RELATIONS OF THE AIR TO OUR CLOTHING. 673 



It is easy to see from this table how much quicker linen works 

 than wool in every direction. 



During the first 75 minutes there evaporated from 1,000 parts of 

 linen 511, from 1,000 parts of flannel 456 water; afterward the re- 

 verse took place: in the following 30 minutes 130 evaporated from 

 linen, 148 from flannel, and in the last 30 minutes only 44 per 1,000 

 from linen, but 115 from flannel. 



It is also evident how much more evenly the drying proceeds in 

 wool: in the first 15 of the whole 135 minutes 219 evaporated from 

 linen, in the last 15 minutes 28 per 1,000, while with w r ool it was re- 

 spectively 212 and 97 per 1,000. I must not forget to mention that 

 all these experiments were made with pieces of nearly equal size and 

 shape. 



It is self-evident that all textiu*es lose their permeability to the 

 air in proportion to their state of humidity, the water partly at least 

 obstructing the pores. Coarser stuffs with larger pores will keep 

 their permeability longer; if the pores are equal, the difference in the 

 adhesion of the water to the substances will come into play. Linen, 

 cotton, and silk are very different in this respect from sheep's-wool. 

 The former become very quickly air-tight by wetting, the latter 

 scarcely so, or only after a longer soaking. Soldiers can tell how 

 damp and vaporous the air becomes under a wet tent, and how quick- 

 ly the tent becomes airy when it begins to dry. 



As the porosity of all fabrics depends chiefly on the elasticity of 

 the fibres of their material, it must be of great importance how far 

 that elasticity keeps under wet and dry. There, again, wool stands 

 apart ; its fibres do not lose much elasticity when they get wet : it is 

 not so with other fibres. Wet linen and silk are just like Krieger's 

 shorn fur, when it was coated with varnish or gum-arabic. The 

 greater facility of catching cold in wet linen or silk than in wet wool 

 is in exact proportion to the greater facility with which water expels 

 theair contained in their fibres. Many of you may have learned a 

 lesson from a wet linen or cotton and a wet woolen sock. 



On the other hand, there is an advantage in these materials if we 

 want to keep ourselves cool and dry. By means of them we part 

 with heat and moisture from our surface much quicker, and hand them 

 over to other layers for further removal. 



To be quite methodical I ought now to treat of the different parts 

 vol. x. 43 



