MICHAEL FARADAY — HIS LIFE AND WOEKS. 239 



the passage and interruption of the current in the wire. "We all know the 

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

 powerful apparatus. We also know how', from 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 current by the influence of an exterior current) 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 b}- 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 effect produced — that, of the various 

 bodies, some facilitated the development of electricity at a distance, whilst 

 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, &c., enjoy this property of transmitting electricity by influ- 

 ence in different degrees, whilst there is not in this respect any difference 

 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)ut that it is effected 

 by the intermediation of the particles inteq^osed between the inductor and the 

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

 other, which ]\I. Matteucci afterwards demonstrated directly by experiment; 

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

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

 from this to the analysis of the different 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, eff"ected by the mechanical disjunction of the particles 

 of the interposed 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 phenomena — that 

 these polar forces emanate from contiguous particles ; such are the principles 

 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, 

 refeiTing 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 c^m- 



