ELECTRO-CHEMICAL ACTION. 209 



hydrogen at the other, the electro-chemical influence 

 taiiig exerted only where the cur-rent or motion is 

 transferred from one medium to another.* The im- 

 perfect character of this view is freely admitted; no 

 other, consistent with known facts, presents itself by 

 which the effect can be explained. The fact stands as a 

 truth ; the hypothesis by which it is attempted to be 

 interpreted is open to doubt, and it is opposed to some 

 favourite theories. 



Before we pass to the consideration of the other 

 sources of electricity, it is important we should under- 

 stand that no chemical or physical change, however 

 slight it may be, can occur without the development of 

 electrical power. If we dissolve a salt in water, if we 

 mix two fluids together, if we condense a gas, or convert 

 a fluid into vapour, electricity is disturbed, and may be 

 made manifest to our senses, f 



It has been shown that this power may be excited by 

 friction (machine electricity) and by chemical action 

 (voltaic electricity, galvanism) ; it now remains to speak 

 of the electricity developed by heat (thermo-electricity), 

 the electricity exhibited under nervous excitement by 



* " This capital discovery (chemical decomposition of electricity) 

 appears to have been made in the first instance by Messrs. 

 Nicholson and Carlisle, who observed the decomposition of water 

 so produced. It was speedily followed up by the still more impor- 

 tant one of Berzelius and Hisinger, who ascertained it as a general 

 law, that, in all the decompositions so effected, the acids and 

 oxygen become transferred and accumulated around the positive,, 

 and hydrogen, metals, and alkalies around the negative, pole of a 

 voltaic circuit ; being transferred in an invisible, and, as it were, 

 a latent or torpid state, by the action of the electric current, 

 through considerable spaces, and even through large quantities of 

 water or other liquids, again to reappear with all their properties 

 at their appropriate resting-places." Discourse on the Study of 

 Natural Philosophy : by Sir John Herschel, Bart, F.R.S. 



f Numerous beautiful illustrations of this fact will be found in 

 Becquerel's Traite Experimental de lElectricite et du Magnetisme 



P 



