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CHAP. IX.] the evaporation shall not take place on the skin, but from the surface of the clothes, which prevents chill. The mere fact of covering impedes loss of heat by convection, and radiation, and provided our garments are made of non-conducting materials they necessarily minimize that loss of heat by conduction which is always going on between two bodies of different temperatures, such as the human body and the air, just on the same principle that a tea-cosy retains heat in the teapot. We stuff our tea-cosies with wool in perhaps unconscious obedience to the principles I have explained, and we should clothe our bodies in the same way.

Stationary air, as has been observed,1 is a bad conductor of heat; but particles of air rise, when heated, and give place to colder ones. Hence it is desirable that the covering of the body should have a rough surface, so as to entangle in it particles of air, which becoming heated, and being unable to rise, form a sort of warm atmosphere round the body. It is an advantage, moreover, for garments to be loosely woven, so that a certain quantity of air may be entangled in the meshes of the material, and for the same reason, instead of the clothes consisting of one very thick garment, successive layers of clothing are and should be worn, as a considerable amount of air is then imprisoned between them.

The human body has a tiny atmosphere clinging to its hairs, in proportion to their size, as may