MICHAEL FAEADAY — HIS LIFE AND WORKS. 239 



tlie passage and interruption of the cniTcnt in the wire. We all know tliG 

 advantage that has been taken of this combination in the construction of very 

 powerful apparatus. Wo also know how, fi'om one improvement to another, 

 we have come to find in induction, and consequently in the simple mechanical 

 movement which gives birth to it, the most simple and economical principle for 

 obtaining electricity, especially with regard to its application to therapeutics 

 and illumination. 



The discovery of electro-dynamical induction (that is to say, the production 

 of a cuiTcnt by the influence of an exterior cun-ent) led Faraday to examine 

 more closely than had previously been done into the phenomenon of statical 

 induction — ^that is to say, the development at a distance of tension-electricity 

 in an isolated conductor by the influence of an electrized body. He ascertained, 

 what no one had previously suspected, that the nature of the body interposed 

 between the source of electricity and the conductor submitted to the action of 

 this source had a great influence upon the e2"ect produced — that, of the various 

 bodies, some facilitated the development of electricity at a distance, 'v\hilst 

 others completely stopped it. He named the former dielectrics ; and he proved 

 that these dielectrics, which are essentially resins, sulphur, shellac, oils of tur- 

 pentine and naphtha, Sec, enjoy this property of transmitting electricity by influ- 

 ence in different degrees, whilst there is not in this reepect any ditiereuce 

 between the gases, which have the same dielectric power, whatever their nature 

 or their density may be. On the other hand, none of the metals are dielectric j 

 they are subject to the electrical influence, but do not transmit it. 



From the investigation which we have just summarized, Faraday drew the 

 conclusion that induction does not take place at a distance, l)nt that it is effected 

 by the intermediation of the particles interposed between the inductor and the 

 inducted body. He assumed that these particles are polarized one after the 

 other, which M. Matteucci afterwards demonstrated directly l)y experiment j 

 that consequently the mode of propagation of electricity is the same in insu- 

 lating as in conducting bodies ; and that the various substances only difler from 

 each other by the greater or less facility or rapidity with which this polarization, 

 necessary for the transmission of electricity, takes place in them. Then, passing 

 fi'om this to the analysis of the diflerent modes in which electrical discharges 

 take place, some obscure, others luminous, some electrolytic, (that is to say, 

 accompanied by the chemical decomposition of the conducting body,) others 

 disruptive, (that is to say, effected by the mechanical disjunction of the particles 

 of the interjiosed substance,) he applied himself more particularly to the study 

 of the various forms displayed by the electric spark in more or less rarefied 

 gases. I should never have done if I were to attempt to explain all the experi- 

 ments which he made to elucidate these different points and to arrive at an idea 

 of the actual nature of the electric current. The identity of the current, what- 

 ever may be its origin — that its production is due to polar forces which may 

 exert a transverse action, as is the case in electro-dynamical jihenomena — that 

 these polar forces emanate from contiguous particles ; such ai'c the })riuciple3 

 which Faraday endeavored to establish as the consequences of his experimental 

 researches, at the same time that he rejected the idea of actions at a distance, 

 i;efemng all electrical manifestations to the presence of ponderable matter. 



Whether or not we completely admit all Faraday's ideas, it is impossible not 

 to acknowledge the immense advance which he caused the theories of electricity 

 to make, either by demonstrating by experiment the falsity of certain concep- 

 tions generally accepted up to his time, or by opening up perfectly new points 

 of view as to the actual nature of electrical phenomena. We have just had the 

 proof of this in the consequences to which he was led by his investigations on 

 statical induction. His discoveries in electro-dynamical induction have had 

 still more important consequences, by introducing the notion of mechanical move- 

 ment into the essence of electrical movement, and thus enabling Weber to oom- 



