124 NATURE AND LIFE. 



trie light, may occasion it. The violet and the ultra-violet 

 parts of the sunbeam seem to be the cause of this action, 

 for screens of uranium glass, that absorb these portions, 

 protect the eyes of experimenters occupied in studying the 

 electric light. This disorder is a true inflammation. 



The action of light on the human skin is manifest. It 

 browns and tans the teguments, by stimulating the produc- 

 tion of the coloring-matters they contain. The parts of 

 the body usually bare, as the skin of the face and hands, 

 are darker than others. In the same region, country-people 

 are more tanned than town residents. In latitudes not far 

 apart, the inhabitants of the same country vary in com- 

 plexion in a measure perceptibly related to the intensity 

 of solar light. In Europe three varieties of color in the 

 skin are distinctly marked : oh' ve-brown, with black hair, 

 beard, and eyes; chestnut, with tawny beard and bluish 

 eyes; blond, with fair, light beard and sky-blue eyes. 

 White skins show more readily alterations occasioned by 

 light and heat ; but, though less striking, facts of variation 

 in color are observable in others. The Scythe- Arabic race 

 has but half its representatives in Europe and Central Asia, 

 while the remainder passes down to the Indian Ocean, con- 

 tinuing to show the gradual rising heat of climate by deep- 

 ening brown complexions. The Himalayan Hindoos are 

 almost white ; those of the Deccan, of Coromandel, Mala- 

 bar, and Ceylon, are darker than some negro tribes. The 

 Arabs, olive and almost fair in Armenia and Syria, are 

 deep-brown in Yemen and Muscat. The Egyptians, as we 

 go from the mouths of the Nile up-stream toward its source, 

 present an ascending chromatic scale, from white to black, 

 and the same is true of the Tuariks on the southern side of r 

 Mount Atlas, who are only light-olive, while their brethren 

 in the interior of Africa are black. The ancient monuments 

 of Egypt show us a fact equally significant. The men are 

 always depicted of a reddish brown ; they lived in the open 



