360 Win. Loive: 



mented Chinaman with his head shorn and bare except his pig- 

 tail, clothed in his native garb, sauntering along flapping his 

 fan, evidently for the sake of comfort rather than from any fear of 

 his safety. He is sensitive to heat and not to light. Putting 

 this into scientific phraseology, his skin, in relation to the 

 demands of his environment, is diathermanic and non-actinic. 



Diathermancy is not a term often used in experimental physi- 

 olog}', vegetable or animal, for I have only met the word once, 

 and then in Ewarfs translation of Pfeffer, where it is stated that 

 the essential oil exuding from a plant interferes with the diather- 

 mancy of the atmosphere. Deschanel gives experimental evi- 

 dence on this subject. Diathermancy is the quality of trans- 

 parent bodies which permits the passage of radiant heat. This 

 quality varies with the nature of the substance, also with its 

 colour and its degree of opacity. This property of transparent 

 bodies can easily be demonstrated in the sunlight with a few 

 pieces of window glass, plain and coloured, a convex glass con- 

 denser, and some inflammable material, such as paper or 

 matches. 



Interpose these glasses between the condenser and the match, 

 and note the time it takes to ignite them. Still better, use 

 aniline dye, first with' a transparent dye and then adding a 

 mordant which causes a deposit on the glass, and makes it 

 more or less opaque. It then resembles the condition of the pig- 

 ment in the skin. This experiment distinctly shows that colour 

 interferes with the passage of radiant heat ; but with a deposit 

 thrown down by the mordant, the heat can be entirely excluded. 



The skin, which is more or less transparent in a white man, 

 as shown in the act of blushing, permits the transmission of 

 radiant heat as well as light ; but the black man is born to 

 blush unseen, for his pigment makes his skin opaque and pre- 

 vents the passage of these rays. 



The comparative value of pigment in obstructing the passage 

 of the sun's rays has been already referred to' in this paper by 

 the experiment of introducing an electric light into the mouth 

 and noting the illumination. In the white man the transparency 

 is most marked, less in the yellow and least in the black man. So 

 it is safe to assert of the Chinaman and his fan that his yellow 

 skin will control actinic radiations, while it permits the passage 

 of yellow light, and with it more or less radiant heat. 



