the Shape of the Atom. 233 



of the ratio is much larger than it should be on that assump- 

 tion, but if it is taken as diatomic the ratio fits in well with 

 the others. This suggests that a molecule of mercury in the 

 gaseous state at zero temperature is probably diatomic. 



We have compared the values of Q for different gases at 

 zero temperature. It is probable, however, that the proper 

 temperatures for comparison are corresponding temperatures. 

 The range of the data is, however, not sufficiently extensive 

 to allow a comparison to be made for corresponding states. 



The coefficient of viscosity 77 of a gas is given by the 



fflV 



equation y=-j — 2, where v * s the velocity of translation of 



a molecule. The equations for 77 and Q thus both contain 

 the square of s, and the relative values of each of these two 

 quantities for the substances belonging to one of the groups 

 given in Tables I. and II., can therefore be obtained with the 

 same degree of accuracy from these equations on m 3/3 being 

 substituted for s 2 . This applies also to the coefficient of 

 diffusion 8 of a molecule in a gas composed of molecules of 



the same kind, which is given by 8= — -, where p denotes 



the pressure of the gas. ~p7rs 



The coefficient of diffusion S 12 of a gas 1 into a gas 2 is 

 given by the eauation 



where K is constant at constant pressure and temperature, 

 and s„ 5 3 are respectively the radii of the spheres of action 

 of the molecules 1 and 2. Now s 1 and s 2 are, according to 

 the results obtained in this paper, proportional to (XmY 6 ) 1 ' 2 

 and (%ml /s ) 1/2 respectively, and the above equation may 

 therefore be written 



Kx 



810 = 



ml'mtm^+iXm'/yi'} 



2v 



where Kj is a constant. This equation may be used to 

 calculate relative values of S ]2 . 



Table IV. contains the coefficients of diffusion of a number 

 of gases into each other, they were taken from Meyer's 

 ' Kinetic Theory of Gases/ p. 275. The values in the table 

 labelled " calculated " were obtained by means of the above 

 formula. The value for N 2 — C0 2 was put equal to the 

 observed and the other values reduced correspondingly. 

 The calculated values, it will be seen, are approximately 



