of the Stability of Dr. A. IV. Stewart's Atom. 

 Hence for stability 



26:] 



f So? 



sin 



w 



+2 



a 4 + r 



1 

 'Jar cos 



{?♦>)} 



-2 



9 79 -1 7 XVIT, 



<r -f a z — lad cos -f 



?)* 



S 



(«) 



must be positive. 



Special Cases. 



I. Helium — group — no. of electrons = two; no. of 

 valency electrons = 0. 



Consider the configuration of the atom in which the two 

 positives and two negatives are in one straight line. Then 

 apply equation (5) for the condition of equilibrium. 



' \ 4a 2 (a-r) 2 + (a + r) 2 ) 



(a — r) 2 ' (a+r 

 But the quantity inside the bracket is 



. 2 = 0. 



(9) 



always negative 



(r>a). Hence for the particular configuration considered, 

 equilibrium, cannot be maintained. Thus, when the atom in 

 the course of its existence arrives at this configuration, the 

 inner ring breaks up spontaneously. 



A note might be added here concerning the a particle. 

 Of this Dr. Stewart writes as follows : — " With regard to 

 the expulsion of charged helium atoms from radioactive 

 elements, it is assumed that the a particle consists of four 

 positive and two negative electrons: the pair of negative 

 electrons being situated at the foci of an ellipse around the 

 circumference of which two positive charges revolve. The 

 extra pair of positive charges travel in longer, ' cometary ' 

 orbits; so that they are easily detachable when in aphelion." 

 (The italics are the present author's.) 



There are serious objections to such a view of the con- 

 stitution of the ol particle both from the dynamical and 

 physical standpoint : 



(1) Tt is difficult to see how the two inner positives could 

 revolve in an ellipse of which both of the foci were 

 occupied by a negative electron. They certain lv 

 could not, if the law of force was that of "inverse 

 squares.'''' It would have been more in accordance 

 with the previous part of the paper if Dr. Stewart 

 had assumed that these positive and negative electrons 

 revolved in concentric circular orbits. 



