense with these envelopes, and to substitute perfora- tions, channels, or grooves in the lead plates, by which the adhesion of the oxide is facilitated. It was thought by many, upon the introduction of the Faure cell, that the difficulties attending the storage of electrical energy had all been overcome, and that re- sults heretofore impossible were now to be gained ; but it does not, after a lapse of two years, appear that these expectations have been realized, except to a very limited extent. 297. Give a description of the Plante cell. A containing-vessel of any suitable material, such as glass or earthenware, is partly filled with a solution consisting of nine- tenths water and one-tenth sulphuric acid. In this liquid two sheets of lead rolled together, but kept from touching by strips of rubber rolled be- tween them, are placed. Figure 147 represents the appearance of the sheets while being rolled, and also shows them after they are rolled into form. An air-tight stopper, in which Is a hole for introduc- ing or withdrawing the liquid and for the escape of gas, covers the vessel, which is very tall. The battery at 344 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. this stage of its manufacture is represented by Figure 148. The whole is now surmounted by an ebonite cover, which is fitted with two binding-screws to attach to the Fig. 147. wires of the charging battery, these terminals being permanently connected with the leaden plates. This cell, as already indicated, is inert until one of the electrodes becomes completely oxi- dized, which, when the cell is new, takes a very long time. When, how- ever, the cell has once been brought to its proper condition it is recharged very quickly. The charging may be done by the use of two or three Grove or chromic-acid cells, as shown in the accompanying engraving, or by a dynamo-electric machine. The " forming" of the cell, after it is once set up, simply consists in alternately passing the charging cur- rent through it and discharging it, each alternate charge being sent through the secondary cell in the Fig. MS. opposite direction to the one imme- diately preceding. The time of each charge is gradually increased, and the work of formation thus goes on for 345 OTHER APPLICATIONS OF ELECTRICITY. several months, until a thoroughly formed cell duced. The electro-motive force of this cell when charged may be as high as 2.38 volts ; and as its inter resistance is not greater than 0.1 2 of an ohm, the curre through a short wire of large size is of very considerable Fig. 149. strength. As a method of economically charging a number of these cells, M. Plante adopted the plan repre- sented by Figure 150. The cells, arranged in a frame as shown, are surmounted by a rotatory commutator, or circuit-changer, which, when turned in one way, connects them in multiple arc, so that the entire series, irrespec- tive of number, may all be regarded as one cell ; and which, when turned to a right angle from this position, connects them in series, the positive pole of the first to 346 ELECTRICITY. MAGNETISM, AND TELEGRAPHY. the negative of the next, and so on. By this arrange- ment a great number of secondary cells can be simul- taneously charged in multiple by a couple of cells of acid battery, and may then be turned into a serial arrangement for use by simply rotating the commutator. This is very convenient when strong currents are re- quired for a short time, as for experimental or instruc- tive purposes, as it produces all the effect of a large Fig. 150. number of Grove cells without the trouble and expense of setting them up. 298. How may a small secondary battery be easily construct- ed illustrating the foregoing principles f Take a glass of any convenient size and shape (a tum- bler, for example), and nearly fill it with water acidu- lated with one-eighth of its bulk of sulphuric acid. Now cut two small strips of clean sheet-lead of a size to match the glass, perhaps three inches long, three-quar- OTHER APPLICATIONS OF ELECTRICITY. 347 ters of an inch wide, and one-sixteenth of an inch thick. A card-board cover may be made for the glass, with two slits cut in it so that the ends of the lead strips may be passed through and bent over ; they are thus held in place, and the ends which pass through are fastened to wires. Couple up two or three cells of any battery (the gravity battery will do) in series, and one of the battery wires with one of the lead strips, and the other battery wire to the other strip. The lead strip attached to the wire leading from the positive pole of the battery will soon be seen to have a deposit of an oxide of lead formed on it. After the action has continued for a short time, if the battery wires are disconnected and the wires at- tached to the leaden plates are connected together with a galvanometer in circuit, a current may be observed passing in the opposite direction to the original current. An ordinary gravity cell has an electro-motive force of about one volt. It takes about three volts to form a secondary cell ; and when formed and completely charged it has an electro-motive force of about two volts. 299. How is the secondary cell, as improved by Faure, con- structed ? The improvement of M. Faure consists chiefly in the adaptation and adop- tion of devices which aid materially in shortening the tedious process of formation. This is ac- complished by giving Fig IM each of the leaden plates a thick coating of red lead prior to its immersion in the dilute acid. A box is provided with guides in the ends, and in these guides flat sheets of lead, heavily paint- ed with a paste made of red lead and dilute acid, are placed ; a piece of felt is pressed against each side, in order to retain the red lead in position. As indicated in the annexed diagram, the sheets of lead are arranged 348 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. Fig. 152. like the plates of a condenser ; those attached to one end of the box being interleaved with those of the other end, but kept from touching them. All the sheets on one side are connected with a binding- screw, to which one of the leading-in wires is attached ; and the sheets fixed to the other side are correspondingly connect- ed together, and also with a second binding-screw for the other lead- iug-in wire. The cell .then pre- sents the appear- ance shown in Figure 152. The box is filled up with dilute acid, and a charging current is sent through it for over a week, when the red lead is reduced gradually on one side to metallic lead, and on the other is developed into the peroxide of lead. 300. What is meant by the popular expression " storage of elec- tricity " ? The popular term is a misnomer, and rightly stated should be the " electrical storage of energy." The real state of the case is that by means of electri- city chemical work is done, and energy is thereby stored up ; so that if we permit the chemical work to react electrical currents in a reverse direction are generated. In other words, the phrase " storage or accumulation of electricity" means simply the combination, by means of electricity, of certain elements and compounds in a certain way, by which a tendency to react, and so pro- duce electrical currents, is given to the said combina- tion. 301. Have secondary batteries become commercially successful ? No ; these batteries have, up to the present time, not OTHEK APPLICATIONS OF ELECTRICITY. 349 been so successful or so useful as might have beeii ex- pected from the statements made in regard to them when the Faure cell was first introduced ; and it is very clear that a commercially successful and practical sys- tem of storage of electrical energy has yet to be de- veloped. It is certain that a force which has once been evolved and utilized to do work must be more costly when reproduced than when first developed, by the cost of the work done ; that is, even supposing there is no loss in the transformation, first, of electrical energy into chemical energy, and, secondly, of the chemical back again into electrical energy. In point of fact, however, a considerable loss occurs in storage. Several important considerations militate against the use of the secondary cell, made even in the best method now known. These are as follows : The first cost, which is very great ; the expense and time required in charging ; their great weight and bulk each cell weighing at least fifty pounds and the necessity of a great number of cells to work even a single incandescent lamp. To these must be added the comparatively high internal resist- ance of the Faure cell, as generally constructed, some of them showing a resistance as high as half an ohm. It must be stated, however, that it has valuable qualities namely, portability, lessened risk from high- tension currents, steadiness in production within certain limits, and also the fact that, although it takes a great number of cells to work one lamp, the same number can, prop- perly arranged, operate several lamps. There can be no doubt that if these batteries are even- tually proved to be practical they will give a great im- petus to electric lighting. 302. Has electricity been applied to other purposes than those already described ? Yes, the applications of electricity are too numerous to be mentioned here ; many of the proposed applica- 350 ELECTRICITY, MAGNETISM, AND TELEGRAPHY, tions of the force, however, are impractical and vision- ary. It has been used as a means of measuring the velocity of rapidly moving bodies, such as cannon-balls, for per- forming upon musical instruments, for gas-lighting, and even for killing whales. The only application which it is necessary to speak of here is that of gas-lighting. This has been done in seve- ral ways. By using a thermo-electric battery, and flash- ing a spark produced by the current between two pla- tinum contact-points placed directly over the burner. In this case the current first attracts an armature and opens a conical gas-stopper ; this plan is, therefore, well adapted for street-lighting. A second way is to ar- range the secondary circuit of an induction-coil with points over each burner, making the circuit in a num- ber of sections, so that one section can be lighted after another. This plan utilizes the secondary current. A third plan, much used in private houses and work- shops, is adapted for individual burners. Six or seven cells of a suitable battery are placed in circuit with a large, continuous coil of covered wire with a soft-iron core, and a circuit-closer also in the circuit is fixed upon each burner, so that the act of turning on the gas brings the two points of the circuit-closer into moment- ary contact with one another just over the escaping gas. The spark occurs at the moment when the points again separate, and is partly due to the extra current result- ing from the self-induction of the convolutions of the coil, and partly to the magneto-currents generated by the demagnetization of the core. CHAPTER XXIY. ODDS AND ENDS. THE tenacity of a copper wire is diminished after an electric current has for some time passed through it. In an iron wire the tenacity, in the same circumstances, increases. A piece of wood cut from a tree is a good conductor ; let it be heated and dried, it becomes an insulator ; let it be baked to charcoal, it becomes a good conductor again ; burn it to ashes, and it becomes once more an insulator. Professor Gr. S. Ohm was born March 16, 1787 ; died July 7, 1854. Wheatstone' s bridge was devised by S. Hunter Chris- tie in 1833, and is described in the " Philosophical Transactions," February 28, 1833. According to Faraday, so small a quantity of electri- city is stored in a Leyden jar that the decomposition of a single grain of water required 800,000 discharges of his large Leyden battery. Sir Charles Wheatstone was born in 1802; died Oc- tober 19, 1875, aged seventy-three. The incandescent electric light was first ^patented in England by an American named Starr, in the name of Edward Augustin King. The number of the patent is 10,919, and the date November 4, 1845. A. Graham Bell's first telephone patent was issued March 7, 1876, and is numbered 174,465. The second patent for the Bell telephone bears date January 30, 1877, and number 186,787. The resistance of the primary circuit of the induction- 851 352 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. coil of a Blake transmitter is from two- tenths to three- tenths of an ohm. The resistance of the secondary circuit averages about one hundred and fifty ohms. The resistance of a Bell telephone- coil is about sev- enty-five ohms. Speaking of duplex and other multiple telegraphs, Sabine's ''History and Progress of the Electric Tele- graph," republished in 1869, says: "Telegraphing in opposite directions, and telegraphing in the same di- rection, more than one message at a time, must be looked upon as little more than 'feats of intellectual gymnastics,' very beautiful in their way, but quite use- less in a practical point of view." The discovery of the Leyden jar was first announced in a letter addressed on the 4th of November, 1745, by Kleist, a Pomeranian ecclesiastic living in the town of Cammin, to Dr. Lieberkuhn, of Berlin. It was rediscovered the following year by Cuneus, a pupil of Professor Muschenbroek. Michael Faraday was born September 22, 1791, and died August 25, 1867. The first practical electro-magnet was made in 1825 by William Sturgeon. Du Verney, in 1700, was aware that the limbs of a frog were convulsed by the action of electricity. Twenty- two years before that date " Swammerdam showed the Grand Duke of Tuscany that when a portion of muscle of a frog's leg, hanging by a thread of nerve, bound with silver wire, was held over a copper support so that both nerve and wire touchecj the copper, the muscle immediately contracted." Not until 1786 did Galvani make the same discovery, upon which was based the so-called science of galvanism, which was later ascertained to be one of the most useful develop- ments of electricity. It has been demonstrated by experiment in England that one mile of buried or submerged cable develops as ODDS AND ENDS. 353 much electro-static capacity as twenty-three miles of ordinary overhead wire. Yolta invented and described the electrophorus in 1776. The first magneto-electric machine was constructed in 1833 by Pixii. The Siemens armature was invented in 1857 by E. Werner Siemens, and is now universally employed in the well-known magneto-telephone bell. Sulzer, of Berlin, in 1762, is believed to have been the first who noticed the peculiar taste occasioned by a piece of silver and a piece of lead when placed in con- tact with each other and with the tongue. This is the earliest suggestion of the voltaic battery. In 1800 Volta announced his invention of the battery. It is stated in the 1852 edition of the ' ' Encyclopaedia Britannica ' ' that in May, 1793, a voltaic pile was con- structed and used by a Mr. John Robison, the publi- cation of the account being made by Dr. Fowler, of Edinburgh. The current generated in a magneto-telephone is esti- mated by De la Hue not to exceed that which would be produced by one Daniell cell in a circuit of copper wire four millimetres in diameter, and of a length sufficient to go two hundred and ninety times round the earth. Oersted discovered in 1819 that a freely and horizon- tally suspended magnetic needle would deflect under the influence of an electric current. Romagnosi, of Trente, made and published the same discovery in 1805. The electric light was first produced by Sir Humphry Davy in 1802. Faraday discovered that electricity could be produced from magnets in 1831. The dynamo-electric machine is first described in a patent issued in England, October 14, 1854, to Soren Hjorth, and was reinvented in 1866 by four persons 354 Alfred Varley, who also patented his machine, Werner Siemens, Sir Charles Wheats tone, and Moses Gr. Farmer. Galvanized iron wire, to have the same conductivity as the same length of copper wire, should weigh about six times as much per unit of length. The resistance per mile of iron wire at sixty degrees Fahrenheit is ascertained in ohms by dividing 395,000 by the square of the diameter of the wire in mils. A mil is one-thousandth of an inch. The resistance of iron wire increases about thirty-five hundredths per cent, for each additional degree. The resistance per mile of pure copper wire at sixty degrees Fahrenheit may be found by dividing 54,892 by the square of the diameter in mils. The resistance of copper wire increases about twenty- one hundreths per cent, for each additional degree Fahrenheit. Ampere, the founder of the science of electro-dy- namics, was born in January, 1775 ; died in June, 1836. The identity of lightning and electricity was discovered and demonstrated by Benjamin Franklin in 1747. The first lightning-rod was erected by Franklin upon his own house in 1752. Franklin, the father of American electricians, was born in Boston January 17, 1706, and died in Phila- delphia April 17, 1790. The first experimental gutta-percha insulated cable was made and submerged in September, 1847, at Bound Creek, between Newark and Elizabeth, New Jersey, by John J. Craven. A similar cable was laid by the Mag- netic Telegraph Company across the Passaic River in February, 1848, and across the Hudson River June 15, 1848, the latter being one mile in length, all of which were successful. The first long submarine telegraph-cable was laid across the English Channel in August, 1850. When called upon to give his opinion concerning the nature of electricity, Faraday gave utterance to the fol- ODDS AND ENDS. 355 lowing remarkable statement : " There was a time when I thought I knew something about the matter ; but the longer I live, and the more carefully I study the subject, the more convinced I am of my total ignorance of the nature of electricity." Philip Reis, the inventor of the now well-known Reis telephone, died January 14, 1874. In Wheatstone's bridge systems, when the galvanome- ter resistance is greater than the battery resistance, the galvanometer should be made to connect the junction of the two greater resistances with that of the lesser. The dip of the magnetic needle was discovered in 1576 by a compass-maker named Norman. M. Steinheil, though not the first to use the earth as a portion of an electrical circuit, was the first to com- plete the circuit of a voltaic battery through the earth, and to use the earth circuit in telegraphy. Steinheil died September 14, 1870. S. F. B. Morse, the inventor of the electro-magnetic telegraph, was born April 27, 1791 ; died April 2, 1872. Professor Leonard D. Gale, in a deposition in con- nection with a telegraphic lawsuit in 1851, said: " I saw Mr. Morse translate a message, while in an ad- joining room to the magnet, by the sound only. This was in the city of New York in 1837." The first printing telegraph was invented by Alfred Yail in 1837. The conducting power of carbon is much lower than that of the metals, and instead of decreasing, as in the metals, with a rise in temperature, it decreases. 356 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. INTERNATIONAL MORSE CHARACTERS. ALPHABET. A B C A D E . F__ G EL- H I J K L M N P N 6 Q R S_._ T _ U V W__l__ U X Y z NUMERALS. 1 2 PUNCTUATION MARKS. Period (.) ... Comma (,) _ Interrogation (?) Exclamation (!) ODDS AND ENDS. 357 AMERICAN MORSE CHARACTERS. ALPHABET. A B C D E . F._ G _- H- I J K L M N () P Q R. _ S T U V W X Y Z &- , NUMERALS. I 2 ._ 3- 4 5 6 . PUNCTUATION MARKS. Period () -- Comma (,)-__ Inter.rogati'on (?) _ Exclamation (0 TABLES. TABLE I. (From Culley's Hand-Book}. COPPER WIRE. 1 n Ta |*| fi^v-s. y^f *o ^* ii^ >^ *f? bflrt Number of Dvi WUn'S IK s .1^ 8 PQ.fao, Diameter. yards in I pound. .'!._;. ft go 2* s4||| ^ * " . pl&l Inches. Milli- metres. Oz. 4^ .2302 5-847 2.095 84O.09 1. 00 5 .226 5-740 2.175 809.20 1.038 6 .198 5.029 2.834 62I.OO 1-352 7 .183 4.648 3-3I7 530.59 1-583 8 175 4-445 3.628 485.10 1-731 9 .I6O 4.064 3-35 4O4.6O 2.068 10 .136 3-454 6.007 292.99 2.867 ii -.128 3-251 6.781 259-55 3-237 12 .107 2.717 9-705 I8I.35 4-623 13 IO 2-54 ii. ii 158.41 5-300 .092 2-336 13-125 134.40 6.266 ^4/2 .08 2.032 17.36 101.39 8.288 ^"5 /2 .07 1.778 22.67 77^3 10.82 16 , .065 1.651 26.29 66.96 12.25 . . .0625 1.587 28.472 61.81 13-59 . . .06 1.521 30.864 57.02 14-73 17 .058 1-473 33-03 53-29 15-76 .056 1.422 35-432 49-67 16.91 . . 054 I-37I 38.104 46.19 18.18 . . .052 1.32 41.091 42.83 19.61 jX 18 05 1.274 44-444 39.60 21.21 /2 . . .048 1.219 48.225 36.50 23.02 . . .046 1.168 52.51 33-52 25.06 19 .044 1.117 57-39 30.67 27-39 . . .042 i. 066 62.98 27.94 30.06 20 .04 1.016 69-444 25-34 33- x 4 . . .038 965 77.16 22.81 36.72 21 .036 .914 85.766 20.52 40.92 -034 .864 95-29 18.47 45-48 >" ^ .032 .813 108.5 16.22 51.79 22 03 .762 123.46 14.26 58-93 J TABLES. 359 TABLE I. -(Continued). COPPER WIRE. Birmingham Wire Gauge (Ap- proximate). Diameter. Number of yards in I pound. y pf M * ::-: |S3 . h& seat* fe!| sal* |i fssP p! era K Inches. Milli- metres. Oz. 23^ .028 .026 .711 .660 141.72 164.36 12.42 10.71. 67.65 78.46 t * 24^ .024 .609 I92. 9 9.12 92.08 25 .022 558 229.56 7 .6i 109.58 26 .02 .508 277.78 6-33 132-59 27 .Ol8 457 342.94 5-i3 163.69 f" I 28 .Ol6 .406 434.03 4-05 207.17 30 .OI4 355 569-5I 3-09 270.58 31 .012 305 771.60 2.28 368.30 32 .01 254 IIII. II 1-58 530.35 34 .0095 .241 1231.10 i-43 587.64 [ i# .009 .228 I37I-7 1.28 6 54.75 35 .0085 .216 1537-8 1. 14 734-05 36 .008 .203 I736.I I.OI 828.67 ) .0075 .190 '975-3 0.8910 942.84 f 2 .007 .177 2267.6 0.7761 1082.4 ) 37 .0065 .165 2629.9 0.6692 1225.3 1 38 .006 .152 3086.4 0.5702 H73-I I 23/ 0055 '39 3673-1 0.4791 1753.2 f 2 /\ . . .005 .127 4444-4 0.3960 2121.4 \ 39 .0045 .114 5487.0 0.3207 2619.0 40 .004 .106 6944.4 0-2534 33M.7 0035 .088 9070.3 0.1945 4329.4 4i .003 .076 12346.0 0.1425 5892-7 .O025 .063 17777.0 0.099 8485.6 To find the percentage of conductivity in a sample of wire, pure copper being taken as = 100 : Divide the resistance of i mile of pure copper wire of the same size (column 6) by the actual resistance of i mile of the wire tested (re- duced to 32 Fahr.), and multiply by loo. 360 TABLES. TABLE II. DIAMETER, WEIGHT, RESISTANCE, AND BREAKING STRAIN OF IRON WIRE E. B. B. (Prescott.) <3d if- 0) Diameter in thousandths of inch. Resistance at 76 Fahrenheit. Weight in pounds per mile. Breaking strain in pounds. Feet per ohm. Ohms per mile. I 300 135 391 1249.7 4000 2 284 I2II 4-36 II20.0 3400 3 2 59 I008 5-24 931-5 2900 4 238 958 5-51 886.6 2500 5 220 727 7.26 673.0 2200 6 20 3 618 8*54 572.0 l8oo 7 180 578 10.86 449-9 1520 8 165 409 12.92 378.1 1200 9 148 328 16.10 304.2 95 10 134 269 19.60 249.4 820 ii 120 216 24.42 200.0 650 12 109 179 29.60 165.0 5io 13 95 135 39.00 125-3 400 14 83- 104 51.00 95-7 35 IS 72 78 67.83 72.0 300 16 65 63 83.20 58.7 200 17 58 55 96.00 5o-9 150 18 49 35-9 147.00 33-3 H5 19 42 26.0 J 99-34 24-5 85 20 35 18.4 287.30 17.0 65 f TABLES. TABLE III. SHOWING THE DIFFERENCE BETWEEN WIRE GAUGES. 361 No. London. Stubs. Brown & Sharpe's. No. London. Stubs. Brown & Sharpe's. oooo 454 454 .460 19 .040 .042 .03589 000 .425 425 .40964 20 .035 .035 .03196 00 .380 .380 . 36480 21 .0315 032 .02846 .340 340 .32495 22 .0295 .028 025347 I .300 .300 .18930 23 .027 .025 .022571 2 .284 .284 .25763 24 .025 .022 .0201 3 .259 259 .22942 25 .023 .020 .0179 4 .238 .238 .20431 26 .0205 .Ol8 .01594 5 .220 .220 .18194 27 .01875 .Ol6 .014195 6 .203 .203 .16202 28 .0165 .OI4 .012641 7 .ISO .180 .14428 29 .0155 .013 .011257 8 .I6 5 .165 .12849 30 .01375 .OI2 .010025 9 .148 .148 II443 31 .01225 .OIO .008928 10 134 134 .lOlSg 32 .01125 .009 00795 II .120 .120 .09074 33 .01025 .008 .00708 12 .ICQ .lOg .08081 34 .0095 .OO7 .0063 13 ,095 095 .07196 35 .009 .005 .00561 14 .083 .083 .06408 36 .0075 .004 .005 15 .072 .072 .05706 37 .0065 .... .00445 16 .065 .065 .O5O82 38 00575 .... .003965 17 .058 .058 .04525 39 .005 .... .003531 18 .049 .049 .04030 40 .0045 .... .003144 TABLE IV. APPROXIMATE WEIGHT OF INSULATED WIRES AMERICAN GAUGE. Braided Wire. No. 4 8 ft. tolb. " 6 12 u *' 11 8 . . 20 II " 12 35 M u " 13 45 '* 11 " 14 55 44 u " 16 95 It 44 120 *' " 18 135 U || " 19 145 II " " 20 155 || 362 TABLES. TABLE IV. -(Continued). APPROXIMATE WEIGHT OF INSULATED WIRES AMERICAN GAUGE. Double- Wound Wire. No. 4 8 ft. to Ib. " 6 12 " " 8 20 " " 18 160 " " " I 9 200 " " 20 225 " Owing to the difference in gauges, and to the fact that nearly every manufacturer has his own gauge, it is almost impossible to compile a standard table of the properties of iron, wire with anything more than ap- proximate exactness. Hence the figures in Table 2, which is taken from Mr. Prescott's book, is more a table of what the wire should be than what it is. The short table we give below will be found to be nearer the mark for the gauges to which it refers. TABLE V. STANDARD WEIGHT AND RESISTANCE OF GALVANIZED WIRE. No. Resistance. Weight. Per mile. 6 10 ohms. 538 Ibs. 11 7 I2.I " 461 " " 8 I4.I " 389 " " 9 16.4 " 3^3 " u 10 20. 264 ' it ii 25- 211 " " 12 3^-7 163 " M 14 52.8 " 97 " U 16 91.6 " 57 " TABLES. 363 TABLE VI. RESISTANCE AND WEIGHT TABLE FOR COTTON AND SILK COVERED AND BARE COPPER WIRE AMERICAN GAUGE. The resistances are calculated for pure copper wire. Our wire is about 98 per cent, of the conductivity of pure copper. The number of feet to the pound is only approximate for insulated wire. No. Feet per pound. Resistance, Naked Copper. Cotton Covered. Silk Covered. Naked. Ohms per looo feet. Ohms per mile. Feet per ohm. Ohms per pound. 8 2O .62^0 3-J l6oO. OI2^ 9 25 Wrfc J? .7892 o 4.1 1272. .W A f. J .0197 IO 52 .84.4.1 4-4. Il85. .O27O II O 40 VMfJf 4 1.254 T- t 6-4 **y 798. / .0501 12 42 4 6 50 1.580 t 8 '3 633. .079 13 55 60 6 4 i-995 IO.4 504. .127 14 68 75 80 2.504 13.2 400. .2OO 15 87 95 IOI 3.172 I6. 7 316. .320 16 no 120 128 4.001 23- 230. 512 I 7 140 150 161 5-4 26. 198. .811 18 75 190 203 6.36 33- 157- 1.29 '9 220 240 256 8.25 43- 121. 2. II 20 280 305 324 10.12 53- 99 . 3.27 21 360 39 408 12.76 68. 76.5 5.20 22 45 490 5U 16.25 85- 6l.8 8-35 2 3 560 6i5 649 20.30 108. 48.9 J 3.3 24 7i5 775 8x8 25.60 135- 39- 20.9 25 910 990 1030 32.2 170. 31.0 33-2 26 1165 1265 1300 40.7 214. 24.6 52.9 27 1445 i57o 1640 51-3 270. 19-5 84.2 28 1810 1970 2070 64.8 343- 15-4 134. 2 9 2280 2480 2617 8l.6 432- 12.2 213. 3 2805 35o 3287 I0 3 . 538. 9 .8 338. 3 1 3605 3920 4144 130. 685. 7-7 539- 32 4535 4930 5227 164. 865. 6.1 856. 33 .... 6200 6590 206. i33- 4-9 1357- 34 .... 7830 8330 260. 1389. 3-8 2166. 35 .... 9830 10460 328. 1820. 2.9 352i. 36 12420 13210 414. 2200. 2.4 5469- 364 TABLES, TABLE VII. SHOWING THE RELATIVE CONDUCTIVITY AND RESISTANCE OF METALS. Pure Metals. Conductivity Silver at 32 being 100. Resistance Silver at 32" taken as i. Aluminum , 32 76 2 C)6 Antimony 4 62 21 (X 476 J 2 I O I 12^ 80 oo Cadmium 27. 72 A 21 Cobalt 17 22 ^8 07 Copper (hard) / QO Q ^ I OO (soft) yy-yo Q7 Q^ Gold y / *yo no6 I 28 16 81 r o r Lead 8 T2 o-yo 12 O2 Mercury 1.63 61 71; Nickel * i Vii 7 6^ 18 03 c cc Silver (hard) IOO OOD I " (soft) .. 108 7 O Q2 Thallium 0.16 IO.Q2 Tin 12 "*6 8 oo 2Q O2 w y 3 4.4. O.6o 14^ OO TABLE VIII. SHOWING THE RELATIVE RESISTANCES OF LIQUIDS. (JBecquerel.) Copper taken as standard Solution sulphate of copper, saturated. . " * diluted to half of zinc, saturated. '' diluted to half.. Chloride of sodium (common salt) Chloride of sodium, diluted to half Sulphuric acid, diluted i to n Nitric acid Distilled water saturated 16,855,52 26,327,637 15,861,267 12,835,836 3,965,421 1,032,020 976,000 6,754,208,000 TABLES. TABLE OF RELATIVE CONDUCTIVITIE 365 Silver, Copper, Gold, Zinc, Platinum, Iron, Tin, Lead, Mercury, Carbon, Acids, Saline Solutions, Rarefied Air, Melting Ice, Distilled Water, Stone, Dry Ice, Dry Wood, Porcelain, Dry Paper, Wool, Silk, Glass, Sealing Wax, Sulphur, Resin, Gutta-Percha, India-Rubber, Shellac, Paraffin e, Ebonite, Dry Air. There is no known absolute conductor. In the foregoing table each substance conducts better than the one which follows it. ELECTRO-MOTIVE FORCE OF BATTERIES IN VOLTS. Volts. Daniell 079 Grove 956 Smee, when not in action .102 " when in action 510 Bunsen 926 Bichromate or Chromic Acid 967 Marie Davy 533 Leclanche 662 Plante secondary 2. 100 Faure 2. 100 RELATIVE INDUCTIVE CAPACITIES OF THE PRIN- CIPAL INSULATING SUBSTANCES. Standard being air, taken as 100 Resin is 177 Pitch " 180 Beeswax " 186 Grass 190 Sulphur : 193 Shellac " 195 Paraffine '. 198 India-rubber 280 Gutta-percha " 420 Mica " 500 The above are from Jenkin's " Electricity and Magnetism." 366 TABLES. (From Culley's Hand-book?) METRIC WEIGHTS AND MEASURES. Millimetres. Inches. Millimetres. Inches. Millimetres. Inches. I 0.039 45 I.77I 125 4.941 2 O.OyS 5 1.968 I 3 5.II8 3 O.II8 55 2.165 J 35 5-3I5 4 0-157 60 2.362 140 5-5 12 5 0.197 65 2 -559 145 5-7o8 6 0.236 70 2.756 15 5.906 7 0.275 75 2-953 i55 6.103 8 0-3I5 . 80 3-149 160 6.299 9 o-354 85 3-346 165 6.496 10 0-394 90 3-543 170 6.693 15 0.590 95 3-740 175 6.890 20 0.787 100 3-937 180 7.087 25 0.984 I0 5 4-134 185 7.284 30 1.181 no 4.331 190 7.480 35 i-378 II 5 4.528 195 7.677 40 i-575 120 4-744 200 7.874 i inch = 25.4 millimetres. Inches. Feet. Yards. i Millimetre .. . . 0.039 i Centimetre. . . . 0-393 .... .... i Decimetre .... 3-937 .... .... i Metre 3Q ^7O 7 280 I.OQ3 i Kilometre 30, ^7o 7QO ?,28o 8oQ I.OQ "? 6 ^ 3 Miles Kilometres i 1.609 2 3.219 3 4.828 4 6-437 5 8.047 6 9.656 7 11.265 8 12.874 9 14.484 TABLES. 367 Grains Troy. Pounds Avoirdupois. i Milligramme O OI ^ w.wj.^ O.I ^4. r **D*r I ^4"? i Gramme . "OT-O I 432 i Kilogramme . A J-T-O^ I tl A^2 ^A8 2 204.6 2 Kilogrammes ^JJT-U^'OT-" 4/1OO2 3 ^f^y^ 6.61^8 8 8184 t 1 1 0230 6 i "? 2276 7 " I ^ 4"?22 8 " ^j-T-o^- 6 17 6^68 o " IQ 8414. 7,000 grains Troy = i pound Avoirdupois, i Litre = 35.275 fluid ounces = 1.764 pints = 61.024 cubic inches. i cubic centimetre = .0610 cubic inches. INDEX. Aerial cables, 181 ; description of, 182. Alarms, electric, operated by clock- work, 328. Alphabet, Morse telegraphic, 356, 357. Amalgamation of zincs, 25. Amber, 9. Ampere, 95. Applications (miscellaneous) of Blasting, 329, 332. Clock-alarms, 328. Electric bells, 286, 298. Electric clocks, 323, 327. Electricity, 266. Electric lighting, 266, 280. Electric-metallurgy, 281, 285. Electro-motion and transmission of power, 332, 340. Electro-therapeutics, 318, 322. Gas-lighting, 350. Storage of electric energy, 340, 349. Telephony, 299, 317. Time-balls and guns, 328. Armature, 48. Siemens, 67, 353. Arrangement of batteries for maxi- mum effect with given number, 148, 150. Artificial magnet, 44. Astatic galvanometer, 100. Attraction of magnets, 44. Automatic circuit-breaker, 83. Bar magnet, 48. Batteries, electric, 18. Best arrangement for given num- ber of cells, 148, 150. Bunsen, 26. Batteries Callaud, 26. Care of batteries, 32, 34. Chromic acid, 26. Daniell, 26. Depolarizing mixture batteries, 26. Earth, 42. . Gravity, 26. Grove, 26, 28. Internal resistance of, 118, 121= Invention of, 353. Leclanche, 26, 30. Local action in, 25. Other methods of arranging, 145. Poles of, 31. Proportionment to short lines, 148. Rule for obtaining greatest mag- netic effect from, 146. Secondary, 340. Single-fluid, 26. Smee, 26. Thermo-electric, 37. Two-fluid, 26. Usual arrangement of, for tele- graph lines, 136, 144. Voltaic, 24. Watson, 26. Bells, electric (see electric Mis, 286). Blasting by electricity, 329. Frictional, 330. Relative advantages, 332. Voltaic, 331. Brush dynamo, 74, 76. Cables, aerial, 181. Description of principal forms, 182. Submarine, 189, 191, 354. Candle, electric, 277, 279. 370 INDEX. Carbon battery, 29. Circuits, voltaic, 142, 152. Arrangement of, to connect regis- ter or sounder, 217. Conditions of current strength in, 144. Constitution of, 142. Earth as part of, 142, 144. Faults, 231, 233. Testing, 233, 241. Circuit-breaker, 83. Automatic, 83. Circuit-changers, 200. Circuit-closers, press-button, 291. Pull, 292. Clocks, electric, 323. Bain's clocks, 323, 326. Description of, 324. Governed clocks, Jones system, 326. Shepherd system, 327. Closed-circuit system of telegraphy, 133, 135. Coercive force of magnets, 48. Compound magnets, 48. Condensers, 85, 86. Coulomb, 95. Cross-arms, 155. Crosses, in telegraph or telephone lines, 232. Swinging, 233. To test for, 239. Weather, 233, 240. . Current strength, 92, 93. Conditions of, in a circuit, 144. x How varied, 93. Cut-outs, 203. Daniell battery, 26, 28. Care of, 32. Deflection, to compensate shunted, 128. Dia-magnetism, 50. Dielectrics, 18. Differential galvanometer, 105. Dip of magnetic needle, 46. Disconnection, or break, in electric circuits, 231. Disconnection in district systems, 235. Intermittent, 235. Partial, 236. To test for, 233. District telegraphs, 137. Duplex telegraphy, 242. Bridge, 247. Differential, 245. Gintl's, 243. Historical sketch of, 243. Sabine's opinion of,- 352. Stearns's, 244, 249. Duplicate transmission in same di- rection, 249. Du Yernay's anticipation of Galva- ni's discovery, 352. Dynamic induction, 19. Dynamo-electric machines, 69, 79. Arrangement to act as motors, 336. Brush, 74, 76. Gramme, 72, 74. Invention of, 353. Reversibility of, 335. Ring-armature machines, 72, 76. Term denned, 76. Uses of, 79. Earth battery, 42. Earth circuit, 142, 144. Early examples of, 143. First utilization in telegraphy, 142. Earth currents, 41. Method of obviating effects of, 41. Earth faults, 231. Intermittent, to test for, 239. Swinging, 232. To test for, 237. Earth wires, in offices, 193, 228. Defective, 233, 240. For lightning-arresters, 195. For testing purposes, 195. Proper construction of, 194. Uses of, 193. Electrical machines, 12. Cylinder machine, 14. INDEX. 371 ^Electrical Machines Holtz machine, 16. Plate machine, 13. Electrical measurement, 98, 129. Electrical resistance, 91. Of wires, 91, 92. Electrical units, 93, 97. Electric battery, 18. Electric bells, 286. Arrangements for various bell cir- cuits, 292, 296. Construction of simple bell circuit, 290. For telephone lines, 297. Individual, 297. Magneto, 297. Polarized, 288. Press-buttons for, 291. Pull circuit-closer, 292. Single-stroke, 287. Vibrating, 287. Electric clocks (see clocks, electric, 323). Electric gas-lighting, 350. Electricity a form of energy, 9. Atmospheric, 20. Battery, 18. Conductors of, 11. Distribution of, 18. Dynamical, 17. Electrical machines, 12, 16. Electrics and non-electrics, 12. Electrometer, 12. Electrophorus, 14. Electroscope, 12. Frictional, 10, 20. Magneto, 20, 59. Methods of developing, 20. Miscellaneous applications of, 266. Non-conductors of, 11. Oersted's discovery, 353. Plus and minus, 11. Positive and negative, 10. Relationship to magnetism, 50, 51. Romagnosi's anticipation of, 353. Statical, 17. Thermo, 20. Electricity- Vitreous and resinous, 10. Voltaic or galvanic, 22. Electric lighting, 266. Arc, 266. Arc lamps, 268. Brush lamp, 269. Divisions of, 266. Edison's lamp, 275. Electric candle, 277. First produced, 353. Illuminating power of, 277. Incandescent, 273. Jablochkoff candle, 277. Lane-Fox lamp, 276. Maxim, Bernstein, and Weston lamps, 277. Semi-incandescent lamps, 279. Starr's lamp, 274. Sun lamp, 280. Swan's lamp, 276. Wilde's candle, 278. Electric potential, 89, 90. Electric quantity, 92. Term applied to current electri- city, 92. Applied to static electricity, 92 Electrics and non-electrics, 12. Electrodes, 32. Electro-dynamic induction, 19. Electrolysis, 32. Electrolytes, 32. Electro-magnet, 19, 52. Construction of, 52. For long circuits, 56. For short circuits, 56. Length of core, 54. Resistance of, 54. When devised, 53, 352. Electro-magnetic induction, 19. Electro-magnetism, 52. Laws of, 54, 55. Electro-metallurgy, 281. Electro-plating, 281, 283. Electro-typing, 283. General explanation of, 281. Outline of art, 283. 372 INDEX. Electrometer, the, 12. Electro-motion, and transmission of power, 332. Dynamo-machine as a motor, 336. Froment's motor, 333. Jacobi's motor, 332. Page's motor, 333. Power electrically transmitted, 337, 340. Railways, 337, 338. Reversibility of dynamo-machine, 335. Electro-motive force, 90. Comparison of, 124. Measurement of, 125, 126. Of batteries, 90, 91. Electrophorus, 14, 353. Electroscope, 12. Electro-static induction, 18. Electro-therapeutics, 318. Definitions of, 319. Electrical probe, 321. Electro-physiology, definition of, 318. Electro-surgery, 320. Energy, definition of, 9. Escape in telegraph or telephone lines, 232. To test for, 238. Extra current, 84, 85. Farad, 96. Fire-alarm telegraphs, 136. Frictional electricity, 10. Applications of, 20. Galvanometer, the, 98. Astatic, 100. Constant of, 113. Definition of, 98. Differential, 105, 107. Invented by Schweigger, 99. Resistance, measurement of, 121, 123. Sine, 104. Tangent, 101, 104. Galvanometer Thomson's reflecting, 107, 110. To reduce deflection of, 123. Uses of, 100. Wheatstone's bridge, 110, 113. Gas-lighting, electric, 350. Gauge, wire, 166, 168. Gramme machine, 72, 74. Gravity batteries, 26. Care of, 33. Reactions of, 28. Ground wires, 193, 196, 228. For lightning-arresters, 195. For testing purposes, 195. Should be soldered, 195. To construct, 194. Uses of, 193. When to be used, 228. Grounds in telegraph or telephone lines, 231. Intermittent, 239. Swinging, 232. To test for, 237. Grove battery, 26, 28. Care of, 33. Harmonic telegraph, 254. Gray's, 255. Holtz's electrical machine, 16. Reversibility of, 16. Horseshoe magnets, 48. Illuminating power of the electric light, 277. Individual signals, 297. Induction, 18. Dynamic, or voltaic, 19. Electro-magnetic, 19. Electro-static, 18. Magnetic, 20, 45, 46. Magneto-electric, 19, 59. Induction-coil, 80. Circuit-breaker, 83. Condenser, use of, 85. Description of large coils, 87. Primary circuit of, 82. Secondary coil of, 82. INDEX. 373 Induction-coil Soft-iron core, 86. Use of in telephone transmitters, 309. Uses of, 88. What it is, 80. Why so called, 80. Insulators for land lines, 159. Brooks's, 164. Earthenware, 163. Glass, 163. Requisite qualifications of, 162. Rubber hook, 165. Joint resistance, 150. Calculation of, 151. Joints or splices in line- wire, 177. Bell-hanger's joint, 178. Britannia joint, 178. Soldering, 178. Twist joint, 178. Kerite, what it is, 184. Keys, telegraph, 211. Care of, 226. Defects in operation, 225. Morse, 211. Open-circuit, 213. Reversing, 213. Ladd's dynamo-electric machine, 70, 72. Lamps, arc, 268, 273. Incandescent, 273, 277. Semi-incandescent, 279. Sun, 280. Leakage-conductors for land lines, 160. Leclanche battery, 26, 30. Care of, 34. Ley den jar, 17. When discovered, 17, 352! Light, electric, 266, 280. Lightning-arrester, 201, 203. Lightning-rod, 20. Line construction, 153. Conductors, material of, 165. Line Cross-arms for, 155. Dip of, 175. Insulators, 159, 162, 165. J Joints or splices, 177, 179. Poles for use in, 153, 155. Sizes of, 166, 169. To ascertain proper dip, 176. Lines, house-top, 155. Supports for, 156, 159. Lines, supplying a number from one battery, 146. Line-wire, 165, 175. Aerial cables, 181. For telephone lines, 169, 170. Galvanized, 170. Humming in, 179. Iron, 165. Method of leading into terminal station, 181. Method of leading into way-sta- tion, 179. Sizes chiefly used, 152. Steel, 169. Liquids, resistances of, 118. Magnet, 43. Artificial, 44. Natural, 43. Magnet, properties of, 44, 46. Bar, 48. Compound, 48. Dip, 46. Horseshoe, 48. Permanent, 47. Polarity, 46. Magnetic field, 49. Magnetic induction, 20, 45, 46. Magnetism, 43. Relationship to electricity, 50. Residual, 53. Rule for obtaining maximum ef- fect from, given battery, 146. Magnetization, process of, 49. Magneto-bells, 297. Magneto-electric induction, 19, 59. Discovery of, 353. 374 INDEX. Magneto electricity, 20, 59. Advantages of, 62. Applications of, 61, 63. Magneto-electric machines, 60, 65. Definitions of, 60, 65. First invented, 60. Mutual accumulation machines, 69, 70. Wilde's, 68, 69. Measurement of resistance, 115, 123. By differential galvanometer, 116. By substitution, 116. Internal resistance of batteries, 119, 121. Land lines, dispensing with earth- wires, 117. Resistance of galvanometer, 121, 123. Using Wheatstone bridge, 116, 117. Miscellaneous applications of elec- tricity, 266. Electric bells, 286. Electric lighting, 266. Electro-metallurgy, 281. Morse's telegraph, 133, 136. Alphabet, 356, 357. Instruments, 196. Key, 211. Register, 215. Relay, 206, 209. Repeaters, 218, 221. Sounder, 214. Multiple telegraphy, 242. Duplex, 242, 250. Electro-harmonic, 254, 265. Quadruplex, 250, 254. Multiplying power of shunts, 128. Odds and ends, 351, 355. Office-wire, 192. Practical arrangement of, 192. Ohm, 94. Ohm's law, 96. Application of, 97. Partial disconnection, 231. Partial disconnection, to test for, 236. Permanent magnet, 47. Plates of battery, 31. Polarity of magnets, 46, 47. Polarization, voltaic, 23. Explanation of, 23. Injurious effects of, 24. Methods of obviating, 24. Polarized bells, 288. Polarized relay, 209, 211. Poles of battery, 31. Poles, for telegraph lines, 153. Setting up of, 154. Police telegraph, 139. Potential, definition of, 89, A relative term, 89, 90. Difference of, 90. Properties of magnets, 44, 46. Proportionment of battery power for short lines, 148. Quadruplex telegraphy, 250, 254. Changes and improvements in,. 253. Edison's, 251. Historical sketch of, 250. Quantity, 92. Definition of, 92. Railways, electric, 337. Register, telegraphic, 215. _ Adjustments, and management of, 226. Relay, telegraphic, 206. Adjustments, 208, 222, 225. Construction, 206. Polarized, 209, 211. Use of, 206. Repeaters, telegraphic, 218, 221. Bulkley's, 218. Button, 218. Edison's, 221. Uses of, 218. Repulsion of magnets, 45. Residual magnetism, 45. Resistance, 91. INDEX. 375 Resistance Internal of battery, 118. Measurement of, 119, 121. Of any given wire, 9l, 92. Of a telegraph line, 91. Of battery in reference to entire circuit, 53. Of cells in common use, 119. Of electro-magnets, 54. Of human body, 321. Of liquids, 118. Resistance-coils, 114. Resistance, joint, 150. Calculation of, 151. Resistances, measurement of, 115, 123. By differential galvanometer, 116. By substitution, 116. By tangent galvanometer, 120. By Wheatstone's bridge, 116, 117. Retardation, 188. Rheostat, and resistance-coils, 113, 115. Present arrangement, 114. Wheatstone's, 113. Robison's anticipation of Volta's in- vention of the "voltaic pile," 335. Ronald's underground line, 184. Secondary batteries, 340. Faure cell, 347. Historical sketch of, 341. Plante cell, 343, 346. Small-size Plante, 346. Shunts, 126, 129. Compensation of shunted deflec- tions, 128. Definition of term, 126. Their use, 126. To ascertain multiplying power of, 128. Value of shunts, 127. Siemens armature, 67. Signals for telephone lines, 297. Sine galvanometer, 104. Single-fluid battery, 26. Single-stroke electric bells, 287. Soldering joints in line- wire, 178. Sounder, 214. Adjustments of, 226. Spring-jacks, 205. Static, and dynamic, definition of, 16. Static induction, 18. Storage of electric energy, 340, 348, 349. Submarine cables, 189. Adaptation for telephony, 190. Insulating material employed in, 189. Subterranean lines, 184. Adaptation for telephonic circuits, 185. Conductor usually employed, 184. First laid, 184. Static induction in, 185. Where now used, 185. Sulzer's experiment in voltaic elec- tricity, 353. Swammerdam's anticipation of Gal- vani's discovery, 352. Switchboard, 197. Universal, 197. Uses of, 197. Western Union pin, 198. Switches, and circuit-changers, 200. Automatic telephone, 200, 315, 317. Button, 200. ' Cut-out, 203. For changing circuit between sounder and register, 217. Plug, 200. Secrecy, 200. Tables, of copper wire, 358, 359. Difference between wire-gauges, 361. Electro- motive force of batteries, 365. Iron wire, 360. Metric weights and measures, 366, 367. Relative conductivities, 365. Relative conductivity and resist- ance of metals, 364. 376 INDEX. Tables- Relative inductive capacity of in- gulators, 365. Relative resistance of liquids, 364. Weight and resistance of covered and bare copper wire, 863. Weight and resistance of galvan- ized iron wire, 362. Weights of insulated wire, 361. Tangent galvanometer, 101, 104. Tangents, 101. Telegraph, Morse American, 133, 136. Alphabet, 356, 357. Arrangement of batteries, 136, 144. Circuit arrangement of, 133. Key, 211, 213. Local circuit, 135. Proportionment of batteries, 145. Register, 215. Relay, 206, 209. Repeaters, 218, 221. Setting up instruments, 196. Sounder, 214. Telegraph lines, construction of, 153. Covered wires for, 183. Poles, 153, 155. Telegraph offices, hints for care of, 229. Telegraphic circuits, 130. Faults in, 231, 233. Loops, 201. Systems still in use, 132. Testing for faults in, 233, 241. Telegraphs, early experimental, 131. District or messenger-call systems, 137. Fire-alarm, 136. Operated by make and break of circuit, 140. Operated by reversals, 140. Police; 139. Stock-reporting, 139, 141. Type-printing instruments, 140, 141. Multiple, 242. Duplex, 242, 250. Telegraphs Electro-harmonic, 254, 265. Quadruplex, 250, 254. Telephone, the, 299. Ader, 304. Battery telephones, 304. Blake, 307. Construction of, 316. Crossley's transmitter, 311. Crown, 303. Definition of word, 299. Dolbear's receiver, 314. Edison transmitter, 3.06. Hunnings's form, 313. Induction-coils for, 309, 351, 352. Magneto-telephone, 299. Operation of as transmitters 305. Patents, 351. Pony crown, 303. Standard Bell telephone, 302. Strength of current generated by, 353. Telephone switch, 315. Uses of, 316, 317. Telephone lines, uninsulated, 183. Aerial cables for, 181, 183. Signals for, 297. Wire adapted for, 169. Telephone switches, 200. Telephonic communication through submarine cables, 190. Testing for circuit faults, 233, 241. For cross, 239. For defective ground terminal, 240. For disconnection, 233, 235. j For escape, 238. For ground, 237. For intermittent disconnection, 235. For intermittent ground, or cross, 239. For partial disconnection, 236. For weather-cross, 240. Thermo-electric battery, 37, 39. Applications of, 39, 40. Thermo-electricity, 20, 36. Discovered by Seebeck, 36. INDEX. 377 Thomson's reflecting galvanometer, 107, 110. Time-balls and guns, electrically operated, 328. Underground lines, 184. Adaptation to telephony, 185, 188. Electro-static capacity of, 353. First laid, 184. Materials of conductors and in- sulators, 184. Retardation in, 188. Where laid, 185. Units, employed in electrical mea- surements, 93, 97. Of capacity, '96. Of current, 95. Of electro-motive force, 94. Of quantity, 95. Of resistance, 94. Universal switch, 197. Vibrating electric bells, 287. Volt, definition of, 94. Volta invented electrophorus, 353. Voltaic cell, 23. Battery, 24. Voltaic electricity, 22. How it differs from frictional, 22. Volta's pile, 26. Weather-cross, 233, 240. Western Union pin-switch, 198. Wheatstone bridge, 110. Description of, 110, 111. Explanation of principles involv- ed, 111. Method of using, 111, 112. When introduced, 110. Wire, to ascertain weight per mile from diameter, 174. For telephone lines, 169. Galvanized, 170. Killing process, 175. Mechanical and electrical tests for, 171, 174. Preferable sizes for long lines, 168. Reason for preferring large wire, 168. Resistance, variation with tempe- rature, 174. Sizes chiefly used, 166. Used for land lines, 165. Wire for inside construction, 192. Arrangement of in offices, 192. Wire-gauge, 166, 168. Zincs, amalgamation of, 25. Offices of J 32 Park Place, New York City, Solicitors of United States and Foreign Patents for Electrical Inventions, Experts in all proceedings in Electrical Patent Causes. 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