274 PHENOMENA DEPENDENT ON MOLECULAR PATHS 102 



The possibility of such a calculation from our formulae is 

 at once evident when we remember that the absolute values 

 of the free paths 



L l = \ 3 /^iV2, L 2 = X 8 /w* 8 V2, 



of each of the two diffusing gases in an unmixed state, in 

 which they are under the normal pressure p and contain N 

 molecules in unit volume, can be calculated from the co- 

 efficient of viscosity, and that therefore the magnitudes 



Nir 9l V2 = 1/r 1 , Nirs**/Z = L^ 



are known. Stefan used further the hypothesis already 

 mentioned in 96, viz. 



a = i(^ + , 2 ), 



which allows us to evaluate the magnitude 



Since also the molecular speeds H are known, we have all 

 the magnitudes given which come into the formula for the 

 coefficient of diffusion, and the value of this coefficient, 

 therefore, can be calculated in absolute measure if the co- 

 efficient of viscosity is measured for each of the two gases 

 that take part in the diffusion. 



Stefan has carried out this calculation for the gases 

 the diffusion of which has been experimentally investigated 

 byLoschmidt, and has arrived at a tolerably good agree- 

 ment between the theoretically calculated numerical values 

 and those deduced from the observations. But since he 

 made his calculation from another formula, I have had to 

 repeat the calculation. 



Since Lose h mid t has always in his experiments allowed 

 equal volumes of the two diffusing gases to mix together, I 

 have put the numbers N l and N 2 equal to each other, and 

 so have made my calculation by the formula that is given at 

 the end of 100. The values of the molecular free paths 

 and speeds that are introduced are those we have given 

 before ; the values, however, at C. are not used directly, 

 but are reduced to the temperature ofLoschmidt's experi- 

 ments. In the following table the values so calculated are 



