IDENTICAL CHANGES 



the water actually passes from above the dam to 

 below the dam. And yet neither the pond above 

 nor the brook below need necessarily contain less 

 water or more, when the wheel is running, than 

 when it is not running. For there is really more 

 to the mill, and the Waterpower, than water wheel 

 and mill pond and brook below ; sun and moon and 

 stars work to replenish one, and drain the other. 



And so every manifestation or transmission of 

 electricity is not confined to the two dissimilar 

 bodies, between whom it is manifested to us as 

 electricity; but on both ends electricity and every 

 other manifestation of force is connected with the 

 whole Universe. (Prop. VIII, B. 3.) 

 The question of the nature of electricity then 

 resolves itself into the question, how does elec- 

 tricity differ from other forces ? How can a stream 

 of void matter encountering the atoms or particles 

 of substances produce the different phenomena of 

 electricity ? 



When electricity is generated or separated by 

 friction, the mechanical work performed on the 

 two rubbing surfaces must then be the direct cause 

 of electricity. And the friction is possible only 

 because of the inequalities of the surfaces, and 

 these must engage each other. And always this 

 friction will produce heat, and always a part of 

 the surfaces will be torn loose; there is nothing, 

 however hard, but will be worn by friction. Evi- 

 dently, then, in all friction there is a breaking up 

 of atoms as well as of organizations of higher 

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