﻿298 Prof. A. 0. Rankine on the Molecular Structure 



formed by circles 2 and 1. The first of these quantities is- 

 the area of the central cross-section of the argon sphere 

 itself, viz. 0*648 x 10 -15 cm. 2 ; the two latter are readily 

 obtained from the graph in the paper already mentioned *.. 

 They prove to be 0*217 x 10~ 15 cm. 2 and 0*226 x 10~ 15 cm. 2 

 respectively. The total is 1*09 x 10 ~ 15 cm. 2 , and this provides 

 our upper limit. 



10. With regard to the lower limit, we can obtain a 

 satisfactory value by contemplating a variation of our model, 

 which avoids the special type of overlapping responsible for 

 complications. A suitable change for this purpose is to 

 substitute for the sphere 1 a smaller sphere having the same 

 centre but of such magnitude that its projection becomes 

 just eclipsed by projection 2 at the same orientation of the 

 symmetrical axis for which projection 2 is just eclipsed by 

 projection 1, as shown by the dotted circles in fig. 2. o The 

 radius of the necessary sphere is found to be 0*93 A as 

 compared with the original value 1*15 A. Examination of 

 the projection of a sphere of this size, in relation to the other 

 two projections, shows that for no orientation does eclipsing 

 of the shaded type appear, and the formulae already available 

 enable the mean area of projection to be calculated exactly.. 

 The value so obtained will, however, obviously be less than 

 the true value aimed at, on account of the reduction of size 

 assumed for sphere 1. Using the graph already mentioned,, 

 the lower limit thus derived is 



0*648 x 10" 15 cm. 2 -f 0*217 x 10~ 15 cm. 2 + 0*138 x 10" 15 cm. 2 



= l-00xl0- 15 cin.* 



11. The foregoing justifies the assertion that a molecular 

 model having the dimensions of an argon atom succeeded 

 by two neon atoms in line and spaced according to the- 

 demands of outer electron contiguity may be expected to* 

 have a mean collision area intermediate between 



1*09 x 10- 15 cm. 2 

 and 1-00 xlO- 15 cm. 2 



The actual value of the mean collision area of the COS- 

 molecule, as determined from viscosity is 



with a possible error of 2 or 3 per cent. It falls definitely 

 between the upper and lower limits obtained from our 

 calculations, and seems to provide striking corroboration of 



* A. O. Rankine, Proc. Phys. Soc. vol. xxxiii. p. 371. 



