164 COUNT RUMFORD. 



internal evidence of its perfectly independent character, 

 while the extent and variety of Leslie's labours render 

 it practically impossible that they could have been de- 

 rived from anything that Rumford had previously done. 

 The two philosophers had no personal knowledge of 

 each other, and the credit to be awarded, where they 

 deal with the same subject, belongs, I think, equally 

 to both. 



Rumford's experimental work was far smaller in 

 quantity than that of Leslie, butin regard to theory he 

 must be conceded the highest place. In theory Leslie was 

 inconsistent and confused, while Rumford, judged by 

 the circumstances of his time, was in the main clear and 

 correct. The part played by the luminiferous ether in 

 the phenomena of light had been revived and enforced 

 by the powerful experiments of Dr. Thomas Young. 

 The undulatory hypothesis was therefore at hand, and 

 Rumford made ample use of it. He has written a paper 

 entitled ' Reflections on Heat,' in which he describes 

 the views regarding its nature that were prevalent in 

 his time. ' Some,' he says, ' regard it as a substance, 

 others as a vibratory motion of the particles of matter 

 of which a body is composed.' The heating of a body 

 is, on the one hypothesis, due to the accumulation 

 within it of caloric, while others hold the heating to be 

 due to the acceleration of the vibratory motion. ' On 

 the hypothesis of vibratory motion, a body which has 

 become cold is thought to have lost nothing except 

 motion ; on the other hypothesis, it is supposed to have 

 lost some material substance.' The loss of motion 

 Rumford clearly apprehends to be due to its communica- 

 tion to ' an eminently elastic fluid — an ether which fills 

 all space throughout the universe.' The theoretic notions 

 thus expressed are, in point of clearness and correct- 

 ness, far in advance of those entertained by Leslie. 



