191 1.] THROUGH A PARTITION OF WATER. 121 



A/' = 24 X -997 X 981 = 23470 dynes/cm.2 

 Hence per dyne/cm.- per sec. 



io~^^ X 5.346 



10x2.347 



= IO~*"X 2.25 



grams of air escape from the swimmer. 



A few comparisons with a case of viscous flow may here be inter- 

 esting. 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 .194 X 10"^ cm.- of the .0314 cm.^ of right section at d is open 

 to intermolecular transpiration. The assumption of capillary trans- 

 piration is of course unwarrantable and the comparison is made 

 merely to show' that relatively enormous resistances are in question. 



Again the coefficient of viscosity 



^ 1 !_ J^(p2_.2^ 



I +4^/r~"w 16 IRr^ ^ ^ 



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

 grams of air transpiring in t seconds through the section irr- and in 

 virtue of the pressure gradient {P — /')/i, when -q is the viscosity 

 and ^ the slip of the gas. Hence the value r;/(i -f 4l/r) =4.8 X 10^ 

 would have to obtain, a resistance, which would still be enormously 

 large relative to the viscosity of air (t/=i.8oX io"*'), even if the 

 part of the section of the channel which is open to capillary tran- 

 spiration is a very small fraction. 



7. The Coefficients of Transpiration. — To compute the constants 

 under which flow takes place the concentration gradient dc/dl 

 may be replaced either by a density gradient dp/dl or a pressure 

 gradient dp/dl. If the coefficients in question be k^ and kp respec- 

 tively 



k -i^ "±^ (.\ 



^~ Rt~ adpjdl ^^^ 



where a is the section taken equal to the area of the mouth of the 

 swimmer, R is the absolute gas constant, r the absolute temperature 

 of the gas, and m the loss of imprisoned air in grams per second. 

 If ^; = iiiRr/p is the corresponding loss of volume at r and p 



