A HISTORY OF SCIENCE 



sider it at length. It bears the title, " On the Calorific 

 Effects of Magneto - Electricity, and the Mechanical 

 Value of Heat." The full text, as published in the 

 Report of the British Association, is as follows : 



"Although it has been long known that fine plati- 

 num wire can be ignited by magneto-electricity, it 

 still remained a matter of doubt whether heat was 

 evolved by the coils in which the magneto-electricity 

 was generated ; and it seemed indeed not unreasonable 

 to suppose that cold was produced there in order to 

 make up for the heat evolved by the other part of the 

 circuit. The author therefore has endeavored to clear 

 up this uncertainty by experiment. His apparatus 

 consisted of a small compound electro - magnet, im- 

 mersed in water, revolving between the poles of a pow- 

 erful stationary magnet. The magneto-electricity de- 

 veloped in the coils of the revolving electro-magnet 

 was measured by an accurate galvanometer; and the 

 temperature of the water was taken before and after 

 each experiment by a very delicate thermometer. 

 The influence of the temperature of the surrounding 

 atmospheric air was guarded against by covering the 

 revolving tube with flannel, etc., and by the adoption 

 of a system of interpolation. By an extensive series 

 of experiments with the above apparatus the author 

 succeeded in proving that heat is evolved by the coils 

 of the magneto-electrical machine, as well as by any 

 other part of the circuit, in proportion to the resist- 

 ance to conduction of the wire and the square of the 

 current; the magneto having, under comparable cir- 

 cumstances, the same calorific power as the voltaic 

 electricity. 



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