SCIENCE AN* PHILI(g*PHY 135 



or electrons which all bodies give off under suit- 

 able treatment, such as raising to incandescence 

 or exposure to ultra-violet light. The atom is 

 now supposed to be built up of units of negative 

 electricity and of an equal number of units of 

 positive electricity, of very much greater mass, 

 the number of either kind being proportional to 

 the atomic weight; and the whole system is in a 

 state of equilibrium or of steady motion. 



We must understand, however, that this elec- 

 trical theory of matter is far beyond verification, 

 that it makes big assumptions, and that it leaves 

 many difficulties. Prof. Poynting writes in regard 

 to it: "The chief value of such a hypothesis lies, 

 not hi its objective truth, but in its success in 

 accounting for, in co-ordinating, what we actually 

 observe, and in predicting results which are after- 

 wards verified. It is to be regarded as a 'working 

 model ' which gives the same results as the actual 

 atom, though, it may be, by quite different 

 machinery." 



So that, after all, the theory of the electric atom 

 does not do more than represent the unknown 

 reality in a faithfully symbolical matter. It is a 

 working thought-model. But how far we are get- 

 ting from the old "matter" of the naive material- 

 ists. And yet the difficulties have only begun, 

 for the matter of physical analysis is an abstrac- 

 tion, whereas the matter of our direct experience 



