of JVo Division Range Shelf Received \s&tM&<' Frontispiece. THE INDUCTORIUM, OR INDUCTION COIL; BEING & ^Popular lEiplanation OF THE ELECTRICAL PRINCIPLES ON WHICH IT IS CONSTRUCTED. WITH THE DESCRIPTION OF A SERIES OF BEAUTIFUL AND INSTRUCTIVE EXPERIMENTS ILLUSTRATIVE OF THE PHENOMENA OF THE INDUCED CURRENT. BY HENEY M.NOAD, PH. D., F.K.S., F.C.S., &c., LECTURER ON CHEMISTRY AT ST. GEORGE'S HOSPITAL. Author of "A Manual of Electricity," #c., #c. SECOND EDITION. PUBLISHED FOR THE PROPRIETOR BY JOHN CHURCHILL & SONS, NEW BURLINGTON STREET, M.DCCC.LXVI. LONDON : PRINTED BT WERTHEIMER AND CO., CIRCUS PLACE, FINSBURY CIRCUS. PREFACE TO SECOND EDITION. THE object of this little book is to place in the hands of persons possessing or desiring to possess an Induction Coil (or Inductorium, as it has been called by the German Physicists) a clear and succinct account of the Electrical principles on which the instrument is constructed. Also to describe the various apparatus used, and the principal experiments to be made therewith. It has been written at the request of, and for Mr. Ladd, the well known successful manufacturer of these machines. That some such work was wanted has been fully proved by the rapid sale of the first impression. In the present Edition, ^'without materially increasing the size of the book, I have endeavoured to trace the progress of the development of this wonderful instrument, which promises to become a powerful means of research in many physical inquiries. THE Library. INDUCTOKIUI, Ofi INDUCTION COIL 1. DISCOVERY OF ELECTRO-MAGNETISM. In the year 1820, Professor Oersted, of Copen- hagen, announced his famous discovery of the reciprocal force exerted between magnetic bars and wires uniting the opposite terminals of a voltaic battery, and thus laid the foundation of a new science that of Electro-Magnetism. The discovery of the Danish philosopher was thus simply stated : When a properly-balanced magnetic needle is placed in its natural position in the magnetic meridian, immediately under, and parallel to, a wire along which a current of voltaic electricity is passing, that end of the needle which is situated next to the negative side of the battery immediately moves to the west ; if the needle is placed parallel to and over the wire, the same pole moves to the east. When the uniting wire is situated in the same horizontal plane as that in which the needle moves, no declination takes place, but the needle is inclined, so that the pole next to the negative end of the wire is depressed when the wire is situated on the west side, and elevated when situated on the east side. To assist the memory in retaining the directions of these deviations, Ampere devised the following formula: "Let any one identify himself with the current, or let him suppose himself lying in the direction of the positive current, his head represent- ing the copper and his feet the zinc plate, and looking at the needle ; its north pole will always move towards his right hand." 2. ELECTRO-MAGNETIC ROTATION. Reasoning on the fact that this action of a con- ducting wire on a magnet is not a directly attractive or a repulsive one, Faraday was led to the conclusion that if the action of the voltaic current could be con- fined to one pole of the magnet, that pole ought, under proper conditions, to rotate round the wire ; and conversely, if the magnet were fixed and the conducting wire moveable, the wire ought to rotate round the magnetic pole ; both of these phenomena he realised, and described the apparatus for exhibit- ing them in the " Quarterly Journal of Science," Yol. xii., p. 283 (January, 1822). Ampere subse- quently caused a magnet to rotate round its own axis ; and Barlow devised an ingenious apparatus for exhibiting the rotation of a conducting body round its axis. 3. THE GALVANOMETER. Shortly after the discovery of Oersted, Schweigger, a German physicist, applied it to the construction of an apparatus for indicating the direction and measuring the intensity of voltaic currents. This instrument is called the multiplier or rheometer, or more popularly the galvanometer. In its original form it consisted of a rectangular coil of silk or cotton-covered copper wire, in the centre of which was suspended, on a pivot, a magnetic needle, and a card graduated into 360 degs. ; the instrument being so placed that the needle lies parallel to the coil ; on causing a current of electricity to circulate through the latter, the needle becomes violently affected, even by very feeble currents, it being obvious, from a consideration of Oersted's funda- mental law, that the needle, being placed between the two horizontal branches of the conducting wire, will be impelled in the same direction by the current traversing the wire above and below it. A great improvement was subsequently made in the instru- ment by Gumming and Nobili, who applied the astatic needle to the multiplier, thereby greatly in- creasing its sensibility, by annulling the directive action of the earth on the needle. There appears to be scarcely any limit to the sensibility which the galvanometer may be made to attain; as far as experiment has yet gone, it increases in delicacy in proportion to the length, purity, and insulation of the copper wire composing the coil. Du Bois- Eeymond constructed, for his researches on the currents of electricity existing in animal structures, a multiplier, the length of which was 16,752 feet long, and passed round the frame 24,160 times ; the sensibility of this instrument is almost incredible. The galvanometer is an indispensable instrument to those engaged in electrical researches. 4 . ELECTRO-DYNAMICS. When two wires are traversed simultaneously by an electrical current, attractions or repulsions ensue, similar to those which take place between the poles of two magnets. If the currents are moving in the same direction in the two wires, they mutually attract; if in a contrary direction, they mutually repel. This discovery we owe to Ampere, and the discussion of the phenomena to which it gave rise constitutes the science of electro-dynamics. The analogy between wires conducting electricity and magnets is strikingly illustrated by turning the wires corkscrew fashion, making them helices. A helix has, indeed, all the properties of a magnet, but the nature of the pole at either end will depend on the direction of the turns of the helix ; a helix in which the turns are from left to right upwards is a dextrorsal helix ; a helix in which the turns are from left to right downwards is a sinistrorsal helix. In the former, the S pole is formed at the end at which the current enters ; in the latter, the N pole is formed at that extremity. The analogy extends to fracture. If a magnetic bar be broken in two, each piece is a perfect magnet, and the fractured parts have opposite poles ; so it is with a helix, which, if divided in the middle, exhibits attraction between the fractured ends. If a helix be suspended vertically and loosely, its upper end being held by a binding screw, and its lower end dipping into mercury ; and if a voltaic current be passed along- it whilst thus suspended, there will be mutual attraction manifested between the coils, and the helix will be contracted. 5. AMPEEE'S THEORY OF MAGNETISM. On the analogy which exists between helices and magnets Ampere founded his theory of magnetism. According to this theory, the phenomena of magnetism depend on voltaic currents circulating round the molecules of the magnetic bodies. In their unex- cited state these molecular currents move in all directions, and thus neutralize one another; but when the bar becomes a magnet, the currents move parallel to each other, and in the same direction, and the effect produced is that of a uniform current moving corkscrew fashion round the bar, which thus becomes in effect a helix, and the attractions and repulsions of the magnet are consequences of the actions of the currents on each other. In applying this theory to the explanation of the phenomena of terrestrial magnetism, it is necessary to suppose the incessant circulation of electrical currents round the globe from east to west perpendicular to the mag- netic meridian. 6. MAGNETISM EXCITED BY ELECTRICITY. A consideration of the influence exerted by elec- trical currents on magnets, leads naturally to the conclusion that the neutral condition of bodies susceptible of magnetism would be disturbed by an electrical current, and that they would become mag- netic, and the fact is easily verified by plunging the wire uniting the opposite poles of a voltaic battery into iron filings, which attach themselves to the wire, and remain adhering to it as long as the current continues to circulate, but drop off the moment the circuit is interrupted ; filings of copper or tin exhibit no such action. The magnetizing power of electricity is also illustrated by winding a silk or cotton- covered copper wire round a glass tube enclosing an unmagnetized steel needle and connecting the ends of the helix with the terminal plates of the voltaic battery; the needle becomes magnetized to satura- tion even by a momentary passage of the current through the helix ; the magnetization of the needle also takes place if, instead of passing the current from a voltaic battery along the helix, a Leyden phial be discharged through it, an interesting experi- ment, as proving the magnetizing power of ordinary (statical) as well as of voltaic (dynamical) electricity. The sense in which the needle will be magnetized will depend on the nature of the helix ; if it be a right-handed one, as S FIG. 1. N the north pole of the needle will be formed towards the extremity at which the current enters; if the he.lix be left-handed, as FIG. 2. then the end of the needle nearest the extremity at which the current enters will be a south pole. A tube of wood may be substituted for one of glass in this experiment, but not one of copper, which, if thick, destroys entirely the effect of the current. The tube in this experiment may be altogether dis- pensed with, and the silk or cotton-covered copper wire wound round the FlG - 3 - steel bar itself, which thus becomes intensely and permanently magnetized by a very feeble current. Soft iron, treated in a similar manner, acquires a high degree of tempo- rary magnetism iron, if pure, not being able to retain the magnetic force, although if not pure, it does not wholly lose its polarity. Bars of iron thus temporarily mag- netized by the voltaic current are called electro- magnets ; they are generally made horse-shoe shape, the covered copper wire being wound several times round each arm in the same direction ; the ends of the curved bar acquire opposite magnetic polarity. A convenient arrangement of the electro-magnet is shown in Fig. 3 ; the iron cores are 10^ x 2 inches, and are each covered with 120 yards of copper wire, T ^th of an inch in diameter. It is provided with conical soft iron armatures for convenience in diamag- netic experiments. The power of the electro -magnet depends on the dimensions and purity of the iron, the intensity of the current, and on the length and thickness of the wire. It has been shown by Dub, that the power of the electro-magnet to effect a mag- netic needle and to sustain weights, is proportional to the square root of the diameter of the bar. The applications of the electro -magnet to electro-tele- graphy, to the construction of electro-magnetic and horological machines, and to the elucidation of the phenomena of diamagnetism, have received import- ant developments during the last few years. 7. YOLTA-ELECTBIC INDUCTION. On the 21st of November, 1831, the first series of Faraday's celebrated " Experimental Researches in Electricity" was read before the Royal Society. It related to the induction of electric currents. Two hundred and three feet of copper wire in one length were coiled round a large block of wood ; other two hundred and three feet of similar wire were inter- posed as a spiral between the turns of the first coil, and metallic contact everywhere prevented by twine. One of these helices was connected with a galvano- meter, and the other with a powerful voltaic battery. When contact was made, there was a sudden effect at the galvanometer, and a similar slight effect when the contact with the battery was broken ; but whilst the voltaic current was continuing to pass through the one helix, no disturbance of the galvanometer took place, nor could anything like induction upon the other helix be perceived. The force of the 10 induced current, which partook of the nature of an electrical wave, produced by the discharge of a common Leyden jar, was greater on breaking than on making contact ; the direction of the current was, on making contact, the reverse of that of the in- ducing current, but on breaking contact it was in the same directions as that of the battery current. 8. MAGNETO-ELECTRIC INDUCTION. When the helices of copper wire were wound round a ring of soft iron, but carefully insulated from it, the effects were far greater, but they were not more permanent, the galvanometer needle speedily reas- suming its natural position while battery contact was maintained, but being again powerfully deflected in the contrary direction the instant the contact was broken. When the ends of the helices were tipped with charcoal, a spark could be obtained at the moment of making contact between the other helix and the poles of the battery. Faraday next wound a similar series of helices round a hollow cylinder of pasteboard, and connected the respective ends with the galvanometer. He then introduced into the axis of the cylinder a soft iron bar, which he made temporarily magnetic, by bringing its opposite ends into contact with the opposite poles of two powerful bar magnets ; the moment this was done, the needle was deflected ; continuing the contact, the needle became indifferent, and resumed its first position. On breaking contact it was again deflected, but in the opposite direction, and then it again became indifferent. When the magnetic contacts were re- versed, the deflections were reversed likewise. Here, then, was a distinct evolution of electricity from magnetism alone. The action of the current from the voltaic battery is called volta-electric induction; 11 that produced by the magnet is called magneto -electric induction, and the reason why the effects at the galvanometer are so much greater when the helices are arranged round an iron bar, than when they are coiled simply round a block of wood, is because, in the former case, we have volta- electric and magneto- electric induction combined, whereas, in the latter case, the effect is due to the action of volta- electric induction only. Powerful effects at the galvanometer were obtained on bringing the ends of the system of helices with an enclosed iron cylinder, between the poles of a strong magnet, and even when the coil, without the iron core, was introduced between the poles of the magnet, but without touching, so that the only metal near the magnet was copper, the needle of the galvanometer was thrown 80, 90, or more, from its natural position. Faraday was unable to obtain chemical effects by the induced current, but on repeating his experiments with an armed loadstone capable of lifting about thirty pounds, he succeeded in convulsing powerfully the limbs of a frog, and in obtaining physiological effects upon himself. An important element in magneto -electric induc- tion, which was noticed by Faraday during the prosecution of his earliest experiments, is time. Volta- electric induction is sudden and instantaneous, but magneto-induction requires sensible time, and experiment proves that an electro-magnet does not rise to its fullest intensity in an instant. Fig. 4 shows a convenient arrangement for exhibiting and illustrating magneto-electric induction. Two or three hundred feet of cotton or silk -covered copper wire are wound round a hollow pasteboard or wooden cylinder, and the ends connected with a galvanometer placed at a distance. On thrusting a tolerably powerful bar magnet into the axis of the cylinder, 12 the needle is immediately and strongly deflected; on allowing the bar to remain at rest, it soon regains its natural position, but is again deflected in an Fia. 4. opposite direction when the magnet is suddenly withdrawn ; the motions of the needle are reversed when the opposite end of the magnet is thrust into the cylinder. Faraday's great discovery of magneto- electric induction has been utilized in a variety of ways. Pixii, of Paris, was the first (in 1832) to make public a machine by which a continuous and rapid succession of sparks could be obtained from a per- manent magnet. In the following year his machine was much improved by Saxton, who exhibited in the Gallery of Practical Science, which at that time existed in Adelaide Street, Strand, an instrument by 13 which platinum and iron wires could be fused ; chemical decomposition energetically effected; soft iron magnetized ; and powerful shocks given. Im- provements continued to be made, until in 1842 a patent was secured by Mr. Woolwich, of Birming- ham, for the application of the magneto -electrical machine to the art of electro-plating. A full and illustrated account of this ingenious apparatus will be found in the "Mechanics' Magazine, "Vol. xxxvin., p. 146. In the celebrated "depositing" works of Messrs. Elkington, of Birmingham, a large magneto- electric machine is in continuous operation ; it de- posits 17 oz. of silver per hour. To Mr. Holmes is due the important application of magneto-electricity to the production of electric light. His machine must be familiar to all who visited the International Exhibition of 1862. The currents are induced by the rapid passage of coils of copper wire wound round soft iron cores between the poles of powerful horse-shoe magnets. The alter- nately inverted currents thus produced are trans- mitted by means of a commutator in one direction only, through the carbon electrodes of an electric lamp, likewise his invention, and an extremely brilliant, regular, and constant light, without flashes, is produced. A somewhat similar machine had previously been constructed by Mr. Shepard, for the purpose of producing illuminating gas by the de- composition of water. Holmes's machine and lamp has been in successful operation at Dungeness light- house since June, 1862. The applications which have been made of mag- neto-electric machines to the administration of shocks for medical purposes are very numerous ; none are more convenient, economical, or effective than the arrangement of Mr. Ladd, shown in Fig. 5. The force of the shocks is regulated simply and accurately 14 by an arrangement by which the distance of the armature from the poles of the magnet can be increased or diminished, and the noise which in the FTG. 5. earlier machines was produced by the working together of the metallic cog wheels, has been obvi- ated by the substitution of discs of vulcanized rubber. Another important application of magneto-electri- city is the explosion of mines and submarine gun- powder, or gun-cotton charges, in military or engineering operations. A very compact arrange- ment of magnets was devised for this purpose by Mr. Wheatstone, by which an extremely rapid succession of currents could be established in such a manner that the effect was almost equal to a con- tinuous current, and he has since effected further important improvements in the " magnetic exploder" whereby its size and weight have been very con- siderably diminished. A remarkably sensitive com- 15 position for the priming material used in the fuze has been discovered by Professor Abel, and if the fuzes so charged are arranged in the branches of a divided circuit, their ignition in numbers varying from two to twenty-five is certain ; the only im- portant precautions to which it is necessary to attend rigidly in order to ensure uniform access are the proper insulation throughout of the main wire and branch-wires leading from the instrument to the charges, and the thorough protection of all con- nections of wires from access of moisture. The magnetic exploder has important advantages over the application of the voltaic battery for firing charges, the principal FIG. 6. being its constant fitness for use, its por- tability, and its small liability to derange- ment. The magnet fuze is, moreover, more certain than any fuze arrangement ap- plied with voltaic bat- teries. It may be preserved for a great length of time in any climate, and will bear very rough treatment without chance of injury. The latest improvement in the construction of the magnetic exploder is shown in Fig. 6. 9. INDUCTION OF A CURRENT ON ITSELF. In his ninth series of Experimental Researches, read before the Eoyal Society, Jan. 29th, 1835, Faraday makes known a new action of the electric current, viz., an induction on itself. The inquiry 16 arose out of a fact communicated by Mr. Jenkin, which, is as follows : If an ordinary wire of short length be used as the medium of communication between the two plates of an electromotor, consisting of a single pair of metals, no management will enable the experimenter to obtain an electric shock from this wire ; but if the wire which surrounds an electro-magnet be used, a shock is felt each time the contact with the electromotor is broken, provided the ends of the wire be grasped one in each hand ; a bright spark also occurs at the place of disjunction. The same effects occur, though by no means in the same high degree, when a simple helix of copper wire is used to connect the opposite poles of the battery without any coil of iron. Thus on connect- ing one end of a helix of eighty or a hundred feet of stout copper wire with one plate of the battery, and making and breaking contact between the other end of the helix and the opposite pole of the battery, which is best done by dipping it into, and quickly withdrawing it from, a cup of mercury in good metallic connection with the battery, a distinct shock is experienced every time the wire leaves the mercury, although none can be perceived when it enters the fluid metal. If the same quantity of wire be used, not in the form of a helix, the spark is much less bright on breaking contact, nor can any, or only very feeble, physiological effects be obtained; the phe- nomenon is best observed by taking about 100 feet of copper wire and winding 50 feet into a helix, then bending it in the middle so as to form a double termination, and allowing the other 50 feet to remain extended ; on using each half of the wire alternately as the connecting wire of an electromotor, the helix will be found to give by far the brightest spark ; it even gives a brighter spark than when it is used in conjunction with one extended half of the wire. The 17 brightness of the spark with the helix is however no proof that more electricity, or electricity of higher intensity, is passing through it than through the extended wire connecting the plates of the battery. Faraday found the effect at the galvanometer and the electrolyzing power to be the same, whether he used a short wire, a long wire, a helix, or an electro- magnet ; under certain circumstances, however, proof can be obtained that there is a diminution of the battery current when a long wire is used, in conse- quence of the resistance it sets up ; thus, on solder- ing an inch or two of fine platinum wire to one end of a long wire, and also a similar length to one end of a short wire, and then using each to connect the plates of the same electromotor, Faraday found that the latter became ignited, though producing but a feeble spark, while the former remained cold, though giving a bright spark. This bright spark is due to a momentary extra current induced in the wire at the moment the primary or inducing current from the battery ceases to flow through the wire. This extra current, or wave of electricity, may be examined as to direction and intensity by a very simple expedient ; thus, by using an electro-magnet, and connecting the ends of the principal wire by a short cross-wire, the bright spark ceases to appear in the mercury cup on breaking battery contact, because the extra current which would have produced it now passes along the connecting wire. If the cross wire be divided in the middle, a spark may be obtained by rubbing the two ends together, while contact is broken and renewed between one of the principal terminal wires, and one of the mercury cups of the battery ; chemical decomposition may also be effected there, and a fine platinum wire ignited. The direc- tion of the extra-current is shown by introducing a galvanometer between the divided ends of the cross 18 wire ; whilst the current from the battery is circula- ting the helix of the electro -magnet, the galvano- meter is affected in the direction of the battery current, because the cross-wire carries one part of the electricity excited by the battery ; but, if the needle be forced back to its normal position, and secured there by pins, and if battery contact be then broken, the needle is powerfully deflected in an opposite direction, thus proving that the wave of induced electricity the extra current moves in the wire, at the moment of disruption with the battery, in a direction contrary to that of the electrical current set in motion by the battery itself. 1 . EXTKA-CTJRRENT . This extra current may be removed from the wire carrying the original current, to a neighbouring wire ; if two helices be arranged on the same hollow paste- board or wooden cylinder, in close proximity, but nowhere actually touching, and one used for making and breaking contact with a battery, the usual bright spark appears at the moment of disruption ; but if the two ends of the second helix be brought into contact, so as to form an endless wire, the spark be- comes scarcely sensible, and all the phenomena described (9) as occurring between the divided ends of the cross wire may be re-produced between the two extremities of the second helix. " The case," therefore, says Faraday, "of the bright spark shock on disjunction may now be stated thus : If a current be established in a wire, and another wire, forming a complete circuit, be placed parallel to the first, at the moment the current in the first is stopped, it induces a current in the same direction in the second, the first exhibiting then but a feeble spark ; but if the second wire be away, disjunction of the first wire induces a current in itself in the 19 same direction, producing a strong spark. The strong spark in the single long wire or helix, at the moment of disjunction, is therefore the equivalent of the current which would be produced in a neighbour- ing wire if such a second current were permitted." A brighter spark, then, is produced at the moment of disruption of a long wire joining the plates of a battery than of a short wire, because, though it carries less electricity, it induces on itself a more powerful wave current ; if wound round into a coil, the spark is still brighter, because of the mutual inductive action of the convolutions, each aiding its neighbour ; and the brightnes of the spark is exalted still higher when the coil encloses a bar of soft iron, because the bar, losing its magnetism at the moment of disruption, tends to produce an electric current in the wire around it, in conformity with that which the cessation of the current in the helix itself also tends to produce. It is not so easy to demonstrate the induction of a wave current at the moment of making contact ; by using certain expedients however Faraday succeeded in doing so ; thus, when a gal- vanometer was introduced between the ends of the cross wire, a part of the current from the battery was diverted through it ; when the needle had taken up its position it was retained there by pins, contact was then broken, but the needle was prevented from obeying the impulse which the reverse wave would have given to it by the stops; contact being now again made, the needle immediately moved onwards, showing, by a temporary excess of current in the cross communication, a temporary retardation in the helix. 11. INDUCTION OF SECONDARY CURRENTS AT A DISTANCE. On the 2nd of November, 1838, a memoir on 20 electro-magnetic induction was read at the meeting of the American Philosophical Society, by Dr. Joseph Henry, professor of natural philosophy in the College of New Jersey, Princeton. This ingenious electrician employed in his experiments flat coils of insulated copper riband, and helices and spools of fine- covered copper wire ; with electricity of low intensity, as from a single pair of plates, he obtained with a flat riband coil 93 feet long brilliant deflagrations and loud snaps from a surface of mercury, but no shocks ; but when the length of the riband was increased to 300 feet he obtained strong shocks but less brilliant sparks ; with electricity of higher intensity as from a series of pairs of plates, the action of the riband was decreased, but when the current from ten pairs was sent through a spool of wire one-sixteenth of an inch in diameter and five miles long, the induced shock was too severe to be taken through the body, though the spark was feeble ; a shock was indeed passed through twenty- six persons at once from this spool, when a battery consisting of six pieces of copper bell wire and corresponding pieces of zinc wire, only one-and-a-half inch long, was employed ; nevertheless, when a single pair of plates exposing one square foot and three-quarters of zinc surface was used, scarcely any physiological effects could be obtained. In these experiments, contact with the battery was broken and renewed by drawing one end of the riband or helix across a rasp which was kept in good metallic contact with one of the plates of the battery. When the current from a small battery was sent through a copper riband on the top of which was placed a helix containing 3,000 yards of covered copper wire 0-02 inch in diameter, a plate of glass being interposed between the riband and the helix, powerful shocks were obtained from the latter as often as the current through the former was interrupted ; when the helix 21 was removed and a copper riband sixty feet long substituted for it, very feeble shocks could be ob- tained ; but sparks were produced ; on rubbing the ends of the riband together, needles were magnetized, temporary magnetism in soft iron was developed, and water was decomposed; none of these latter effects could, however, be obtained with the helix. Intense shocks, and magnetizing, and chemical effects also were obtained from the* five-miles spool of wire, when the riband was opened so as to receive it in the centre, and an interrupted current from a single pair of plates sent through the riband. From these experiments it will be seen that the in- duced or secondary current obtained from ribands or short stout copper wire partakes of the character of what is called quantity, while that from great lengths of fine wire exhibits the qualities of what is termed intensity. When the current from an extensive series of plates was sent through a riband and intermitted, no secondary effects could be obtained in the helix, but when the same battery was used with a helix, powerful shocks were induced in a second helix, and sparks and magnetizing effects obtained with a riband; "hence," observes Henry, " an intensity current can induce one of quantity, and a quantity current can induce one of intensity." The induction of a secondary current at a distance from the primary was illustrated by Dr. Henry in a surprising manner, by coiling the wire of the five-mile spool into a ring four feet in diameter, and placing parallel to it another ring of copper riband 270 feet long; on sending an intermitting current from a single pair of plates, zinc surface 35 feet, through the latter, shocks could be obtained from the former at a distance of four feet, and at a distance of twelve inches they were too severe to be taken through the body. 22 12. INDUCED CURRENTS OF THE THIRD, FOURTH, AND FIFTH ORDER. Professor Henry was the first to show that the in- duction of electricity does not stop with the produc- tion of secondary currents, but that currents of a third, fourth, and even of a fifth order may be ob- tained. An intermittent current from a single pair of plates was sent through a copper riband, a second riband being placed over it to receive the induced secondary current. The ends of this second riband were connected with the ends of a third placed at a distance, and over this a helix of 1,660 feet of fine wire. On grasping copper handles metallically con- nected with the ends of this helix, powerful shocks were obtained ; thus the secondary current produced a new induced current in a third conductor. By a similar arrangement shocks were received from currents of a fourth and fifth order, and with a more powerful primary current and additional coils, a still greater number of successive inductions might be obtained. The arrangement of coils and helices is shown in Fig. 7, where a represents a cylindrical Fio. 7. copper and zinc single-cell battery; b, a coil of copper riband, about 100 feet long, and an inch and a half 23 wide ; c and d similar ribands, about 60 feet long ; e, a helix of 1,660 yards of copper wire, one forty- ninth of an inch in diameter ; /, a helix of about 1,200 yards of the same wire ; </, a copper riband, 60 feet long, and three-quarters of an inch wide ; and A, a cylinder of about thirty spires of copper wire, so small as just to admit a sewing needle in its axis. Now here, as with a primary current only, it is found that a quantity current can be induced from one of intensity, and the converse ; for the induction from coil, b, to helix, e, produces an intensity current, and from helix, /, to coil, g, a quantity one, as is demon- strated by the magnetization of the steel needle in the copper spiral h. Then, as to the direction of these induced currents, it was found that there exists an alteration in the direction of the several orders, commencing with the secondary, as follows : Primary current + Secondary current + Current of the third order . . Current of the fourth order . . -t- Current of the fifth order ... the directions being determined by the nature of the polarity of the magnetized needle, by decomposition, and by the galvanometer. Induced currents of the different orders are also produced from ordinary elec- tricity. On discharging a large Leyden phial through a spiral of tinfoil pasted round a glass cylinder, a similar spiral of foil being pasted inside the cylinder, the ends of which were connected with a magnetizing spiral enclosing a steel needle, the latter was magnetized in such a manner as to indi- cate an induced current through the inner riband in the same direction as that of the current of the jar ; a spark was also produced when the ends of the spiral were separated by a small interval. Induced 24 currents of a third and fourth, order were obtained when a large Leyden phial was substituted for the battery, the coils being furnished with a double coating of silk, and the conductors separated by a plate of glass. . By using a powerful Leyden battery, Dr. Henry obtained evidence of the induction of a secondary current at the surprising distance of twelve feet. This subject has more recently been investi- gated by Reiss, who found that the currents of the third, fifth, and other odd orders have the same direction as the original current, and those of the second, fourth, and other even orders, have among themselves one and the same direction. 13. THE ELECTBO-MAGI^ETIC COIL MACHETE. We are now prepared to understand the modus operandi of those arrangements, which in so many forms have been rendered familiar to the scientific world under the general name of the Electro-magnetic Coil. Various as are the external appearances of these machines, they are all based on Faraday's great discoveries of electric and magnetic induction. The first induction coil without an iron core is described by Faraday in par. 6 of the first series of the " Experimental Eesearches " (Nov. 24th, 1831) ; the first with an iron core in par. 34 of the same series. By these the important discoveries of electric and magnetic induction were made, and they were carried forward to higher conditions in the ninth series (Dec. 18th, 1834), pars. 1,053, 1,063, 1,090, 1,095, in relation to the action of an electric current upon itself. Having discovered the power, Faraday abstained from proceeding to exalt it. He says, par. 159, second series, "I have rather been desirous of discovering new facts and new relations dependent on magneto-electric induction than of exalting the 25 force of those already obtained, being assured that the latter would find their full development here- after "; and again, in par. 1,118, ninth series (Dec. 8th, 1834), "In the wire of the helix of magneto- electric machines an important influence of these principles of action (the inductive action of a current) is evidently shown. From the construction of the apparatus, the current is permitted to move in a complete metallic circuit of great length during the first instants of its formation ; it gradually rises in strength, and is then stopped by the breaking of the metallic circuit, and thus great intensity is given by induction to the electricity which at that moment passes (see pars. 1,064 and 1060 of the same series). This intensity is not only shown by the brilliancy of the spark and the strength of the shock, but also by the necessity which has been experienced of well insulating the convolutions of the helix in which the current is formed ; and it gives to the current a force at these moments very far above that which the apparatus could produce if the principles which form the subject of this paper were not called into play." The anticipations of Faraday that his discoveries would find their " full development hereafter" were not long in being realized. One of the first electro- magnetic coils which obtained public notoriety was that designed by Professor Callan, of Maynooth College. It consisted of a coil of thick, insulated, copper bell-wire, wound on a small bobbin, to serve as the primary coil, and of a coil of about 1,500 feet of thin insulated wire wound round a large cylinder, into the axis of which the smaller coil could be introduced, to act as the secondary. The ends of each coil are attached to binding screws, to establish, on the one hand, a communication between the primary coil and 26 the battery, and, on the other, for the convenience of interposing any apparatus on which the effects of the secondary current are to be tested. Various contrivances have been adopted for breaking and renewing battery contact, some of an automatic character, others requiring manual assistance. Dr. Bird was the first in this country, at least, to employ the permanent magnet to effect rupture of contact ; this he did by causing a small bar electro-magnet to vibrate between the opposite poles of a pair of steel horse-shoe magnets in such a manner that every time each arm of the electro-magnetic bar rose and fell it should effect a disruption and a renewal of contact between the battery and the primary coil ; in this way he obtained 300 oscillations in a minute, and a series of induced currents, capable not only of communicating intense shocks, but of exerting powerful electrolytic action ; when a bundle of soft iron wires was introduced into the axis of the primary, the physiological and chemical effects were greatly exalted; the sparks at the contact-breaker were much increased in brilliancy, and were accom- panied by a loud snapping noise and a vivid com- bustion of the mercury. In other arrangements the coil is placed vertically, and battery contact broken and renewed by the rotation of a soft iron bar, mounted between two brass pillars, and situated immediately over the axis of the coil, in which is placed a bundle of iron wires ; in others, a small disc of iron is kept vibrating, with amazing rapidity, over the bundle of iron wires, contact being broken and renewed between surfaces of platinum, which dispenses with the use of mercury. Mr. Henley, some years ago, made and presented to the writer a very powerful electro-magnetic machine, consisting of a series of U-shaped bars of soft iron, round which were wound four coils of No. 34 wire. Con- 27 tact was broken and renewed by mercury. With this instrument a secondary spark could be obtained passing one-eighth of an inch through air; by a very simple contrivance the ends of the secondary coil could be united and disunited by merely turning an ivory knob ; the instrument is, therefore, well adapted for demonstrating the inductions and reac- tions of electrical currents ; when the ends of the secondary are disunited the sparks of the primary are large and brilliant ; when united, they are small and faint. But the secondary coil may be dispensed with altogether, and this is one of the best arrange- ments when the instrument is to be used for medical purposes. The writer constructed a machine of this kind some years ago, containing 100 yards of covered bell- wire surrounding a core of iron wires, battery contact being broken and renewed by clock-work, so that the frequency of the induced shocks could be regulated with the greatest regularity and precision ; wires leading from either end of the coil, and attached to suitable binding screws on the stand of the apparatus, served to convey the extra current, in accordance with the principles laid down in 9 and 10. The frequency of the shocks was regulated by the clock-work mechanism, and the intensity by a water regulator which ingenious and useful append- age to the medical coil was the invention of the Rev. F. Lockey. This was included in the circuit of coil, and by increasing or diminishing the distance between the wires, so as to interpose a greater or less thickness of water, the power of the shocks could be modified to any required degree, giving the operator such perfect command over the instrument as to enable him to apply this form of electricity to as delicate an organ as the eye, or to administer powerful shocks. It has recently been discovered by Mr. Wilde, 28 Professor Royal Society, April 26th, 1866, that an indefinitely small quantity of magnetism is capable of evolving an indefinitely large amount of dynamic electricity. When the wires forming the polar terminals of a magneto-electric machine of peculiar construction were connected for a short time with those of a very large electro-magnet, a bright spark could be obtained from the helices of the latter twenty-five seconds after all connection with the magneto -electric machine had been broken ; hence it would appear that the electro-magnet possesses the power of accumulating and retaining a charge of electricity in a manner somewhat analogous to that of the Ley den jar. Mr. Wilde also noticed that the helices of the electro-magnet opposed a certain resistance to the magneto- electric current, and that it required in some cases nearly half a minute before the current attained a permanent degree of intensity. Four permanent magnets which collectively could only sustain 40 Ibs., could be made to evolve an amount of electricity sufficient to excite an electro- magnet to such a degree as to enable it to sustain 1,080 Ibs., and by suitable arrangement the electro- magnet could be made to evolve a large amount of dynamic electricity. The magneto- electric current produced by a machine containing six permanent magnets, which weighed only 1 Ib. each, and collec- tively could only sustain 60 Ibs., was made by Mr. Wilde instrumental in producing a prodigious amount of dynamic electricity. The direct current from the magneto-machine was sent through the coils of the electro-magnet of an electro-magnetic machine, and the direct current from the latter was sent through the coils of the electro-magnet of another much larger electro -magnetic machine. The result was the production of an amount of magnetism in the latter far exceeding anything that has 29 hitherto been produced, accompanied by the evolu- tion of an amount of dynamic electricity so enormous as to melt pieces of cylindrical iron rod, 15 inches in length and one quarter of an inch in diameter, and to produce in the electric lamp a light which cast the shadows from the flames of the street lamps a quarter of a mile distant upon the neighbouring walls, and threw rays from the reflector having all the rich effulgence of sunshine. The light and heat are increased according to the amount of mechanical force employed. Fig. 8 represents the permanent magnetic arrange- ment of the above machine, and consists of sixteen magnets, each weighing 3 Ibs. The armature is FIG. 8. rotated by a multiplying wheel arrangement turned by hand. The current obtained by this means is sufficient to heat to whiteness 5 inches of platinum wire, -012 in. diameter, and with one of Mr. Ladd's 30 Inductoria containing three miles of secondary wire 2-in. sparks can be obtained. The commutator can be arranged to send the currents in one direction, and will then liberate from acidulated water one- and-a-half cubic inches of the gases per minute. It can also be used for the various lecture experiments, where a battery has hitherto been indispensable. It is well adapted for blasting purposes, and likely to be extensively used for electro -plating, etc. 14. ELECTRO-MAGNETIC COILS FOB THE MEDICAL ADMINISTRATION OF ELECTRICITY. At the International Exhibition of 1862, a great number of induction coils for medical purposes were exhibited ; they were generally arranged with much ingenuity, and with varied means of altering the number of shocks per minute, as well as of the strength of the shocks. Mr. Ladd's very convenient arrangement of the electro-magnetic medical coil is shown in Fig. 9. The electromotor is a sulphate of mercury battery, which has been chosen for its extreme cleanliness, and high electro-motive force. The apparatus when closed resembles a small book with a clasp, and is very portable. On the left-hand side of the book is a small door, which, upon being opened, exposes the sulphate of mercury battery. The tray is made of ebonite ; within this is a cell of carbon cut out of a solid block; this is lined with a piece of cloth or lint, and upon this is placed a slab of zinc, a piece of which is bent up, and faced with platinum ; there is also a copper connecting piece for the carbon cell ; on the right-hand side of the tray, the poles, vibrat- ing- spring, etc., are placed. To excite the battery, a sufficient quantity of sul- phate of mercury is placed on the carbon tray to 31 cover it over and make an even surface ; the lint is placed above this and left sufficiently large to turn up at the sides, so as to prevent contact between the zinc and carbon ; about a teaspoonful of water is then poured on it and the zinc plate placed on the lint ; the tray is now put back into the box and closed. The battery is now in circuit with the primary wire of the coil ; the spring must next be adjusted by the eccentric button, which must be gently turned round until the vibrations show that the battery is in action ; by turning the button back a little, the vibrations are diminished in frequency. On either 32 side of the vibrating spring will be perceived two nuts with holes through them, those on the left marked P + and P , those on the right S + and S . P + means the positive pole of the primary wire. P the negative pole of the primary wire. S4- signifies the positive pole of the secondary or finer wire ; S the negative pole of the same wire. If a very gentle current be desired, the copper pegs of the conducting wires must be inserted into P+ and P respectively, and upon holding the conductors in the hands, the physiological effects are scarcely perceptible ; to increase these, the brass handle in front of the box to the right of the clasp is gradually drawn out, and the soft iron core contained in the centre of the coils is gradually exposed and mag- netized, increasing the strength of the induced current. On pushing back the brass tube and inserting the pegs of the conducting wires into the nuts S + and S the current from the secondary wire, which is far more powerful than that from the primary wire, is obtained. If now, magnetic induction be added to volta-induction by gradually drawing out the brass tube, the current becomes by degrees so powerful as to be unbearable ; thus, with this little battery, any requisite amount of power may be obtained. If it is in regular daily use, the carbon cell will have to be cleaned about once a week ; the lint should be taken out and well washed, so as to remove all the yellow deposit ; the carbon cell then rinsed out with fresh water, and the under surface of the zinc well washed ; the lint is now replaced, and the battery is ready to be re- excited ; the process of cleaning need not take more than two or three minutes. The form of voltaic battery in which sulphate of mercury and carbon electrodes are substituted for the sulphate of copper and copper electrodes of the 33 Daniell's battery, is known as the "pile Marie Davy," an arrangement of many hundred cells has been constructed by Mr. Grassiot, with which he now exhibits some of his most beautiful and striking experiments on electrical discharge through various vacua. The Marie Davy battery has not the power of that of Daniell, but it is clean and remarkably constant. 15. THE INDUCTION COIL. Up to about the year 1842, the only object sought by makers of electro-magnetic machines would seem to have been the production of shocks, and the regu- lation of their intensity and frequency. It was M. Masson who first directed attention to other static phenomena which the instrument was capable of developing ; in that year he constructed, in conjunc- tion with M. Breguet, an apparatus with which, though consisting of a single coil only, and that very imperfectly insulated, he was able to obtain sparks in rarefied air of sufficient length to show the un- equal heating powers of the two poles of the circuit ; to charge a condenser, and to ignite platinum wire ; these electricians were therefore the first to show that, by the process of induction, the electricity of the galvanic battery (dynamic) is converted into the electricity of the ordinary electrical machine (static). In 1851, M. Ruhmkorff, an intelligent and well- known philosophical instrument maker in Paris, directed his particular attention to the more perfect insulation of the wire, which, after covering in the usual way with silk, he surrounded with a coating of gum-lac, and attached the ends to glass rods, rightly concluding that the wooden frame of the instrument, though sufficiently insulating for voltaic, 34 was not so for static electricity. He moreover diminished the diameter of the coil, thereby, with the same quantity of wire, obtaining a greater num- ber of convolutions ; and he greatly increased the length of the secondary, extending it in some of his machines to the length of nearly six miles. Lastly, from a conviction that the magnetic current was more effectual in arousing an induced current than the mere coil, that is, that the secondary effects were referrible more to magneto- than to w/fo-electric induction, he gave in his coils a great development to the former, by introducing into the axis of the primary a large bundle of iron wires, which he found to acquire a much higher degree of magnetism than an equal weight of iron in the form of an iron bar. To interrupt the inducing current, he employed a simple piece of mechanism known as " Neef's " hammer, consisting of a small block of iron, which vibrated between the projecting end of the coil of iron wires and a small anvil connected with the primary coil, in such a way that when the anvil and hammer were in contact the current was on, but the moment they separated it was off. It will be unnecessary to describe minutely this form of contact- breaker, as it has given place to other and far more efficient arrangements. With these improvements Euhmkorff obtained effects which were at that iime surprising ; he not only got brilliant sparks between the terminals of the secondary wire, but between the wire itself and a body out of the circuit in communi- cation with the earth ; and he obtained a discharge, in a vacuous globe, of great brilliancy, the spark filling the balloon with that magnificent phenomenon, stratified light, about which we shall have more to say presently. These effects were greatly exalted in degree, by interposing in the circuit of the primary, a simple condenser, as recommended by M. Fizeau ; 35 brilliant and crepitating sparks in free air were now obtained, three-quarters of an inch long-, and the shock was so violent, that it is stated by Du Moncel, that M. Q-uet, incautiously getting himself into the circuit, was knocked down, and so much injured as to be obliged to keep his bed for some time, never- theless the battery only consisted of six elements. We are reminded by this story of the account given by Muschenbroek of the effects on himself of his first shock from a Leyden phial, which he declared deprived him of his breath, and made him ill for two days; it is, however, true that great care is necessary in experimenting with the induction coil as at present constructed, as an incautious contact with the secondary wire communicates a most disagreeable shock; though how M. Q,uet came to be so much affected, unless he wantonly placed himself directly in the circuit, we are at a loss to understand. Various forms are given by M. Kuhmkorff to his coil ; the bobbin is sometimes arranged vertically, though generally horizontally, and the ends are backed up and supported by discs of glass or gutta percha, through which the wires of the secondary pass to their insulating pillars. The size of the primary wire is about 0'078 in. in diameter; the secondary wire is the No. 28 of commerce; and the instrument is furnished with a commutator, for the purpose of reversing at will the direction of the current. Shortly after Kuhmkorff's improvements were an- nounced, Mr. Hearder exhibited one of his improved machines at the Royal Cornwall Polytechnic Society ; it was six inches in length, and contained about a mile and a half of fine secondary wire ; it was wound upon a hollow bobbin of wood, covered with gutta- percha, and having its centre large enough to contain the primary coil with its iron core. The secondary 36 wire was covered with silk, and the layers insulated from each other with oiled silk and gutta-percha ; it was provided with a condenser, gave sparks between the terminals more than one inch in length, and charged a Ley den jar containing three square feet of surface, so as to give a torrent of brilliant dis- charges between platinum terminals. For this instrument Mr. Hearder received the Society's first silver medal. In September, 1856, Mr. Charles Bentley showed the writer a coil of his own construction, which gave sparks between terminals of silk- covered wire an inch and a half long, the primary being excited by five of Grove's cells. In building up this coil he used, as an axis, a hollow iron tube, nine or ten inches in length and half an inch in diameter ; round this he arranged a considerable number of insulated wires, the same length as the tube, and sufficiently numerous to form a bundle of an inch and three- quarters in diameter. This core was insulated by being covered with six or eight layers of waxed silk. Thirty yards of No. 14 cotton-covered copper wire were then wound carefully round the iron core, forming two layers, which were then insulated from each other by eight thicknesses of waxed silk. The secondary wire consisted of 3,000 yards of No. 35 silk-covered copper wire, and the coils which it formed were insulated by several layers of gutta- percha tissue ; it was wound so as to leave a space of about one-sixteenth of an inch at either end of the coil beneath, so that ij: formed a cylinder with rounded ends a form preferred, from its obviating the necessity of glass checks for keeping the wire in its place. The condenser, which was contained in a, separate box, consisted of 100 sheets of tinfoil, 4x9 inches, each sheet of foil being placed between two sheets of carefulty-varnished paper, and the 37 alternate ends connected with, appropriate binding screws. The induction coil, as now constructed by Mr. Ladd, which is shown in Fig. 10, and more con- spicuously in the frontispiece, consists of the usual 'primary,' which is of covered copper wire, -10 inch in diameter, or No. 12 wire gauge, wound into a coil of three thicknesses, enclosing a bundle of iron wires 1 -8 inches in diameter ; the ends of this fasciculus project -7 inch beyond the gutta-percha ends, which are seven inches in diameter and '6 inches thick ; these gutta-percha discs are firmly fixed on the base- FIG. 10. board of the machine, and serve both to support and to insulate the coil. The secondary ' is a coil of No. 35 silk-covered wire, three miles long; it is very carefully wound round the primary in about thirty layers, each layer insulated from its neighbour by a sheet of gutta-percha. The total length of the coil is eleven inches, and its diameter, including the velvet jacket, five inches. The ends of the secondary pass through one of the terminal gutta-percha discs to an insulated discharger, the arms of which move in ball-and-socket joints, so that the terminals may be separated any distance from one another up to about four and a half inches. The arm in connec- tion with the wire proceeding from the interior of the 38 coil is provided with an ivory handle, with which the arm may be moved ; the other arm, in connection with the exterior, terminates in a brass knob ; this must not be touched while the machine is in action, if the operator wishes to avoid a powerful and painful shock. One of the ends of the primary is brought out through the anterior and the other through the posterior gutta-percha disc, to two brass studs, from which they are conducted underneath the wooden base to the commutator and the contact- breaker. The wires from the battery (five pairs of Grove's arrangement, immersed platinum 5J x 3 inches), are attached to two binding screws, one on either side of the commutator, as shown in the frontispiece. The condenser is conveniently placed in a box underneath the base of the instrument, to which it is firmly attached. It is composed of about fifty sheets of tinfoil, 18 x 8 inches, and between each sheet is laid a sheet of varnished paper ; one- half of the foil is in metallic connection with each side of the break, so that when contact is broken the interrupted ends are respectively in metallic com- munication with the opposite coatings of the con- denser. The contact-breaker merits especial notice, as it is to the improvements introduced into this part of the apparatus that the surprising effects of the coils of the present day are in a great measure to be ascribed. In Buhmkorff's original instrument, the interruption of the battery current was, as we have seen, effected by the rising and falling of a small iron hammer ; this, whilst it accomplished the general purpose of breaking and renewing battery contact, set up no resistance, the hammer being raised as soon as the iron core had received sufficient magnetism to enable it to attract a very small piece of iron, whilst the falling of the hammer on the 39 interruption of the current was in no way influenced by the degree of magnetization of the iron core. The contact-breaker is now constructed by Mr. Ladd, with the object of giving the operator the means of setting up a greater or less resistance to the attrac- tive force exerted by the magnetic iron core. This is accomplished by attaching the hammer to a stiff spring, placed vertically, as shown in Fig 11. where A is the disc of iron capping one end of the iron core; B, the iron hammer of the contact-breaker, surmounting a stiff spring attached to a brass stand screwed to the base-board of the instrument ; c is a little projecting nipple, tipped with platinum ; d, a FIG. 11. corresponding little disc of platinum, soldered to the end of a screw, which passes through the top of a brass pillar, firmly screwed down to the base-board ; the distance between d and c can be regulated with the greatest nicety by the thumb-screw, e. Now, when c and d are in contact, and the commutator is turned on, the battery current is circulating round the primary coil, the fasciculus of iron wires becomes 40 a more or less powerful magnet, according to the power of the battery ; B is attracted to A, by which act c and d are separated ; battery contact is hereby broken, and the effects of the induced current are obtained at the terminals of the secondary. But if the action of the contact-breaker ended here, it would be nothing more than Neef's hammer placed verti- cally ; it will be seen, however, that by turning the screw #, the point / attached to its axis may be made to press with greater or less force on the spring supporting the hammer, thereby keeping c and d more or less firmly in contact, and necessitating a corresponding degree of magnetization of the fasci- culus to part the platinum discs ; when, however, this has been attained, contact with the battery is instantly broken, and the hammer is forced back with violence by the conjoint action of the spring and screw ; d and c again come into contact, the iron core again becomes magnetic, A attracts B, and the battery current is stopped, c is again forced upon d, and so on. Now a degree of pressure may be exeited on the spring support of B by the screw g sufficiently great entirely to overcome the attractive force of A ; under such circumstances the instrument is, of course, passive, but by gradually relaxing the tension to a certain degree, the magnetic power of the core just overcomes the antagonistic force of the spring, and then it is that the most powerful inductive effects are obtained, evidently because then the fasciculus has received from the battery its maximum amount of magnetism, which it loses instantaneously by the interruption of the battery circuit, giving rise to a powerful wave of induced static electricity in the secondary coil. The influence exerted by the resist- ance thus set up to the rupture of battery contact on the strength of the induced current is far greater than could have been anticipated. The instrument 41 we have been describing gives between the terminals of the secondary, when the screw g is entirely relaxed, thin thready sparks, about 1^ inch long, but when the spring is strained to the utmost, brilliant flashes upwards of 4 inches long, pass continuously. The control which this form of breaker gives to the operator while performing experiments in which con- siderable variations in the power of the induced current are required, renders it of great value. The Condenser. The function of this very import- ant part of the modern Induction Coil is by no means clearly understood. Fizeau, who suggested it, says, that it condenses and destroys, by a static effect, the electricity of tension or induction which gives rise to the extra current in the induction wire, and which reacts on the induced current in the secondary wire in a direction contrary to that of the voltaic current. Faraday seems to have much the same opinion. He says : " When the secondary current is interrupted, the inducing power of the primary current acts in its own wire to produce certain hurtful or wasteful results ; the condenser takes up this extra power at the moment of time, and converts it to a useful final purpose upon principles belonging to static induc- tion." Poggendorff's view is that the function of the condenser is to draw away the electricity of tension which, when the battery current is inter- rupted, accumulates at the two ends of the inducing coil, where it would otherwise be retained by the resistance of the air reacting on the fluid set in motion in the thin wire, and so diminishing its intensity. Hearder suggests, that at the moment of breaking the contact the induced current exhibits its intensity at the points of separation by overleaping the interval ; but if these two interrupted ends be in contact with the extended conductors of the condenser, a portion of this intensity may possibly be reduced 42 by its being determined in the direction of the two conductors, which, by inducing upon each other, have their capacities for electrical charge considerably increased, and thereby act as capacious reservoirs, in which these intensities may expand and exhaust themselves. Whatever may be the true explanation of the modus operandi of the condenser, it is certain that it increases vastly the static effects of the in- duced current, although it does not increase the quantity of the electricity set in motion. Mr. Ladd fits up some of his coils with a simple arrangement for detaching the condenser ; if this be done while sparks or flashes four inches in length are leaping between the wires of the discharger they immedi- ately cease, and the terminals require to be brought within half an inch of each other before thin thread- like sparks can be made to pass between them. Since the former edition of this little work was written, the induction coil has received wonderful developments. Some fine instruments were shown at the International Exhibition of 1862. One by Siemens and Halske is especially noticed in the Jurors' report for the great length of spark obtained (from one to two feet in length) with a comparatively very small length of wire in the secondary coil, which is stated to be 6j miles. A singular mistake, was, however, made in stating the length of the secondary coil instead of being 10,755 metres, about 6l miles, it was in reality 129,000 metres, or nearly 80 miles, so that the instrument was in noway remarkable for power. An admirable coil was con- structed for Mr. Gassiot by Mr. Ritchie, a philo- sophical instrument maker, of Boston, TJ.S. The primary wire is wound in three courses on a helix of 150 feet in length. The secondary helix is divided into three bundles, each 5 inches long, wound on cylinders of gutta-percha, the upper and lower coils 43 are each 25,575 feet in length, and the middle 22,500 feet. The maximum effect with the three coils is to produce a spark 13 inches long ; with five cells of Grove's battery, Mr. Gassiot obtains sparks or dashes 12 J inches long. Ruhmkorff now constructs coils containing 100,000 metres of wire in the secondary. The writer has had the pleasure of witnessing some experiments with one of these magnificent instruments, the property of Mr. Atkinson. When excited by a single cell of the carbon nitric acid battery (Bunsen's), sparks 3 inches in length are obtained ; two cells give sparks 6J inches long; three cells, sparks 10-| inches; four cells, 12| inches ; five cells, sparks 14 inches ; six cells, 1 5 inches ; and seven cells, sparks 1 6 inches. Beyond this it is hardly safe to go, for fear of injury to the coil ; but sparks or flashes upwards of 1 9 inches in length have been obtained. Mr. Ladd constructs (and showed at the Inter- national Exhibition) induction coils from which he obtains 5 -in. sparks, using five cells of Grove's battery with plates 5 x 3 in. immersed. The con- struction is as follows : On a core of iron about a foot long are wound fifty yards of copper wire of No. 12, B.W.G. (0-034 inches) insulated with cotton. This coil forms three layers, round which five or six thin gutta-percha sheets are wrapped. The secondary coil, formed of three miles of No. 35 copper wire (0-005 inches), insulated with unvarnished silk, is wound backwards and forwards along this core with each layer insulated from the preceding one by five or six sheets of thin gutta-percha. Mr. Ladd also exhibited a coil of very different proportion. The iron core and primary coil are about 8 inches long ; but the secondary coil, placed in the centre of its length, is only 4 inches long, but 7 J inches in diameter. Much the same results may be obtained with this as with the preceding coil. 44 An induction coil constructed by Mr. Ladd for Dr. Robinson, of Armagh, in which there were two secondary coils each containing 5,690 yards of wire, together therefore 6 miles 820 yards gives results which, considering the length of the secondary, are certainly very remarkable. Thus Dr. Eobinson writes : 1 cell gives a spark . 2-04 inches long. 2 cells ,, . 5-06 3 ,. . 6-45 4 : . . 7-65 5 ,, ,, . . 8*38 ,, The battery cells referred to are Grove's 5^ x 4 in. immersed platinum. In describing these results, Dr. Eobinson re- marks : " There was no internal discharge in any part of the coils. Whilst making these trials, the barometer was at 30-25 inches, which high density of the air from its greater resistance materially shortens the spark : had it been our mean pressure 29 -6 in., I feel satisfied that the spark would have been 9 inches." An end view of one of Ladd's coils is shown in Fig. 12, from which the positions of the con- tact-breaker a, commutator 6, and the binding screws for communicating with the battery, etc., may be seen. The binding screws, c d, are used for getting the battery spark in connection with the induced magneto-spark and for showing bright scintil- lations from iron and other metals. The contact- breaker must be firmly united, and the ends of the secondary coil connected. Battery contact is made in the usual way, by the screws on either side of the commutator, and the effects are obtained at the terminals represented by the binding screws, c, d. 45 In a memoir " On increasing the Electricity given by Induction Machines," recently published, (May 31st, 1866) by Dr. Eobinson, some useful practical maxims as to the construction of the Inductorium (as FIG. !2. the Germans have named the instrument) are given. By increasing the length of the spark, the object to which the attention of instrument makers has chiefly been directed ; no addition to the quantity of electri- city is made; this is however the most important object, for in most applications of the inductorium, all tensions above what is necessary to force the necessary quantity of current through the circuit is useless, nay, sometimes injurious. Dr. Eobinson thinks that a tension which gives sparks of four inches will be found quite sufficient in ordinary cases, and this will be given by about 20,000 spires, all beyond only adding to the weight of the instrument, its cost, and the difficulty of insulation. It must be kept in mind that the mere quantity is independent 46 of the length, of wire ; it was found actually the same for a flat spiral of twenty-one spires, and for a helix of 13,655. The quantity increases with the diameter of the wire of the core up to a maximum which is attained when this is about the sixty-fifth of an inch. Helices may be combined either for tension, or quantity, without much loss of their respective powers. If for the former, they are combined in aeries, the general tension is the sum of the individual ones, and in this way we can obtain sparks of a length limited only by the strength of the insulator, which is inter- posed between the primary and secondary helices. If the latter be all of the same wire, the quantity remains unchanged ; if they differ in this respect it will be intermediate between the weakest and strongest. If they are combined for quantity, they must be set collaterally, i.e., all their positive termi- nals connected, and their negative. The resulting current will be the sum of all the separate ones, but the tension is not increased ; the sparks seem even a few hundredths of an inch shorter, but are much denser, and in the higher combinations, approach to the character of a jar discharge, hence there is no risk to the apparatus by extending this mode of combination to any extent. In combining these instruments, the primaries should not be consecutive if of large numbers, for so, the action of their extra-current (10) would be very destructive to the rheotome ( contact breaker.) With two primaries containing 726 spires in series, the spark in the mercurial break was almost explosive, but when they were collateral the action was quiet. "Were, however, ten or twelve to be so combined, it would require a battery of very large cells to main- tain the current, and it is better to have a separate battery for each pair of primaries. The negative pole 47 of all the batteries should be connected with the mercury of the rheotoine ; from its platinum point separate wires must go to the entering bind-screw of each primary ; other wires must go from their exit bind-screws to the positive poles of the respective batteries, and thus their action is perfectly synchron- ous. In this way Dr. Robinson thinks that an amount of electric power which has not hitherto been approached by the inductorium may be obtained. 16. EFFECTS OF THE INDUCED CURRENT. In making the following experiments, it is assumed that the operator is working with an instrument such as is figured in the frontispiece, with larger coils the phenomena are of course exalted in a proportionate degree : Example 1 . The battery being well-charged the zinc cells, with a mixture of one part of oil of vitriol and six or eight of water, and the platinum cells with ordinary nitric acid draw the ends of the discharger about three inches apart, and turn the commutator ; brilliant zigzag crepitating flashes will dart between the points, the length of which may be increased to four inches, and sometimes even more, by withdraw- ing the points gradually (take care not to touch the arm which has the brass knob) ; now bring the points to within about two inches of each other, and observe the spark, it will be found split up into bundles, and to be surrounded with a sort of yellow-green atmos- phere, which may be expanded into a mass of irregular violet-coloured flame by gently blowing it. The two parts of the induction-spark, viz., the point of light and the luminous atmosphere, may be com- pletely separated by opposing to one of the electrodes another of a V-shape. By suitably regulating the distance of the extremities of the latter from the 48 former, M. Serrot succeeded in establishing an atmospheric current, which carried the luminous atmosphere towards that branch of the Y-shaped electrode which was more remote from the opposite pole. Under these circumstances, the luminous atmosphere appeared only at this latter branch the other branch receiving the ordinary spark. Du Moncel has also shown that of the two parts of the spark the luminous atmosphere only is affected by the magnet. Dr. P. L. Bijke has made experiments, from which he concludes that the point of light in the inductive spark is to be attributed to the re- compositions of the electric charges accumulated at the extremities of the secondary wire, while the luminous atmosphere is produced by the electric fluid contained in the parts of the wire nearer to its middle point. When the inductive wire is discharged, the electric charges of the two extremities first unite, and the spark is bright, while the charges of the parts nearer the centre, meeting with considerable resistance, require a sensible time, and the spark becomes altered, diminishing in illuminating power and increasing in volume. Ex. 2. While the 4-inch sparks are passing, re- move the wire which connects the two binding screws on the left-hand side of the base of the instrument (see Fig. 12), thereby disconnecting the condenser ; the sparks will immediately cease, and the wires will have to be brought within a half of an inch before they reappear, now very faint and thin ; re-connect the screws, and the flashes will reappear with their former length and brilliancy. If the spark from an Inductorium be projected on a screen by the electric current, and the impression contrasted with that of the flame of a candle in the former, two cones are seen to issue from the terminals instead of the single one of the latter, one being more powerful, 49 and overcoming or beating back the other ; and this effect is reversed as the direction of the current is reversed. In the voltaic arc there is a transmission of matter, principally from the positive (which is the more intensely heated) to the negative terminal ; in the spark from the coil the dispersion is principally, and in some cases appears to be entirely, from the negative terminal, which is now the more intensely heated. Ex. 3. Attach to the terminals of the discharger, two platinum wires, each about two inches long, and gradually approach them ; the wire on the negative side will become intensely heated, and will ulti- mately fuse ; now turn the commutator, thereby changing the direction of the current; the same phenomenon will occur with the other wire ; substi- tute for the platinum wires thin wires of iron, the negative wire will speedily begin to burn with brilliant scintillations ; replace the iron by zinc, the negative wire will burn with a brilliant white light. This heating property may be taken advantage of to determine the direction of the induced current. While vigorous sparks are passing between the terminals, introduce a piece of paper, or a thin shaving of wood ; either will be speedily kindled. Ex. 4. Attach iron filings to a large pane of glass, by means of a suitable varnish, and when dry place it between the terminals ; flashes of light more than a foot in length may thus be obtained. Moisten a piece of cork, ten inches long and four inches wide, with dilute sulphuric acid, place the terminals upon it, first about two inches apart ; great heat will be set up on the line of discharge, which will vaporize the water, and the cork, becoming charred by the sulphuric acid, will begin to burn ; now slowly separate the terminals, drawing one along the surface of the cork, in a zig-zag manner, the flame will D 50 follow it, charring the cork in its progress and leaving behind a line of light. In this way you may proceed from one end of the cork to the other, making a complete lake of fire, which has, in the dark, a very beautiful appearance. The best way of making the experiment is to lay the cork upon the table, and stick into one end a wire in connection with the inner terminal of the coil ; a wire, leading from the outer terminal, is attached to a brass rod provided with a varnished glass handle, and to this a stout wire ; the operator directs the wire along the cork by this contrivance without the chance ot getting a shock. If a sheet of silvered leather be substi- tuted for the cork, it becomes brilliantly illumi- nated with a green-coloured light ; or if common leather be moistened with dilute sulphuric acid, it may be used instead of cork. It must be observed that both cork and leather, after having once been rendered conducting by acid, retain their conducting power for a long time after they have become dry. Ex. 5. Separate the arms of the discharger be- yond the striking distance ; in the dark, brushes of light will be seen to dart from the positive electrode, and the negative will be illuminated by a character- istic star of light, also throwing off smaller brushes which re-curve over the wire. Ex. 6. In liquids of good conducting power no spark can of course be obtained, but in non or im- perfectly conducting fluids short crepitating sparks pass. In oil these sparks have a greenish white colour ; in alcohol they are red and crepitating ; in oil of turpentine, and in bi- sulphide of carbon, they are very brilliant. Pour some oil on the surface of water in a glass vessel ; introduce a wire covered with gutta-percha, and proceeding from the interior of the coil, underneath the water, just below the oil ; and plunge a protected wire from the other extremity 51 within striking distance, in the oil ; strong crepitating sparks are obtained, and hydrogen gas is liberated, which burns on the surface of the liquid. Decomposition of Gaseous Compounds. When the spark- current from the induction coil is sent through ammonia, it exhibits a violet light, surrounded with a blue edge. At first the mercury over which the gas is confined falls rapidly, the rate of expansion diminishing with the progress of the decomposition ; in five minutes the decomposition of a moderate volume of ammonia is accomplished. The FIQ 13 original volume is then doubled ; the spark current exhibits the pure violet light characteristic of hydrogen, and water in- jected into the tube produces no diminution of volume. The coil thus becomes a valu- able instrument for demonstrating the com- position of this interesting gaseous alkali in the lecture room. For the introduction of the spark current through this and other gaseous compounds, the simple apparatus shown in Fig. 1 3 was contrived by Buff and Hofmann. A fine platinum wire is fused into the shorter limb of a thin U-shaped glass tube, and filed off so as scarcely to project beyond the glass. At a distance of a few millimetres from the platinum pole thus obtained, the loop of a second platinum wire is thrown over the tube, and the wire wound round the tube until it nearly reaches the bend. The tube is then filled with mercury, and the shorter limb introduced into the graduated gas-tube inverted over mercury in a deep cylinder trough. The pole wires of the induction coil being now introduced, the one into the open end of the U-tube filled with mercury, and the other into the mercury of the cylinder trough, 52 FiG.U. the spark current may be established or interrupted at will, by either depressing the U-tube until the outer platinum wire reaches the mercury surface, or by lifting it so as to break contact. Occasionally Buff and Hofman effected the decompositions by incandescent coils of iron or platinum, or by the electric arc. For experiments of this nature, both limbs of the U-tube remain open. The iron or platinum wire is inserted into the shorter limb, and then coiled downwards round the tube, as shown in Fig, 14. Since the powerful heat emitted from the coil is apt to crack the U-tube, it was found convenient to surround the latter with a somewhat wider glass tube, which separates it from the incandescent coil. The U-tube, as in the previous case, is filled with mercury, and the pole wires of the battery are adjusted in a similar manner. By depressing the U-tube until the lower end of the coil dips into the mercury, the coil may be readily heated ; by raising the end to a proper height above the level of the mercury in the tube, the arc may be conveniently ad- justed. Amongst the results obtained by these chemists are the following : Cyano- gen was not decomposed by the spark- current, but perfectly by electrically incandescent wires, and more rapidly by the electric light, fifty volumes of the gas leaving, after half an hour, fifty volumes of pure nitrogen ; nitrous oxide was slowly decomposed by the spark- current into nitrogen and oxygen ; rapidly by incandescent iron, with the formation of sesqui- oxide of iron and a volume of nitrogen equal to that of the original gas. Nitric oxide was decomposed 53 slowly by the spark-current, rapidly by the incan- descent iron coil, the iron burning with splendid scintillations; the residual volume of nitrogen was one-half the original volume of gas. Through dry carbonic oxide the spark-current passes with a blue light, but without effect, nor was this gas decom- posed either by the incandescent coil or by the electric arc. Carbonic acid was decomposed by the spark- current into carbonic oxide and oxygen ; the mixture then exploded, reforming carbonic acid; unfortu- nately the decomposition is too slow for a lecture experiment ; the colour of the spark in the gas is violet. Marsh gas was partially decomposed by the spark- current, ten volumes of the gas becoming, in half an hour, eighteen volumes, and the colour of the spark changing from pale blue to violet. Olefiant gas was decomposed by the spark- current, which traversed the gas with a pale red light, into carbon and hydrogen; after about twenty minutes, seven volumes of the gas became 12 ; had the decom- position been perfect, the volume should have been doubled. Sulphuretted and phosphoretted hydrogen were both rapidly decomposed by the spark-current, the former with the deposition of sulphur, the latter with that of phosphorus, in the form of a brown powder. These results are sufficient to show what a powerful, elegant, and useful agent of gaseous analysis the Induction Coil is likely to become. Ex. 7. Place several lighted spirit-lamps side by side, between the terminals of a universal discharger, connected with ends of the coil ; separate the points twelve inches, the sparks will flash through the flames; with a small coil, not capable of giving sparks more than one inch long in cold air, sparks four inches long may easily be obtained through flame. Ex. 8. Connect the terminals of the coil with the 54 inner and outer coatings of a large Leyden phial, and separate the points of the discharger about of an inch, turn on the commutator, whereupon an ex- tremely brilliant discharge will take place between the points, assuming quite the character of the ordinary Leyden discharge ; the noise of this con- tinuous discharge is too great to be borne long without discomfort. " I have never," writes Mr. Grove, who first described this magnificent experi- ment, "witnessed such a torrent of electrical dis- charges; it is curious to see the absorption, so to speak, of the voltaic power by the Leyden battery. When the maximum effect for a given Leyden jar has been passed, the contact-breaker shows by its sparks the unabsorbed induced electricity, which now appears in the primary wire ; an additional jar acts as a safety-valve to the contact-breaker and utilizes the voltaic power, and so on," With the larger coils, electrical batteries may be charged and discharged with a continuous and almost deafening noise. When a series of Leyden jars are arranged for charging by cascade that is, each jar insulated, the outside of the first in the series con- nected with the inside of the second, the outside of the second with the inside of the third, and so on, the outside of the last jar being in communication with the earth, the effects produced with Euhm- korff's 100,000 metre instrument are brilliant in the extreme. A continuous stream of dazzling light, six inches in length, passes between the terminals, accompanied by a roar that cannot long be endured. By arranging the jar or battery in the manner shown in Fig. 15, a permanent charge may be given to it. The outer coating is brought into communica- tion with one of the poles of the secondary coil, and the tnner coating with one of the arms of the universal discharger, the other arm of which is in 55 communication with, the other pole of the coil ; the points of the discharger are set two or three inches apart. By this arrangement the wave of induced FIG. 15. electricity, which is produced as making battery con- tact, is stopped oif from the secondary wire; that produced on breaking contact, which is by far the most intense, being brought into action. The jar receives therefore a direct instead of an alternating charge, and after a few sparks have passed it may be re- moved and discharged in the usual manner. With Ruhnxkorff's large coil a battery containing ten square feet of glass is charged to saturation in a few seconds. Ex. 9. Introduce a card between the terminals, arranged as in the last experiment ; it will be per- forated precisely as with ordinary electricity. Mr. Grove has proposed to count the discharges, by causing a piece of paper to pass with a given velocity per second between the discharging points, and the number of perforations thus made per second may 56 be registered. Mr. Hearder has invented a very ingenious apparatus for carrying out this idea, with which he has endeavoured to compare the effects of the coil with that of an electrical machine, by esti- mating the amount of glass surface necessary to be rubbed to produce effects equal to those of the coil. The rapidity of the discharges will depend upon the nature of the interrupting spring employed in the coil, and as many as 100 to 200 per second may be obtained. Ex. 10. Substitute for the Ley den jar a ''fulmi- nating pane," consisting of a square of common window glass, about fifteen inches square, coated on either side with tinfoil ; attach to one of the coatings a band of foil, of sufficient length to fold over the edge of the glass and touch the other coating. If this band be wound round a glass rod, the two coat- ings may be brought within any required distance of each other, by simply winding or unwinding the foil ; adjust to the maximum striking distance, and turn the commutator ; the discharge now amounts to a positive roar, the vividness of the light of which may be appreciated by darkening the room. Ex. 11. Fix apiece of platinum wire horizontally across the ball of a Ley den jar, and bring the terminals of the secondary coil respectively near its ends ; two interruptions are produced in the secondary circuit, the sparks at which are like each other and equal in quantity of electricity, for the jar as yet forms only an insulating support ; now connect either terminal by a wire with the outside of the jar ; the spark on that side assumes a bright loud character, but ceases to fire gunpowder, or wood, or paper ; and no one would suppose at first, what is the truth, that there is the same electricity passing in one as in the other. The effect of the jar is not to vary the quantity of electricity, but the time of its passage. That electri- 57 city, which, moving with comparative slowness through the great length of the secondary coil, pro- duces a spark having a sensible duration (and, therefore, in character like that of a Ley den jar passing through a wet thread) is, when the jar is used, first employed in raising up a static induction charge, which, when discharged, produces a concen- trated spark of no sensible duration, and therefore much more luminous and audible than the former. If one of the secondary terminals be connected with the outside of a Leyden jar, and the other be con- tinued until near the knob or wire connected with it, a soft spark appears at such intervals for every succes- sive current in the primary circuit. This spark, however, is double, for the electricity thrown into the jar at the moment of induction is discharged back again at the same place the instant the induction is over ; the first discharge heats and prepares the air there for the second discharge, and the two are so nearly simultaneous as to produce the appearance of a single spark to the unaided eye. (Faraday.) Ex. 12. The difference in the thermal properties of the induced current, with and without the inter- vention of the Leyden jar, is well shown by the following excellent experiment, devised by Hearder : Connect a thermo- electrometer and a Lane's dis- charging electrometer with the terminals of the coil. Upon an adjoining table place a disc of wood, covered with tinfoil, exposing a flat surface of five or six square feet, and connect it also with one terminal of the coil. Take a second similar disc of wood, covered with tinfoil, and suspend it over the first one by means of a string passing over pulleys, in a frame so constructed as to admit of the second disc being raised to the height of five or six feet above the lower one. Connect this disc by means of a flexible wire, with the other terminal. By this arrangement 58 the two terminals have virtually their conducting surfaces increased, and the sparks consequently are much brighter, though the thermo-electrometer is unaffected. If now the upper coated disc be gradually lowered, the sparks rapidly increase in power, and when they are within three or four inches of each other they assume the character of the discharges of a Leyden jar, and the thermometer begins to be affected. As the discs are gradually lowered still further, their faces being kept parallel to each other, the sparks become still louder, and the thermometer rises 15 or 20, thus acting as coatings to a charged plate of air. On removing the upper plate these effects subside, and the spark reassumes its original character. Ex. 13. If a Leyden jar, coated with detached, diamond-shaped pieces of tinfoil inside and out, be connected with the terminals, it will be brilliantly illuminated during the whole time that the machine is in action. The best effects are obtained when the coatings are connected by two or three broad bands of tinfoil passing over the edge of the jar. If this be tolerably large, and if the rows of diamonds be so placed inside the jar that their horizontal points nearly touch one another at the centres of the circular holes cut in the diamonds of the outside, the dis- charge is exceedingly beautiful in a darkened room, far more so than with a common electrical machine. Ex. 14. If the discharges from a Leyden phial be made to pass over a lump of white sugar, or a crystal of alum, they will be beautifully illuminated ; if through a fine iron two or three feet long, suspended by silk threads in a festoon, sparks, accompanied with brilliant scintillations, occur at every link. Should the chain be rusty, the brilliancy of the effect is increased. Ex. 15. Pass the discharge through a small heap 59 of gunpowder on the table of the universal dis- charger ; it will be thrown about in all directions, but not ignited ; now interpose a piece of wet string in the portion of this circuit between the discharger and the jar, the gunpowder will immediately be inflamed. This is precisely what occurs with ordinary electricity. Ex. 16. The following experiment is one of the most beautiful that can be made with the Induction Coil. It is called the ''Cascade," and was thus described by Mr. Gassiot, who originated it : Coat a beaker, about 4 inches deep by 2 inches wide, with tinfoil, so as to leave \\ inches of the upper part naked. On the plate of an air-pump is placed a glass plate, and on it the beaker, covering the whole with an open-mouthed glass receiver, on which is placed a brass plate, having a thick wire passing through a collar of leathers ; the portion of the wire within the receiver is covered with a glass tube ; one end of the secondary coil is attached to this wire, and the other to the metallic plate of the pump. As the vacuum improves the effect is truly surprising : at first a faint, clear, blue light appears to proceed from the lower part of the beaker to the plate ; this gradually becomes brighter, until by slow degrees it rises, increasing in brilliancy until it arrives at that part which is opposite, or in a line with, the inner coating, the whole being intensely illuminated ; a discharge then commences from the inside of the beaker to the plate of the pump, in minute but diffused streams of blue light; continuing the ex- haustion, at last a discharge takes place, in the form of an undivided continuous stream, overlapping the vessel, as if the electric fluid were itself a material body running over. If the position of the beaker be reversed, by placing the open part on the plate of the air-pump, and the upper wire either in contact 60 with, or within an inch of, the outside of the vessel, streams of blue lambent flame appear to pour down the sides of the plate, while a continuous discharge takes place from the inside coating. On turning the commutator, so as to reverse the current, the cascade appears to flow upwards instead of downwards. This truly magnificent experiment has been arranged by Mr. Ladd so as to dispense with the trouble of ex- hausting the receiver on each occasion. Fig. 16 shows the apparatus. The cup, or beaker, is not FIG. 16. coated either inside or outside with tinfoil, but the wire through which the induced current is passed reaches to the bottom of the glass, and terminates in a metal disc. The receiver is permanently exhausted by an excellent pump, as shown in Fig. 17, it having 61 been first, as well as the cap, firmly secured by cement. It is then screwed on to a stand, and thus rendered permanently portable. It may here be remarked that no ordinary air pump is of much use in those experiments with the Indue- FIG. 17. tion Coil, in which a very good vacuum is required. In almost all the experiments about to be described, the most brilliant and gorgeous effects only appear when the exhaustion is approaching perfection. In the air-pump shown in Tig. 17, Mr. Ladd has arranged an extra barrel, a valve in which is mechanically opened by the movement of the piston ; and though this is not adapted for the first process of exhaustion, it will, after the ordinary barrels have done their work, very materially increase the goodness of the vacuum. But still more satisfactory results are obtained by the use of a modification of Greissler's mercury air- pump, shown in Fig. 18. It consists of two stout globular glass vessels, a tube from the bottom of the 62 upper passing air-tight through, the top of the lower aiid reaching nearly to the bottom. To the stem of the upper globe is sealed a lateral tube, and both it FIG. 18. and the vertical stem from which it proceeds are furnished with stop-cocks. The cock on the lateral tube c is intended to communicate with the vessel to be exhausted, a syphon mercurial gauge being placed between them to register the degree of ex- haustion. The stop-cock on the end of the vertical tube d is connected by means of elastic tubing with the air-pump or exhausting syringe. To the neck of the lower glass vessel b an elastic tube is also fitted, and this likewise is attached to a three-way cock on the air-pump. The working of this apparatus is as follows : The mercury (about 42 Ibs.) being in the lower 63 vessel b ; the upper globe a is exhausted ; the mercury rises and fills the vacant space. On opening the lateral stop-cock c, the air rushes in from the vessel to be exhausted, and the mercury sinks again partially into b. When the equilibrium is established, there will of course be mercury in both globes ; the air in b is now exhausted > and the whole of the mercury is thus brought down to the lower vessel ; the lateral stop-cock c is then closed ; air is admitted into b, the mercury rises, and the air that has been drawn into a is exhausted at d. By continuing these operations, the air in the vessel to be exhausted becomes very highly attenuated. Ex. 17. De la Rive describes the following ex- periment in illustration of his theory of the Aurora Borealis: Place the pole of a powerful electro- magnet underneath the surface of mercury con- nected with the negative pole of a powerful voltaic battery; bring over and near it the positive pole armed with a charcoal point; a voltaic arc is formed, and the mercury is agitated above the magnet; luminous currents rotate round the pole, throwing out occasionally brilliant rays. This phenomenon of the rotation of electric light round a magnetic pole is exhibited in a most superb manner by the appa- ratus (Fig. 19). Into the brass cap of a large globular or egg-shaped glass receiver a soft iron bar, surrounded with a coil of covered copper wire, is fixed ; the receiver is then exhausted. On sending the induced current through the vacuous receiver, a splendid band or riband of purple light makes its appearance, which immediately commences rotating round the iron rod, when that is converted into an electro -magnet by sending the current from a small voltaic battery through its surrounding coil; on turning the commutator, so as to change the direc- tion of the induced current, the direction of the 64 rotation changes also. In this truly magnificent ex- periment electric light takes the place of the con- FIG. 19. ducting wire in Faraday's discovery, mentioned in page 4. This experiment may be made more simple with the little apparatus shown in Fig. 20, con- sisting of a small iron rod, enclosed air-tight in a small receiver which is exhausted ; the iron rod is surrounded with a glass tube, round which there passes, towards the bottom, a metallic ring attached to a wire which passes through the re- ceiver ; a wire is also sealed into the top of the glass, and through these wires the discharge is made to pass ; the riband of purple light instantly 65 makes its appearance, and begins to rotate round the iron rod, on placing the receiver on one of the poles Fid. 20. of a powerful permanent steel magnet or a small electro-magnet. Ex. 18. Exhaust a tube, such as shown in Fig. 21, which may be from two to seven feet long, and from 11 to 3 inches in diameter, having previously connected the wires at each end with the terminals of the coil. As the exhaustion proceeds, a splendid Aurora Borealis fills the tube with corruscations, and as the vacuum gets more perfect a broad crimson riband is obtained, extending throughout the entire length of the tube. Now turn the stop-cock very gradually, so as to admit a very small quantity of air, the effect of which is instantly seen by the dis- appearance of the riband and the re-appearance of the corruscations ; but these gradually die out as the air enters. A few strokes of the pump, however, bring them back again, and thus, by increasing or diminishing the density of the air, the appearance in the tube may be made to undergo corresponding variations. FIG. 21. 66 Stratifications in Electrical Dis- charges in Vacuo. The striated condition of the electrical dis- charge in vacuo under certain conditions, was first announced by Mr. Grove, in a communica- tion to the Royal Society, 7th January, 1852. The following was one of his first experiments : A small piece of perfectly dry phosphorus was placed in a pla- tinum capsule on the lower ball of the electric egg. To keep the receiver dry, a stick of caustic potash was suspended in a tube from the upper wire ; the exhaustion was then made as perfect as possible, when the crimson light became gradually furrowed with beautiful stratifi- cations through a length which maybe extended to 12 inches, and when once obtained, the experiments may be stopped, and after 20 minutes or more, re- sumed with more brilliancy than before. Mr. Grove afterwards found that the transverse dark bands could be produced in other gases when much attenuated, probably in all, and he thought the reason why they are more easily seen in phosphorus vapour is that, all the oxygen having been consumed, a better vacuum is formed. About the same time, Euhmkorff noticed similar 67 phenomena in an alcohol vacuum, and the subject engaged the attention of Massen, Quet, and Du Moncel. The following modification of Grove's fine experi- ment with phosphorus is thus described by Mr. Jerry Barrett, and forms one of the most brilliant experiments that can be made with the Induction Coil : "A glass tube not less than eighteen inches long by three inches in diameter is provided with a brass ball at the top attached to the ordinary flat brass plate and sliding wire, and at the bottom with a small metal cup half an inch in diameter attached to the nipple of the air-pump plate. This is to con- tain a piece of thoroughly dry phosphorus, about the size of half a pea; and the tube, after being rubbed inside with a warm cloth to insure the absence of moisture, is placed on the plate of the air-pump, and the top with the brass ball adjusted on it ; after getting a good vacuum, the phosphorus will begin to glow, and contact with the coil should be made in the usual way that is, the upper part of the tube should be connected by means of a fine wire with the arm of the instrument that is not provided with an ivory holder, and the other arm with the brass- work of the air-pump ; it is very necessary in this as indeed in all experiments with the Induction Coil, that the connection should be carefully secured in order that no wire should become displaced when the room is darkened and so endanger the operator: contact being thus established, and the phosphorus allowed to glow for about five minutes, the com- mutator may be turned on, the phosphorus will then, by means of the electric spark, show signs of igni- tion, and the stream of electricity will become brilliantly stratified ; then on continuing to work the extra barrel of the air-pump the light will become wider and fill the whole tube. Should the phos- 68 phorus at the commencement of the experiment have shown sufficient activity, the stream of electricity will now begin to assume a faint salmon colour, the stratification becoming still more brilliant, until the colour becomes white or silver, and the effect, to a close observer, gorgeous in the extreme. The changes of motion and form are produced by means of the screw attached to the break, by re- versing the commutator, and by varying the power of the battery, but they are by no means certain. It appears to be important for the success of this beautiful experiment that the phosphorus, after a good vacuum has been obtained, should be well ignited by the electric current; but this does not generally happen when the exhaustion has been carried too far; it is equally necessary that the vapour from the phosphorus be not too much deposited on the surface of the glass tube so as to obstruct the view, which would happen were the phosphorus too soon ignited. Sometimes the effect produced is that of a number of cones of light chasing each other from below upwards, and vice versa ; sometimes they are flat tables of light, an inch or more apart ; sometimes they are rings apparently revolving or oscillating and vanishing one into the other, and not unfrequently the whole mass assumes the form of a cloud with no motion whatever; sometimes there are two clouds, and the effect of intercepting the current for a minute or so is to bring back the stratification, which lasts but for a very short time, and the cloud remains as before, resisting all endeavours to produce strati- fication, except for two or three seconds after the current is turned on. A very common effect is the formation of one large column of little cones in rapid motion, filling the whole tube, and reminding one of the ripple of the sea by moonlight, and again 69 four or five streams of cones filling the tube from end to end all at the same time. On more than one occasion, after varying the effects for upwards of an hour, I have succeeded in obtaining from sixteen to twenty layers of stratifica- tion, each layer being composed of two colours dis- tinctly divided in the centre, the upper half green, the lower magenta, and vice versa according to the directions of the current, exhibiting an effect similar to the very beautiful experiment in vacua produced by Mr. Gassiot with his large battery. If, at the conclusion of these experiments, a small quantity of air be admitted into the tube, the effect will be extremely beautiful; it should be done as quickly as possible, and instantly checked ; unless too much air has been admitted the stratification will not be destroyed, but a brilliant stream of magenta- coloured light will gradually blend with the whole : it is not always, however, that the original silver colour can be again restored. These effects, which can be shown with still more magnificence in a larger tube, are continually varied, and this constitutes not the least of the charms of this remarkable experiment." Ex. 19. Fig. 22 is copied from the work of the last-named accomplished electrician, and very cor- rectly represents the appearance presented in alcohol, wood-spirit, or turpentine vacua. When the poles are five or six inches apart, two distinct lights are produced, differing in colour, form and position. That round the negative ball and wire is blue it envelopes it regularly ; that round the positive is fire-red it adheres to one side and stretches across towards the negative, and has for its lateral limits a surface of revolution about the axis of the receiver. On close examination this double light is seen to have a singular constitution ; it is stratified, being 70 composed of a series of brilliant bands, separated from each, other by dark bands. In a good vacuum, the appearance is that of a pile of electric light. In FIG. 22. the red light, the brilliant bands approaching nearest to the negative ball have the form of capsules, the concave part being turned towards the ball; their 71 position and figures are sensibly fixed, so that it is easy to see that there is a solution of continuity in passing from one to the other. The extreme capsule does not touch the violet light of the negative pole, being separated from it by a dark band, greater or less according to the nature and perfection of the vacuum, that with spirit of turpentine giving the greatest. It was found by M. Q,uet, that when a galvanometer was interposed at the circuit, no current was indicated as passing through the electric egg till the exhaustion was tolerably good, and the light con- tinuous; the needle then became permanently deflected. A light, though less brilliant, may be obtained from one pole only, that of the exterior wire of the secondary, which possesses electricity of the highest tension ; and if the vacuum be very good, this light may be made to bifurcate by placing the finger against the outside of the glass. If currents from two coils be made to circulate in opposite direc- tions through the receiver, the red light disappears from the positive pole, giving place to a blue light the positive and negative lights are now the same. The same occurs when a resistance is introduced into the induced circuit, as by interposing a condenser between one of the poles and one of the balls of the egg. A uniform blue light is thus obtained round both balls, which, with a good exhaustion, may be stratified. Discharge in Torricellian Vacua. The conditions necessary to enable the experimentalist to produce the phenomena of striae or band discharge, have been stated to be : 1st. That the vacuum in the receiver should be as perfect as the air-pump can make it ; 2nd. That care should be taken to absorb all trace of moisture ; 3rd. That means should be used to introduce the vapour of naphtha or phos- phorus, or other similar substances. In the baro- FIG. 23, 72 metrical vacuum, previous to the researches of Mr. Gassiot, detailed in the Bankerian Lecture (March 4, 1858), no striae had been observed, the inductive spark being white and filling the whole tube; by making these vacua, however, with great care, Mr. Gassiot has succeeded in obtaining stratifications very distinct and well defined. Ex. 20. Into the glass tube (Fig. 23) are sealed two platinum wires about eighteen inches apart ; the tube itself is twenty-eight inches long, and about five-eighths of an inch internal diameter ; it is ce- mented into a brass plate, and when carefully filled with boiled mercury is placed on the open mouth of a receiver on the air-pump, the lower part of the tube being at the same time immersed in a basin of mercury ; by this arrangement the length of the discharge could be regulated from one- sixteenth of an inch to eighteen inches, either suddenly or very gradually, by allowing the air to enter into the. receiver, or by ex- hausting it with the pump ; the vacuum is never perfect, a very minute bubble of air always remain- ing ; the stratifications are, however, very distinct when the discharge traverses the full length of eighteen inches. In this experiment a single cell of the battery may be used to excite the coil, and the condenser need not be used. If the discharge be made constantly in the same direction, the upper wire being negative, the upper portion of the tube, as far down as a line drawn even with the end of 73 the wire, becomes covered with platinum in a minute state of division ; when this deposit is examined by transmitted light it is transparent, presenting to the eye an extremely thin bluish-black film ; but by re- flected light, either on the outside or inside, it has the appearance of highly-polished silver, reflecting the light as from the finest mirror. If the upper wire be made positive, and the lower negative, as soon as the mercury ascends above the negative wire a beautiful lambent bluish-white vapour appears to rise, while a deep red stratum becomes visible on the surface of the mercury ; as the mercury ascends in the tube the stratified discharge from the positive wire collapses, giving the appearance of a compressed spiral ; on exhausting, the mercury descends in the tube, and the stratification expands as if the pressure on a spiral spring had been removed. In the course of his experiments on the inductive discharge through Torricellian vacua, Mr. Gassiot found a great want of uniformity in different tubes prepared in precisely the same manner ; in some, no stratifications at all could be obtained, the discharge being clear, bright, and white ; in others, the discharge was a wavy line unaccompanied with strise ; in others the stratifica- tion was confused and indistinct, while in others it was clear and well-defined. He therefore prepared some tubes by the non-boiling process, first proposed for filling barometer tubes by the late Mr. Welsh, of the Kew Observatory (for an account of which see Phil. Trans., Yol. 146, p. 507), and with these he obtained clear, well-defined, and distinct bands, not only with the Induction Coil, but with the ordinary electrical machine. The important feature in Mr. Welsh's method of filling barometer tubes is the perfect cleansing and drying of the tubes before the introduction of the mercury, by sponging with whiting and spirits of wine. 74 If the hammer of the contact-breaker be removed, and one of the terminals of the primary firmly fixed to a bright copper plate having a sharp edge, and the circuit completed by steadily pressing the end of the other wire on the plate, using one or two cells to excite the primary, no trace of any discharge will be perceived in the tubes ; but if a sudden break of the battery circuit be effected, by bringing the wire quickly across the sharp edge of the plate, the strati- fications immediately appear in the tube in a very distinct and beautiful manner ; the more sudden the break, the more distinct will be the effects, and by using eight or ten cells they are distinctly visible on making contact. Contact with the battery may be also made and broken by dipping the wires in mercury. That the effects on making should not be equal to those on breaking contact, will be readily understood by considering that in the Induction Coil the induc- tive effects are principally due to the electro-magnetic condition of the iron core, and that while the iron wires require a certain time to reach their maximum power, they lose their magnetism instanter when contact is broken, provided the iron be very soft, and therefore the more suddenly the contact is broken, the more intense will the discharge appear in vacuo. In experimenting with vacuous tubes, the operator should always pass the current in the same direction, as the emanation of the platinum particles, and the consequent deposit on the glass, only takes place from and around the negative wire, the positive end of the tube remaining clear and bright. When the discharges of two separate coils were passed, by means of four platinum wires, through the same tubes, Mr. Grassiot found no signs of inter- ference, the separate stratification of each coil re- maining visible, although producing a degree of confusion from their interposition ; he found also that 75 the stratifications were very powerfully affected by the magnet, when the discharge is passing from wire to wire ; if a horse-shoe magnet be passed along the tube, so as alternately to present the poles to different contiguous positions of the discharge, the latter will assume a serpentine form, in consequence of its tendency to rotate round the poles in opposite direc- tions, as the magnet in this position is moved up and down the side of the tube. Pliicker, who has greatly distinguished himself by his researches in various branches of physics, and par- ticularly in electricity, has devised amongst many others the two following experiments for illustrating the action of magnetism on electrical discharge in highly attenuated media : In Fig. 24 two aluminum rings are hermetically sealed into a glass tube, four FIG. 24. or five inches long and about one and a half inches in diameter, the air in the tube is then exhausted as perfectly as possible. On passing the discharge from the Induction Coil between the two rings, the tube becomes filled with a beautiful pale blue light. If the small ring be made negative and the tube placed between the poles of the electro-magnet (Fig. 3), the moment the latter is excited the light arranges itself in the form of a broad arc between the rings, having a very beautiful appearance. On rendering the electro-magnet passive the arc disappears, the 76 light in the tube re-assuming its diffused character ; but on re-exciting the magnet, the arc reappears. If instead of two rings the terminals in the tube are two aluminium wires, as shown in Fig. 25, the long FIG 25. wire being made positive and the short wire negative, the arc produced is very broad and brilliant. Two Distinct Forms of Stratified Electrical Discharge. Ex. 21. These are illustrated by employing the simple tube shown in Fig. 26, which is thirty-eight FIG. 26. b rf inches long, and is exhausted by Mr. Welsh's pro- cess ; the wires, a 5, are thirty-two inches apart ; CC' are moveable coatings of tinfoil, two inches long, wrapped round the tube. When the discharges from an Induction Coil are made from wire to wire, the stratifications appear as already described; and if the tube be placed in a horizontal position over the pole of a magnet, the stratifications evince a tendency to rotate as a whole in the direction of the well- known law of magnetic rotation (2) ; but when the discharge is made from coating to coating, or from one wire to one coating, an entirely new phenomenon 77 arises, the stratifications have no longer a tendency to rotate as a whole, but are divided. If the tube be now placed between the poles of a powerful electro-magnet, one set of stratifications are repelled from, and the other attracted towards, or within, the bent portion of the magnet ; when the tube is placed on the north pole the divided stratifications arrange themselves on each side of the tube, changing their respective positions when placed on the south pole, but in all cases each set of stratifications are concave in opposite directions. Mr. Grassiot, to whom this singular experiment is due, designates these dis- charges as the direct or conductive, and the recipro- cating discharge. The former is that which is visible when taken from two wires hermetically sealed in a vacuum tube. This discharge has a tendency to rotate as a whole round the poles of a magnet ; the latter is that which is visible in the same vacuum when taken from two metallic coatings attached to the outside of the tube, or from one coating and one wire. The induced charge is divisible by the magnet into two sets of stratifications, each set having a tendency to rotate round the pole of the magnet in opposite directions; the character of the electrical discharge, with relation to these two forms, can always be determined by the magnet. Discharge in Different Rarefied Media. In dry hydro- gen gas no discharge takes place from the Induction Coil, if the wires be separated in the tube beyond the striking distance in air ; but when the gas is rarefied by the air-pump, the discharge first appears as a wavy line of bluish-grey colour ; on continuing the exhaustion, and assisting the rarefaction by heating gently, the tube becomes filled with a luminous discharge to within about one inch of the negative wire ; the stratifications appear gradually increasing in width as the vacuum becomes more 78 perfect ; and if care be taken to continue the pump- ing so as to prevent air being introduced, the tube can be sealed without the stratifications showing the slightest appearance of redness. If the extremity of a vacuum tube be presented to the prime conductor of an electrical machine, or to one of the terminals of an Induction Coil, a spark can be taken, and the glass will be perforated. The perforation is extremely minute, but sufficient, under the pressure on the vacuum, to admit air or gas ; but, so slowly does the air or gas enter, that the experimentalist is en- abled to note the gradual change which takes place during the progress of the discharges of the coil. Mr. Gassiot connected the extremity of a vacuum- tube, after perforation, by means of a tight-fitting gutta-percha tubing, to a glass cylinder containing fused chloride of calcium, through which air, hydro- gen, oxygen, or nitrogen was permitted to pass into the vacuum. The result of many repeated experi- ments showed that with hydrogen and oxygen no change in the colour takes place ; with air or nftrogen the colour of the stratifications changes from bluish- grey to fawn, and ultimately to a deep red tinge ; and, during this addition of gas or air, the cloud- like stratifications gradually close, becoming narrower and narrower until they are utterly destroyed, passing to a mere luminosity filling the entire tube, and finally into the wave discharge. The writer can confirm this description of the appearance presented when atmospheric air slowly makes its entrance into a vacuous tube. The ex- periment is interesting and instructive, although somewhat costly, and not one which amateurs will be very likely to repeat. On a late occasion, whilst ex- hibiting to an audience the beautiful stratifications in a carbonic acid vacuum, in a tube such as exhibited in Fig. 16, the strise suddenly disappeared, and the 79 discharge, winch was at first nearly white, became first grey, then bluish-grey, and finally resolved itself into a riband of red light ; this continued for some time, and then died away, and the discharge ceased to pass. On examining the tube, a very minute crack was observed proceeding from one of the platinum wires, probably the negative, which had become too highly heated. Too much battery power had been employed. The accident is related as a warning to those inexperienced in those experiments to be very careful not to excite the coil too strongly whilst passing the inductive discharge through the vacuous tubes. Two cells of Grove will be found amply sufficient, and even with this power it will be well to relax somewhat the spring of the contact- breaker. Influence of Temperature. The following results were obtained by Professor Faraday and Mr. Gassiot, in Torricellian vacua, through a range of upwards of 700 deg. Fahr. A vacuum which gave good cloud- like stratifications, exhibited no change when the temperature was lowered to + 32 ; but at a temp- erature of 102, obtained in a bath of ether and solid carbonic acid, all traces of stratifications were destroyed, and in this state the red or heated appear- ance of the negative wire disappeared, the discharge filling the entire vacuum with a white luminous glow. On the temperature being raised by the application of heat to the mercury, the stratifications re-appeared. When the mercury was boiled, indicating heat of upwards of 4 600 Fahr., the stratifications were all destroyed, but in this case the discharge passed along the mercury as it condensed in the cooler part of the tube. When the mercury was frozen the stratifica- tions disappeared, and the discharge did not illuminate the entire length of the tube, but merely the terminals. In this state, when a horse-shoe magnet was brought 80 near the tube, the cloud-like stratifications immedi- ately appeared from the positive wire, very distinct and large, but not so clearly separated as when the tube was at its normal temperature. Discharge in Carbonic Acid Vacua. At the sugges- tion and with the assistance of Dr. Frankland, Mr. Grassiot prepared tubes in which the carbonic acid with which they were filled was absorbed, after ex- haustion, by a good air-pump, by caustic potash. In vacua obtained by this process, the discharge from an Induction Coil is first in a white wave line, strongly affected by the magnet, or by the hand when placed on the tube. In this state the discharge does not generally present the stratified appearance, or if present the stratifications are only near the positive terminal. After a time, however, as the carbonic acid becomes absorbed by the potash, the stratifica- tions gradually appear more clearly defined ; they assume a conical form, and, lastly, the cloud-like appearance of the best mercurial vacua. After this, under some conditions, the stratified appearance entirely ceases, the whole length of the tube being filled with faint luminosity. When in this state, if the outside of the tube be touched with the finger, pungent electrical discharges arise, and sparks one- eighth of an inch in length can be elicited. The appearance presented when the discharge was sent through a tube four inches long, the wires which FIG. 27. were one inch apart being terminated with gas -coke balls one-eighth of an inch in diameter, was as shown in Figs. 27 and 28. On the positive coke, minute 81 luminous spots were visible ; the negative coke was surrounded with a brilliant glow. At intervals, apparently by some energetic action, flashes of bright stratified light would dart through the vacuum, but by carefully adjusting the contact-breaker, the dis- charge could be made to pass, without to the eye affording any appearance of an intermittent dis- charge. A large egg-shaped glass vessel, the globular portion being eighteen inches long and seven inches in diameter, was made under Mr. Gassiot's direction ; the wires were twenty-two inches apart, and caustic potash was placed in the narrow end. It was filled with carbonic acid, and exhausted by Dr. Franldand's process. A portion of the potash being heated by a spirit-lamp, in about two months the discharge assumed, in a very marked manner, the character of large distinct clouds, most clearly and separately de- fined ; they were strongly affected by induction as the hand approached the globe, presenting a very striking appearance. There was a slight tinge of red, showing that a very minute quantity of air remained ; the cloud-like stratifications extended to the entire diameter of the vessel. Fig. 29 is another form of apparatus. The tube is FIG. 29. fourteen inches long and about one inch internal diameter ; it has a glass division in the centre, F 82 perforated with a hole about one-eighth of an inch in diameter. The striae on the negative side are here very clearly defined, while on the positive side they are indistinct. When the discharge has assumed the cloud-like appearance, the aperture in the diaphragm only affects the discharge by contracting the cloud which passes immediately through it. That the passage of the discharge depends upon the presence of matter, and the stratifications probably to pulsa- tion, or impulses of a force on highly attenuated matter, seem to be rendered probable by the fact that, in some of Mr. Gassiot's tubes, in which the absorption of the carbonic acid by caustic potash contained in one end of the tube was complete, no discharge could be made to pass ; the same was the case with other tubes containing, besides caustic potash, fused chloride of calcium, sulphur, and selenium. Luminous Discharge of Voltaic Batteries when examined in Carbonic Acid Vacua. When the discharge from a water-battery of 3,520 cells was sent through car- bonic acid vacua tubes, stratified discharges, similar in character to those of the Inductive Coil, were ob- tained, and Mr. Gassiot found that whenever the potash in any of the tubes was heated the discharge entirely ceased. From the steady deflection of the galvanometer needle placed in the circuit, the dis- charge had the appearance of being continuous, but closer examination showed them to be intermittent. From a Daniell's battery, consisting of 512 series of elements, no stratified discharge could be obtained through any of the vacuous tubes, but in one, a bril- liant glow was observed round the negative, and a trifling luminosity round the positive coke ball ter- minal. With 400 series of Grove's nitric acid bat- tery, each cell carefully insulated, the most magnifi- cent effects were obtained. The different vacuum 83 tubes used were introduced between one of the copper discs of a micrometer- electrometer and the battery, as also a galvanometer. By this arrangement the circuit could be gradually completed without any risk of disarranging the apparatus, and the spark dis- charge obtained before the copper discs of the micrometer-electrometer came into contact. Dr. Robinson thus describes an experiment which he witnessed in Mr. Gassiot's laboratory, with a tube 24 inches long and 18 in circumference, one terminal being a copper disc, 4 inches in diameter, and the other a brass wire : " On the completion of the current, the discharge of the battery passed with a display of magnificent strata of most dazzling bright- ness. On separating the discs, by means of a micro- meter screw, the luminous discharges presented the same appearance as when taken from an Induction Coil, but brighter. On the copper plate in the vessel there was a white layer, and then a dark space about an inch broad ; then a bluish atmosphere, curved like the plate, evidently three negative envelopes on a great scale ; when the plate was positive the effect was comparatively feeble." Between coke terminals a stream of light, of intolerable brightness, was presented, in which strata could be observed through a plate of green glass ; this soon changed to a sphere of light on the positive ball, which became red hot. On heating the caustic potash, the discharge again burst into a sun-like flame, subsequently subsiding in three or four large strata, of a cloud-like shape, but intensely bright. The appearances presented when the potash was heated are depicted in Figs. 30 and 31. Mr. Gassiot arranged the apparatus by attaching gold-leaf electroscopes to both terminals, and introducing the galvanometer so as to enable him to examine more carefully the action that would take place when the potassa was heated. On heating the 84 potassa, the fine negative glow was developed ; the leaves of the electroscope did not close, but as the FIG. 30. FIG. 31. negative glow increased, the needle of the galvano- meter was suddenly deflected, immediately returning to zero. As more heat was applied, a small globe of light appeared on the positive ball, and the needle was gradually deflected 40 to 50. On withdrawing the lamp, as the potash cooled, the positive glow dis- appeared, the needle of the galvanometer receded, the glow on the negative remaining more or less brilliant ; this action and reaction alternating as the heat of the lamp was applied to, or withdrawn from, the potash. When the heating of the potash was further increased, four or five cloud-like and remark- ably clear strata came out from the positive ball, (Figs. 32 and 33), and these were quickly followed by a sudden discharge of the most dazzling brightness, which remained for several seconds. The needle of the galvanometer was suddenly and violently de- flected. By these and many other equally striking experiments, Mr. Gassiot proved that the luminous and stratified appearances obtained in carbonic acid 85 vacua do not arise from any peculiar action of the Inductive Coil, whatever the real cause of the phenomena may ultimately prove to be. FIG. 32. FIG. 33. More recently (Proceedings of the Eoyal Society, Dec. llth, 1862), Mr. Gassiot has studied minutely the stratified appearance in electrical discharges, employing in his experiments a battery of 3,360 pairs of elements charged with salt and water and care- fully insulated, and an extensive series of the sulphate of mercury battery also carefully insulated. " The discharge of the battery," he observes, "is much more sensible to the slightest variation of the state of tension in the vacuum tubes, than that of the Induction Coil ; the sudden disruption in the dis- charge of the latter presenting greater obstacles to the more careful study of the phenomena than is offered by the direct discharge of the battery." The battery was arranged in three groups, each consisting of 1,520 pairs of elements, and the general practice was to place the experimental tube between either the one or the other of them the positive terminal of one battery A being attached to one wire, 86 and the negative terminal of another battery B to the other wire, the opposite poles of A and B were then connected and the circuit thus completed. In order to vary the resistance at pleasure, two tubes containing distilled water were included in the circuit. By varying the depth to which the wires attached to the terminals of the battery were plunged in one or both of the tubes the resistance could be regulated with great precision. When the discharge was passed through a tube 20 inches long and 4 inches in diameter, one terminal consisting of aluminum, cup-shaped, about 3 inches in diameter, and the other a wire of the same metal, it was, when examined by a revolving mirror, intermittent, and distinct sounds were heard when a magnet was pre- sented to the tube. With a tube about 5 inches long, the terminals being balls of aluminum, the discharge from the entire battery was of dazzling brilliancy, exhibiting twelve or fourteen striae. When the water resistance tubes were interposed, the phenomena were in the highest extraordinary. The tubes were each 1 8 inches long, and were connected with each other from the bottom by a wire. As soon as the battery wires touch the surfaces of the water, a faint luminous discharge is observed at each ball of the vacuum tube ; as one wire attached to the negative is slowly depressed, the two luminous discharges appear to travel towards or to attract each other. Depress- ing the wire very gradually, the positive discharge becomes sharply defined, the negative retaining much of its irregular termination, but each separated from the other by a dark interval of about 1 inch in length. As the wire is further depressed in the water, the brilliancy of the positive and negative glows increase ; and when about 3 inches of one wire have been immersed in the water a single clearly defined luminous disc bursts forth from the positive, remain- 87 ing steady and apparently fixed. As the wire is further depressed in the water, the luminous dis- charge at the positive slowly progresses along the tube until another bright disc appears remaining stationary like the first. When the resistance is again reduced by depressing the wire still further into the water a third luminous disc is developed, and at 18 inches depression or the entire length of one column of water a Jonrth disc is observed. In this state, while the four luminous discs are stationary, if the wire attached to the positive terminal of the battery is depressed, the luminous discs gradually closing on each other become more compressed, whefl a, fifth is developed. By continuing in this manner gradually to diminish the resistance new discs start one by one into view, until the number is increased to thirteen or fourteen. On gradually raising the wires, the discs one by one disappear. Many other beautiful phenomena are described by Mr. Grassiot in this memoir, to which we must refer our readers. In summing up his results he says : " May not the dark bands be the nodes of undulations arising from impulses proceeding from positive and negative dis- charges ? or can the luminous stratifications which we obtain in a closed circuit of the secondar3 r coil of an induction apparatus, and in the 'circuit of the voltaic battery, be the representation of pulsations which pass along the wire of the former and through the battery of the latter, impulses possibly generated by the action of the discharge along the wires ?" Geissler's Vacua Tubes. It would be quite im- possible, by any description, to do justice to the extreme beauty of the phenomena observed when the inductive discharge is passed through many of the tubes so ingeniously prepared by M. Geissler, of Bonn ; neither indeed could any description, how- ever correct, serve any useful purpose, as, in conse- 88 quence of the almost impossibility of preparing two tubes precisely alike as to form, and as to the exact condition of the attenuated media they enclose, it is very difficult to find two which present the same appearances; moreover, we are for the most part ignorant of the nature of the matter with which these tubes have been filled, so that Mr. Gassiot, in his investigations, was compelled to prepare his own tubes. " Though," he writes, " I had the opportunity of experimenting with upwards of sixty of Geissler's vacua tubes, in which many beautiful and novel results are produced, not being able to ascertain with accuracy what is the gas, which, however attenuated, must remain in each tube, and from most of them being constructed of a varied form in consequence of FIG. 34. which the discharge presents, in the several portions of the same tube, an entirely different appearance, both of colour and in form of stratification, I was 89 reluctantly compelled to lay them aside, and either to charge and exhaust each tube myself, or have them charged and exhausted in my presence." By way of reference, we have, however, figured some of the most striking of these vacua tubes, and would beg to remark that Mr. Ladd, from whom they may all be procured, is constantly receiving novel accessions from Germany. In the frontispiece the inductive discharge is represented as passing through a spiral tube, in which twenty-five bulbs have been blown. In the tube in the writer's possession, the light is white, with a pale green tinge, the effect of which is greatly exalted by placing behind it a black curtain ; after the discharge has ceased the tube remains for some seconds phosphorescent. A similar tube is shown in Fig. 34. The operator is warned in this and all the vacua experiments, not to employ more than two, or at most three, battery cells. Fig. 35 is a similar spiral tube, containing only sixteen bulbs. FIG. 35. Fig. 36 represents a very brilliant design adapted 90 for an illumination The thick parts of the letters contain the fluorescent solutions (p. 92), producing a very pleasing contrast. Fio. 36. Fig. 37. Bulbs pale green, the connecting tubes pale red, with stratifications ; phosphorescent after the discharge has ceased. FIG. 37. Fig. 38. Bulbs pale green, connecting tubes red, with stratifications ; phosphorescent. Fig. 39 and 40. These are beautiful experiments ; the bulbs in Fig. 39 vary from 5 inches to 3 in diameter ; the centre bulb, and tne two smaller ones, are filled with a pale green light, with magnificent stratifications, the connecting tubes pale red ; the bulb in connection with the negative terminal is of a FIG. 39 Fio. 40. delicate mauve colour ; that connected with the positive is red ; but by turning the commutator, these colours change places ; the stratifications are urged from the negative towards the positive terminal. In Fig. 41 the left-hand bulb is of uranium glass, FIG. 41. which gives the characteristic yellow colour; the tube connecting it with the centre bulb is of lead 92 glass, and the colour of the light is blue, and the centre bulb is pale green. Fig. 42. The bulbs are filled with a pale green light, except the terminal ones ; the negative being FIG. 42. mauve and the positive pale red; the connecting tubes are pale red and beautifully stratified ; when the discharge is suspended the bulbs remain for some seconds phosphorescent. Fig. 43. The spirals are made of uranium glass, FIG. 43. which come out of a fine green colour ; the centre bulb is pale red ; the positive bulb is red and the negative mauve ; this is a nitrogen vacuum. Fig. 44. The spirals in this tube are enclosed in two separate tubes, one of which is filled with solu- Fio. 44. tion of disulphate of quinine and the other with water, through which a few drops of infusion of horse-chesnut bark have been diffused ; the light on the spiral tube is red, surrounded on the quinine side by a beautiful blue, and on the cesculine side by a fine green. Other fluorescent liquids with which tubes of various shapes are filled are : Solution of 93 amido-phthalic acid which gives a fine uranium colour ; solution of amido-terephalic acid which gives a mag- nificent blue; and pavine from willow-bark which gives a rich brown. Tincture of the seeds of stra- monium, of turmeric, and of chlorophyll, likewise exhibit the phenomena of fluorescence. There are certain solids which, after being exposed to solar light or to the sparks from the Induction Coil, continue to emit light for a considerable time. Among these substances Cantor's phosphorus (sulphide of calcium), and Baldwin's phosphorus (fused nitrate of calcium), and Bologna stone (sulphide of barium), have long been known ; but the researches of Becquerel have shown that this property of phos- phorescence is possessed by many other compounds, amongst which may be mentioned : Sulphide of strontium, and the salts of the alkalies and alkaline earth generally ; certain varieties of diamond and of fluor spar, and most transparent objects, particularly those of an organic origin. Small boxes are fitted up with tubes filled with various phosphorescent solids, and the phenomena 'produced by exposing these tubes for a few seconds to the intense light of the induction spark and then removing them into the dark are very striking. Fig. 45. When the vacuum in this tube is pure FIG. 45. carbonic acid, the light is white ; when pure hydro- gen, the centre bulb is pale green, stratified, and the connecting tubes vivid red ; when from bi-chloride of 94 tin, the bulbs are pale blue, and the connecting tubes yellow. Fig. 46. This form, of tube is intended for medi- cal use ; it furnishes the practitioner with an excellent FIG. 46. and convenient means of examining the throat, for which purpose the tube enclosing the spiral is intro- duced at the mouth, and the inductive discharge passed through the bulbs, which have been filled with carbonic acid and well exhausted ; a brilliant white light is produced, -which illuminates the interior of the mouth and throat. Tubes of the simple shape shown in Fig. 47, are Fio. 47. well adapted for observing the nature of the dis- charge, and the stratification in different gaseous vacua. "When vacua tubes are so arranged that continuous rotatory motion can be given to them, very beautiful effects are produced. Fig. 48 shows the mode in which Mr. Ladd mounts his tubes; they may, of course, be varied ad libitum in shape and in mode of preparation. By turning the wheel with different 95 degrees of velocity, and altering the frequency of the discharge and direction of the current, various optical phenomena are brought out, which greatly FIG. 48. increase the magnificence of the display, apparatus is called Gassiot's revolving star. This 96 The following is a summary of the effects produced by the electric discharge through Torricellian vacua. (Grove). If the vacuum be equal to that generally obtained by an ordinary air-pump, no stratifications are per- ceptible ; a diffused lambent light fills the tube. In a tube in which the rarefaction is carried a step further, narrow striae are perceptible, like those ob- tained with phosphorus vapour. A step further in rarefaction increases the breadth of the bands. Next we get the conical or cup-shaped form ; and then, the rarefaction being still higher, we get a series of luminous cylinders of an inch or so in depth, with narrow divisions between them. Lastly, with the best vacua which have been obtained, there is neither discharge, light, nor conduction. The fact of non-conduction by a very good Torricellian vacuum was first noticed by Walsh, subsequently carefully experimented on by Morgan, and afterwards by Davy ; the latter did not, however, obtain an entire non-conduction, but a considerable diminution both of light and conducting power. From these experi- ments it may be concluded that in vacuo, or in media rarefied beyond a certain point, electricity will not be conducted, or, more correctly speaking, trans- mitted, an extremely important result in its bearing on the theory of electricity. The following is Mr. Grove's view of the rationale of the phenomena of stratification. When the bat- tery contact is broken, there is generated the well- known induced current in the secondary wire, in the same direction as the original battery current, to which secondary current the brilliant effects of the coil are due ; but in addition to this current in the secondary wire, there is also a secondary current in the primary wire, flowing in the same direction, the inductive spark at the moment following the disrup- 97 tion of contact, completing the circuit of the primary, and thus allowing the secondary current to pass. This secondary current in the primary wire produces, in its turn, another secondary, or what may be termed a tertiary current in the secondary wire, in an opposite direction to the secondary current. There are thus almost synchronously two currents in oppo- site directions in the secondary wire ; these, by causing a conflict or irregular action on the rarefied medium would give rise to waves or pulsations, and might well account for the stratified appearance. Mr. Grove quotes the following experiment as strongly in favour of this theory. It is obvious that the secondary must be more powerful than the tertiary current. Now, supposing an obstacle or resistance placed in the secondary circuit which the secondary current can overcome, but the tertiary cannot, we ought, by theory, io get no striae. If an interruption be made in the secondary current, in addition to that formed by the rarefied medium, and this interruption be made of the full extent which the spark will pass, there are, as a general rule, no stride in the rarefied media, while the same vacuum tube shows the striae well if there be no such break or interruption. The experiment was shown by Mr. Grove, in a lecture, at the Royal Institution (January 28, 1859), with a large vacuum cylinder (16 inches by 4) and Mr. Gassiot's micrometer- electrometer ; this tube showed numerous broad and perfectly distinct bands when the points of the micrometer were in contact ; but when they were separated, to the fullest extent that would allow sparks to pass, not the slightest symp- toms of bands or striae were perceptible, the whole cylinder being filled with an uniform lambent flame. With a spark from the prime conductor of the electrical machine, the striae do not appear in tubes which show them well with coil; occasionally, and 98 in rare instances, striae may be seen with sparks from the electrical machine, but not when the spark is un- questionably single. All this Mr. Grove thinks is in favour of his theory ; but without regarding that as conclusive, or as a proved rationale, it is clearly de- monstrated by the above experiments, that the identical vacuum tubes which show the striae, with certain modes of producing the discharge, do not show them with other modes, and that therefore the strise are not a necessary condition of the discharge itself in highly- attenuated media, but depend upon the mode of its production. Certain experiments, described by Mr. Gassiot (Phil. Trans., 1859), do not harmonize with Mr. Grove's view. He found that when a Leyden discharge was sent through a vacuum tube, stratifications, as clear and as distinct as those from an Induction Coil, may be obtained by reducing the intensity of the discharge, by the introduction into the circuit of a piece of wet string ; he hence inferred that in Mr. Grove's experiment, the absence of strise, when the circuit was interrupted, was due to the heightened intensity of the discharge. He repeated Mr. Grove's experiment with the large cylinder, and obtained a similar result ; the stratifi- cations were entirely destroyed when the secondary circuit was interrupted, but they were restored when a second interruption was made in the circuit, and this closed by a wet string ; in this case it is evident that the appearance of the strige does not depend upon the conflict of secondary and tertiary currents, but upon the manner in which the discharge passes. Mr. Gassiot found, moreover, that when, by means of an interrupted discharge, the stratifications are destroyed, they are reproduced in a carbonic acid vacuum tube when heat is applied to the caustic potash ; here the increased resistance arises from the greater density of the matter formed in the tube ; 99 and the experiment favours the view of Mr. Gassiot, viz., that the stratifications arise from the effect due to pulsation or impulses of a force acting on highly attenuated matter. Spectra in highly rarefied Gases of different kinds, during the passage of the ELtctrical Discharge. In order to observe and analyze the spectra, Professor Pllicker concentrated the luminous electrical dis- charge current in thermometer tubes whose internal diameters were nearly the same for the different gases examined, being about 0'6 millimetre. Fig. 50 shows the form of the perfect separate gas tubes, as well as the manner in which they may be con- nected on a piece of board, so that the narrow parts Fio. 50. of both (at the parts where they are bent at an angle of rather more than 90) touch one another, and have exactly the same direction. By turning the glass cock (e) the gases in the two tubes could be put into communication. The spectra were observed 100 by means of a telescope (such as that employed by Fraunhofer, in the observation of the lines of the solar spectrum) without angular measurements. This was set up at a distance of from 4 to 5 metres from the vertical line of light in the tube. The flint-glass prism, whose refractive angle was 45 degrees, was fastened immediately before the object glass, whose aperture was 1 5 Paris lines. 1. Hydrogen. Almost the whole of the light is concentrated into three bands, namely, a dazzling red, at the extremity of the spectrum ; a beautiful greenish blue ; and finally a violet of inferior bright- ness, whose distance from the greenish blue is about two-thirds of the distance of the latter from the dazzling red. In the narrow tube the electric light stream appears red. 2. Nitrogen. In the spectrum of this gas all the colours are fine, none of them being faded, as in the broad spaces lying between the bright bands of the hydrogen spectrum. In the spaces of the red, orange, and yellow, there are about fifteen narrow dark-grey lines at nearly equal distances apart ; six of these belong to the orange and yellow ; both of these colours are beautiful. The red, in the direction away from the orange, is shaded off into brown, but becomes brighter and purer towards the extremity of the spectrum, which stretches beyond the dazzling red bands of the hydrogen spectrum. A broad green space is separated from the yellow by a narrow black band. The greater part of this space appears shaded with black in the direction away from the black band. On a more careful examination, this shading is seen to consist of very fine black lines, which are at equal distances apart, but nearer together than the previously mentioned bands on the red, orange, and yellow. The rest of the green space is again subdivided. The green is bordered by 101 two beautiful bright blue bands, which are sharply separated from one another, and from the green, by narrow black bands. The blue and red violet ends of the spectrum form nine sharply-bordered violet bands, alternating with dark ones. The fourth and fifth bright bands, separated by a black band, possess the most light; the four following ones are less prominent; the last one, however, which forms a sharp boundary to the whole spectrum, is the most distinct. The light of the discharged current in the narrow tube is yellowish-red. 3. Carbonic Acid. Six bright bands sharply separate the bright portion into five spaces, of which the two first are of equal breadth ; the third, and especially the two last, are somewhat broader. The first of the six bands is situated on the extreme boundary of the red, the second is reddish-orange, the third greenish-yellow, the fourth green, the fifth blue, and the last violet. Both of the two first spaces are divided into three equally broad subdivisions by narrow black-grey bands, of which two always border upon the bright band. The first space is brown-red ; the second dirty-orange and yellow ; the third and fourth spaces are of rather faded green, and much subdivided by different degrees of shading ; the fifth space, which is very faded, is divided into two equal spaces, which are shaded off from the red side towards the violet. After the last-mentioned violet band, another dark portion of the spectrum occurs, about as wide as the red-yellow portion. In this dark portion, three spaces are separated by three prominent and well-marked violet bands, whose breadth is of the same value as that of the before- mentioned six bands. The last of the three violet bands forms the visible boundary of the spectrum. The first of these three spaces, which is contiguous with the above six bright bands, is somewhat broader 102 than the third. Both are perfectly black. The second and middle space is about as broad as the first and third together, and is of a very dark violet colour. The first band, which at Ihe moment of commencing was of an especially brilliant red, lost almost the whole of its brightness after the streams had passed through the tube for a long time. This was occasioned by the decomposition of the gas into carbonic oxide and oxygen, the latter combining with the platinum of the negative electrode, and forming oxide of platinum, which was deposited of a yellow colour upon the neighbouring internal glass surface. 4. Ammonia. On exhausting a single tube that has been filled with ammonia, and passing the current, a spectrum was produced which was evidently the result of the superposition of the two spectra for hydrogen and nitrogen ; the ammoniacal gas was immediately decomposed into its constituents, and it was not possible to obtain the spectrum of the chemically combined gases. When one of the double tubes, Fig. 50, was filled with carbonic acid, and the other with hydrogen, and then exhausted as far as possible, a greenish white light was obtained in one tube and a red light in the other. On now putting the two gases into communication, by opening the stop-cock, c, and observing the spectrum of the car- bonic acid through the telescope by the prism, a dazzling red line was at first seen merely flickering now and then at the boundary of the spectrum, and soon took up and maintained a constant position ; this was the red band of the hydrogen gas. The colour of the light in the two narrow tubes was the same the two spectra had become constant and identical in kind. 5. Oxygen. A good spectrum could not be obtained with this gas, on account of its gradual disappearance and combination with the platinum of the negative 103 electrode. Oxide of platinum, of a yellow colour, was deposited upon the neighbouring internal glass surface, showing, by reflected light, the colours of Newton's rings in a very beautiful manner. If the tube contains traces of hydrogen or nitrogen, metallic platinum is transferred to the glass surface. The colour of the electric light current in the narrow tube was at first red ; it passed through a flesh colour to a green, and then through blue to a reddish-violet, and then became extinct, proving that no current can exist in absolute vacuse. 6. Binoxide of Nitrogen. This gas was decomposed, the spectrum for nitrogen being obtained with a modification evidently attributable to pure oxygen (a bright band near the red) ; this was gradually extin- guished, and the result was the formation of the pure spectrum of nitrogen gas of a splendour which Pliicker had never before witnessed. Binoxide of nitrogen, present in so small a quantity as to be scarcely recognizable by the most sensitive balance, was thus chemically analyzed ; with nitrous acid the red band due to the oxygen was at first of great brilliancy, but it gradually disappeared ; the same was the case with protoxide of nitrogen. 7. Aqueous Vapour. The electric current in the narrow tube showed the most beautiful deep red. The spectrum was that of pure hydrogen, with its three prominent bands, in comparison with the brightness of which the rest of the luminous divisions were so insignificant that here the shading off of colour and luminous intensity was scarcely to be recognized. The aqueous vapour had separated into its simple constituents. 8. Iodine, Bromine, and Chlorine. Pure spectra have not yet been obtained with these substances, because the manner in which the tubes have hitherto been made did not admit of complete exclusion of the 104 air. That which the three spectra have in common, and by which they are distinguished, as far as present observations extend, from all other gas spectra, con- sists in lines of light, which at first are constant, but afterwards only flickering, and whose width is about the same as that of the narrow Eraunhofer's black lines. The chemical results hitherto obtained are summarized briefly by Pliicker, as follows : 1. Certain gases (oxygen, chlorine, bromine, and iodine vapour) combine more or less slowly with the platinum of the negative electrode, and the resulting compounds are deposited upon the neighbouring glass surface. When the gases are pure, we thereby gradually approach to a perfect vacuum. 2. Gases, which are composed of two simple kinds (aqueous vapour, ammonia, nitrous oxide, nitric oxide, nitrous acid), immediately split up into their simple constituents, and then remain unchanged, if these latter (ammonia) do not combine with the platinum. If one of the constituents is oxygen (in water, and the different stages of oxidation of nitro- gen) this gradually disappears, and the other gas alone remains. 3. If the gases are composed of oxygen and a solid simple substance, complete decomposition by the current only takes place gradually, while the oxygen goes to the platinum of the negative elec- trode. (Sulphurous acid, carbonic oxide, carbonic acid). Carbonic acid is instantly decomposed into the gaseous lower state of oxidation, and into free oxygen, which gradually goes to the platinum. The carbonic oxide is gradually decomposed, by the oxygen leaving the carbon, and combining with the negative electrode. Fig. 5 1 shows a very convenient arrangement for experimenting upon the spectra produced by different metals, comparing them with that produced by 105 platinum. The metals, in the form of wires, are attached to screws, passing through clamps of vul- canite, which can be adjusted at any required height and angle by means of the spring tubes connecting them with the upright pillar. The wires on the left- hand clamp are permanently platinum, those on the FIG. 51. right-hand clamp may be of any other metal or metals ; they are held by pincers, so that they may readily be removed and replaced by others. The two lower screws are metallically connected. The two upper are connected with the secondary terminals of the coil, and then with the Leyden jar, as in Ex. 8, p. 53. A brilliant discharge takes place 106 simultaneously between the wires in each clamp, provided the distances be properly adjusted, and the apparatus being accurately arranged before the spectrum box, one spark is reflected through a prism, and the other is received directly through the slit ; the two spectra immediately become apparent, one over the other, so that the peculiarities in each may be at once detected. By employing the little capped glass tube, shown on the left-hand side of the figure, spectra may be obtained in various gases, the gas being passed through the tube while the discharge is taking place. The Ozone Tube. It is well known that when electric sparks are taken between two conductors in atmospheric air a peculiar odour is developed. To the substance producing this odour the name Ozone has been given. It is supposed to be oxygen in an allotropic state, in which its chemical activity is greatly increased. It may be prepared Istly by the action of clean moist phosphorus on atmospheric air ; 2ndly, by the electrolysis of water acidulated with sulphuric acid ; Srdly, by passing electrical discharges through air or oxygen. A very ingenious little apparatus for the latter purpose is shown in Fig. 5 1 . FIG. 61. It consists of a glass tube about the size of an ordinary test tube, coated with tinfoil (or still better 107 silvered), and enclosed in an outer tube lined outside with tinfoil. The two tubes are sealed together at the neck of the outer one, and so adjusted that the space between them shall be as narrow as possible. At the projecting end of the inner tube is a brass button, which is connected by a spring with one of the binding screws on the frame of the apparatus, which screw is to be connected with one of the terminals of the secondary coil of an inductorium, and the other with another binding screw in metallic connection with the coating of exterior tube. The apparatus is in fact a sort of slit Leyden phial, and air or oxygen admitted through the lateral tube seen in the figure becomes, during its passage through the apparatus, powerfully ozonized. The air may be driven through by means of a bladder or india- rubber bag, or drawn through by an aspirator. Ozone is a powerful oxidizing agent ; it corrodes organic matter ; it bleaches indigo ; it oxidizes the metals converting even moist metallic silver into per- oxide ; but at the same time it seems, in some cases, to act as a deoxygenant : thus it decomposes per- oxide of hydrogen and peroxide of barium with the evolution of inactive oxygen derived from both the ozone and the peroxide. Schonbein regards ozone as permanently negative oxygen, and he believes in the existence of a permanently positive oxygen or antozone ; inactive oxygen he considers to be the pro- duct of the union of ozone ~ and antozone +. New form of Thermo-Pile. The discovery of the production of electricity by heating one of the junc- tions of a metallic circuit, consisting of two metals soldered together, was made by Professor Seebeck, of Berlin, in 1821. The metals which give the greatest amount of electro -motive force are bismuth and tellurium, next comes bismuth and antimony, and this latter metal, on account of its cheapness and 108 better conducting power, is generally substituted for Tellurium. The antimony is negative and the bis- muth positive, the current going from the bismuth t'o the antimony across the junction. Numerous improvements on the original thermo-pile of Seebeck have been made by Nobili, Locke, Gumming, Dove, Van der Voort, etc. ; but the most efficient arrange- ment is that of Marcus, a representation of whose thermo-battery is shown in Fig. 52. It consists of thirty-six elements ; the negative bars, which are 6 FIG. 52. inches long, being composed of Antimony, 12 parts ; Zinc, 5 parts ; Bismuth, 1 part ; and the positive bars, which are 7 inches long, being composed of Copper, 10 parts; Zinc, 6 parts; Nickel, 6 parts. The bars are ranged on a frame in the slanting position shown in the figure, the positive bar of the first pair being metallically connected with the nega- tive bar of the second, and the two extreme bars connected with binding screws, which form the terminals of the battery. The upper ends of the bars are heated by a series of Bunsen's burners, the flames of which can be easily regulated. Thermo-electricity is characterized by very feeble tension ; it can only therefore produce feeble chemical 109 action. The battery above described will, however, though 011 so small a scale decompose water (feebly) give small sparks between iron points without the intervention of a coil ; will enable the electro- magnet, shown in Fig. 3, to sustain 2 cwt. ; and, when substituted for the voltaic battery with one of Ladd's 6-inch spark coils, will cause the produc- tion of sparks 1 inch long between the terminals of the secondary. WORKS ON CHEMISTRY. FOWNES' MANUAL OF CHEMISTRY. Edited by H. BEXCE JONES, M.D., F.R.S., and A. W. HOFMANN, Ph. D., F.R.S. Ninth Edition, fcap. 8vo, cloth, 12s. Gd. HANDBOOK OF VOLUMETRIC ANALYSIS; or, the Quantitative Estimation of Chemical Substances by Measure. By Francis SUTTON, F.C.S., Norwich. With Engravings. Post 8vo, cloth, 7*. Gd. THE USE OF THE BLOWPIPE. By Professors PLATT- NER and MUSPRATT. Third Edition, 8vo, cloth, 10s. Gd. THE FIRST STEP IN CHEMISTRY. By ROBERT GALLOWAY. Third Edition, 310 pp., fcap. Svo, cloth, 5*. By the same Author, THE SECOND STEP IN CHEMISTRY ; or, "the Stu- dent's Guide to the higher Branches of the Science. With Engravings. Fcap. Svo, cloth, 10s. By the same Author, MANUAL OF QUALITATIVE ANALYSIS. Fourth Edition, post Svo, cloth, 6s. 6d. By the same Author, CHEMICAL TABLES. On Five Large Sheets, for Schools and Lecture-rooms. Second Edition, 4s. Gd. the Set. PRACTICAL CHEMISTRY, INCLUDING ANALYSIS. With numerous Illustrations on Wood. By JOHN E. BOW- MAN. Edited by C. L. 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It is satisfactory to us, and will no doubt be so to the public, to know that no profane hands have meddled with a work which all regard as belonging to the classical literature of photography." The British Journal of PJiot ography. 8vo, cloth, 2 10s. AN EXPOSITORY LEXICON OF 50,000 SCIENTIFIC TERMS, ANCIENT AND MODERN, Including a Complete Medical and Medico-Legal Vocabulary, and presenting the Correct Pronunciation, Derivation, Definition, and Explanation of the Names, Analogues, Synonymes, and Phrases (in English, Latin, Greek, French, and German), employed in Science and connected with Medicine. By E. G. MAYXE, M.D. This Lexicon is suited to the requirements of every educated gentleman. It embraces the correct pronunciation, derivation, definition, and application of the names, analogues, synonymes, and phrases (in English, Latin, Greek, French, and German), connected with Medicine, and employed in Anatomy, Animal Pathology, Astronomy, Botany, Chemistry, Comparative Anatomy, Conchology, Crystallography, Entomology, Geology, Geography, Geometry, Ichthyology, Materia Medica, Medical Jurisprudence, Medicine, Microscopy, Mineralogy, Natural History, Natural Philosophy, Nosology, Obstetrics, Ornithology, Pathological Anatomy, Pathology, Pharmacy, Phrenology, Physiology, Surgery, Trigonometry, and Zoology. In one volume of 1,400 pages, with Engravings, Fourth Edition, greatly enlarged, 28*. COOLEY'S CYCLOPEDIA OF PRACTICAL RECEIPTS AND PROCESSES. Being a General Book of Reference for the Manufacturer, Trades- man, Amateur, and Heads of Families. From the " TIMES," Nov. 16, 1864. " A much improved edition. It has become a standard work, not only as a supplement to the pharmacopoeias, but also as u book of reference in con- nexion with the arts, manufactures, and trades." JOHN CHURCHILL AND SONS, NEW BURLINGTON-STREET. CATALOGUE OF Jllatfemafimt, and INSTRUMENTS. MANUFACTURED AND SOLD BY WILLIAM LADD, 11 & 12, BEAK STREET, REGENT STREET, LONDON, W. fHtcroscopc anti Philosophical Instrument fftanufactuter, BY APPOINTMENT TO THE ROYAL INSTITUTION OF GREAT BRITAIN; THE GOVERNMENT SCHOOL OF MINES; THE WAR DEPARTMENT ; THE EAST INDIA GOVERNMENT; HER MAJESTY'S COMMISSIONERS OF NATIONAL EDUCATION; THE GOVERNMENTS OF THE BRAZILS AND NETHERLANDS; THE UNIVERSITIES OF OXFORD, CAMBRIDGE, LONDON, ETC. 1866. CATALOGUE. Honourable Mention was awarded to W. LADD at the Great Exhibition of 1851, for his Improvements in Microscopes ; also Prize Medal, 1862, for Microscopes, Induction Coils, &c. MICROSCOPES. s. d. LARGE SIZE COMPOUND MICROSCOPE, of very superior workmanship and great solidity, the stage having 1-inch motion; plain and concave mirrors, fine adjustment (100 turns to the inch), secondary stage for holding achromatic condenser, spotted lens, &c., to which is applied the horizon- tal and vertical adjustments for insuring the perfect centricity of all its parts 18 18 Ditto, with binocular arrangement . , . . . 26 Apparatus for the above ; Parabolic Condenser 1 10 Achromatic Condenser . . . . . . . . 5 10 Spotted Lens 15 Condenser on Brass stand 100 Polariscope, with selenite stage . . . . . . . 250 Camera Lucida 100 Animalcule Cage 060 Extra deep eye- piece . . . . . . . . . 0150 Quarter-inch and 1 and 2-inch object-glasses of large angular aperture 770 One- eighth -inch object-glass . . . . . . . 770 Mahogany Cabinet, with box for apparatus . . . . 2 15 0' 4 WILLIAM LADD, 11 & 12, BEAK-ST ., REGENT-ST. LADD'S IMPROVED COMPOUND MICROSCOPES, For which the Prize Medal was awarded, 1862. LADD'S IMPROVED COMPOUND MICROSCOPE: s. With magnetic stage and two eye-pieces . . . . . PO Ditto, with mechanical stage, having rectangular movements . 100 Ditto, with Binocular arrangement 10 Quarter-inch object-glass . ....... 4 4 1 and 2-inch object-glass, combined 33 Condenser on stand 18 Spot-glass for dark ground illumination . . . . . 012 Polariscope ........... 1 15 Animalcule Cage 06 Stage Forceps 05 Mahogany Case 1 10 to 2 10 The 'above is strongly recommended in the '< The Microscope," by Dr. Carpenter, page 81; and in " The Microscope ; its History, Construction, and Application ," by Jabez Hogg, page 164. COMPOUND ACHROMATIC MICROSCOPE, with moveable stage, having | of an inch motion in rectangular directions, with sliding and revolving object -holder, two eye-pieces, double mirror, fine adjustment, diaphragms 800 -inch and 1-inch object-glasses . . . 2 15 Condenser on brass stand . . . . . 18 Animalcule Cage . . . . . . 060 Mahogany Cabinet 1 10 14 9 Ditto, with Binocular arrangement . . . . . 12 MICROSCOPE, designed by the late Geo. Jackson, Esq , in which the compound body, stage, and sub-stage are fitted in a dove-tailed slide running from top to bottom of the instru- ment, with improved magnetic stage, and eye-piece, in mahogany case 50 The above with ^ and 1-inch achromatic object-glasses, and animalcule cage and forceps . . . . . . 86 EDUCATIONAL MICROSCOPE, with sliding stage, eye- piece, achromatic object- glasses, ranging from 30 to 300 diameters, condenser, animalcule cage, forceps, and mahogany case . 55 EDUCATIONAL COMPOLND MICROSCOPE, with set of three achromatic object-glasses, eye-piece, and forceps, in mahogany case, with drawer . . . . . . 310 LADD'S AQUARIUM AND SEA-SIDE MICROSCOPE. The stage and mirror can readily be removed from the stand, so that the object-glass may be brought to bear upon the aqua- rium, and to follow an object with facility . . . . 40 PROFESSOR QUEKETT'S portable Dissecting Microscope, with drawer .... .... 2 10 Compoundbodyforditto,makingitaportableSea-sideMicroscope 10 Ladd's Dissecting Microscope, for botanical and other purposes . 15 Condenser on stand for ditto, and can be used as a Microscope . 06 Coddington Lens, of high magnifying power, very useful foropaque objects, mounted in ivory, German Silver, or silver 4s. to 5 Stanhope Lens, in various mountings . . . from 02 Cloth Microscopes or Linen Provers, to fold for the pocket, 2s. to 04 Set of three lenses, for the pocket . . from 3s. Od. to 07 WILLIAM LADD, 11 & 12, BEAK- ST., REGENT-ST. MICROSCOPIC APPARATUS. *. Camera Lucida, for taking drawings of objects . . 15s. and 1 Neutral-tint Glass, for the same purpose ..... 7 Erecting Glass, for dissecting with the Com'pound Microscope . 015 Side Reflectors, for illuminating opaque objects . . . . 18 Apparatus for Polarisation of Light . . . 1 5s. to 25 Achromatic Condensor, for transparent objects . 2 10s. and 5 10 Condensing Lens, on brass stand .... 18s. and 1 Parabolic Condenser, for dark ground illumination 1 os. and 1 10 Spotted Lens, for low powers, by which a perfect black field is obtained 7s. 6d. to 15 Micro-Spectroscope, arranged for direct vision, and to shew two spectra at the same time, in the form of an eye -piece . 5 Compressorium 15 Extra Eye- pieces 12s. and 15 Animalcule Cage . . . . . . . 3s. to 06 Glass Micrometers, for measuring the diameter of various objects, lOOths and lOOOths 05 Micrometer, mounted in brass frame, with screw adjustment fitted to eye- piece of Microscope 10 Slips of Glass, 3 inches by 1 . . per packet of 3 dozen 2 Glass Circles for Covers per ounce 5 Ditto Squares 04 Canada Balsam, pure Glycerine, Dean's Gelatine, Asphalt, Gold Size, &c per bottle, Is. to 1 Machine for cutting Sections of Wood . . 7s. 6d. to 11 Turntable for building up cells and varnishing the edge of covers . . . 07 Brook's Double Connecter . . . .. . . . 110 Valentin's Knife, in case 16 Set of Microscopical Dissecting Instruments, in case . . . 1 10 Maltwood's Finder 07 A large assortment of Microscopic objects, sections of teeth, bone, &c 01 Insects, Infusoria, and Vegetable Structures . . Is. to 01 Anatomical Injected Preparations .... from 2 Microscopic Photographs 01 Mahogany Cabinets for holding 264 objects, and place for apparatus . 17 Mahogany Cabinets, with glass doors, for Microscope objects from 2 2s. to 5 5 Glass Trough, for fixing fish, &c 2s. 6d. to 05 Frog Plate 10 Glass Dissecting Trough ........ 4 Dr. Beale's Cabinet, for Chemical Analysis, containing the fol lowing: Platinum foil, test tubes, pipette, urinometer, graduated glass measure, spirit lamp with wire ring, watch glasses, glass slides, thin glass covers, and 8 re-agents in glass bottles, with capillary orifices 15 Injecting Syringe, with three jets and stopcock . . 12s. and 15 Improved Gas Lamp, with bath and plate for mounting objects 115 Diamond for writing on glass 5s. to 07 Ditto, for plate or window glass 18 Apparatus for cutting thin glass circles . . . . . 17 WILLIAM LADD, 11 & 12, BEAK-ST., REGENT-ST. ACHROMATIC OBJECT-GLASSES FOR MICROSCOPES. Object Glasses. Angular Aperture. Price. Magnifj-ing Power with the various Eye-Glasses. 2-inch !* 1 1&2 1 5 degrees 20 15 25 65 95 135 150 s. d. 10 15 1 11 6 330 4 4 7 20 40 60 11 100 220 320 400 30 15 80 130 350 510 570 40 70 100 180 500 700 900 W. LAPD SUPPLIES THE FOLLOWING WORKS . Quekett's Practical Treatise on the use of the Microscope . The Microscope, by Dr. Carpenter How to work with the Microscope, by Dr. Lionel Beale Half-hours with the Microscope, by Dr. Lankester . Hogg on the Microscope . . ' s. d. 1 1 12 6 5 6 2 6 060 TELESCOPES. EQUATORIAL, with 4-in. object-glass, 5 ft. focal length; 6 astronomical eye pieces ; diagonal and transit eye-pieces ; double parallel- wire Micrometer, with 4 eye-pieces ; illumin- ating apparatus; declinating and hour circles, graduated on silver, with Vernas and Microscope. Supported on stout iron pillar 110 Clock-work for the above 20 FOUR-FT. ASTRONOMICAL TELESCOPE, 34-inch object- glass, 5 eye-pieces, and brass tripod, with horizontal and vertical movements, packed in mahogany case . . . 31 10 3-ft. 6-in. ditto, 3 eye- pieces, 2|-in. object-glass, in mahogany case 21 3-ft. ditto, 3 eye-pieces, 2f-in. object-glass, in mahogany case 15 2-ft. 6-in. ditto, 2 eye-pieces 10 Tripod Garden Stand, suitable for either of the above 35s. to 2100 21-in. Navy Telescope 250 18-in. ditto 1 16 15-in. ditto 1 10 Day and Night Telescopes from 1 10 Pocket Telescopes of every description and of best quality. Achromatic Stereoscope from 110 Revolving Stereoscope, to hold two dozen glass slides . . 3100 A large assortment of Glass Stereoscopic Slides from 4s. 6d. to 066 Wheatstone's Reflecting Stereoscope .... from 200 Ditto Pseudoacope 1 10 WILLIAM LADD, 11 & 12, BEAK-ST., BEGENT-ST. 7 OPERA AND RACE GLASSES, With achromatic eye-pieces, with ivory, pearl, tortoiseshell, enamelled, or leather mounts. MAGNIFYING GLASSES, For viewing prints and paintings. SPECTACLES AND EYE-GLASSES In every variety of mounting. Theodolites, Levels, Compasses, Sextants, and Quadrants. MAGIC LANTERNS, DISSOLVING-VIEW APPARATUS, ETC. s. d. Magic Lanterns from 7s. to 1 10 Phantasmagoria Lantern, with best Argand Lamp, 3 -in. conden- sers, in a deal case . . . . . . . . 300 Ditto, with 3^ -inch condensers 400 Ditto, with Microscope, 3^-inch condensers, microscopic objects and water trough, packed in case 5 10 Oxycalcium Lantern, for exhibiting 3 -inch pictures on a screen 10 feet diameter, with apparatus complete . . . . 900 Dissolving- View Apparatus, with 3^ -inch condensers, for show- ing 3-inch pictures 900 Ditto, with Oxycalcium apparatus complete . . . 15 Microscope for ditto ....... from 100 Dissolving- view Apparatus, with oxy-hydrogen lime light, 4-inch condensers, 2 gas bags, pressure boards, tubing. gas generators, purifier, and copper retort complete . 30 0- Dissolving-view Apparatus combined in one lantern, with stop- cock arrangement for producing dissolving effect, with gas bags, &c., complete 24 Improved Oxy-hydrogen Microscope, with 3 powers and maho- gany lantern 7 10 Ditto, with Oxy-hydrogen jet, gas bags, pressure boards, tripod stand, and apparatus for making gas, &c SO Apparatus to show magnetic curves 12 Clockwork movement for revolving the lime cylinders . each 250 Opaque screens, 8-feet square, on rollers Ditto 10-feet Ditto 12-feet One dozen Lime Cylinders, in sealed bottle . . . . 030 Dissolving-views, separate or in sets, to illustrate Astronomy, Geology, Natural History, &c The whole and parts of insects, sections of woods, &c., prepared specially for the Oxy-hydrogen Microscope, each, 2s., 2s. 6d. and 030 8 WILLIAM LADD, 11 & 12, BEAK-ST., REGENT-ST. APPARATUS FOR ELECTRIC LIGHT, POLAR- ISATION, &c. *. Ladd's improved Electric Lamp . . . . . . 10 10 Lantern for ditto, with Condensers 6 10 Holmes' Improved Electric Lamp for Lighthouses, &c. . . 180 Parabolic Reflectors, thickly silvered . . . . . . 22 Revolving Diaphragm for Lantern 015 Rectangular ditto 110 Mahogany Box, containing Flyers, extra pair of Carbon Holders, Forceps, and 6 ft. of Carbon Points 10 Best Carbon Points per feet 1 Microscope for the Electric Light, with best Achromatic Ob- jectives 10 Improved Polariscope for above 12 10 Prisms of heavy Glass, on Stand . . . from 2 to 3 10 Ditto of Quartz from 3 to 50 Polyprisms of Six Glasses of various density, on Stand . . 310 Bottle Prisms of Bisulphide of Carbon ." . from 12s. to 18 Prism with movable sides, on Brass Stand, "with adjusting Screws 60 Adjustable Stand for Prisms .' . 07 4-inch Condenser, on Stand, for focusing image on screen . . 1 10 Bunsen's burners ..... from 4s. 6d. to 10 4 Sets of 10 Grove's Batteries for Electric Light . . * . 20 Biot's Reflecting Polariscope, with Apparatus .... 5 5 Tourmaline Polariscope, to illustrate the system of coloured rings, in crystals, &c 22 Ditto, Pincers for ditto from 1 10 Selenites of various devices ..... from 5 Specimens of unannealed Glass, of various shapes . from 3 Apparatus to shew Newton's rings ' . 1 2 Prisms to illustrate Achromatism on stand . . . . 1 10 2 Glasses ruled with fine lines to shew Iridescence . from 10 -Concave and Convex Mirrors " Spheres of Iceland Spar 20 Plates of Arragonite, Quartz, Topaz, Nitre, Calc-spar, Borax, &c., for exhibiting the coloured rings . . . from 5 Apparatus to show the polarising structure, communicated to glass by pressure .... from 7s. 6d. to 11 Rectangular Prisms of Glass for ditto Rhombs of Iceland Spar. Polished Plates of Tourmaline. Double and Single Image Prisms. Polarising bundles of Crown Glass. Polariscopes fitted to Microscopes. Selenite Plates. Gutta Perch a covered Wire, per yard, 3d. to 6d. SPECTROSCOPES AND APPARATUS. Apparatus for Spectrum Analyses with four Prisms, very superior Spectroscope with two Prisms, graduated circle, brass support &c., packed in mahogany case 15 Spectroscopes with (me Prism, Photographed Micrometer Scale,&c. . . . - 60 .WILLIAM LADD, 11 & 12, BEAK-ST., REGENT-ST. s. d. Ladd's Universal Spectroscope with two Prisms packed in case . 550 The above can be used in any position either with or without Microscope. Pocket Spectroscope for direct vision 330 Micro-Spectroscope arranged for direct vision, and to shew two Spectra at the same time in the form of an eye-piece - 5 Bunsen's Burners, for the above from 046 Apparatus consisting of a Brass Stand, with two Insulated Dischargers for obtaining the Spectra of Metals, by means of the Induced Spark, with tube for Gases (Fig. 51) . . 1 15 LADD'S IMPROVED INDUCTION COILS & APPARATUS. For which Prize Medal was awarded at the Exhibition, 1862. INDUCTION COIL, to give H-inch spark nfair . . . 10 10 Ditto ditto 2^-inch ditto . . . 12 12 Ditto ditto 4-inch ditto . . . 15 15 Set of 5 Grove's Batteries, with platina plates 5x2} -inch, in tray 2 15 Ditto ditto 6* X 3-inch . . 4 10 Apparatus consisting of glass tube with two platinum terminals, with brass plate and glass receiver to fit upon air-pump, for experiments with Torricellian vacuum (Fitr. 23.) . . 1 10 Gassiot's Torricellian Vacuum Tube, for broad, cloudy strati- fication (Fig. 26.) 1 10 Ditto, packed in case 1 16 Uranium Glass Tube, mounted on Stand, with stopcock 1 Is. to 220 Glass Tubes for showing the Aurora Borealis, fitted with stop- cock, and capable of being charged with various gases, from 2 to o ft. long, and I to 4 inch diameter (Fig. 21) Apparatus for showing the rotation of a spark round an electro- magnet (Fig. 19.) 3 10 Ditto ' (Fig. 20.) . . . . . . . . 1 10 Bar Electro-magnet, for experimenting with the electric spark from 18 Egg-shaped Glass, with stopcock and sliding wire (Fig. 22) . 250 GASSIOT'S CASCADE, permanently exhausted (Fig. 16) . 3 10 Gassiot's Revolving Star (Fig. 48) * . . . 3 3s. to 4 10 Geissler's Sealed Vacuum Tubes. These tubes have been charged with the various gases, and then exhausted to the utmost, and hermetically sealed. Carbonic Acid Vacuum Tube, with stick of caustic potash at one end (Fig. 29) 1 5s. and 1 10 Vacuum tubes composed of two or more distinct vacuums, showing a variety of colours according to the gases contained Double Garland Tube (Fig. 34) 200 10 WILLIAM LADD, 11 & 12, BEAK-ST., REGENT-ST. s. d. Single Garland Tube (Fig. 35) 1 10 Ditto ditto with letters (Fig. 36) . . each 220 Vacuum Tubes (Figs. 37, 38, 40, &42) . . . .each 150 Ditto (Figs. 39,43, & 44) each 1 10 Ditto (Fig. 41) each 110 Ditto (Fig. 47) 15s. to 110 Ditto of Uranium Glass 15s. to 1 10 These tubes vary in size, and consequently in price. Vacuum Tubes, charged with various Gases for Spectrum Analysis (Fig. 45) 10 Gassiot's support for six ditto ; the tubes become successively illuminated when in front of the Spectroscope . . . 200 Vacuum Tube, for surgical purposes (Fig. 46) . . . . 110 Vacuum Coronets. Ditto, Miners' Lamps. Ditto, to show extraordinary effect when placed between the poles of a powerful electro -magnet. (Figs. 24 and 25). A variety of other Tubes always it stock. Udiometer to be used with Inductorium . . . from 050 Apparatus for producing Ozone in large quantities by aid of the Induction Coil. (Fig. 52$ 110 Uranium Glass Vessel for showing fluorescence . . . . 050 Block of Uranium Glass, in mahogany case . . from 150 Glass Tubes, containing Becquerel's Phosphorescent Powders in sets of six 15s. and 150 Revolving Colour Disc, for showing white light, also for proving that the Induction Spark is not continuous . . . 070 Spotted Jars 7s. 6d. to 220 W. Ladd has been appointed Sole Agent for Geissler's Vacuum Tubes and Chemical Apparatus. The above figures refer to " Treatise on the Induction Coil," by Dr. H. M. Noad, F.R.S., &c., with 40 illustrations, price 3s. W. Ladd, Beak St. APPARATUS FOR FRICTIONAL ELECTRICITY. 36-inch, Plate Electrical Machine, mounted upon the best prin- ciple with Electrometer attached 22 30-inch, ditto ditto 15 15 24-inch, ditto ditto 10 10 18-inch, ditto ditto ... 7 and 850 15- inch, Plate Electrical Machine 500 12-inch, ditto ditto without Electrometer . . 400 9-inch, ditto ditto ditto . . 300 Cylinder Electrical Machines made to order. Improved form of Electrometer, with Condenser (very delicate) 330- Bohnenberger's Electroscope ....... WILLIAM LADD, 11 & 12, BEAK-ST., REGENT-ST. 11 s. Quadrant Electrometer 07 Cnthbertson's Self-acting Electrometer 1 18 Bennet's Gold Leaf Electrometer .... 14s. to 1 10 Medical Jar 05 Henley's Universal Discharger, with Press and Table 1 5s. and 2 Electrical Cannon, with brass carriage . . . . . 18 Electrical Flask, with cap and valve ...... 6 Electrical Pistol 05 Luminous Conductor ......... 18 Electrical Sportsman . . . . . . . 15s. and 1 1 Egg-stand 07 Egg-shape Glass, with stopcock and sliding wire for showing ligtit in vacuo ......... 1 15 Hand Spiral 3s. 6d. and 5 Set of tive Spirals 18 Luminous Words, in frame ........ 10 Revolving Spiral, on stand . 08 Image Plates with brass stand Dancing figures made of pith Electrical See- saw Pith -ball Stand . Pith Balls . 8s. 6d. and 10 1 12 5 per dozen, 9d. and 1 Carved Head with hair . . . ... 3s. 6d. and 5 Diamond Jar 7s. 6d. and 0. 12 Bucket and Syphon ......... 5 Electrical Orrery . 07 Sturgeon's Apparatus for firing Gunpowder, &c. . .09 Insulated Brass or V\ 7 ood Stands Electrical Spider . . . 01 Electrical Obelisk 07 Thunder House 07 Fire House 12 Gamut of Bells 110 Set of three Bells . . . 07 Insulated Stool 12 Jointed Discharger . .... . 7s. 6d., 9s., and 10 Discharging Rods 03 Apparatus for showing the falling star . . . . . 15 Electrical Cylinders Glass Handles and Legs Brass Chain . . . . . . . . per yard Amalgam per box 1 Circular Glass Plates for Electrical Machines .... Ditto Ebonite discs for ditto Conductors Leyden Jars from 3 Brass Balls from Electrophorous from 10 Glass Jar, with movable tin coatings 10 Set of Electrical Apparatus for Educational purposes, consisting of the following articles : Plate Electrical Machine, Leyden Jar, Pith-ball Stand, Jointed Discharger, Hand Spiral, Brass Clamp, Head of Hair, Amalgam, and Chain, packed in coloured deal case, with lock and key .... 5 5 12 WILLIAM LADD, 11 & 12, BEAK.-ST., REGENT-ST. VOLTAIC AND MAGNETIC APPARATUS- s. , WILDE'S Magneto- Electric Machine (Fig. 8). This Machine can be used for a variety of experiments, and is an excellent substitute for a Voltaic Battery 21 Medical Galvanic Coil, of improved construction, which can be regulated so as to apply it either to an infant, or to the most obstinate cases, in mahogany box .... 4 4 Improved Medical Coil, with sulphate of mercury battery, com- plete in the form of a book (Fig. 9). . . . . 44 Medical Galvanic Machine, in mahogany box .... 3 3 Ditto ditto small size 22 Improved Magneto-electric Machines, for medical purposes, in mahogany case (Fig. 5) 25 Electro- magnet from (5 Mahogany support for ditto . . . . . . . 05 Powerful Electro-magnet on stand ...... 2 Ditto, very powerful with double wires, movable coils, mahogany stand, &c., (can be used for Dia-magnetic experiments) . 10 Rheostat from 5 10 Rheochord 1 15 Wheatstone's Bridge . . . , Galvanometer from 10 Galvanometers with Astatic Needle, with levelling screws and glass shade from 1 8 Ditto (very delicate) (Fig. 4) . . . . from 3 3s. to 4 4 Barlow's Wheel 10 Sturgeon's Disc, to go with the above ... .03 Oersted's Experiment 7s. 6d. and 10 Dipping Needle, on brass stand with divided arc ... 11 Ladd's Improved Electro -motive Engine, will raise 30 Ibs., size of stand, 7 by 5 inches 70 Apparatus for showing the rotation of Electro-magnet between the poles of a soft horse-shoe 10 Richie's Electro-magnetic Apparatus, consisting of horse- shoe- magnet, on stand, with levelling screws, Armature, Ampere's Bucket, wire frame, helical coil, and two flood cups . . 2 10 Marsh's Vibrating Suspended Wire 07 Working Model of Telegraph, by which sentences may be trans- mitted . . . , Morse's Printing Telegraph, consisting of receiver, relay, and key 10 10 Apparatus for Ringing a Bell by Electro-magnetism ...11 Apparatus for Ringing a Bell, of improved construction . Double Commutater . . . 15 Commutator ( the same as used with the Induction Coil) . . 11 Decomposition Apparatus ...... 7s. 6d. to V Tube for Decomposition 07 Faraday's Voltameter 55 Melloni's Thermo-electric Battery of twenty-five pairs of Anti- mony and Bismuth Bars Ditto (very delicate), with conical reflector .... o 5 Large Thermo-Electric Battery (Fig. 53) . . ... . 88 WILLIAM LADD, 11 & 12, BEAK-ST., REGEXT-ST. s. Ampere's Stand (improved form), by which the experiments relating to the mutual attraction and repulsion of electrical currents can be shown 20 Smee's Batter}' (pints) ........ Ditto (quarts) Set of six Smee's Batteries, in vulcanised cells, in mahogany trough ........... Ditto, with adjustments for raising it out of the cells ; may be arranged for either quantity or intensity .... Grove's Platinum Battery Set of eight of Grove's Batteries in tray Set of ten ditto, in tray ..... 4 sets of ditto, for electric Light .... Improved Coke Batteries, in glass or stoneware cells Brass Clamps for Batteries Glass and Porous Cells . ... Platinum Foil and Wire . . per oz. Platinised Silver ....... Amalgamating Zinc Plates per Ib. Copper Wire of all sizes, covered with silk or cotton Set of Electro -Magnetic Apparatus for Educational purposes, con- sisting of an Electro-magnetic Coil Machine, Smee's Battery, Galvanometer, Richie's Experiment, Oersted's ditto, Electro- magnet and mahogany stand, Barlow's Spur-whel and Permanent Magnet, packed in coloured deal case with lock 10 4 4 10 12 5 6 24 1 12 10 1 ABEL'S FUZES, FOR FIRING MINES AND CANNON BY MAGNETIC ELECTRICITY. W. L. is appointed sole manufacturer of these by order of the Secretary of State for War. Experimental Fuzes per doz. 2 Blasting 02 Cannon . . . . . . . . m . . . 03 Magneto- Electric Exploder, in mahogany case, with two keys 7 Ditto, very powerful 17 17 Ditto, with six keys, Fig. 6 18 18 Induction Coil, specially adapted for blasting purposes where a large number of fuzes are required to be fired simultaneously, in strong oak case . . . . . . . . 10 10 G. P. Insulating Wire, for connections . per 100 yards from 1 Ebonite Electrical Machine, or Austrian Exploder . . 13 Oak case for ditto 22 14 WILLIAM LADD, 11 & 12, BEAK-ST., REGENT-ST. DRAWING INSTRUMENTS, &c. s. d. Sets of Drawing Instruments, for youths 5s. 6d., 7s. 6d. and 10 6 Ditto, in mahogany cases 110 Ditto ditto 220 Ditto ditto, German silver ...... 2 10 Ditto ditto, very superior ditto 3 10 Architect's case of ditto, for the pocket 220 Ditto ditto, best make, German silver . . . 3 10 A complete set of Mathematical Drawing Instruments, of the best construction, with proportional compasses, rule, and scales from 10 10s. to 21 Pentagraph, for copying, reducing, and enlarging plans, draw- ings, maps, <tc., with case, 18- in., 4 10s. ; 24 in , 5 10s. ; 30 -in., 6 10 Drawing Pens 3s., 4s^ and 060 Proportional Compasses, 6-inch . . . . 1 10s, and 2 10 ( Engineers' Pocket Compasses . . * ....... 100 Ditto ditto, best make, German silver . . . . 200 Bow, Pen, and Pencils. Spring and Hair Dividers. Spring Dividers, Pen and Pencil, the set 10s. 6d. to 1 5s. 6d. Rolling Parallel Rules, 6-in., 6s. ; 9 -in., 7s. ; 12-in., 8s. 6d. ; 15-in., 11s. Rolling Parallel Rules, brass, Is. 6d. per inch. Protractors. Sectors. Mahogany and Ebony T-squares. Drawing Pins. METEOROLOGICAL INSTRUMENTS, Standard Barometers from 660 Pedestral Barometers, in mahogany, walnut, or rosewood frames, 2 2s. to 770 Wheel Barometer .1 15s. to 660 Board of Trade Marine Barometer, in case .... 5 ( Fitzroy's Sea-coast Barometer 4 ( Marine Barometer 3 3s. to 550. Marine Barometer and Simpiesometer, in one instrument from 5 ( Pocket Barometer . . . 2 15 Barometer, with compensating tube and extended scale (very delicate) 1 15s. and 2 10 Ditto ditto, Standard Aneroid Barometer from 2 10 Ditto, for the pocket 3 ( Patent Mercurial Maximum Thermometers . . . . 15 ( Standard Thermometers . . . . . 10s. 6d. to .10 Ditto, with spiral bulb, very delicate 1 10 Thermometers for registering extreme heat and cold . from 086 WILLIAM LADD, 11 & 12, BEAK-ST., REGENT-ST. 15 4s. 6d. to from Ivory Thermometers, in leather case . . . Chemical Thermometers, divided on glass . . Botanical Thermometers, in tin case ... Air Thermometers Leslie's Deferential Ditto ..... Boxwood Thermometers Wet and Dry Bulb Thermometer Mason's Hygrometer . ....... 1 Robinson's Anemometer, for ascertaining the velocity of the wind 3 Lind's ditto ...... , . . . 2 Electrometer, for Atmospheric Electricity .... 2 Rain-gauge, in japanned tin or copper . . . from 1 W. L. is sole Agent for Geissler's Chemical Thermometers. 10 4 9 10 15 1 2 2 PNEUMATIC APPARATUS. LADD'S SUPERIOR large size double-barrel Air-pump, with additional barrel for very accurate exhaustion, barometer, gauge, &c., on strong mahogany stool, 12-inch plate . Ditto, ditto, smaller size, for table, Fig. 17 . . 15 and Auxiliary Mercury Pump for obtaining a perfect Vacuum (Fig. 18) Grove's Pump, with 7-in. plate, mercurial gange,and two clamps Tate's Pump, with gauge, two clamps, and key . Large size double-barrel Air-pump, with raised plate, 10 inches in diameter, gauge-plate, mercurial gauge, clamp and key Second size double-barrel table Air-pump, with raised plate, 9 inches diameter, gauge-plate, gauge and key Ditto, ditto, with plate 8 in. in diameter, on stand (not raised) with gauge -pi ate, gauge and key .... Ditto, ditto, without gauge -plate, gauge and key Third size double-barrel Air-pump, diameter of plate 6 in. Smaller size double-barrel Air-pump, diameter of plate 5 in. Small size single-barrel Pump, 3^ -inch plate No. 2,ditto, ditto, 4 -in. plate 4, sloping barrel, 6^-in. plate .... Flat Brass Plate, with sliding wire . . . 10s. 6d. and Exhausting or Condensing Syringes Ditto ditto, in one instrument Apparatus, consisting of Glass Cylinder and Piston, to show the effect of pressure upon gases . -. "v . Fire Syringe . . . < . r Bell Experiments . .-*.-=.-. . 7s. 6d. and Bacchus Experiment Balloons of Goldbeater's skin, that will ascend with ordinary gas, 9-in. Is. ; 10^-in. 2s ; 12-in. 2s. 9d. ; 14-in. 3s. 6d. ; pear shape each 35 20 770 500 440 11 10 9 10 800 6 10 440 3 10 100 1 10 1 15 220 13 070 10 100 036 100 180 050 16 WILLIAM LADD, 11 & 12, BEAK-ST., REGENT-ST. s. d. Hand and Bladder Glass 026 Lungs Glass , ..... 6 V Large size Hemispheres . . * . - 180 Middle size ditto . . \ .* . . . . 16 Small size ditto . . . . , , . . . . 12 Filtering Cup, with Brass Plate 066 Three-fall Guinea-and-Feather Apparatus . . . . 110 Two-fall ditto 15 Tall Glass Receiver for ditto . ..... 7s. Gd. and 10 6 Windmill (improved) 1 15 Double Transferor . .'....:.-. . . 1 16 Single ditto ...*;, 12s. and 18 Bladder Frame and Lead Weights . . . . . 080 Copper Bottle, Beam, and Stand ".'."'. . .. 250 Fruit and Taper Stand 030 Syringe and Lead Weights . 080 Balance Beam and Cork Ball, with counterpoise weight . . 0100 Torricellian Experiment 15 6 Ditto, having the Barometer fixed in the cap of glass receiver . 176 Glass Globe, with brass cap and stopcock for weighing air . 080 Leslie's Apparatus for freezing water 10 Breaking Squares 013 Wire Cage for ditto . V -, 046 Brass Stopcocks 2s. 6d. and 036 Apparatus for showing fountain in vacuo 12 Tall receiver for ditto . ...,.', . . . . 076 LADD'S EDUCATIONAL SET OF PNEUMATIC APPARATUS. As supplied by him to the various Educational Societies, consisting of the folloioing Articles : Single-barrel Air-pump and Receiver, Brass Clamp, Filtering cup for Mercury, Magdeburgh Hemispheres with handles, Bladder Frame and Weights, Guinea-and-Feather Appara- tus, Fruit and Taper Stand, Hand and Bladder Glass, Single Transferer and Fountain Apparatus, Brass Pipe for ditto, Bell Experiment, Brass Syringe for instantaneous Light, Glass for Fountain and Guinea-and-Feather Appa- ratus, and Plate for Top of Fountain Glass, packed in coloured case, with lock and key . . . , . 660 ACOUSTICS. Stand, with Organ bellows and sound-board, with holes for organ pipes, &c t , . from 500 Set of eight organ pipes 220 Set of organ pipes to illustrate various methods of producing musical notes. Organ pipe with membranes and gas jets to illustrate the nodal : points in a column of air 1 15 WILLIAM LADD, 11 & 12, BEAK-ST., KEGENT-ST. s. Syrenes from 2 to 40 Perforated disc, mounted on revolving stand, with jet and mouthpiece, to illustrate the production of musical sound by regular and irregular impulses . . . . . 2 10 Tuning-fork, mounted on sound case . . . . . . 1 10 Set of 4 smaller ditto, making a perfect chord . . . . 410 Ditto ditto, mounted on stand, to record vibrations upon smoked glass ......... 4 10 Set of eight ditto, on sounding cases, forming the gamut . . 90 Set of 4 Forks, with reflectors for showing the curves produced by the composition of rectangular vibration . . 10 10 Two stands for ditto 1 10 N.B. This set shows the following figures, unison, second, third, t fourth, fifth, sixth, seventh, and eighth, and intermediate semitones, oet of eight ditto, with reflectors, supports, and lamp ; also with support and sliding frame, for recording vibrations on smoked glass 28 Apparatus consisting of 2 vibration-springs fitted to lantern, by means of which, the whole of the above figures can be pro- jected on the screen . 3 10 Large Tuning Fork with Electro-magnet to keep up constant vibration of strings. Whirling apparatus for showing notal points in vibrating strings. Whirling Table 2 and 4 10 Apparatus consisting of a bell, with sliding tube to augment sound ...... ..... 2 12 Wheatstone's Kaleidophone .... from 10s. to 1 10 Apparatus to illustrate normal or transverse undulations in a row of particles .... ..... 4 14 The Monochord from 2 2s. to 55 A long tube, with piston, for experiments on the reciprocation of sound and on multiple resonance 22 Wheatstone's Apparatus for proving the simple mode of vibra- tion of a tube open at both ends . . . . . . Ill Long Vertical Gas Jet, with brass foot and stopcock, to produce musical notes in glass tubes 15 Apparatus lor rotating Gas Jet in a Glass Tube, with multiply- ing wheel and stand 22 Willis's Tube for the production of vowel sounds 2 2s. and 3 3 Set of Membranous Apparatus to illustrate the production ot the human voice ......... 7 Stands for damping-rods at the ends, or at one or more nodal points, to show their transverse vibrations. Large double brass clamp for holding plates . . . . 18 A series of Six Glass plates of different forms to illustrate the vibrations of elastic surfaces 09 Circular Metal Plate, on stand, to show ditto . . . . 18 Set of 3 ditto 25 Square Metal Plate, ditto ditto 18 Extra Large ditto ditto 11 Pounce Boxes ......... each 1 A Square, Circular, and Tria.igular Frame, over which is stretched a delicate tissue, to show the vibrations of elastic membranes .... 15 18 WILLIAM LADD, 11 & 12, BEAK-ST., REGENP-ST. s. Apparatus for exhibiting the nodes of a bell consisting of a glass vessel over the rim of which is suspended a row of cork balls 1 18 Hopkin's Apparatus to show the interference of sound . . 10 Various Apparatus for showing that sonorous vibrations are always transmitted in the direction they were originally propagated. Various Apparatus to show the interference of sonorous undu- lations and the analogies between these and the interference of light. Trevyllian's Rocking Bar and Lead Weight . . . . 12 Long glass tube, with brass plate, to produce sound by the flow of water through a small aperture. Set of Steel Spirals, mounted on a sounding box, with hammer 2 2 Strong Violoncello Bows for vibrating various apparatus from 12 2 Circular Brass Plates separated by long brass rod . . . 015 Glass Rod, with square or circular disc attached to show the in- fluence of the surrounding medium on the acoustic figures produced. MECHANICS, HYDRAULICS, &c- Educational Set of Mechanical Powers . . from 3 3s. to 20 Sets of Levers, various , from 1 Is. to 4 Sets of Pulleys, in frame, to how various arrangements . . 20 Single and Double Incline Planes, with rollers, from 10s. 6d. to 3 10 Various apparatus to illustrate the resolution and composition of force, the Equilibrium and Centre of Gravity of bodies, &c. Gyroscopes ........ from 25s. to 55 Whirling Tables for demonstrating the laws of central forces. Atwood's Machines from 4 4 Apparatus to illustrate the laAvs of collision .... 2 Dissected Cones from 9 Geometrical Solids per set 10 Large set of ditto (2-inch cube) I 10 Working Model of Bramah's Hydrostatic Presses from 5 to 25 Apparatus to illustrate the principle that fluids will rise to the same height . from 5 Tantalus Cup 10 Glass Syphon 2s. and i Glass B'alloons, Divers, &c each Ditto, ditto, with Tall Jar from Model of Centrifugal Pump Model of Lifting Pump, with glass barrel 18 Ditto of Forcing Pump 18 Model of Archimedes' Screw, with glass worm .... Ditto of Undershot Wheel 15 Ditto of Overshot Wheel 1 15 Ditto of Diving Bell, with Force- pump 11 WILLIAM LADD, 11 & 12, BEAK-ST., REGENT-ST. Fountain Apparatus, consisting of strong metal vessels, stop- cock, condensing syringe, and set of jets . . from 220 Philosophical Water Hammer 050 Woolaston's Cryophorus . . . . . .4s. and 060 HEAT. Ferguson's Pyrometer ........ 5 Daniell's ditto 50 Metal Ball and Ring 010 Set of 5 Balls of different metals, to illustrate their specific heat 10 Compound Bar of Iron and Brass 10 Metal Bar and Gauge . . . - 06 Iron and Brass Bars, supported on mahogany stand, with con- nections for battery, to illustrate the different expansion of metals. Appaiatus for showing the force exerted by the contraction of solids 15 Iron Bottles to show expansion of water at freezing point, and Bismuth on cooling each 2 2 Metal Bars on stand, with spirit lamp, &c., to show expansion 18 Ditto, with gas burner ........ 1 5 Metal Bar, on stand, to show conduction, with cups, balls, and lamps 08 6 different Metal Bars, emanating from one centre, to show ditto 5s. 6d. and 7 Faraday's Convection Apparatus lo Glass Globe and Bucket, to illustrate the circulation of heated water. Fire Balloons. Parabolic Reflections for radiation and reflection . per pair from 2 2s. to 12 12 Iron Ball and Stand for ditto ..... . .05 Leslie's Thermometer . . . . . . . . 15 Pewter or Tin Cubes for radiation . . . from 2s. 6d. to 12 Copper Flask, Lined with Silver, to show spheroidal state of water 15 Marcet's Steam Boiler, complete 55 Flask, with stopcock, to show ebullition of water under diminished pressure .05 Geissler's Patent Vapormeter, for ascertaining the quantity of alcohol in wine, &c. Brequet's Metallic Thermometer 40 Thermometer, in glat-s tube containing water, to show develop- ment of heat on its freezing . . . . . . 16 Syringe, with glass barrel, for igniting gases, &c. ... 1 Candle Bombs per doz. Rupert's Drops 02 Bolognean Flasks 06 Hero's Rotary Engine. Wollaston's Apparatus to illustrate the ordinary condensing engine ....... 7s. 6d. and 10 20 WILLIAM LADD, 11 & 12, BEAK-ST., REGENT-ST. a. d. Tin Vessel and stopcock, to illustrate the condensation of steam and pressure of the atmosphere . . . . . . 056 Oscillating Engine, Working Model .... from 1 15 Working Models of Steam Engines made to order. Sectional Models of Steam Engines . . . from 500 Zinc Ethyl Fountain Apparatus . . . . . . 18 Apparatus to show the compressibility of Liquids and liquefac- tion of Gases under pressure 10 10 PHOTOGRAPHIC CAMERAS & APPARATUS. MODELS OF INVENTIONS, AND ALL KINDS OF APPARATUS, MADE TO ORDER. Wholesale and Shipping Orders executed with despatch. Orders from Foreign parts must be accompanied by a Remittance, or Order for payment in London. Post Office Orders to be made payable in Regent Street, W. The greatest care will be taken in the packing of Goods, to prevent breakage, but W. L. will not hold himself responsible for damage done during transit. Packing Cases cl'aryed Coft Piice, und NOT allowed for if returned. Wcrtlieitncr & Co., Printers, Circus Place, Fiusbury Circus. RETURN TO the circulation desk of any University of California Library or to the NORTHERN REGIONAL LIBRARY FACILITY Bldg. 400, Richmond Field Station University of California Richmond, CA 94804-4698 ALL BOOKS MAY BE RECALLED AFTER 7 DAYS 2-month loans may be renewed by calling (510)642-6753 1-year loans may be recharged by bringing books to NRLF Renewals and recharges may be made 4 days prior to due date DUE AS STAMPED BELOW JUL141994 ^~^~ VA 01 146-