670 THE POPULAR SCIENCE MONTHLY. 



and frequency of respiration ; they were 102 and 100 per minute. 

 He did not use any varnish, to avoid any possible suppression of 

 evaporation from the skin, but enveloped the shorn animal in a wet 

 cloth. The temperature of the room being at 66, the animal lost so 

 much heat that, after five hours, its interior temperature had fallen to 

 75, and its respiration to 50 per minute. 



A fur is so arranged that its fine hair, projecting into the air, in- 

 tercepts all the heat, which flows from the surface by radiation and 

 conduction, and distributes this heat through the air, which circulates 

 between the single hair-cylinders ; the finer the hair of the fur, the 

 more of the outgoing heat is taken up by the air, which, however cold 

 the temperature may be, reaches the nerves of the skin as a warmed 

 air. Furred animals, in winter, when touched superficially, give a 

 very cold sensation; it is only near the skin that their hair feels warm. 

 In severe cold, certainly little of our animal heat comes as far as the 

 points of the hair, from which it would radiate or be conducted into 

 the air ; the current of air in the fur cools the hair from its point tow- 

 ard its roots, and a severer cold penetrates only a little farther into 

 the fur, without necessarily reaching the skin of the same. This takes 

 place only when the temperature is uncommonly low, and the air in 

 violent motion. Travelers in high latitudes all agree that extreme de- 

 grees of cold can be borne very well when the air is calm, but scarce- 

 ly so when there is a brisk wind. 



This tends to show that in very severe cold the outflow of heat, by 

 the skin into the air contained in the fur or within the dress, takes 

 place through one route only that of conduction ; when a fur is 

 worn, no heat comes to the surface for radiation, as soon as the jioints 

 of the hair have the temperature of the sm-rounding air. Evapora- 

 tion also sinks to a minimum, because at 68 Fahr. under freezing- 

 point all formation of aqueous vapor already ceases, and nearly all 

 the heat in the fur and the dress is employed to heat the arriving air, 

 whose velocity increases according to the difference of temperature. 

 In a well-furred animal the changes of temperature in the surround- 

 ing air only change, if I inay say so, the latitudes of the cold and 

 warm zones in the fur; the place where the temperature of the body 

 and the air equalize each other moves between the roots and points 

 of the hair, and for this reason such a well-furred animal is not warm- 

 er in summer than in winter. Its blood keeps always at the same 

 temperature, because in summer a great part of its heat leaves at the 

 points only of the hair by radiation and conduction, while in winter 

 the heat departs already near the roots of the hair. 



Air-proof fabrics ought to have only a very limited use. In India- 

 rubber or gutta-percha textures we feel highly uncomfortable when 

 we have to undergo much exercise, or have to give off more heat than 

 usual. They become inconvenient, not because they stop the change 

 of air entirely which they cannot do in fact, on account of the neces- 



