474 Life of Count Rumford. 



sage thermometer, the tube of which was suspended in 

 a cylindrical glass tube terminating in a glass globe 

 around the bulb of the thermometer. The space be- 

 tween the inner surface of the globe and the outer sur- 

 face of the bulb was then filled successively by various 

 substances whose conducting powers he wished to test. 

 The instrument, when filled, was heated in boiling 

 water, and afterwards plunged into a freezing mixture 

 of pounded ice and water, or vice versa. The times of 

 cooling or heating were carefully observed by the scale 

 of the thermometer and a watch which beat half-seconds. 

 He subjected to this test raw silk, sheep's wool, cotton- 

 wool, linen lint, the fur of the beaver, the fur of a white 

 Russian hare, and eider-down. The relative warmth 

 of these substances proved to be as follows : hare's 

 fur and eider-down were the warmest ; then came in 

 order beaver's fur, raw silk, sheep's wool, cotton-wool, 

 and lastly lint. Rectifying his tests by others which 

 allowed for the respective density and the internal struc- 

 ture of these various substances, he proceeded with his 

 experiments on other solids. In revising the matter of 

 this Essay he was enabled to correct his own error, when 

 he first wrote the paper, as to the conducting power of 

 air. 



The Count's ninth Essay is <c An Inquiry concern- 

 ing the Source of the Heat which is excited by Fric- 

 tion." The substance of it was read before the Royal 

 Society, January 25, 1798. It was after he had been 

 summoned back to Munich in 1796, and in the two 

 years following, while war, with the dread of new cam- 

 paigns and preparation for them, were engrossing the 

 anxieties of every European sovereign and people, that 

 Rumford made the experiments which he here described. 



