Reflections on Heat. 185 



excited in the lungs by the act of breathing ; and when 

 man is placed in a situation where the air and all objects 

 about him are almost as warm as his blood, the sur- 

 face of his body ought to be of such a character as to 

 be readily cooled ; else the rays, very slightly cooling in 

 their action, which reach him from the surrounding ob- 

 jects, would not suffice to free him from the heat gener- 

 ated continually in his lungs, and he would soon find 

 himself oppressed and overcome by the accumulation of 

 this heat. 



In a cold country, where the cooling of the surface 

 of a body by the cold objects which surround it is more 

 than sufficient to counterbalance the heat continually 

 produced by respiration, the body can be protected from 

 this excessive cooling action by clothing ; but we know 

 of no sort of clothing fitted to promote sufficiently the 

 cooling of the human body in a very hot climate. 



What has Nature done, to supply this want ? She 

 has given to the inhabitants of hot countries a black 

 skin ; this colour gives to the negro such facility for 

 becoming cool that he feels perfectly comfortable in a 

 situation where a white man would be overcome by 

 the heat. But, in return, the negro shivers with cold 

 in a climate which the white man finds perfectly agree- 

 able. 



Every one knows that a black surface reflects fewer 

 rays of light than a white surface ; and the results of 

 all the experiments performed by myself and by others 

 seem to show that those surfaces which are of such a 

 character as to reflect light also reflect the calorific or 

 frigorific rays which all bodies send continually from 

 their surfaces ; and if the temperature of a body is 

 changed in consequence of the action of surrounding 



