MEASUREMENTS 327 



Assume y = 32 and v = 18-05 Cal. for an adult. Then 



a = 35 5 = 30 (according to Lefevre) and K' = 0-009. 



Taking a = 35 12 = 23C, v = 12.8 Cal. Lefevre obtained 

 11-70 Cal. 



253. Measurement of the Hygrometric State The use of 



Crova's hygrometer (fig. 231) has already been recommended 

 ( 173). 



This instrument consists of a brass tube, polished internally, 

 closed in front by a sheet of ground glass V and at the back by a 

 lens L, which allows a view cf the interior. The tube is immersed 

 in a brass vessel containing carbon bi-sulphide, and crossed from 

 A to C by a current of air, which causes a fall of temperature 

 indicated by the thermometer T. 



By means of the bulb P, air is drawn through the tube B, and 

 the formation of dew can be observed through D. As soon as 

 dark patches appear, the temperature t' is read by the thermo- 

 meter T, the external temperature t being known. Regnault's 

 tables give the values / and F, the following being a portion of 

 these tables for temperatures between 10 and + 50 C. 



TABLE OF THE TENSIONS OF VAPOUR IN MILLIMETRES OF 

 MERCURY (REGNAULT, THIESEN and SCHEEL.) 



