8 THE BEGINNINGS OF LIFE. 



seen that a very considerable quantity of heat may be 

 excited by the friction of two metallic surfaces, and 

 given off in a constant stream or flux in all directions^ 

 without interruption or intermission, and without any 

 signs of diminution or exhaustion. In reasoning on this 

 subject we must not forget that most remarkable circum- 

 stance^ that the source of the heat generated by friction 

 in these experiments appeared evidently to be in- 

 exhaustible. It is hardly necessary to add, that any- 

 thing which any insulated body or system of bodies can 

 continue to furnish -without limitation cannot possibly 

 be a material substance , and it appeals to me to be 

 extremely difficult, if not quite impossible, to form any 

 distinct idea of anything capable of being excited and 

 communicated in those experiments, except it be 

 MOTION/ In 1812 also, Sir Humphrey Davy in his first 

 Memoir J brought forward most valuable scientific evi- 

 dence to show that no such thing as c caloric' existed, 

 that heat was not an elastic fluid, and that the Maws 

 of the communication of heat are precisely the same as 

 those of the communication of motion.' One of his 

 experiments was of the most conclusive nature. c He 

 succeeded in melting two pieces of ice by rubbing 

 them together in vacuo, at the same time preventing 

 the access of external heat. The water produced in 

 this experiment has a much higher relative heat than 

 the ice; hence the potential heat which caused the ice 

 to melt must have been obtained by the conversion of 



1 Sir Humphrey Davy's Works, vol. ii. 



