1883.] 071 Count Bumford, Originator of the Itoyal Institution. 449 



were not only talked about and executed before learned societies, but 

 that tliey were in part published prior to the appearance of Leslie's 

 celebrated work in 1804. Still the style of that work furnishes, I 

 think, 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 derived 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, but in regard to theory he must be conceded the 

 highest place. In theory Leslie was inconsistent and confused, while 

 Eumford, 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 able 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 

 matfirial substance." The loss of motion Rumford clearly apj^rehends 

 to be due to its communication 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 correctness, far 

 in advance of those entertained by Leslie. 



As already mentioned, the fact of water changing its density at a 

 temperature of 40° Fahr., powerfully affected the mind of Rumford. 

 On this subject he made many experiments ; and one of the minor 

 applications of the knowledge thus derived may be here noted. In 

 company with his friend Professor Pictet, of Geneva, he i:)aid a visit 

 to the Mer de Glace, and discovered in the ice a pit " perfectly cylin- 

 drical, about 7 inches in diameter, and more than 4 feet deep, quite 

 full of water." He was informed by his guides that these pits are 

 formed in summer, and gradually increase in depth during the warm 

 weather. How can these pits deepen? Rumford answers thus: — 

 The warm winds which in summer blow over the surface of the 

 column of ice-cold water, communicate some small degree of heat to 

 the fluid. The water at the surface being thus rendered specifically 

 heavier, sinks to the bottom of the pit, to which the heat thus carried 

 down is communicated, the depth of the pit being thereby increased. 

 "We have here a small specimen of Rumford"s penetration, but it is a 

 very interesting one. The sun's invisible rays, however, are probably 



