﻿552 Dr. A. 0. Rankine on the 



plane, the velocity of the fluid increasing behind and dimin- 

 ishing in front of the moving sphere. 



Fisr. 12. 



Accelerated motion of sphere Ya/v=3 (Theoretical). 



The solutions thus obtained are of course only applicable 



to values of — - slightly above the critical value ; the form 



v 

 of the stream-lines in figs. 7 and 8 seems to show that a solu- 

 tion for these cases maybe obtained by starting with the 

 discontinuous motion worked out by Kirchhoff and Rayleigh, 

 and some encouraging results have been obtained which will 

 be given in a later paper. 



LVI. Note on the Relative Dimensions of Molecules. By 

 A. 0. Rankine, D.Sc, Fellow of and Assistant in the 

 Department of Physics in University College, London*. 



IT is well known that the knowledge of the viscosity of a 

 gas makes it possible to calculate upon the kinetic 

 theory the mean free path of the molecules, and hence their 

 dimensions. According to Maxwell the relations are as 

 follows : — 



*7 = 0-307/>\G, (i.) 



where r\ is the viscosity, p the density. \ the mean tree path, 

 and G the root mean square velocity of the gas molecules. 



The value of G is a /_i?> where p is the pressure of the gas. 



V \ P 

 Further, the equation 



(ii.) 



\ = 



v 7 ^ 



Communicated by Prof. A. TV. Porter, F.E.S. 



