﻿300 Mr. F. P. Slater on the Rise of 



apart of their centres have already been stated ; and both 

 modified models have mean areas of projection which are 

 very easily calculated. The upper limit thus determined 

 proves to be 2*12 times the collision area of the argon atom ; 

 the lower limit is 1*90 times the same area. Using the 

 known value 0*648 xlO -15 cm. 2 for the collision area of the 

 argon atom, we find that the mean area of projection of the 

 model consisting of two argon atoms with an intermediate 

 neon lies between 



1*37 x 10" 15 cm. 2 



and l'23xl0- 15 cm. 2 



We may venture to predict with some confidence that the 

 mean collision area of the CS 2 molecule, when determined, 

 will be found to be between the above values. A more 

 exact estimate could of course be made, but the degree of 

 accuracy at present attainable in determining molecular 

 dimensions from viscosity measurements is not sufficient to 

 render the additional calculation worth while. 



Summary. 



On the assumption of the validity of the Lewis-Langmuir 

 view of molecular constitution, the probable behaviour during 

 encounters has been examined for the molecules of carbon 

 oxysulphide and carbon bisulphide. In the former case it is 

 shown that the molecular dimensions as derived from the 

 application of the kinetic theory to the viscosity measure- 

 ments of C. J. Smith, are in striking accordance with the 

 results of the above examination. In the latter case 

 comparison is not yet possible, on account of the absence of 

 necessary data. 



Imperial College of Science and Technology, 

 May 11th, 1922. 



XXVII. The Rise of <y-Raij Activity of Radium Emanation. 

 By F. P. Slater, MISc. (Vict.), B. A. [Cantab.)*. 



XN a previous paper t it has been shown how the initial 

 rise of 7-ray activity, starting from pure radium 

 emanation, depended on the nature of the walls of the tube 

 containing the gas, the reason . being that a small but 



* Communicated by Prof. Sir E. Rutherford, F.R.S. 

 t Slater, Phil. Mag. vol. xlii. p. 904 (1921). 



