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

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



"I T is pretty generally, I believe, taken for granted that the 

 -*- electric forces which are put into play by the magneto- 

 electrical machine, possess, throughout the whole circuit, the 

 same calorific properties as currents arising from other sources. 

 And indeed when we consider heat not as a substance, but as 

 a state of vibration, there appears to be no reason why it 

 should not be induced by an action of a simply mechanical 

 character, such, for instance, as is presented in the revolution 

 of a coil of wire before the poles of a permanent magnet. At 

 the same time it must be admitted that hitherto no experi- 

 ments have been made decisive of this very interesting ques- 

 tion ; for all of them refer to a particular part of the circuit 

 only, leaving it a matter of doubt whether the heat observed 

 was generated, or merely transferred from the coils in which ■ 

 the magneto-electricity was induced, the coils themselves be- 

 coming cold. The latter view did not seem to me very im- 

 probable, considering the facts which I had already succeeded 

 in proving, viz. that the heat evolved by the voltaic battery is 

 definite-^ for the chemical changes taking place at the same 

 time; and that the heat rendered "latent" in the electrolysis 

 of water is at the expense of the heat which would otherwise 

 have been evolved in a free state by the circuit % — facts which, 

 among others, seem to prove that arrangement only, not gene* 

 ration of heat, takes place in the voltaic apparatus ; the simply 

 conducting parts of the circuit evolving that which was pre- 

 viously latent in the battery. And Peltier, by his discovery 

 that cold is produced by a current passing from bismuth to 

 antimony, had, I conceived, proved to a great extent that the 

 heat evolved by thermo-electricity is transferred § from the 

 heated solder, no heat being generated. I resolved therefore 

 to endeavour to clear up the uncertainty with respect to mag- 

 neto-electrical heat. In this attempt I have met with results 

 which will I hope be worthy the attention of the British As- 

 sociation. 



* Read before the Section of Mathematical and Physical Science of the 

 British Association, meeting at Cork on the 21st of August 1843; and now 

 communicated by the Author. 



f Phil. Mag. S. 3. vol. xix. p. 275. 



j Memoirs of the Literary and Philosophical Society of Manchester, 2nd 

 series, vol. vii. (part 2.) p. 97. 



§ The quantity of heat thus transferred is, I doubt not, proportional to 

 the square of the difference between the temperatures of the two solders. 

 I have attempted an experimental demonstration of this law, but owing to 

 the extreme minuteness of the quantities of heat in question, I have not 

 been able to arrive at any satisfactory result. 



