i 86 Reflections on Heat. 



bodies through these radiations, it is seen clearly why 

 the negro suffers less from the heat of the tropics, and 

 more from the cold of the polar regions, than the man 

 with a white skin. 



But when the negro is exposed to the action of calo- 

 rific rays to those of the sun, for instance must he 

 not be heated more than a white man ? It would be so, 

 without doubt, if Nature had not foreseen the danger 

 and provided means for warding off the evil. 



When the negro is exposed to the rays of the sun, an 

 oily matter appears immediately at the surface of his 

 skin, and causes it to shine ; the calorific rays which 

 fall upon it are reflected to a great extent, and he finds 

 himself but little heated. 



The sun sets, or the negro enters his hut ; the oil 

 which covers the surface of his body retires under his 

 skin, and he retains all the advantages which his colour 

 affords in aiding him to become cool. 



If a coating of oil on the skin serves to protect the 

 body from the too violent action of calorific rays, it 

 ought to serve also, without doubt, to protect it from 

 the too violent action of frigorific rays in very cold 

 countries, especially in winter, when the sun never rises. 

 And, indeed, do not the Laplanders besmear themselves 

 with oil ? 



But in the case of a question of so great interest, I 

 wished to omit nothing which might throw light upon it. 



The following experiment seemed to me to establish 

 beyond doubt the principal facts. 



Having covered two of my cylindrical vessels with 

 an animal substance, namely, with gold-beater's skin, I 

 painted one of them black with Indian ink, leaving the 

 other of its natural white color. Having filled both of 



