The secret of a clear head / by J. Mortimer-Granville.
- Granville, J. Mortimer (Joseph Mortimer), 1833-1900
- Date:
- 1879
Licence: Public Domain Mark
Credit: The secret of a clear head / by J. Mortimer-Granville. Source: Wellcome Collection.
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![the radiation of heat than white, although the dark colour absorbs more rapidly than the lighter. On the other hand, she has given the denizen of the Frigid Zone a pale skin, and clothed the Polar bear with a white fur because white does not so free]3* part with the heat it holds or covers, as black. .Radiaiio7i of heat takes place when the sur¬ roundings are cool, and, if the radiating body be a living animal organism, the aim must be to prevent too rapid dispersion. This points to the choice of materials and colours for clothing which hold the heat in winter, and of those which, so to say, resist it in summer. Reflection is in practice a part of radiation, except that the reflecting body may, in theory at least, be impervious to the heat it throws off from its surface, while that which, more strictly speaking, radiates must first have become charged with caloric. Evaporation is the great cooling process by which perspiration reduces the tempe¬ rature of the body. When Nature covers the body with fluid the physical effect intended is the same which we produce artificially by sprinkling the surface of any object with water. In the act of passing off as vapour, the fluid takes away heat and thus cools the skin. This is, in some measure, how sweating reduces the heat of the body in fever, and, in the absence](https://iiif.wellcomecollection.org/image/b29287030_0020.jp2/full/800%2C/0/default.jpg)
