360 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK iv. 



to use clothing is the disagreeable sensation we feel by the contact 

 of our skin with cold air or air greatly heated by the rays of the sun, 

 and the accidents which result to our health from the sudden change. 

 There are three things which render a fabric unsuitable for the 

 conduction of heat; the nature of the substance of which it is 

 composed, the structure of the fabric itself, and its thickness. With 

 regard to the first point, the following is the order in which the 



FIG. 245 The clothes of the Esquimaux. 



various substances may be ranged, commencing with the most and 

 ending with the least conducting. The results are due to the experi- 

 ments of Itumford : spun silk, cotton or wool, sheep's wool, taffeta, raw 

 silk, beaver's hair, eider down, hare's skin. 



We see from this that silk is a better conductor than wool, and as 

 the fabrics of silk are of a closer set structure than woollen stuff, the 



