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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. BLOXAM, Professor of Practical 
 Chemistry in King's College, London. Fifth Edition, fcap. 
 Svo, cloth, 6s. Gd. 
 
 By the same Author, 
 
 MEDICAL CHEMISTRY. With Illustrations on Wood. 
 Fourth Edition, fcap. Svo, cloth, 6s. Gd. 
 
 NOTES FOR STUDENTS IN CHEMISTRY : being a 
 Syllabus of Chemistry and Practical Chemistry. By ALBERT 
 J. BERNAYS, Professor of Chemistry at St. Thomas's Hos- 
 pital. Fourth Edition, Revised, fcap. Svo, cloth, 3s. 
 
 INSTRUCTION IN CHEMICAL ANALYSIS. By C. 
 REMIGIUS FRESENIUS. Edited by LLOYD BULLOCK. 
 QUALITATIVE. Sixth Edition, Svo, cloth, 10s. Gd. QUAN- 
 TITATIVE. Fourth Edition, Svo, cloth, 18s. 
 
 JOHN CHURCHILL AND SONS, NEW BURLINGTON-STREET. 
 
HARDWIOH'S PHOTOGRAPHIC 
 CHEMISTRY. 
 
 Seventh Edition, thoroughly revised by GEORGE DAWSON, M.A., 
 Lecturer on Photography, and E. A. HADOW, Demonstrator 
 of Chemistry, in King's College, London. Fcap. 8vo, cloth, 
 7-v. 6d. 
 
 " In selecting the two gentlemen whose names are appended as editors the 
 publishers have shown much discrimination. 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. 
 
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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-