OF MOTIVE PO WER. 42 1 



heat developed, except by the friction in the fluid 

 itself. 



It was pointed out that the heat thus obtained 

 is not produced from a source,but is generated ; and 

 that what is called into existence by the work of 

 a man's arm cannot be matter. 



Davy's experiment, in which two pieces of ice 

 were melted by rubbing them together in an 

 atmosphere below the freezing point, was referred to 

 as the first completed experimental demonstration 

 of the immateriality of heat, although not so 

 simple a demonstration as Joule's ; and although 

 Davy himself gives only defective reasoning to 

 establish the true conclusion which he draws from 

 it. Rumford's inquiry concerning the " Source of 

 the Heat which is excited by Friction " was re- 

 ferred to as only wanting an easy additional 

 experiment a comparison of the thermal effects 

 of dissolving (in an acid for instance), or of burn- 

 ing, the powder obtained by rubbing together 

 solids, with the thermal effects obtained by dis- 

 solving or burning an equal weight of the same 

 substance or substances in one mass or in large 



