COEFFICIENCY OF UTILITY OF CLOTHING 353 



the mass of air passing in t mins., is heated by 6, then the heat 



0-237 x0xM . w . 



lost per minute --= calories, where 0-237 is the specific 



t 



heat of air. 



TABLE LXIV. 



It will be noticed that heat production increases with the 

 lowering of the temperature of the wind and also with increasing 

 the speed of the wind. It is obvious that, under similar conditions, 

 the heat lost (and the heat produced) by the clothed is less than 

 that of the naked subject. 



The colour of clothes has also something to do with their pro- 

 tective action. Quite apart from psychological effects, certain 

 colours conduce to warmth and others to coolness. This is a 

 problem that exercised the minds of those responsible for the health 

 of white troops in tropical countries. The final result of one 

 series of investigations was to recommend the wearing of white 

 clothes with a black lining. The student may find it an interesting 

 exercise to furnish a reason for this. 



23 



