ON THE NATURE OF HEAT. iQ^ 



rlidance of four inches, to one of the balls of the thermofcope. 

 The bubble immediately moved towards the cold body, and 

 palFed through the fpace of one inch. A nearer approach of 

 the cold body produced a tlill farther motion itt the fame di- 

 rection. 



- Exp. 18, 19. Though this refult appeared to the Gount to Exp. 18, 19. 

 prove mdifputably that cold bodies emit riys capable of gene- J^^J^^^"^^^^-^^"^"^ 

 rating cold in warmer bodies, yet* from the importance of the neatk the ther- 



faa, he chofe to vary th€f fubftance prefented to the inftru- !"f«°P^! cp°l«^ 



1 /• r r I f-»- f It by radiation, 



ment, as well as to remove all fufpicion or the action of cold No current of air 



currents of air. He therefore laid the thermofcope on one could here 



fide, and placed underneath one of its balls a folid cake of ice, •' 



at the diftance of fix inches. The refult of this experiment 



was the fame as of the other, and the bubble was moved one 



inch in the tube. Ice-cold water produced the fame effe6t as 



ice itfelf. 



Exp, 20. Whether this effect of cold bodies be governed by lExp. 26. Metal 

 the fame laws as thofe obferved by varying the nature of the fmoke cooird"the 

 furface in heated bodies, or by any other, now remained toinftrumentmore, 

 be afcertained. It was before found that metal blackened J;^ "^^^^°"' 



than a clear lur- 



over a candle, did emit much more of calorific rays than the face at fame tern- 

 fame metal when naked. The fame experiment was now perature. 

 made with cold bodies. One of the cylinders had its end 

 blackened, and the other cylinder was left bright and naked, * 



Both were filled with ice and falt> and at the fame inftant 

 they were fufFered to a6t from equal diftanCes on the thermo- 

 fcope. The bubble moved towards the blackened body ; not 

 indeed fo much as when the bodies were heated in the fornner 

 experiments, becaufe the temperature was not here fo far 

 diftant from the common temperature of furrounding bodies 

 as in that experiment ; but on feveral repetitions of the ex- * 



perinient with thefe cold bodies, the effe6l was conllantly the 

 fame. It was found that the precipitation of ice out of the Ice radiates more 

 furrounding air tended fpeedily to raife the temperature, an^^ '^"a" " etal. 

 alfo that the clean furface, vthen covered with ice, had a 

 greater frigorific efie€l than when the metal was naked i 



Exp. 21. The radiation of heat from animal fubftances ap- Exp. ai. GoM- 

 pearing, from fome fafts, to be confiderable, a piece of gold- ^f^'^^'"'^ ^|" ^*' 



• " . . . ' '^ diates 25 times 



beater's Ikin was applied wet to one of the vefiels, and re- more than meral, 



mained firmly adherent when dry. This, when filled with hot Hot water mthe 

 water at 180^, and prefented to the thermofcope in oppofition 



02 to 



