CHAPTER XVII. 



FURTHER CONSIDERATIONS REGARDING THE 

 STRUCTURE OF AN ATOM. 



THE hypothesis that has been already referred to, 

 No. 3 in Chap. XV., that an atom consists of a 

 globular mass of positive electricity with minute 

 negative electrons embedded in it either at rest, or 

 vibrating about a position of equilibrium, or revolving 

 in regular annular orbits, is obviously not free from 

 difficulties ; though its success in explaining many 

 observed facts seems to justify an attempt to mini- 

 mise those difficulties, and to render hopeful an 

 effort ultimately to overcome them. 



One objection that can easily be raised is to ask 

 how a mass of positive electricity can hold together 

 against the mutual repulsion of its parts. This diffi- 

 culty is felt more in the case of positive electricity 

 than in the case of negative, because by hypothesis 

 the positive charge has some perceptible bulk, namely 

 the size of an atom, whereas the negative charge or 

 electron is exceedingly small. But however small an 

 electron is, it must be supposed to have parts, and 

 there is just as much reason for supposing the parts 

 of a negative unit to be mutually repulsive as there 

 is in supposing the parts of the positive unit to be 

 mutually repulsive. Hence the question is equally 



