200 SCIENCE PROGRESS 



doubt any lack of uniformity in the distribution would alter 

 the value of this multiple somewhat, but would not disturb 

 its order of magnitude.) In order to make this expression for 

 the mass agree with actually observed values, one has to 

 give a value to a, the " radius," of the order io" 13 (in cms.). If 

 we now turn to the consideration of the nucleus of an atom 

 according to the model (such as that of Rutherford) at pre- 

 sent found necessary to interpret such phenomena as radio- 

 activity, atomic number, and scattering of charged particles 

 by atoms, we find that in order to account for the mass of a 

 nucleus (which is practically that of its atom) on the same 

 basis as we account for the mass of the electron, we must 

 assign a smaller " radius " to it than to the electron ; yet the 

 nuclei of the more complex atoms must, from certain con- 

 siderations, be supposed to contain electrons and at the same 

 time preserve their minute size. This is a serious difficulty 

 unless we can suppose that electrons and positive charges can 

 actually interpenetrate each other and occupy the same space. 

 Furthermore, there is the difficulty about the coherence of 

 the electron itself in view of the self-repulsive nature of its 

 charge. 



Nicholson points out that if we resort to the view which 

 regards elementary charges as regions of strain in the ether 

 we evade these difficulties if we can find a satisfactory basis 

 for introducing a linear constant such as the " radius " men- 

 tioned above. But he remarks that it would seem more 

 natural that such line constants should possess some signifi- 

 cance throughout the whole ether, rather than merely come into 

 existence in regions where the ether is strained into the form 

 of matter. He suggests that the ether may be, in fact, cellular 

 in structure, with these linear magnitudes involved in the 

 specification of the cells and thereby in any strained structure 

 composed of them. Such speculations apart, however, he 

 works out this idea mathematically for a type of ether-strain 

 which is for practical purposes concentrated at its " centre " 

 and diminishes very rapidly outwards according to an ex- 

 ponential law. Thus his electron (based on that of Larmor) 

 has no definite boundary. It is a region where there is a 

 distribution of electric charge with a density p given by the 

 equation 



P = p e- h ' 



