§ 13 OF ARTS AND SCIENCES. 407 



forces exerted at considerable distances, the atoms beins: 

 hypothetically soft though perfectly elastic bodies. 



In the next section we shall consider the ratio of the 

 molecular diameter, or shortening of the free path, to the 

 whole molecular distance; the object of the present section 

 is to obtain formulae for actual use, from which this troub- 

 lesome factor may have been eliminated. 



We have already obtained three equations independent 

 of the free path, namely, 



JLD 



JLDl _ 



= ^> (0 



K, (2) 



L. = //- //'. (3) 



We have, moreover, equations involving the ratio of/' to 

 /, namely, 



^'"T 77^7=7" (4) 



3 /-/' 



T ^r-2,1 ' 



(5) 



and 



In these equations J, T^ , vl and — L are well-known 



m 



physical constants. 



y= 42,000,000 (C. G. S.) 



'^l = 33?948jC)C)C)?oc)o (C. G. S.) 

 7'„:=273° (Centigrade). 



• — is half the "molecular weight" 



