107 



VII. — Some Remarks on Heat, and the Constitution of 

 Elastic Fluids. By J. P. Joule, F.R.S., &c. 



Read October 3, 1848. 



In a paper, " On the heat evolved during the electrolysis of 

 water," published in the 7 th volume of the Memoirs of 

 this Society, I stated that the magneto-electrical machine 

 enabled us to convert mechanical power into heat; and that 

 I had little doubt that, by interposing an electro-magnetic 

 engine in the circuit of a voltaic battery, a diminution of 

 the quantity of heat evolved, per equivalent of chemical re- 

 action, would be observed, and that this diminution would 

 be proportional to the mechanical power obtained. 



The results of experiments in proof of the above propo- 

 sition were communicated to the British Association for the 

 Advancement of Science, in 1843.* They showed that 

 whenever a current of electricity was generated by a mag- 

 neto-electrical machine, the quantity of heat evolved by 

 that current had a constant relation to the power required to 

 turn the machine ; and, on the other hand, that whenever 

 an engine was worked by a voltaic battery, the power deve- 

 loped was at the expense of the calorific power of the bat- 

 tery for a given consumption of zinc, the mechanical effect 

 produced having a fixed relation to the heat lost in the 

 voltaic circuit. 



The obvious conclusion from these experiments was, 

 that heat and mechanical power were convertible into one 

 another; and it became therefore evident, that heat is 

 * Philosophical Magazine, vol. xxiii. pp. 263, 347, 435. 



