Reflections on Heat. 181 



cool or become warm more slowly than bodies imper- 

 fectly transparent and unpolished. 



I will now detail the results of a series of experiments 

 made with a design of throwing light on this point, so 

 important in the science of heat. 



I had made two cylindrical vessels, four inches in 

 diameter and four inches high, of thin sheet brass, well 

 polished on the outside. Having blackened one of 

 them over the flame of a candle, I filled them both with 

 boiling water, and left them at the same time to cool in 

 the air of a large quiet room. The one which was black- 

 ened cooled almost twice as fast as the one whose metal- 

 lic surface remained bright and clean. When the two 

 vessels had become of the same temperature as that of 

 the room in which they were situated, they were re- 

 moved into a room warmed by a stove, and I found 

 that the blackened vessel was heated twice as quickly as 

 the other. 



The blackened vessel was cleaned and covered with a 

 single covering of fine linen, fitting closely to the 

 body of the instrument. Repeating the experiments 

 with the two vessels, that which was exposed naked to 

 the cold air took up 45 minutes in cooling through an 

 interval of 10 degrees on Fahrenheit's scale, that is, from 

 the 5oth to the 4Oth degree above the temperature of 

 the room ; the other vessel, covered with a coat of fine 

 linen, took up only 29 minutes in cooling through the 

 same interval. 



When the two vessels had become of the same tem- 

 perature, they were removed into a warm room, and I 

 found that the vessel which was clothed with linen 

 acquired heat faster than the one whose surface was 

 naked. 



