﻿Atomic Model with a Magnetic Core. 715 



nucleus of small dimensions carrying a positive charge, and 

 this nucleus is surrounded by electrons in orbital motion. 

 According to Nicholson coplanar rings of electrons are not 

 possible in such a case, and the model can neither be of the 

 " planetary " nor of the " Saturnian " type ; but, provided 

 the electrons are in one plane, can only possess a single ring 

 of electrons. 



In these models only the electrostatic forces due to 

 the positively charged portion of the atom are taken into 

 account. It has been pointed out by the present writer* 

 that it may be necessary to consider not only electro- 

 static but also magnetic forces in the immediate vicinity 

 of the atom. According to this view the atom would 

 consist of a magnetic core which is electrically charged,, 

 surrounded by electrons in orbital motion. Whether it is 

 possible for the electrons to form concentric rings in this 

 case is a point deserving the attention of mathematicians - T 

 experimentally such rings appear to have sufficient stability 

 to allow them to be directly observed as in the striking cases 

 recorded by Birkeland f. In these experiments photographs 

 were taken of the discharge through a large vacuum-tube 

 with a magnetized sphere as cathode. Rings were formed 

 round this globe resembling the rings of Saturn, in some 

 cases as many as three distinct rings could be observed. 



The Scattering of the Alpha Rays. 

 The scattering of alpha rays by atoms of matter has 

 afforded results from which Rutherford has formed an 

 estimate of the size of the nucleus. In the theory of 

 scattering which he has proposed only electrostatic forces 

 are considered. In this case the scattering depends on the 

 inverse fourth power of the velocity of the u particle. If: we 

 consider an « particle moving in the equatorial plane of 

 a simple magnet, it appears that the scattering would depend 

 on the inverse square of the velocity. In the general case 

 of a charged particle projected in any direction in a com- 

 bined magnetic and electrostatic field, it is probable that 

 some intermediate law would be obeyed. The experiments 

 of Geiger and Marsden % agree moderately well with the 



* 'Nature,' vol. xcii. p. 630 (1914). 



t Birkelaud, C. R. vol. cliii. p. 938 (1011). 



X Geiger & Marsden, Phil. Mag. vol. \.w. p. 620 (191S). "Several 

 experiments were made, and in every case the scattering was found lo 

 vary at a rate more nearly proportional to the inverse fourth power of 

 the velocity than to any other integral power. Owing to the comparative 

 uncertainty of the values of the velocity tor small ranges, however, the 

 error of experiment may he somewhat greater than appears ironi column N . 

 of the table." The tabulated numbers vary from 22 to 28. 



