120 BARUS— THE TRANSPIRATION OF AIR [April 21, 



In the intermediate time, I did not return to the measurements 

 until quite recently (January, 191 1), when a second series of obser- 

 vations was made. As much as one fourth of the air contained in 

 1900 had now, however, escaped, in consequence of which the above 

 method had to be modified and all heads measured in terms of 

 mercury. Hence if H denotes the height of the barometer diminished 

 by the head equivalent to the vapor pressure of water, and if m/M 

 be neglected in comparison with i (about .06 per cent.) the equation 

 becomes 



R 



(2) 



in which the first factor of the right-hand member is constant. If 

 the observations are made at the instant the swimmer sinks from 

 the free surface in A, Fig. 2, H must be increased by the mercury 

 equivalent of the height h' of v. The table contains all the data 

 reduced to mercury heads. A ^Mgp„,/R. Consequently 1,842 X 

 10"^ grams of the imprisoned air escaped in the intervening 10.92 

 years ; i. c, .265 of the original mass of air. In other words 

 168.7 X lO""*^ grams per year, .462 X lO"*' grams per day, or 5.35 X 

 lO"^- grams of dry air per second. 



6. Conditions of Flour. — It is now necessary to analyze the above 

 experiment preparatory to the computation of constants. The mouth 

 of the swimmer had an area of but .0314 cm.- When sunk the 

 head of water above the surface z' was li" = 2^ cm. The column 

 of water between z' and d was h"' = S> cm. Hence the length of 

 column within which transpiration took place was 24 -j- 2 X 8 = 40 

 cm. The right section of this column is taken as .0314 cm.- through- 

 out. Naturally such an assumption, accepted in the absence of a 

 better one, is somewhat precarious ; but it may be admitted, inas- 

 much as the pressure of the gas sinks in the same proportion in 

 which the breadth of the channel enlarges. Thus there must be 

 at least an approximate compensation. In more definite experiments 

 a cylindrical swimmer whose internal area is the same as the annular 

 area without will obviate this difficulty (see Fig. 2). 



The pressure difference urging the flow of air from f is 



