122 BARUS— THE TRANSPIRATION OF AIR [April 21, 



^ Rt aRTdpjdr ^^^ 



If in equation (3) the full value of m is inserted and t denotes cur- 

 rent time, or /u = m/t; if 



dl h" + 2h"' 



where pw is the density of water, h" and W" the difference of level 

 (see Fig. 2) of the surface in v below the free surface in A and 

 above the mouth at d, the relations are 



Alp H \-\- 2/1" I h" , , , 



k, = kRT. • (5) 



The acceleration of gravity, g, has dropped from both equations ; k^ 

 is independent of Rt. The coefficient A";,, however, is more per- 

 spicuous. 



If h'" is made very small in comparison with /;" (care being taken 

 to avoid loss of air during manipulation) //" will also vanish; or 

 for /i" = o 



and similarly for ]i" = o 



reduces to 



;// = k^ap^^g. 



Thus the apparatus is most sensitive if a is as large as possible and 

 h"'/h" as small as possible and the length of the column in A is 

 eventually without influence on the result. Hence if for a cylindrical 

 swimmer the internal right section is equal to the area of the annular 

 space between the outer wall of the swimmer and the inner wall of 

 the vessel A^ if the column of water above the swimmer is removed 

 during the prolonged intervals of time between observations, the 



