by Induction-currents. 257 



There is thus perfect proportionality between the quantities 

 of heat disengaged by the induced currents, and the deflection 

 which these produce in the dynamometer. The same result was 

 obtained when the duration of the induced currents was altered, 

 the intensity of the inducing current being kept constant. With 

 this view a second special spring was fixed to the toothed wheel, 

 so as to close another circuit at the moment at which the bat- 

 tery was cut off by the other spring at the opening of the cur- 

 rent. The extra current, produced in the induction-coil on 

 opening the battery, had time to act, and had the effect of 

 making the diminution of the inducing current on opening take 

 place far more slowly than in case there was no secondary cir- 

 cuit. This arrangement produced no change in the induction- 

 current produced by closing the circuit. In order, lastly, to vary 

 the duration of the induced current, an extra induction-coil 

 was introduced at first into the inducing current, in which 

 was a soft iron cylinder. The effect of this latter on the indu- 

 cing current was to diminish its increase on closing. This induc- 

 tion-coil was so distant from that in which was produced the 

 induced current to be measured, that no action could take 

 place between them. In order that the quantity of heat pro- 

 duced should not be too small, the secondary circuit was removed 

 for this case. In the three modes of working, the intensity of 

 the inducing current was virtually constant. 



Without accessory circuit and without electro- magnet, 



Dynamometer. Heat. 



71-75 1100 



With accessory circuit and without electro-magnet, 



30-83 48-0 



Without accessory circuit but with electro-magnet, 



60-01 88-25 



If we calculate the means by the equation x = 1*512 y, we get 



Calculated. 



Observed. 



Difference. 



#=46-6 



48-0 



-1-4 



90-7 



88-25 



+ 2-45 



108-5 



1 10-0 



-]-5 



We see that in this case also the quantities of heat developed 

 by the induced current are proportional to the deflection of the 

 dynamometer. This result proves that the heat disengaged in 

 each moment by the induced current is proportional to the 

 square of the intensity of this current in the same moment, or, 

 what is the same thing, that the heat developed by the entire 



