328 



THE HUMAN MOTOR 



Kir.. 231. 



Crova's Hygrometer. 



In using Crova's hygrometer, it is as well to wait for the dis- 

 appearance of the drop of dew, which takes place at a tempera- 

 ture t' 2 , slightly different from t\ t and to take the average 



1 2" . * as t'. The brass tube should be very clean. f 1 ) 

 Z 



Knowing the tension / the weight in grammes of the water 

 vapour in a cubic metre of the air can be calculated. Thfe is 



the absolute humidity, whilst ^ = e is the relative humidity. 



Now the weight of a litre of gas or vapour is equal to T293 

 gramme (the weight of a litre of air) , multiplied by the density of 

 the fluid in question. The pressure and the temperature are also 

 taken into account by writing : 



p = 1-293 x d x-j 

 For water vapour d = 0-622, about f ; H =/. Therefore : 



p = 1-293 x | ) 

 or : 



or, per cubic metre : 

 (1) 



_ 0-2902 x / 

 P ~ 273 +t ' 



P 



+ 



290-2 X / 

 273 + t' 



Knowing that e = 4 or / = Fe, the expression could be written : 



( l ) Cantor (Wied, Ann., vol. Ivi., p. 492, 1895). 



