LIQUIDS AND ALLIED EXPERIMENTS. 



height h" of v. The table contains all the data reduced to mercury heads. 

 A = Mgp m /R. Consequently 1842 X io -6 grams of the imprisoned air escaped 

 in the intervening 10.92 years; i. e., 0.265 of the original mass of air. In 

 other words 168.7 Xio -6 grams per year, 0.462 X10 -6 grams per day, or 

 5.35 X 1 o -12 grams of dry air per second. 



Table l. — Weight m of the imprisoned air, v, fig. 1. M=\o grams; p m =i3.6; 

 p ff =2.87; mouth of diver, 2r = o.2 cm.; A =0.0465. Time interval 10.92 years. 



Date. 



Barometer. 



Manometer. 



Absolute 

 temperature. 



otXio- 8 



Feb. 27, 1900 

 Feb. 27, 1900 

 Jan. 27, 191 1 ... 



cm. 



77.21 



77.21 



75-77 



cm. 



— 3.20 



— 2.36 

 —21 .02 







297.1 

 299.2 

 296.0 



gms. 

 6952 

 6950 

 51 10 



6. Conditions of Flow. — It is now necessary to analyze the above experi- 

 ment preparatory to the computation of constants. The mouth of the 

 swimmer had an area of but 0.0314 cm. 2 . When sunk, the head of water 

 above the surface v was h" = 24 cm. The column of water between v and d 

 was h'" = 8 cm. Hence the length of column within which transpiration 

 took place was 24+2X8 = 40 cm. The right section of this column is taken 

 as 0.0314 cm. 2 throughout. Naturally such an assumption, accepted in the 

 absence of a better one, is somewhat precarious; but it may be admitted, 

 inasmuch 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 approxi- 

 mate 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 v is 

 Ap = 24X0.997X981 = 23,470 dynes/cm. 2 

 hence per dyne/cm. 2 per sec. 



~ 12 X 5.346 



10 



= 10 



'X2.28 



10X2.347 

 grams of air escape from the swimmer. 



A few comparisons with a case of viscous flow may here be interesting. 

 Using Poiseuille's law in the form given by O. E. Meyer and Schumann's 

 data for the viscosity of air, it would follow that but 0.194X io~ 6 cm. 2 of the 

 0.0314 cm. 2 of right section at d is open to inter molecular transpiration. 

 The assumption of capillary transpiration is of course unwarrantable and 

 the comparison is made merely to show that relatively enormous resistances 

 are in question. 



Again, the coefficient of viscosity 

 V _t 

 i + 4f/r m 16 IRt 

 may be determined directly. In this equation m is the number of grams 

 of air transpiring in t seconds through the section irr 2 and in virtue of the 



■risW-/) 



