74 On the Viscosity of Argon cis affected by Temperature. 

 With the above values we get 



X = 1-812. 



As appears from (5), the integral part of x relates merely to the 

 expansion of the gas by temperature. If we take 







we get n = 0-812. 



This number is, however, subject to a small correction for the ex- 

 pansion of the glass of the capillary. As appears from (4), the ratio 

 [jf, /X as used above requires to be altered in the same ratio as that in 

 which the glass expands by volume. The value of n must accordingly 

 be increased by 0*0 10, making 



n = 0-822. 



The following table embodies the results obtained in a somewhat 

 extended series of observations. The numbers given are the values 

 of n in (7), corrected for the expansion of the glass. 



Air (dry) 0*754 



Oxygen 0'782 



Hydrogen .'. 0-681 



Argon (impure) 0-801 



Argon (best) 0-815 



In the last trials, the argon was probably within 1 or 2 per cent, of 

 absolute purity. The nitrogen lines could no longer be seen, and 

 scarcely any further contraction could be effected on sparking with 

 oxygen or hydrogen. 



It will be seen that the temperature change of viscosity in argon 

 does not differ very greatly from the corresponding change in air arxd 

 oxygen. At any rate the simpler conditions under which we may sup- 

 pose the collisions to occur, do not lead to values of n such as 0-5, or 

 1-0, discussed by theoretical writers. 



I may recall that, on a former occasion,"^ I found the viscosity of 

 argon to be 1-21 relatively to that of air, both being observed at the 

 temperature of the room. 



* 'Roy. Soc. Proc.,' January, 1896. 



