mean tempera, 

 ture more cor- 



ON HEAT. ()9 



It is evident from the remits of this experiment, that the Tne blackened 

 blackened body is conftantly cooled in let's time than the po- cook/more 

 Jithed body ; but it appears by the courfe of the thermometers, quickly than the 

 that the difference between the quick nefs of cooling of thefe ot er ' 

 two bodies varies, and that this difference was lefs confider- 

 able in proportion as the temperature of the bodies was more 

 elevated in comparifon to that of the medium in which they 

 were expofed to cool. 



In cooling from the 55th degree to the 50th above the tern- The difference 

 perature of the furrounding medium, the poltmed, body em- ^ loweft tem- 

 ployed 1 l m 6 s , and the blackened body employed 7 ni 50 s to peratures ; pro- 

 pafs through the fame interval. But from the 10th to the 15th b * h} ? becaufethe 



r ° 4 • thermo.neters 



degree above the temperature of the medium, the poliflied then mewed the 

 body employed 183 m 45% while the blackened body employed 

 only S5 ra 15 s ; but it is extremely probable that this difference redly, 

 between the proportion of the times employed in cooling the 

 two bodies at different temperatures, is only apparent, and 

 that it depends on the greater or lefs time required for the 

 thermometers in the veffels to arrive at the mean temperatures 

 of the maffes of water which furround them. ■ ** 



In order to compare the refults of this experiment with thofe From thefe ex- 

 I made laft year with metallic veffels poliflied and blackened, P erimen5s * ap- 



J ... . P ears *hat the 



and left to cool in the undifturbed air of a large chamber, it rate of cooling 



is neceffary to afcertain how much time the two bodies in J" the P r)llflie£ l 



queftion employed in cooling, from the 50th to the 40th de- with the other, 



gree of Fahrenheit above the temperature of the medium. ls nearl y the 



Now I found by obfervation, that the polilhed veffel A egj- mer ] y d eter . 



ployed 39 1 * 30 s to pafs over that interval of cooling, while the mined with bo- 



biackened velTel B employed only 22 m . Thefe times are in chamber **** 



the proportion of 10000 to 5810. "By one of my experiments 



made laft year, I found that the times employed in paffing 



through the fame interval of cooling in the o,pen air by a clean 



poliflied metallic veffel, and another of the fame form and 



Capacity, but blackened without, were as 10000 to 5654. 



Reflecting on the confequences which ought to remit from If the intenfitles 



the radiations of bddies, on the fuppofition thA trfc tempera- ^ ifvtfel ^f 



tures of bodies are a»vays changing by means of thefe radia- the fquaresof 



tions, I was led to the following conclufion : If the intenfity ^'^nces, 



° ■* bodies will cool 



of the aclion of the rays which proceed from a body, be uni-in the fame time 



verfally as the fquares of the diftances of bodies inverfely, ina " enclofure 

 J ^ . . . of the fame tern- 



3 which 



