IN RARIFIED OASES 



and if we writ* /* for the average value of P for the N molecules in unit 

 of volume, then Uking the sum of the eflecte of the encounters 



(14). 



Wa thn* find 



-(is). 



Now, noe 6 i a function of 6 and V, the definite integral 



B ........................ (16) 





will be a function of V only. 



If the molecules are " rigid-elastic " spheres of diameter s, 



(17). 



If they repel each other with a force inversely as the fifth power of the 

 distance, so that at a distance r the force is *cr' , then 



I. (18) 



where A t is the numerical quantity T3682. In this case B is independent of V. 



The experiments of O. E. Meyer*, Kundt and Warburg t, PulujJ, Von 

 Obermayer, Eilhard Wiedemann|[, and HolmanI, shew that the viscosity of 

 air varies according to a lower power of the absolute temperature than the 

 first, probably the 077 power. If the viscosity had varied as the first power 

 of the 'absolute temperature, B would have been independent of V. Though 

 this is not the case, we shall assume, for the sake of being able to effect the 

 integrations, that B is independent of F. 



We shall find it convenient to write for B, 



where p is the hydrostatic pressure, N the number of molecules in unit of 



Pogg. Ann., 1873, Bd. 148, p. 222. t Ibid. 1876, Bd. 159, p. 403. 



: Witner Sift., 1874 and 1876. Ibid. 1875. 



| Ank. det Sei Phyt. at Nat., 1876, t. 56, p. 273. 



^ American Academy of Arto and Science*, June 14, 1876. Phil. May., a. 5, vol. 3, No. K>, 

 Fh., 1877. 





