and the Mode of its Communication. 57 



throw a new light on the subject which had so long 

 engaged my attention, and to present a wide and very 

 interesting field for farther investigation. 



I could now account, in a manner somewhat more 

 satisfactory, for those appearances in the foregoing ex- 

 periments which were so difficult to explain, for the 

 acceleration of the passage of the heat out of my instru- 

 ments, which resulted from covering them with linen, 

 varnish, &c. ; and I. immediately set about making a 

 variety of new experiments, from which I conceived I 

 should acquire a farther insight into those invisible 

 mechanical operations which take place when bodies are 

 heated and cooled. 



Finding so great a difference in the quantities of calo- 

 rific rays which are thrown off by the polished surface 

 of a metal when exposed naked to the cold air and 

 when blackened, I now proceeded to make experiments to 

 ascertain whether or not all those substances with which 

 the sides of my cylindrical vessels had been covered, and 

 which had been found to expedite the cooling of those 

 instruments, would also facilitate the emission of calo- 

 rific rays from the surfaces of the instruments I pre- 

 sented to the balls of my thermoscope ; and I found 

 this to be the case in fact. 



As the results of all these experiments proved, in the 

 most decisive manner, that all the substances which, 

 when applied to the metallic surfaces of my large cylin- 

 drical vessels, had expedited their cooling, facilitated and 

 expedited the emission of calorific rays, I could no 

 longer entertain any doubts respecting the agency of 

 radiation in the heating and cooling of bodies. Many 

 important points, however, still remained to be investi- 

 gated before distinct and satisfactory ideas could be 



