Page:Popular Science Monthly Volume 10.djvu/689

Rh the velocity of the surrounding air. We need not be anxious to make our clothes prevent the access of air to our skin; they have only to regulate and moderate it to such a degree that our nerves may not feel the air as something in motion. This degree is far from immobility. When in the open air we believe it to be quite calm, there is still a velocity in it of at least one foot and a half per second, or about one mile per hour, as you heard before.

Our clothing not only renders the air still around us, but it also regulates its temperature by the heat which leaves our body; we heat our garments, and they continually heat the air passing through the meshes and pores of the texture. We may compare our clothing to a calorifer or stove, warmed by the heat emanating from our body's engine for the purpose of warming the air round our surface.

We do not feel the loss of heat which our clothing undergoes as we should if the air were to strike our surface without having been previously prepared by our dress; the differences of temperature balance themselves within the material we are clothed in, and of which the ends of our cutaneous nerves form no part. Inside our dress we carry the air of the South wherever we may be. Its temperature averages about 75° to 94° Fahr. We live in our dress like an unclothed tribe in a paradisian country, where the air is constantly calm and the temperature 75° to 94°. It will be easily understood now why rough, loose textures keep us so warm, while newly-carded cotton-wool does so more than when old and compressed; why tissues of fine fibres and threads make the best material. Fur, of which you know so well the properties, consists of hair and skin. Chemically speaking, there is not much difference between skin and hair. In fur the weight or body of the skin is much greater than that of the hair, and still it is essentially the light hair to which the fur owes its warming properties.

There are some interesting experiments on this point. Krieger observed the flow of heat after covering his cylinders with unshorn and shorn fur. Putting down the loss of heat through the entire fur as 100, he found that it rose to 190 when the same piece of fur was used shorn. A dried skin, you know, is always somewhat porous. When he altered this by giving it a coat of linseed-oil varnish, the loss of heat rose to 258; and, when he took a solution of gum-arabic instead, it rose even to 296.

It has been proved that the living organism, in parting with its heat by radiation and conduction, behaves just like a tin cylinder filled with warm water. It is a yet older observation that furred animals, such as dogs, rabbits, etc., cannot live when they are shorn and their skin varnished or oiled. One used to explain their death by the suppression of the evaporation from their skin, but it can be proved that even in a comfortably-warm room these animals literally freeze to death. Krieger sheared a rabbit, after having noted its temperature