FORCES AND ATOMS 347 



one another which concerns us the most. Newton spoke of it in one of the 

 passages which I have just been citing, but the pleasure was denied him of 

 knowing how it resembles gravity. Both follow the law of the inverse- 

 square; yet two centuries were to elapse between the years when Newton 

 proved this for the one and Coulomb for the other. The electrostatic force 

 is broader though than gravity, for it includes an attraction and a repulsion. 

 There are two categories of charge, the positive and the negative: any 

 charge repels those of its own category, attracts those of the other. 



This entry upon the scene of a long-range repulsion modifies the prospects 

 of a successful picture of the world as a congeries of particles, and seems at 

 first glance to brighten them greatly. Dismiss gravity — forget about 

 cohesion — put the question : in an imaginary universe made up of electrified 

 particles some positive and some negative, acting on one another by electro- 

 static forces only, is it possible to have stability with all of the particles 

 standing still? 



Again the answer is no. This is not, however, too disappointing: we are 

 accustomed to motion as the antagonist of gravity in the celestial case; shall 

 we not now introduce it to be an ally to the electrostatic repulsion, the two 

 of them conjointly being the antagonists of the attraction? 



Now with real surprise and disappointment, one stands confronted again 

 by the ruthless negative answer. The past revives : I have said that a pre- 

 Newtonian philosopher would scarcely have accepted motion as the death- 

 less antagonist to gravity, because he would have believed that motion dies 

 out of itself. Well, the motion of an electrified particle does die out of itself 

 — so says the electromagnetic theory. A proviso must here be inserted for 

 correctness' sake, though it does not alter the situation. Uniform motion 

 does not tend to die out — but uniform motion is useless to our ambitions. 

 The orbital motion of a planet, the swing of a pendulum, — on these the 

 theory must be built; but these are accelerated motions; and accelerated 

 motions destroy themselves, when the moving body is electrified. Their 

 energy passes into light, and the body sinks to rest. Aristotle was avenged 

 in the nineteenth century on those who sneered at him; for what he had 

 believed of motion generally, was in effect what they believed of the motion 

 of electricity. Still, as nearly everyone knows, there is, after all, an electri- 

 cal theory of matter; the elementary particles are deemed to be electrified, 

 and the forces between them are deemed to be electromagnetic. 



How is all this to be reconciled? By a statement which is the prelude to 

 the final one — provided, that is, that all works out as well as physicists now 

 hope, and provided also that we avert our eyes from the phenomena called 

 "nuclear". Having imagined the elementary particles as points possessed 

 of mass and bearing charges, and acting upon one another by electromag- 



