CLOTHING AND THE ATMOSPHERE. 793 



the interposed stratum of air. Hence, we should expect in many 

 cases to find a loose garment warmer than a tight one ; and we know 

 that close-fitting gloves or shoes afford but a poor protection against 

 the cold. This reasoning, however, supposes that the protecting layer 

 of air is motionless ; but more frequently an ample and flowing gar- 

 ment favors the circulation of air, and therefore seems to us to be 

 cooler, and is for that reason preferred in summer and in hot climates. 

 "We are now brought to the important fact that the most serious 

 obstacle to the propagation of heat in any body is the discontinuity 

 of its elements. This is because heat is a mode of motion, and every 

 derangement of molecular continuity impedes the transmission of 

 vibrations. This principle is more or less unwittingly put to profit- 

 able use in the manufacture of clothing. We obtain very warm 

 clothes from light, loose, and porous tissues, having a capacity to re- 

 tain in the sj)aces between their fibers a large volume of air. I said, 

 retain ; I might more properly have said, let pass ; for the air which 

 our clothes inclose is not motionless, but circulates and undergoes 

 constant renewal in filtering through the envelopes which we mis- 

 takenly believe are intended to isolate us from the surrounding medi- 

 um. It is, in fact, an essential condition of a good garment that it 

 shall not interpose an obstacle to ventilation. The warmest clothes 

 let the air pass more readily than those which are considered cool. 

 Dr. Pettenkofer demonstrated this fact by measuring the volumes 

 of air which under the same pressure and in the same time passed 

 through a series of tubes stopped by pieces of different kinds of cloth. 

 The numbers^ representing the volumes were for the different goods : 

 flannel, 100 ; linen, 58 ; silk, 40 ; strong cloth, 58 ; buckskin, 51 ; 

 glazed skin, 1. Flannel is, then, a hundred times more permeable to 

 the air than a glazed glove, and we know at the same time that it 

 is infinitely warmer. The volumes of air transmitted are but little 

 changed by doubling the goods. Our clothes are thus continually 

 aerated by an exchange, the activity of which depends on the external 

 temperature, the degree to which the atmosphere is agitated, and the 

 porosity of the tissues ; the essential point is that the change shall be 

 so slow that the nerves of touch shall not be affected by it. The 

 warmest coat is one of fur, and its warmth lies not in the skin only, 

 but chiefly in the hairs, although their mass is relatively insignificant, 

 and is almost wholly due to the air interposed between them. Furs 

 are warmer in proportion as the hairs are finer, because, doubtless, the 

 air that circulates through them is more thoroughly warmed. There 

 are formed around the bodies of furred animals superimposed strata 

 of air, the temperature of which diminishes from the skin to the ends 

 of the hairs ; and in winter the animals seem cold to the touch, while 

 the zone of exchanges retires toward the skin as the cold becomes 

 more intense. The body of the animal is, then, cooled principally by 

 convection and by the ventilation which incessantly removes the heated 



