794 THE POPULAR SCIENCE MONTHLY. 



air. When the atmosphere is much agitated the cold penetrates more 

 readily through the furs, and also through our overcoats, as all know 

 who have been much exposed to cold winds. According to M. Krie- 

 ger's experiments, the loss of heat through the skin is doubled when the 

 fur is shaved off, and tripled when the skin is varnished. These facts 

 bring us to the conclusion that the goods called impermeable are gen- 

 erally anti-hygienic, because they impede the aeration of the garments 

 beneath them. They are good for protection against rain, but they 

 excite perspiration and prevent its evaporation, and are very uncom- 

 fortable in pleasant weather. 



Another very important property in cloths is their hygroscopicity ; 

 they condense moisture from the atmosphere and become impregnated 

 with it the more speedily as the air is more nearly saturated with 

 vapor, and consequently less capable of favoring evaporation. The 

 condensation, which is equivalent to a kind of dew, is increased when 

 the temperature is diminishing. According to M. Courier's researches, 

 the water absorbed by a cloth may be divided into two parts : one 

 part which is not perceptible to the touch and can not be pressed out 

 the hygrometric water proper ; and the other part, that which fills 

 the pores and can be wrung out, and which M. Coulier calls inter- 

 posed water. According to his experiments, wool is more hygroscopic 

 than hempen cloth, and linen than cotton. Dr. Pettenkofer compared 

 the hygroscopic qualities of a piece of linen and a piece of flannel 

 having equal surfaces and nearly equal weights. Having been pre- 

 viously dried at the boiling-point of water, the two pieces of goods 

 were exposed together in places more or less moist, and the variations 

 in weight they went through after several hours of exposure were 

 measured. It was found that wool was nearly twice as hygroscopic 

 as linen. Similar differences between different materials may be ob- 

 served when they are wet by immersion. Linen gets wet much more 

 speedily than wool, but the wool really absorbs the most water. 



The quantity of water that cloths are capable of absorbing is evi- 

 dently more considerable than is commonly supposed. A woolen coat 

 weighing five or six kilogrammes may take up nearly a litre of water, 

 and this will add a kilogramme to its weight. We see also that cloths 

 absorb more moisture when the temperature is low than at ordinary 

 summer heat. Wet garments conduct heat better than dry ones, and 

 consequently give much less protection against chills ; hence the dan- 

 ger of cold combined with dampness. But wool, although it is more 

 hygroscopic than linen, protects better against the effects of humidity 

 because of the slowness with which it absorbs and gives off water, 

 and because of its indestructible porosity. 



As we fill up the meshes and pores of a tissue, it becomes less per- 

 meable to air, and goods with close meshes, like linen, cottons, and 

 silks, feel this effect much more quickly than woolen goods. As Dr. 

 Pettenkofer remarks, the elasticity of the fibers counts for much in 



