258 M. E. Edkmd on the Heat disengaged 



induced current is proportional to §i 2 dt, taking the commence- 

 ment and end of the induced current as limits of the integral. 



III. 



An induced current naturally exerts an action on the prin- 

 cipal inducing current. Hence are formed in the latter induced 

 currents of a higher order, which, according to their direc- 

 tion, add themselves to or subtract from the principal current. 

 Thus the disengagement of heat in the inducing current while 

 induction is taking place may be different from that which takes 

 place during the same length of time but when no induction 

 takes place. Hence, if we are to measure the heat disengaged 

 by induction, we must not only measure the quantity of heat 

 which the induction- current developes in a given time, but also 

 that which the inducing current developes in the same time, 

 first without induction, and then while it is inducing. The 

 experiments were arranged in the following manner with a view 

 to this object. 



The toothed wheel was turned with a constant velocity, making 

 an entire turn in a second; and on the stroke of the fortieth second 

 the deflection in the galvanometer produced by the thermoelec- 

 tric current was observed. To determine the disengagement 

 of heat due to the induced current, the platinum wire to which 

 the thermoelectric pile was attached was interposed in the in- 

 duced current; it was then removed and placed in the prin- 

 cipal inducing current. After that, the disengagement of heat 

 was examined anew in the platinum wire, first when the induced 

 circuit was open and when no induction took place, and then 

 when it was closed, that is, while under the inducing action of 

 the principal circuit. Thus a measure of the heat developed by 

 the induction-current in the platinum wire during twenty 

 seconds, was obtained ; and the same method gave a measure of 

 the development of heat due to the principal current in the same 

 platinum wire and in the same time, at first without induc- 

 tion, and then during the induction exerted by the principal 

 current. 



We shall not mention here the experimental difficulties which 

 the author had to overcome, nor the proofs he adduces in sup- 

 port of the exactitude of the method he followed, and shall only 

 cite the final results. 



In the first series of observations the production of heat due 

 to the induced current in the platinum wire, and received by 

 the thermoelectric pile, gave a deflection in the galvanometer of 

 28- 75. The heat developed by the principal current in the 

 same wire, but without induction, gave 188-84, and when the 



