Masterpieces of Science 



was always opposed in direction to its generator, 

 while that developed on the rupture of the cir- 

 cuit coincided in direction with the inducing 

 current. It appeared as if the current on its 

 first rush through the primary wire sought a pur- 

 chase in the secondary one, and, by a kind of 

 kick, impelled backward through the latter an 

 electric wave, which subsided as soon as the 

 primary current was fully established. 



Faraday, for a time, believed that the second- 

 ary wire, though quiescent when the primary 

 current had been once established, was not in its 

 natural condition, its return to that condition 

 being declared by the current observed at break- 

 ing the circuit. He called this hypothetical 

 state of the wire the electrotonic state: he after- 

 wards abandoned this hypothesis, but seemed to 

 return to it in after life. The term electro-tonic 

 is also preserved by Professor Du Bois Reymond 

 to express a certain electric condition of the 

 nerves, and Professor Clerk Maxwell has ably 

 denned and illustrated the hypothesis in the 

 Tenth Volume of the ' ' Transactions of the Cam- 

 bridge Philosophical Society. " 



The mere approach of a wire forming a closed 

 curve to a second wire through which a voltaic 

 current flowed was then shown by Faraday to be 

 sufficient to arouse in the neutral wire an induced 

 current, opposed in direction to the inducing 

 current; the withdrawal of the wire also gener- 

 ated a current having the same direction as the 

 inducing current; those currents existed only 

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