the polar regions have often seen like results produced by the glare of the snow. When the impression of light on the eye is sudden and overpowering, the retina suffers most. If it is less powerful, but longer continued, the humors of the eye are affected. The phenomenon called sunstroke results from the action of light, and not, as is often supposed, from excessively high temperature. It sometimes occurs in the moderately warm season of spring; or a very intense artificial light, and particularly the electric light, may occasion it. The violet and 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 calling out the production 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 complexion in a measure perceptibly related to the intensity of solar light. In Europe three varieties of color in the skin are distinctly marked: olive-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 Scytho-Arabic race has but half its representatives in Europe and Central Asia, while the remainder passes down to the Indian Ocean, continuing to show the gradual rising heat of climate by deepening brown complexions. The Himalayan Hindoos are almost white; those of the Deccan, of Coromandel, Malabar, 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 upstream 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 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 air, while the women, kept shut up, have a pale-yellow complexion. Barrow asserts that the Mantchoo Tartars have grown whiter during their abode in China. Rémusat, Pallas, and Gutzlaff, speak of the Chinese women as remarkable for a European fairness. The Jewesses of Cairo or Syria, always hidden under veils or in their houses, have a pallid, dead color. In the yellow races of the Sumatra Sound and the Maldives, the women, always covered up, are pale like wax. We know, too, that the Esquimaux bleach during their long winter. These phenomena, no doubt, are the results of several influ-
