﻿716 Dr. H. Stanley Allen on an 



first law, but the point is one of so much importance that it 

 may repay further examination. 



The scattering of a rays by the magneton has been dis- 

 cussed by Hicks *, who has calculated a number of trajectories 

 in the equatorial plane similar in character to those investi- 

 gated by St0rmer |. The difficulty of forming an estimate 

 of the amount of scattering is very considerably increased 

 in the general case when the a particle is projected towards 

 a magnetic atom in any direction whatever, but the results 

 obtained by Hicks go to show that scattering of the right 

 order of magnitude can be obtained by postulating a 

 reasonable number of magnetons in the core. 



There is no idea of calling in question the mathematical 

 investigations of C. G. Darwin J, who dealt with the motion 

 of a charged particle under the action of a central force 

 varying as some power of the distance. The only question 

 -at issue is whether the experimental results on scattering are 

 of so decisive a character as to prohibit the introduction of 

 magnetic forces, and to lead with certainty to the conclusion 

 that the nucleus of a heavy atom cannot have a radius much 

 exceeding 10 ~ 13 cm. 



Hie Size of the Nucleus. 



Two arguments only have been advanced in favour of the 

 extremely small diameter assigned to the nucleus of the 

 Rutherford atom. The first is derived from the wide-angle 

 scattering of a particles, and, as we have seen, the argument 

 is inconclusive because no account has been taken of the 

 possibility of a magnetic field being associated with the 

 atom. The second depends on the assumptions that the 

 whole mass of the nucleus is electromagnetic in origin and 

 that this mass arises from a structureless charge of magnitude 

 N#, where N is the atomic number. Now we know that 

 both a and /3 particles are derived from the nucleus of radio- 

 active substances, and it is hardly thinkable that these should 

 exist in the nucleus save as discrete particles. We conclude 

 tliat at least for the elements of high atomic weight the 

 nucleus must possess a structure, though it remains to some 

 extent doubtful whether the two elements, hydrogen and 

 helium, at the beginning of the periodic table, are to be 

 looked upon as possessing a simple or a complex nucleus. 

 According to the views advanced by Nicholson from a study 



* W. M. Hicks, Proc. Roy. Soc. vol. xc. p. 356 (1914). 

 t Sttfrmer, Archiv for Mathematik, Christiania, vol. xxviii. p. 36 

 (1906). 



% C. G. Darwin, Phil. Mag. vol. xxv. pp. 201-210 (1913). 



