542 Sir J. J. Thomson on the Structure of 



have therefore no data by which we can compare the values 

 of the physical constants for molecules of this type with 

 molecules where the electrons are numerous enough to make 

 up a series of saturated cells. 



We can, however, compare the properties of a gas like 

 nitrogen, whose molecule contains only one cell, with that of 

 the molecule of oxygen which is made up of two cells. It is, 

 perhaps, a little surprising that what is called in the Kinetic 

 Theory of Gases the radius of the molecule is actually less 

 for the two-celled oxygen molecule than for the single-celled 

 nitrogen one. We must remember, however, that unless we 

 regard the atoms and molecules as hard impenetrable solids, 

 the size of the atom depends upon other than geometrical 

 considerations ; it depends essentially upon the range of the 

 forces exerted by the electrons and positive charges in the 

 molecule. Thus a system consisting of a uniform distribution 

 of negative electricity over the smrface of a sphere and an 

 equal positive charge at the centre would produce no effect 

 outside the sphere ; an atom of this character would have a 

 long free path and behave like a small atom ; while an atom 

 consisting of two equal point-charges, one positive and the 

 other negative, would have a large stray field and might 

 behave like a much larger atom than the spherical one, even 

 though the distance between the point-charges were less 

 than the radius of the sphere. The nitrogen molecule, con- 

 taining 10 electrons, has two of these inside the cell ; this 

 will introduce a want of symmetry and increase the stray 

 field, and thereby the apparent size of the molecule. But if 

 there is not a break in the size of the molecule as we pass from 

 nitrogen to oxygen, there is one in another property, which, 

 as it depends essentially on the configuration of the electrons, 

 is, I think, very suggestive. I allude to the effect of the 

 molecule on the scattering of polarized light investigated by 

 Lord Eayleigh (Proc. Roy. Soc. A. xcviii. p. 57). The light 

 scattered by a single electron in a direction at right angles 

 to the incident beam is completely polarized, and can be 

 extinguished by a Nicol prism. The same thing is true 

 when the light is scattered by a perfectly symmetrical body 

 such as a sphere ; if the scattering body is not perfectly 

 symmetrical — if, for example, it is ellipsoidal instead of 

 spherical — the scattered light is never completely polarized, 

 and therefore cannot be completely quenched by a nicol. 

 The ratio of the minimum to the maximum intensity of the 

 light as seen through a nicol, which would be zero for a 

 sphere, would increase with the ellipticity of the ellipsoid, 

 and may be taken as an indication of the deviation of the 

 scattering body from sphericity. 





