184 Reflections on Heat. 



as by two or by a greater number, it seems very difficult 

 to reconcile the results of these experiments with the 

 supposition that a film of air attached to the surfaces of 

 all the vessels, made as they were of different metals, 

 was the cause of their cooling all equally slowly. 



When I repeated the experiment with a vessel of glass, 

 and with one of tinned iron of the same form and di- 

 mensions, I found that the glass vessel cooled much 

 more rapidly in the air than the one made of tinned 

 iron, although its walls were six times as thick as those 

 of the latter. In water the vessel of tinned iron cooled 

 most rapidly. 



The results of all these experiments, and of a great 

 number of others which it would take too long to de- 

 tail here, convinced me that the ease with which a body 

 is heated or cooled depends very much on the nature 

 of the surface of that body, these operations going on 

 more slowly and with more difficulty as the surface of 

 the body is more capable of reflecting the rays which 

 fall upon it; I was therefore impatient to submit the 

 theory of heat which I had adopted to the most search- 

 ing of tests, by employing it to explain some of the 

 grand and interesting phenomena of nature. 



Close to us there occurs a most interesting phenome- 

 non, and one which, assuredly, is calculated to excite 

 our curiosity. 



The people who inhabit hot countries are black, 

 while those who dwell in cold climates are white. 



What advantages do the negroes derive from their 

 colour which makes them better fitted than the whites 

 for supporting without inconvenience the excessive heats 

 of their scorching climate ? 



In all climates a large amount of heat is necessarily 



