Dr Stark on the Influence of' Colour on Heat. 79 



with orange-red in eighteen minutes; and that coated with white 

 in nineteen minutes. The temperature of the air in the room 

 was 50°. 



The demonstration of the influence of colour on the absorp- 

 tion and radiation of caloric, may tend to open up new views of 

 the economy of nature, and perhaps suggest useful improve- 

 ments in the management and adaptation of heat. Dr Frank- 

 lin *, who never lost sight of practical utility in his scientific in- 

 vestigations, from the result of his experiments with coloured 

 cloths on the absorption of heat, drew the conclusion, " that 

 black clothes are not so fit to wear in a hot sunny climate or 

 season as white ones ; that white hats should be generally worn 

 in summer ; and that garden-walls for fruit-trees would absorb 

 more heat from being blackened.*" 



Count Rumford and Sir Everard Home, on the contrary, 

 come to a conclusion entirely the reverse of this. The Count 

 asserts, that if he were called upon to live in a very warm cli- 

 mate, he would blacken his skin, or wear a black shirt ; and, in 

 point of fact, in the decline of his life, he astonished the Pa- 

 risians by appearing in the streets in winter entirely dressed in 

 white. Sir Everard, from direct experiments on himself and 

 on a negro's skin, lays it down as evident, that the power of the 

 sun's rays to scorch the skins of animals is destroyed when ap- 

 plied to a dark surface, although the absolute heat in conse- 

 quence of the absorption of rays is greater -f-. Sir Humphry 

 Davy explained this fact, by saying, that " the radiant heat in 

 the sun's rays is converted into sensible heat." With all de- 

 ference to the opinion of this great man, it by no means explains 

 why the surface of the skin was kept comparatively cool. From 

 the result of my experiments, it is evident, that if a black sur- 

 face absorbs caloric in greatest quantity, it also gives it out in 

 the same proportion ; and thus a circulation of heat is, as it 

 were, established, calculated to promote the insensible perspira- 

 tion, and to keep the body cool. This view is confirmed by the 

 observed fact of the stronger odour exhaled by the bodies of 

 black people. 



The different shades of colour by which races of men inha- 

 biting different climates are distinguished, equally possess, there 



« Dr Franklin's Works, vol. ii. p. 109. I.ond. 1806. 

 t Phil. Trans. 1821, p. 6. 



