I9II.] THROUGH A PARTITIOX OF WATER. 123 



section a through which capillary transpiration takes place is defi- 

 nitely given. It is obvious that the swimmer must be suspended, for 

 instance by fine cross wires, above the bottom of the tank A. 



Reference is finally to be made to convection and to temperature. 

 The manipulation during observation necessarily stirs up the water 

 and distorts the regular pressure gradient. Hence observations are 

 to be made rarely. Again to obviate convection in general the 

 vessel must be kept in a room of nearly constant temperature. 



8. Values of the Coefficients. — If the data of the above summary 

 be inserted in the equations for k,, and kp, 



viRr 5.15 X lO-'- X 2.87 X lo" x 298 . 



^ adpjdl 10314x23470/40 



/. =klRr= .29 x \o-'\ 



Hence for a gradient of i dyne per cm., 2.9 X lO"^^ grams of air 

 flow between opposed faces of a cu. cm. of water per second. This 

 may be put roughly as about 2.4 X iO"^° cu. cm. of air per second. 

 The speed of migration of individual air molecules intermolecularly 

 through a wall of water is thus 2.4 X lO"" cm./sec. for a dyne/cm. 

 gradient. 



Since the. gradient is the energy expended when the cu. cm. is 

 transferred i cm. along the channel and if the number of air mole- 

 cules per cu. cm. be taken as A' = 6oX IO'^ the force acting per 

 molecule to give it the velocity just specified is 1/(60 X 10^^) dynes. 

 Hence the force or drag per molecule if its speed is to be i cm. per 

 sec. is 



/ = Tn z 1^ = s dynes 



•^ 2.4xiO"^°6ox 10'- 144 X 10^ 



/= 6.9 X io~'' dynes, \{ v = cm./sec. 



This may be compared with the force necessary to move a small 

 sphere through a very viscous liquid of viscosity -q. This force is 



f^fyirqrr. 



If z.'=i cm./sec, 2r=iO"* X2 cm. the diameter of the sphere of 

 influence of a molecule, and / = 6.9XiO"^' dynes the value just 

 found, 



