ELECTRICAL AND MAGNETIC DISCOVERIES OF FARADAY 643 



The medium subjected to electrical or magnetic forces is, according 

 to Faraday's idea, polarized in the direction of these lines of force, so 

 that each particle only has to act upon the one next to it in order that 

 the force may be transmitted to any distance. In Faraday's mind these 

 lines had not only an imaginary existence as being the direction in 

 which the north pole of a needle or an electrified particle tended to 

 move in space, but also a real existence. He imagined them as elastic 

 bands repelling each other laterally, and binding the north and south 

 poles of a magnet, or the positive and negative electricities, together. 



It was only in after years that he discovered all the properties of these 

 lines, and I shall therefore return to them again. 



Guided by these lines of force, he investigated the subject of in- 

 duced electric currents in so complete a manner that nothing of funda- 

 mental importance has ever been added to the subject. True, to-day 

 we understand the subject much better than Faraday ever did. The 

 mathematical researches of Helmholtz, Thomson, Maxwell and others 

 have thrown a flood of light upon the induction of electric currents, 

 and the law of the conservation of energy gives us means of proving all 

 its laws, and indeed of showing that magneto-electric induction is the 

 consequence of the magnetic action of the current as discovered by 

 Oersted. 



But fifty years ago this law of the conservation of energy was too 

 little known to be used in this way. It required the support of just 

 such experiments as those of Faraday to bring into existence and to 

 prove it. Hence, Faraday had but little to guide him to the discovery, 

 except that subtle reasoning of a man of genius which almost amounts 

 to instinct. 



The difference of common and voltaic electricity next engaged his 

 attention. A Leyden jar highly charged might have large sparks and a 

 loud sound; it might ignite alcohol and produce a strong shock when 

 passed through the human body, but it was almost incapable of decom- 

 posing water, and could scarcely affect a magnetic needle. The voltaic 

 battery, on the other hand, could produce the latter effects, but not the 

 former. 



How did these two kinds of electricity differ? 



Faraday answered this by producing all the effects with one kind of 

 electricity that could be obtained from the other. He showed that the 

 difference was caused by there being great tension, or, as we call it, 

 potential in one case, with very little quantity, while in the other there 

 was great quantity with low tension. By charging Leyden jar batteries 



