Chap. 2.] Conducing Power of different Bodies. 103 



compared with that of the vacuum, is nearly as 1,000 

 to 605. 



A moid air conducts the matter of fire with much 

 greater rapidity than a dry air ; but the rarity or den- 

 fity of the air appears to have little effect upon its 

 conducting power. 



The proportion of the conducting power in the 

 different fubftances which were the objects of his ex- 

 periments, is as follows : 



Mercury --.------- 1,000 



Moift air--------- 330 



Water ------- - 313 



Common air, the barom. at 27 inc s 9 lines - 8o T Vy 

 Rarified air, - - barom. at 6 - 1 1 lines - 8o T \V 

 The fame, - - barom. at i - 2 - - 78 

 The Torricellian vacuum - - - - -55* 



From the different effects of bodies upon our feel- 

 ings, according to their conducting powers, arifes the 

 distinction which philofopbers have made between 

 abfolute and fenfible heat. It will be remembered, that 

 the fenfation of hot is the entrance of caloric or heat 

 into our bodies, and the fenfation of cold is its depar- 

 ture from them f . Thefe circumftances render the 

 fenfes of animals a very inaccurate meafure of heat ; 

 efpecially if we confider further, that much will alfo 

 depend upon the ftate of the organ of feeling at the 

 particular time. Water, at the temperature of 62, 

 appears cold to a warm hand i but it will appear warm 



* Sir Benj. Thompfon's (now Count Rumford) Experiments 

 on Heat. "Phil. Tranf. vol. Ixxvi. 



f The fudden and unexpected application of an extremely cold 

 fubftanee to the human body, produces a fenfation very fimilar to 

 that of a hot on. 



H 4 . to 



