Biographical Memoir of Count Runifbrd. SI 9 



much is certain, however, that it was to his benevolent schemes 

 that he was indebted for the glory which his name will possess 

 in the history of physics. 



Every one knows that the object of his finest experiments was 

 the nature of heat and hght, as well as the laws of their propa- 

 gation ; and in this, what interested him was, to know how to 

 feed, clothe, warm, and Kght with economy, a great assemblage 

 of men. He first engaged in comparing the heat of different 

 kinds of clothes. This, as is well known, is not an absolute 

 heat, and we only mean by it the property of retaining that 

 which is generated by our bodies, and of preventing its dissipa- 

 tion. Count Rumford enveloped thermometers raised to a 

 higher temperature than the air Avith various substances, and 

 observed the time they took in returning to a state of equili- 

 brium. He arrived at this general result, that the principal re- 

 tainer of heat is the air between the fibres of substances, and 

 that these substances furnish clothes so much the warmer, the 

 more they retain the air heated by the body. It is thus, and it 

 will not fail to be remarked, that Nature has taken care to clothe 

 the animals of cold countries. 



Passing then to the examination of the most effectual means 

 of economising fuel, he saw in his experiments that flame in the 

 open air gave little heat, especially when it was not rapidly agi- 

 tated, and did not strike vertically the bottom of the vessel. 

 He also observed that the vapour of water conduced very little 

 to heat when it was not in motion. Chance gave him the key 

 of these phenomena, and opened up to him a new path of in- 

 quiry. Casting his eyes on the coloured liquor of a thermo- 

 meter, which was cooling in the sun, he perceived in it a con- 

 stant motion, which continued until the thermometer had fallen 

 to the surrounding temperature. Some powders which he dif- 

 fused in liquids of the same specific gravity, were also agitated 

 whenever the temperature of the liquid changed, a circumstance 

 which announced continual currents in the liquid itself. Count 

 Rumford came to think that it was precisely by this transporta- 

 tion of molecules that the heat was distributed in the liquids, 

 which by themselves would have allowed very little caloric to 

 pass. Thus, when the heating commences below, the warm 

 molecules, becoming lighter, ascend, and the cold molecules are 



