258 



Free Path Phenomena 



[CH. XII 



The table is taken from Weinstein's Thermodynamik (i. p. 329) with 

 the exception of the entry Helium, for which the value of n is due to 

 Lord Rayleigh*. 



A similar table, in which the numbers are in almost complete agreement 

 with those given above, will be found in Landolt and Bornstein's tables. 



We notice at once that s is greatest for the molecules of which the 

 structure is simplest. This is what we should expect. In the case of a 

 complex molecule the atoms will not 611 the whole of the circumscribing 

 sphere, so that it will be possible for the circumscribing spheres of two 

 molecules in certain positions to intersect, while the force between them 

 remains comparatively small. A glance at fig. 21 will probably make this 

 clearer than a loog explanation. The effect of including forces such as 

 these in the average of forces at a given distance apart is not only to lessen 

 the average force between two molecules at a given distance apart, but also 

 to lessen the rapidity with which the average force falls off, or, in other words, 

 to decrease s. 



FIG. 21. 

 * See also Schultze, Annalen der Physik, n. p. 302. 



