136 Experimental Investigations 



above the temperature of the medium. Now, I found, 

 by observation, that the polished vessel A employed 

 39 minutes and 30 seconds to pass over that interval 

 of cooling, while the blackened vessel B employed only 

 22 minutes. These times are in the proportion of 

 10,000 to 5810. By one of my experiments, made last 

 year, I found that the times employed in passing through 

 the same interval of cooling in the open air by a clean 

 polished metallic vessel, and another of the same form 

 and capacity, but blackened without, were as 10,000 to 

 5654. 



Reflecting on the consequences which ought to result 

 from the radiations of bodies, on the supposition that 

 the temperatures of bodies are always changing by 

 means of these radiations, I was led to the following 

 conclusion : If the intensity of the action of the rays 

 which proceed from a body be universally as the 

 squares of the distances of bodies inversely, which is 

 extremely probable, a hot body exposed to cool in a 

 close place, or surrounded on all sides by walls, ought 

 to cool with the same celerity, or in the same time, 

 whatever may be the magnitude of this enclosure, pro- 

 vided the temperature of the sides or walls be at a 

 constant given temperature ; and the results of the 

 experiment here described, in which the hot body was en- 

 closed in a vessel of a few inches diameter, compared with 

 those of several experiments made last year, in which 

 the heated bodies were exposed to cool between the walls 

 of a large chamber, appear to confirm this conclusion. 



As to the effect produced by the air in cooling a 

 heated body exposed to cool in a close place filled with 

 that fluid, I have reason to believe that it is much less 

 considerable than has been supposed. 



