of Magneto-Electricity. 2 75 



Were A x x 1 B, &c. perfect rectangles, it is obvious that the 

 heat due to a given deflection of the galvanometer would be 



Fig. 5. 



K 



| of that due to the same deflection and an uniform current, 

 and column 8 of the table would contain exact theoretical 

 results. But as this is not precisely the case, the numbers in 

 that column are somewhat under the truth. 



Bearing this in mind in the comparison of columns 5 

 and 8, it will, I think, be admitted that the experiments 

 afford decisive evidence that the heat evolved by the coil of 

 the magneto- electrical machine is governed by the same laws 

 as those which regulate the heat evolved by the voltaic ap- 

 paratus ; and exists also in the same quantity under compa- 

 rable circumstances. 



Although very little doubt could exist with regard to the 

 heating power of magneto-electricity beyond the coil, I thought 

 it would nevertheless be well to follow it there, in order to 

 render the investigation more complete : I am not aware of 

 any previous experiments of the kind. 



I immersed five or six yards of insulated copper wire of ^ n th 

 of an inch diameter in a flask holding about 12 oz. of water. 

 The terminals of the wire were connected on one hand with 

 the galvanometer of five turns and on the other with the com- 

 mutator, and the circuit was completed by a wire extending 

 from the galvanometer to the other compartment of the com- 

 mutator. The revolving electro-magnet was now subjected 

 to the inductive influence of the large electro-magnet excited 

 by ten cells in a series of five double pairs, and rotated at the 

 rate of 600 revolutions per minute during a quarter of an hour. 

 The needle of the galvanometer, which remained as usual 

 pretty steady, indicated a mean deflection of 32° 40' = 0*31 

 of current: and the heat evolved was found to be 0°*46, after 

 the correction on account of the temperature of the surround- 

 ing air had been applied. Another experiment gave me 0°*4 

 for 0-286. The mean of the two is 0°*43 for 0*298 current 

 magneto-electricity. 



By passing a voltaic current from four cells in series through 

 the wire, I found that 2*02 of current flowing uniformly evolved 

 12 0, in a quarter of an hour. Reducing this to 0*298 of cur- 



T2 



