1£)S ON THE NATURE OF HEAT. 



tween et^ and 65^. The covered inftrument acquired heat 

 the moft rapidly ; for in a quarter of an hour both flood at 

 5]l°, and at the end of four hours the naked inftrument 

 fliewed the temperature 61^^, and the covered 63^^ : whence 

 the Count obferves, that thofe fubftances which part with 

 heat the moft readily, have alfo the greateft facility to ac- 

 quire it. 

 Rays received as [Iq th^,-, proceeds to realbn on the probability that the tern- 

 emitted alter peratures of bodies pnay be changed, not only by the rays 

 the heals of bo- they emit, but by thofe they receive from other bodies ; and 

 '"* as the cooling of hot bodies is fo much accelerated by covering 



their furfaces with fnbftances which affeft the radiation or ab- 

 Radiat'on does forption, he thinks it hij^hly probable that the air is but little 

 ' «ot heat the air. ^^^^^^ ^^ ^^ .^^ temperature, by thefe rays which pafs 

 through it ; and he contemplates the eftablifliment of this fup- 

 pofition, fis promifing to explain various interefting pheno- 

 St?ady tcrypera-nomena; particularly that of the fteady temperature of living 

 turc of animals, ^^i^^ij,^ notwithftanding the great quantity of heat generated 

 in their lungs, and the dilferent temperatures of the fluid 

 which furroiinds them, 

 miy be affected for it is evident, the greater power an aninial may pofTeQ 

 y la lauon. ^^ throwing off heat by radiation, independently of the eft'eft 

 of the contad of the furrounding air, the lefs will his tem- 

 perature be affedled by the changes in that fluid, or ihe op- J 

 Inftancc in ne- preffive heat of the climate. The probability that negroes 1 

 ^^^^' and people of colour, who fupport the heats of tropical cli- 



mates much better than white people, ofters itfelf in this 

 place as the confequence of their colour; a quality which not 

 only enables them to throw off heat, but even, as the Count 

 much fufpe^ts to abforb frigorific'rays from fuch bodies as 

 may emit them. 

 Exp. 27. Black £jp^ 27. When the flat epds of both the horizontal cylin- 

 marmembla^nT dricat vefTels were covered with gold-beater's fkin, and one 

 increafes radia- of them painted black upon the covering with Indian ink, 

 E°"*ffi ^^^^^ ^^^' ^^ indicated by the thermofcope, emitted more 



calorific rays from the included hot water than the other veflel 

 V did. 



and alfo reccp- £jp, 28. When the fame two velfels filled with boiling-hot 



???• water, were fet to cool, the blackened veffel cooled through 



the ftandard interval of ten degrees in 23f minutes, while 



the other, which was not blackened, employed 28 minutes. 



4f The 



