Biographical Memoir of Count Rumford. 37 



M. de Fontenelle said of Dodard, who, in rigorously observing the 

 fasts prescribed by the Church, made accurate experiments on the 

 changes which his abstinence produced in him, that he was the first 

 who had taken the same path for getting to heaven and the academy. 

 Count Rumford may be associated with him, if, as may be believed, 

 the services rendered to men lead to heaven as surely as the practi- 

 ces of devotion. This 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 light, as well as the laws of their propagation ; 

 and in this, what interested him was, to know how to feed, clothe, 

 warm, and light 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 dissipation. Count Rumford enveloped thermometers 

 raised to a higher temperature than the air with various substances, 

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

 um. He arrived at this general result, that the principal retainer of 

 heat is the air between the fibres of substances, and that these sub- 

 stances 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 agitated, and 

 did not strike vertically the bottom of the vessel. He also observed 

 that the vapor 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 inquiry. Casting his eyes on the col- 

 ored liquor of a thermometer, which was cooling in the sun, he per- 

 ceived in it a constant motion, which continued until the thermome- 

 ter had fallen to the surrounding temperature. Some powders which 

 he diffused in liquids of the same specific gravity, were also agitated 

 whenever the temperature of the liquid changed, a circumstance 

 which announced currents in the liquid itself. Count Rumford came 

 to think that it was precisely by this transportation 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 



