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THE CIVIL ENGINEER AND ARCHITECrS JOURNAL. 



LJwiiY, 



metals. The heat thus generated is owing, Professor Faraday obserred, 

 to the passage of electricity through the substances acted on, and to the 

 resistance Ibey offer to iis passage, for when the conductors are sufficiently 

 large and perfect to afl'ord a free passage to the electricity, no effect of heatis 

 observable. A very curious experiment in illustration of this property of 

 electricity was exhibited. In a glass vessel full of distilled water the 

 charcoal points from the opposite poles of the battery were introduced, and 

 when they were brought near to each other a most brilliant light was 

 evolved under the water, dimmed only by the bubbles of steam generated 

 by the heat. Tiie water being an imperfect conductor of electricity, 

 offered suflicient resistance to its passage to bring into action the heating 

 and light-giving powers of the voltaic battery ; but when it was afterwards 

 made a better conductor, by mixing sulphuric acid with it, the effect was 

 greatly diminished. In the preceding lecture. Professor Faraday showed 

 that wires proceeding from the opposite ends of a voltaic battery possess 

 different powers in the decomposition of compound substances, and he now 

 showed that their heating powers also dilier ; for the copper wires from 

 the two poles, on being held close to each other within a short distance of the 

 ends, the one became much hotter than the other. The quantity of heat 

 evolved by the action of the voltaic battery is in proportion to the amount 

 of zinc oxidized, and Professor Faraday remarked there is good ground 

 for supposing that the heat evolved is equal to that produced by the com- 

 bustion of the same weight of zinc. Though the intensity of the light varies 

 in the phenomena of voltaic electricity, just as it varies in different circum- 

 stances during ordinary combustion, yet the heat remains the same in both 

 cases. As an illustration of this position, the Professor directed his 

 breath against a gas light so as to greatly diminish the brightness of the 

 flame, yet in both circumstances, be said the heat of the burning gas was 

 the same. The latter part of the lecture was occupied with the considera- 

 tion of the ell'ects of electricity on the sensitive system of animals, and it 

 was illustrated by several curious experiments. The original experiment 

 of Galvani with the hind legs of a frog was very successful ; for when the 

 legs were placed on a sheet of platinum, and connection was made between 

 that metal and a piece of zinc that touched the nerves, the muscular con- 

 tractions of the limbs made them jump as far as the animal could have done 

 when alive. A large live eel, in a glass jar, plunged about violently when 

 the electric current from the battery was passed through the water, thus 

 showing, that without any direct connection with the battery, the electric 

 shock is felt by fishes when the water they swim in is made part of the 

 circuit. Professor Faraday alluded to the experiment made with the 

 gymnotus ekctricus at the Polytechnic Institution, from which he 

 had obtained all the effects of an ordinary voltaic battery. The eel itself 

 does not feel the shock it communicates to the fishes within its influence, 

 though when an electric current from a voltaic battery is passed through 

 the water, it exhibits as much annoyance as any other fish. The Professor 

 observed that the effects of electricity on the nerves of animals, give an 

 insight into the phenomena of life, since they seem to prove that nervous 

 Irritability, on which the action of the muscles depend, is caused by elec- 

 rical influence, though by what means the electricity is generated remains 

 unknown. 



Tlie commencement of the ffth lecture was occupied with exhibition 

 of the pbenomeua of electricity, when the circuit is not interrupted. 

 The simplest evidence, that a constant action is going on in the conducting 

 wire, is afforded by the deflection of a magnetic needle, when a wire that 

 connects the two poles of a battery is held over it, parallel to the direction 

 of the needle. Small pieces of bent iron, resting on the wire, became mag- 

 netic when the electric circuit was completed, and when the wire was 

 twisted several times round a thick piece of iron, to increase the effect, 

 the magnetic power became so strong, that it lifted an anvil of at least fifty 

 pounds weight. The heating power of the voltaic battery, when the 

 current is passing uninterruptedly along llie wires, was shown by its making 

 charcoal, and various thin wires red liot, in which state they would have 

 remained as long as the battery continued in vigorous action. The con- 

 ducting power of gold being greater than that of platinum, a fine wire of gold 

 became a much brighter red by the passage of electricity through it, than 

 one of platinum ; and yet, when the two wires were joined together, the 

 platinum wire became red hot, whilst the gold was not perceptibly heated. 

 This anomaly Professor Faraday explained, by stating that the platmum 

 wire obstructed the passage of the electricity, consequently the gold wire, 

 which was capable of conducting a larger quantity, did not become 

 sensibly affected by the small quanlity which the platinum allowed to pass. 

 The increase of heat diminishes the conducting power of metals, and 

 several experiments were shown, for the purpose of illustrating this pecu- 

 liar property, the red heat of one part of a fine communicating wire being 

 brightened when another part of the wire was cooled : and the contrary 

 effect being produced when the wire was heated by a spirit lamp. A great 

 part of the lecture was occupied in explaining the two most popular 

 theories respecting the nature of electricity, neither of which, however. 

 Professor Faraday is inclined to adopt. One supposition is, that electri- 

 city is an ethereal imponderable body, distinct from the substances in which 

 it is excited, and that it is transmitted along wires, in like manner to the 

 rushing of fluids through tubes ; the other, and as he observed, the more 

 beautiful theory, is, that the phenomena of electricity are produced like 

 sound, by vibrations. The Professor performed several experiments, for 

 the purpose of showing the facts adduced in support of each of these 

 theories. One of the difliculties to be overcome in any theory that pur- 

 ports to explain the nature of electricity, is to account for the instantaneous 

 transmission of the power, which has been ascertained to exceed the rate of 



five thousand miles in a second. In support of the first theory, it is urged 

 that as there is an immense difference in the rapidity with which different 

 fluids pass along tubes — water, for example, flowing slowly in con)parisoa 

 with hydrogen gas— so it is asserted that the assumed imponderable fluid 

 may pass with a rapidity vastly greater than hydrogen gas. The vibrations 

 of sound, however, present much greater similarity to the transmission of 

 electricity. Though sound passes in air at the rate of only thirteen miles 

 a minute, it passes through water four times as quickly, and through glass 

 sixteen times faster than through air. There is this resemblance also be- 

 tween the passage of sound and the transmission of electricity, that sound 

 may be transmitted sensibly through solid bodies and become audible at 

 the end. Two curious experiments were performed to illustrate this pro. 

 perty of sound. A thin strip of deal was suspended from one end of the 

 lecture-room to the other, and at the farther end it bore against a box. A 

 tuning-fork, when struck and applied to one end of the strip of wood, 

 caused the box at the other extremity to emit a loud musical sound, though 

 the tuning-fork itself could scarcely be heard. In the other experiment a 

 rod of metal passed through the floor of the lecture-room, and was placed 

 in connection with a pianoforte in a room beneath. When the instrument 

 was played, scarcely any sound was heard, until a guitar-case was placed 

 on the rod, and then the notes were distinct and loud, as if proceeding 

 from the guitar-case. There is a similarity also between vibratious and elec- 

 trical shocks, as may be proved by striking a bar of iron when holding it 

 near one of the points of vibration, the jarring sensation bearing a close 

 resemblance to an electric shock. This vibratory sensation is felt yet more 

 strongly when a wet string is fastened round tlie waist, and some one pulls 

 the end of it through the fingers. 



In commencing bis sixth Uctuvc, Professor Faraday said he was about 

 to direct the attention of his auditors to a different condition of the elec- 

 tric force from that in which he had hitherto considered il, wherein the 

 phenomena not only differ from, but are in many respects directly opposed 

 to, those exhibited by chemical action and voltaic electricity ; and yet 

 the forces are the same. In the first place, he exhibited voltaic electricity 

 in a higher state of tension than he had before done, by employing a water- 

 battery, consisting of a great number of pairs of plates, by which ar- 

 rangement a small quantity of electricity in a high state of concentratioa 

 was excited. In this condition voltaic electricity nearly resembles the 

 electricity excited by rubbing a slick of sealing-wax or a rod of glass. 

 In the ordinary development of voltaic electricity, the effect is produced 

 only when the current is passing, and ceases when it is broken ; but in fric- 

 tional electricity the power may be exerted when there is no current, and 

 when the source of power is withdrawn. In this respect, indeed, the 

 water-battery evolves electricity resembling that of the electrical machine, 

 and forms the connecting link between frietional and chemically-excited 

 electricity, serving to prove that they are identical. In the first place, 

 Professor Faraday showed that by touching an electroscope with only one 

 of the wires of the battery, the gold leaves diverged, and continued diver- 

 gent when the wire was removed, thus exhibiting the development and the 

 retention of the power when there was no current passing. AVhen the 

 wire from the opposite pole of the water-battery was brought in contact 

 with the electroscope, the gold leaves collapsed. To show the identity of 

 the electricity thus evolved by the battery with the electricity excited by 

 friction. Professor Faraday caused the gold leaves of the electroscope, 

 when diverged by the battery, to be collapsed when an excited rod of glass 

 was brought near, and to be made more divergent by an excited rod of 

 gutia percha, or by a rod of shellac. The different means by which the 

 effect is produced aflords no ground for supposing the electricity of the 

 battery and that excited by friciion to be distinct, for what is termed frie- 

 tional electricity may be excited in varieties of ways, and is, in fact, con- 

 tinually being called into action, without our being sensible of its presence. 

 The mere act of dusting a piece of metal with flannel was shown to ex- 

 cite electricity by its causing the leaves of the electroscope to diverge. 

 We can scarcely touch anything without exciting this power, which, how- 

 ever minute and imperceptible in its development in these instances, is 

 precisely the same force which produces the grandest phenomena of 

 nature — thunder and lightning. Having given illustrations of the simi- 

 larity of the forces developed by chemical agency and by friction, the 

 Professor dwelt on the apparent differences between them. One remark- 

 able difference is, that the substances by which frietional electricity is 

 excited undergo no change, the metals and the glass remaining just the 

 same after having developed the power as before ; whenas voltaic elec- 

 tricity cannot be excited without chemical action, and an apparent de- 

 struction of the zinc. Another variation in the phenomena of voltaic and 

 of frietional electricity is exhibited in their conduction through various 

 substances. AVater, for instance, which is so imperfect a conductor of 

 voltaic electricity, will readily conduct the whole quantity excited by a 

 powerful electrical machine, through the moisture contained in a vvetted 

 silk thread. Frietional electricity is spread over the surfaces of bodies, 

 and does not enter them. This properly was exhibited by several experi- 

 ments, the most remarkable of which were the following : — A small metal 

 ice-pail was placed on an insulated stand, and then a metal ball, suspended 

 by a silk string, and charged with electricity, was lowered into the pail. 

 The electricity instantly diflused itself on the outside of the ice-pail, and 

 there was none within ; for when the ball was again lowered into the pail 

 and withdrawn, it produced no cli'ect on the electroscope, but when the 

 ball touched the outside the iustrunieut was strongly affected. In the 

 other experiment a wire-gauze vase was substituted for the ice-pail, with 

 exactly similar results. When an electrical machine is excited, every 



