Mr. Joule on the Calorific Effects of Magneto-Electricity. 34? 7 

 dinates of the extremity of the diameter, but x 12 (a 3 — V 2 ) 



+ ,/2 (6 2__ V *)+* /2 (c 2 -V 2 ) = 0, 



P ffl 2 n 2 



M ( a 2_v 2 ) + £> 2 -V 2 + c 2 -V 2 ~ ' 

 which is the equation at- which he arrives when we make / = 1 . 

 I remain, Gentlemen, yours, &c, 

 Trinity College, Dublin, John Wm. STUBBS. 



Jan. 31, 1843. 



XLIII. On the Calorific Effects of Magneto-Electricity, and 

 on the Mechanical Value of Heat. By J. P. Joule, Esq. 



[Continued from p. 276.] 

 Part I. On the Calorific Effects of Magneto- Electricity. 

 I" NOW proceeded to consider the heat evolved by voltaic 

 -*■ currents when they are counteracted or assisted by magnetic 

 induction. For this purpose it was only necessary to intro- 

 duce a battery into the magneto-electrical circuit: then by 

 turning the wheel in one direction I could oppose the voltaic 

 current ; or, by turning in the other direction, I could increase 

 the intensity of the voltaic- by the assistance of the magneto- 

 electricity. In the former case the apparatus possessed all the 

 properties of the electro-magnetic engine ; in the latter it pre- 

 sented the reverse, viz. the expenditure of mechanical power. 



No. 7. 



0) 



2 





Circuits 

 complete. 



Circuits 



broken. 



Circuits 

 complete. 



Circuits 



broken. 



Circuits 

 complete. 



Mean 



circuits 



complete. 



Mean 

 circuits 

 broken 



Revolu- 

 tions of 

 Electro- 

 Magnet 



per 

 minute. 



Deflec- 

 tions of 

 Galvano- 

 meter of 

 1 turn. 



}600 

 }600 

 J600 

 }60Q 

 J600 



600 

 600 



22 40 

 



20 45 

 



23 



Mean 

 Tempe- 

 rature 



of 

 Room. 



57-43 

 57-45 

 59-40 

 59-40 

 59-10 



Mean 

 Differ- 

 ence. 



1-03- 



0-41— 

 008- 

 0-51 + 

 1-29 + 



0-06+ 

 0-05+ 



Temperature of 

 Water. 



Before. After. 



55-62 

 57-08 

 58-65 

 60-00 



59-78 



57-18 

 57-00 

 60-00 

 59-83 

 61-00 



Loss or 

 Gain. 



1*56 gain 

 0-08 loss. 

 1*35 gain 

 0-17 loss. 

 1-22 gain. 



1-38 gain, 

 0-12 loss. 



C °RS d } m 23 ° 8 ' 



= 0-864 of current. 



1*50 gain 



