concerning Heat. 135 



The foregoing table exhibits the depression of the 

 thermometers during eight hours employed in the ex- 

 periment. 



It is evident, from the results of this experiment, 

 that the blackened body is constantly cooled in less 

 time than the polished body ; but it appears, by the 

 course of the thermometers, that the difference between 

 the quickness of cooling of these two bodies varies, 

 and that this difference was less considerable in propor- 

 tion as the temperature of the bodies was more elevated 

 in comparison to that of the medium in which they were 

 exposed to cool. 



In cooling from the 55th degree to the 5Oth above 

 the temperature of the surrounding medium, the pol- 

 ished body employed 1 1 minutes and 6 seconds, and 

 the blackened body employed 7 minutes and 50 sec- 

 onds to pass through the same interval. But from the 

 roth to the 1 5th degree above the temperature of the 

 medium, the polished body employed 183 minutes and 

 45 seconds, while the blackened body employed only 85 

 minutes and 15 seconds ; but it is extremely probable 

 that this difference between the proportion of the times 

 employed in cooling the two bodies at different tem- 

 peratures is only apparent, and that it depends on the 

 greater or less time required for the thermometers in 

 the vessels to arrive at the mean temperatures of the 

 masses of water which surround them. 



In order to compare the results of this experiment 

 with those I made last year with metallic vessels, pol- 

 ished and blackened, and left to cool in the undisturbed 

 air of a large chamber, it is necessary to ascertain how 

 much time the two bodies in question employed in cool- 

 ing from the 5Oth to the 4Oth degree of Fahrenheit 



