ATOMIC DISINTEGRATION. 155 



themselves as though they were on an inner sphere con- 

 centric with the outer one and it is natural to suppose that 

 any number of such corpuscles could be placed over such a 

 sphere and balanced by the attraction of the outer sphere 

 and their own mutual repulsions. Professor Thomson has, 

 however, shown most decidedly by mathematical calcula- 

 tion that such is not the fact. 



As a matter of fact he shows that unless the number of 

 corpuscles is small, not more than five, this arrangement is 

 unstable and consequently could never maintain itself. 

 When the number of corpuscles exceeds five they break up 

 into two groups. The group containing the smaller occupies 

 the surface of an inner shell towards the centre. The others 

 are on an outer shell concentric with the inner one , the 

 sphere of positive electrification surrounding and balancing 

 them all. As the number of corpuscles still further in- 

 creases there comes a stage at which the equilibrium cannot 

 be stable even with two groups and the corpuscles divide 

 themselves into three groups on three concentric shells ; and 

 as the number increases after that, more and more groups 

 are necessary for equilibrium. This has been neatly and 

 elegantly shown by Professor Mayer in an experiment 

 with a model atom in which the forces producing equilib- 

 rium are similar to those producing equilibrium among the 

 corpuscles in the real atom as we are considering it to be 

 in nature. 



In this experiment, a number of tiny magnetized steel 

 needles thrust through discs of cork are floated on water 

 so that the little negative poles are all above the surface 

 of the water while the positive poles are beneath. These 

 little floating negative magnetic poles, just like corpuscles, 

 repel each other with forces varying inversely with the 

 square of the distance. In this way each little negative 



