452 



THE REGULATION OF TEMPERATURE 



an equivalent for a certain amount of food.'''' In other words, if 

 we were to do without the protection afforded by clothing we would 

 have to make good the heat thus lost by eating more food. 



The protective value of clothing mainly depends (1) inversely 

 on the thermal conductivity of the material, (2) on its power of 

 absorbing water, and (3) on the arrangement of the fibres of the 

 material in the cloth. The conductivitv of various materials is 

 given in Tables LXVIII. and LXXII. 



Coefficient of Protection. In order to calculate the coefficient of 

 protection of clothing one must know the thickness of the 

 material. Table LXXIII. compiled by Rubner gives further 

 information regarding the density of the material and of the 

 amount of air enmeshed in the structure. This layer of imprisoned 

 air, as we have already mentioned, has a greater protective value 

 than mere thickness of material. 



A man entirely clothed in a garment of a total surface (.9) of 

 19 X 10^ sq. cm., of a thickness [t) of 75 X 10"^ cm. and having a 

 difference of temperature {d) on the two sides of 10° C, loses 

 heat (Q) as shown by the following formula : 



Q 



c X s X d 

 i 



calories per second, 



where 



I.e. 



Q = 



coefficient of conductivity, 

 c X s X d X 3,600 X 24 



t X 1,000 



Calories per day. 



