RELATIONS OF THE AIR TO OUR CLOTHING. 671 



sary openings in them but only because they limit the universal ex- 

 change of air in the underlying garments. For protection against 

 the wet from without they are well suited, but they produce another 

 wet on our skin by impeding evaporation. They may be used in wet 

 weather, when accompanied with cold or wind, but never, though 

 wet, when it is warm or calm. 



Finally, I have to draw your attention to the relations which the 

 materials of our clothes have to water, by which their functions are 

 considerably altered. They are all hygroscopic ; that means that they 

 condense from the atmosphere a certain amount of water. This hy- 

 droscopic property, very different in different bodies, increases with 

 the decrease in the temperature of the air, so that all of them con- 

 dense more water at freezing-point than at higher temperatures. 

 Partly, also, the relative, moisture of the air is of some influence, so 

 that at 68 the hygroscopic body absorbs more water from an air 

 nearly saturated than from a less moist air. As yet we do not know 

 much abont our clothing materials in this respect. I have made some 

 preliminary researches, and have found unexpectedly great differences. 



I took two equal pieces of flannel and of linen, as representatives 

 of the two most important fabrics made of vegetable and animal 

 fibres, and dried them at 212, a temperature at which they lose all 

 their hygroscopic water. I put them into well-closed boxes of known 

 weight, and noted the weight of the two together. They were then 

 exposed to the air in places of different temperature, and from time 

 to time put back into the tin boxes, and the weights taken again. 

 By this method it was not difficult to ascertain the relative quantities 

 of hygroscopic water which the flannel and the linen had absorbed. 

 These quantities are tabulated below, as they resulted from different 

 localities, temperatures, and lengths of time, the weight of the linen 

 and flannel being 1,000 grammes each : 



