LIQUIDS AND ALLIED EXPERIMENTS. 21 



The data for m calculated with these constants are also inscribed in table 3. 

 The errors show the fluctuation of the temperature cycles. They may be 

 regarded as eliminated from the curve as a whole. The rate m per day 

 reduced to seconds gives 



^ = 4.04X10"^" grams/sec, at about 20° 



Hence 



4.04X10"^° _13 



k= ^^ =1.09X10 



7.05X524 



The new value is thus much smaller than the tentative value, ^ = 2.9 X io~*^ 

 found from the balloon-shaped Cartesian diver, with small mouth (2r = o.2 

 cm.) after a period of eleven years. The uncertainty surrounding the latter 

 datum, in view of the long time-interval and the unfavorable shape, etc., did 

 not lead me to expect more than an order of values. The values of k, 

 moreover, involve the change of the gas constant, or mixture. Nevertheless 

 the agreement should apparently have been closer. Moreover, even in the 

 present method, a, h" , and h'" are not yet very accurately determinable 

 and the equation l = h"-\-2h"' needs a correction for 2h"'. The path out of 

 and around the diver is actually longer than 2h"'. It does not, however, 

 seem worth while to apply these refinements until a room of perfectly con- 

 stant temperature has been secured. 



Finally, it is interesting to compute the virtual viscosity of the inter- 

 molecular space through which the air molecule transpires. The coefficient 

 of diffusion taken per cubic centimeter (k being independent of R and there- 

 fore correct) will be 



1.09X10"" ^^ _!(, 



K= — =0.91X10 



0.0012 



whence the velocity of transpiration for a gradient of dyne/cm. is also 



7; = 9. 1 X io~^° cm./sec. Writing, as above, 



17 = F/6TNrv 



where F= i dyne, N = 6oX 10^^ molecules per cubic centimeter, 2r = 2Xio~^ 

 cm. (O. E. Meyer's values), 



_ I _g 



''" 6X3.i42X6oXio^'Xio-«Xo.9iXio-^°~^^°^'° 

 The viscosity of air is 190X io~^. Thus the virtual viscosity of the medium 

 is to tliis extent about 5 times that of normal air. 

 If we take Millikan's* recent data for N and 2r, viz, 



iV = 2. 64X10'^ 2r = 2.89X10"^ (oxygen) 2r = 3.06X10"^ (nitrogen) 



and regard 2^ = 3X10"* cm. as the average molecular diameter for air, 

 2A''r = o.7932Xio" replaces 27V^r= 12X10" above; whence 



77=1455X10"^ 



or the virtual viscosity of the intermolecular medium would be nearly 8 

 times as large as normal air. 



*Millikan, Physical Review, xxxii, pp. 349 et seq., iqii. 



