CONSTITUTED OF SPHERICALLY SYMMETRICAL MOLECULES. 

 With a similar notation for R' 12) &c., we find that 



459 



R' o / Aji/m+TnY j, . ij3 hmm \ n, 

 , 3 = 9w(v+9 r r[-. -- /JU + s"- r+Ru, 

 1 1 mm' I I m + m'J 



S' 

 , a = 



\hmm 



The terms P' 12) &c., represent the effect of the attractive forces in deflecting the 

 molecules without inducing collisions ; they are functions of the temperature in 



general, and can be expanded in ascending powers of 



Jimm' 

 m+m' 



i.e., in descending 



powers of 9. It may be shown that in each case they are of the form 



( m + m/ Y 



I -- rl 



\hmrn' 



\m+m7 



hmm' \ 3 1 



- ; I +...f, 



m+m7 J 



where s = 3, 4, or 5, according as we are considering P, R, or S. 

 Hence the preceding formulae may be written 







72 / 



mm 



and so on, where we have put C 12 = 1 , .. 



lim+m' 



SUTHERLAND, in his formula for the coefficient of viscosity, neglected all the terms 

 of lower order in 9 than C 12 /0, and the success of the formula in representing the 

 variations of viscosity with temperature (in the case of gases, though not in the case 

 of vapours) seems to show that this procedure is legitimate under ordinary conditions 

 in gases. This is equivalent to the neglect of the effect of the attractive forces in 

 deflecting molecules without producing collisions. 



If we agree to neglect these terms our formulae become 



(52) 



= 



1+1 



Ca 



9 



*, = I 



9 



fc s = i! 



1 + 



9 9 



* R denotes the universal gas-constant of the formula pv = (R/m) 



3 N 2 



