154 PHYSICAL SCIENCE 



tubes with effective momentum. In this way, 

 Thomson regarded electric momentum as similar 

 in kind to ordinary dynamical momentum. Should 

 the inertia of material objects be electrical in its 

 nature, then, on this view, the mass and kinetic 

 energy of ordinary bodies is to be regarded as the 

 mass and kinetic energy of the aether bound to 

 the Faraday tubes which emanate from the con- 

 stituent electrons. If such a scheme be accepted, 

 the problem of the material universe is referred 

 completely to the problem of the nature and 

 properties of the luminiferous aether. A great 

 simplification in our conception of the world is 

 thus effected, but again, as always, an ultimate 

 explanation eludes us. Moreover, some of the 

 consequences of the theory of relativity, which we 

 shall trace in Chapters VIII. and IX., show that 

 caution and restraint are needed in dealing with 

 the luminiferous aether. We probably know less 

 about it than our fathers did. 



Instead of stating matter in terms of electricity, 

 it is simpler, and perhaps less ambitious, to express 

 electricity in terms of matter, as Thomson did at 

 first, and say that electrified atoms contain one 

 or more corpuscles in excess or defect of their 

 normal number. Nevertheless, the electron theory 

 of matter, formerly supported on mathematical 

 grounds, has been strengthened greatly by these 

 developments of experimental science. Moreover, 

 from the point of view of radio-activity, which we 

 shall consider in the next chapter, that theory is 

 of supreme importance, for it gave the first indica- 

 tion that an atom was a complex and possibly 

 unstable body. Now the occasional instability 

 of a complex chemical atom, and its disintegration 



