4G 



Dr. A. 0. Rankine on the Relation between 



The numbers in the second column are the viscosities in 

 absolute units at 0° 0. multiplied by 10 4 . Those in the 

 third column are the values of the constant C in Sutherland's * 

 equation 



V = Vo 



/T\!/C + To\ 

 \T /\C + T/' 



where rj is the viscosity at the absolute temperature T. 



The first five points in fig. 1 show the viscosities at 



Fiar. 1. 



i-o 



IS 



Z-Q 



is 



^e 



,0! 



Kr 



6He 



"o 



+ 

 Em 



100 



200 

 ATOMIC WEIGHT 



0° C. x 10 4 plotted against the atomic weight. The undula- 

 tory nature of the curve is apparent, and it is at once 

 recognized that no simple algebraic relationship obtains. 

 Indeed, such a connexion is hardly to be expected in view of 

 the fact that comparison is made of the viscosities of the 

 gases at the same temperature. It seems much more 

 reasonable to perform the comparison at corresponding 

 temperatures — for example, the boiling points or critical 

 temperatures of the respective gases. With the data 

 available this procedure is only possible if the truth of 

 Sutherland's equation be assumed, and the values of the 

 viscosity found by extrapolation. In this manner the 

 viscosities of the gases have been calculated, with the striking 



* Phil. Mag. 1893, vol. xxxvi. p. 507. 



