Page:Popular Science Monthly Volume 17.djvu/15

Rh check which the presence of haze, mist, or cloud in the atmosphere puts upon radiation. A humid temperate climate is also warmer than others in the same latitude, for it owes its existence in every case to breezes from warm seas. Breezes from cold seas can not produce a true humid temperate climate, because when they strike the land in summer they will be raised in temperature and rendered dry.

In humid temperate climates, since the rays of the sun, falling obliquely through a moisture-laden atmosphere, lose much of their light and heat, a dark pigment is a disadvantage. The vapor-clogged air tends to prevent perspiration, therefore a thin epidermis is desirable. The combination of a thin epidermis with a light pigment will give a fair complexion.

III. By a dry temperate climate I mean one occurring in a temperate zone in which the atmosphere is usually dry. Countries in which this climate prevails are distinguished from others in the same latitude by the great range of the thermometer. Their summers are hot and their winters cold. As a protection against the greater heat and brightness of the sun, a darker pigment than that which serves the purpose in humid temperate regions is necessary. To prevent the too rapid withdrawal of the fluid contents of the capillaries by the dry air, a thick cuticle is required. The combination of a thick cuticle with the pigment suitable to the intensity of the sun's rays will produce various shades of yellow and brown.

IV. By a humid tropical climate I mean one occurring in or near the torrid zone, in which there is no dry season. In such a climate vegetation will be luxuriant all the year round, and man will live in the shade of dense forests, in a steaming and enervating atmosphere, whose temperature will be high, but will vary little. Though the rays of the sun will descend vertically upon him, yet their power will be diminished by the vapor contained in the air, and he will not need so dark a pigment to protect him as the inhabitants of other tropical regions. Add to this, that a thin epidermis will promote perspiration which the moisture-laden atmosphere tends to check, and we come to the conclusion that the natives of such countries will be distinguished by comparatively fair complexions.

V. On the contrary, in a rainless tropical climate, or in one with a well-marked dry season, the rays of a vertical sun will continually, or for considerable periods, descend in all their power, and the blackest and densest pigment and the thickest scarf-skin will be needed. Between the tropics the nights are always long, and, in consequence, when in the dry season there is little moisture in the air to check radiation, the thermometer, as many African travelers have remarked, falls very low before sunrise. To withstand the loss of heat at such times a thick outer skin will be an advantage. Accordingly, in these climates, we find the blackest men and very thick skins.

This theory of the relations between the climate and the skin is, I