476 



NATURE 



{April 13, 1876 



the first kind is devoid of tension, when they treat of the experi- 

 ment known as the induced cylinder. Yet the same physicists, 

 Verdet says, admit this want of tension when they treat of the 

 plate condenser, in the instrument known as Volti's condenser, 

 as if these two experiments were not identical. It is clear, he 

 says, that a similar restriction of the same hypothesis is not 

 established, and that if there be dissimulated electricity upon two 

 conducting discs placed near each other, it ought also to exist, 

 although in a less proportion, on two cylindrical or spherical 

 conductors, such as are ordinarily employed in experiments. 

 All this is confirmed by De la Rive ; ^ "the experiments of 

 Melloni," he says, "appear to me' to account for these anomalies 

 in a satisfactory manner." 



In Gehler's Vocabulary^ we read that Miinck, agreeing with 

 riaff, did not admit the theory of Riess. 



Prof. Tyndall thus expresses himself on the subject under dis- 

 cussion-*: — "When an insulated conductor is under the influ- 

 ence of an electrified body, its repelled electricity is free ; but its 

 attracted electricity is held captive by the inducing electrified 

 body. If for a moment we put the induced inductor into com- 

 muaication with the earth, its free electricity is dissipated ; and 

 if we remove to a distance the inducing electrified body, the 

 captive electricity becomes free, and is distributed over the sur- 

 face of the induced conductor." This manner of conceiving the 

 ])henomenon of electrical induction agrees perfectly with the 

 new theory of Melloni, which, we maintain, satisfactorily ex- 

 plains the same phenomenon. 



Finally, Melloni communicated to the Paris Academy of 

 Sciences* (July 24, 1854) his ideas on electrical induction, 

 and maintained, adducing all his reasons in support, that there 

 was ground for amending the theory of induction commonly 

 adopted, that it must be admitted that induced electricity of the 

 ilrst kind did not possess tension, and that the homonym of the 

 inductor is found on every point of the induced body, including 

 the extreme point nearest to the inductor. 



After having given this brief but complete resumi of the 

 various opinions which have been enunciated on the question, 

 showing that there have never been wanting eminent physicists 

 to maintain that indue i electricity of the first kind is entirely 

 devoid of tension, I shall now recount my own observations and 

 experiments, by which, if I am not mistaken, I have proved the 

 truth of Melloni's theory of electrical induction. 



Experiments. — The experiments I am about to describe 

 should be made when the air is sufficiently dry, as then only are 

 the results perfectly satisfactory. 



First Experiment. — Upon the conducting cylinder, induced and 

 insulated, the following five facts are proved: — i. On the same 

 cylinder the two opposite electricities exist without neutralising 

 each other. 2 . If the extremity of the cylinder nearest to the in- 

 ductor is put into communication with the earth, it is only the 

 homonym of the inductor which is dissipated and not at all the 

 opposite electricity. 3. Of the two kinds of electricity which 

 are in the cylinder, the homonym of the influent alone is dissi- 

 l)ated by contact with the air. 4. Points applied to the ex- 

 tremity of the cylinder nearest to the inductor allow only the 

 homonym of the inductor to escape and not at all the opposite 

 electricity. 5. Induced electricity of the first kind is not trans- 

 ferred from the induced body to the inductor, but the electricity 

 of the inductor may certainly be transferred to the induced body. 



These five experimental facts cannot be logically explained by 

 the old theory of electrical induction, but only by the new, 

 showing that induced electricity of the first kind does not 

 possess tension, i.e., that it is entirely dissimulated, and that 

 induced electricity of the second kind, i.e., the homonym of the 

 inductor, is entirely free on all points of the induced object. 



Second Experiment.^ — In the communication referred to in the 

 note aie analysed the phases of divergence produced in the gold- 

 leaf electrometers applied to the extremity of the insulated 

 induced body nearest to the inductor. The same phases were 

 obtained by means of two simultaneous inductions, the one 

 principal, which came from the inductor, the other secondary, 

 which came from the analyser. 



On this ground it is concluded that these phases, when they 

 are fairly interpreted, prove that the homonym of the inductor 

 exists also on the extremity indicated, and that on this account 

 the induced electricity has no tension. In the same experiment 



' "Archives des Sciences Phys. et. Nat. de Geneve," t. 26, p. 323, note i. 

 - Vol. ii. p. 131. (Leipzig, 1843.) 



3 '* Les Mondes," 2nd series, vol. xxiii. p. 566, § 79, 



4 " Comptes Rendus," t 38, p. 177. 



5 Published in the "Compt«s Rendus," t. 40, p. 246 (Jan. 29, 1855). 



it was seen how these phases may be misleading, if we do not 

 examine carefully the simultaneous effects of the two inductions 

 indicated. The explanation of this experiment allows a much 

 greater development than that of Melloni, published by M. Reg- 

 nault in the " Comptes Rendus," t. 39, p. 177 (July 24, 1854). 



Third Experiment, — When, into the inductive sphere of an 

 electrified body, a, is introduced,^ with the necessary precautions, 

 another insulated body, l>, the electricity of the inductor, a, 

 always attracts and completely di:ssimulates the induced body, b, 

 the opposite electrical condition, expelling the homologue, and 

 rendering it completely free. But this is not all. There is 

 another fact, which has not yet been indicated, viz., that if we 

 bring close to or remove away from the inducing body, a, 

 another body, c, then part of the dissimulated electricity in the 

 induced b becomes free in the former case, while in the second 

 case it increases in l>, at the same time that the opposite condition 

 is developed in it. 



In the paper above cited all the experiments confirming this 

 result are given, from which we conclude that the induced elec- 

 tricity of the first kind does not possess tension. 



Fourth Experiinent. — The first experiments made for the pur- 

 pose of discovering if electrostatic induction can be effected in 

 curved lines, are due to the illustrious Faraday, who, in one of 

 his latest papers, says that by his experiments he believes he has 

 established the possibility of this induction ; perhaps the facts 

 which I have discovered, and which are completely verified when 

 the atmosphere is dry, may establish its certainty. These experi- 

 ments, by which is proved the existence of curvilinear induction, 

 will be found described in "Comptes Rendus," t. 43, p. 719. 



Ftfth Experiment.— 'Y\\\^ fifth experiment '^ contains an account 

 of six considerations and of five experiments, by means of 

 which it is shown that induced electricity of the first kind does 

 not possess tension, and that the induced insulated cylinder 

 shows at all points the existence of the homonym of the 

 inductor. 



Sixth Experiment. — In this^ are described several experi- 

 ments which show the existence of curvilinear induction, and 

 prove at the same time that the separation of the gold-leaf elec- 

 trometers, applied to the extremity of the induced body furthest 

 from the inductor, is produced principally by t'lis influence, and 

 to a very small extent by the homonym of the inductor. 



Seventh Experiment. — In this'' is shown, in a different man- 

 ner, that induced electricity of the first kind has no tension, and 

 that on any point of the induced body there is always found the 

 homonym of the inducing, not excepting the extremity nearest 

 to the inductor, provided that the proper means is employed, as 

 described in the communication referred to. 



Eighth Experiment. — In this'' are analysed the objections 

 made by M. Riess to some of my experiments on electrical 

 induction, and the doctrine of Melloni on this subject is 

 confirmed by other facts. The conclusion is that the ob- 

 jections of M. Riess are not justifiable, and that if this emi- 

 nent physicist had repeated the experiments which he criticises, 

 he would have found them to be genuine, and would not have 

 declared them to be inexplicable. It is now more than sixteen 

 years since I made this reply to M, Riess, always communicatmg 

 other experiments bearing on the same point ; but, so far as 1 

 know, he has raised no other objections to the theory of 

 Melloni. 



Ninth Experiment. — In this communication" eight reasons 

 are adduced to show that induced electricity has no tension. 

 The same reasons do not hold good on the old theory, while 

 Melloni's new theory of electrical induction explains them com- 

 pletely. This new theory does not entirely overturn the old, as 

 some have mistakenly believed ; the former only essentially 

 modifies the latter in some of its parts. 



Tenth Experiment. — This is a reply to the note of M. Gaugain, 

 in which he observes that, notwithstanding the various experi- 

 ments adduced by M. Volpicelli, it is still strongly maintained 

 that induced electricity of the first kind possesses tension." 



Eleventh Experiment. — In this are advanced various observa- 

 tions, some on tension, both electro-statical and electro-dynami- 

 cal, and others on electrical induction.^ 



T'cvelfth Experiment. — In this communication it is observed 



' "Comptes Rendus," t. 41, p. 553 (Oct. 8, iS55\ 



2 Ibid., t. 44, p. 17 (May 4, 1857). 



3 Ibid , t. 47, p. 623 (Oct. 18, 1858). 

 ♦ Ibid., t. 47, p. 664 (Oct. 23, 1858). 



5 Ibid., t. 48, p. 1 162 (June 27, 1859). 



6 Ibid., t. 59, p. 570 (Sept. 26, 1864). 



7 Ibid., t. 59, p. 963 (Dec. 5, i86.i). 



8 Ibid., t. 61, p. 548 (Oct. 2, 1863). 



