THE LAW OF EQUILIBRIUM 127 



stars away off by themselves in space, yet near enough to 

 each other to constitute them a binary system. Now 

 visualize to yourself, if you please, the rays of gravita- 

 tional attraction proceeding from all the stars in the uni- 

 verse, and from all sides, to each one of our pair of stars 

 in turn, and you cannot but see that the two systems of 

 rays thus produced cross each other much as did the two 

 cords within the ring, only far more complicatedly. We 

 may fancy the whole field of stars as divided into suc- 

 cessive pairs and tugging upon their respective cords, 

 and we shall have, as nearly as may be, a copy of the ex- 

 periment in question except in one particular. This 

 particular consists in the fact that the stellar strands, al- 

 though eternally pulling, always stay crossed ; though al- 

 ways unwinding, they never become unwound. Thus does 

 our binary system not only fall to the maximal attraction, 

 but also in a definite direction; the while simultaneously 

 revolving around its center of gravity. 



This mechanical principle is capable of unlimited ex- 

 tension, upward and downward. It applies as well to 

 molecules as to stars, to cohering particles as well as to 

 cosmic orbs separated by the full span of the universe. 

 The sun's next door neighbor is Alpha Centauri, ten 

 thousand times farther from him than Neptune, his outer- 

 most planet. Think of these two stars as we thought of 

 the previous pair, think of any pair of stars, or of any 

 combination of pairs or clusters of stars, in their relation 

 to the sum of the universe, and there will be borne in upon 

 you the realization that the whole body of the macrocosm 

 is perpetually writhing within itself in the throes of 

 equilibristic evolution. The physical universe is built on 

 the principle of action, not stagnation ; on that of autom- 

 atism, not blind chance ; on perpetuity, not finiteness. 



Concentrating our attention on the solar system, we 

 note that the planets revolve around the sun in (seeming) 

 ellipses, that their radii vectores sweep over equal areas 

 in equal times, and that the cubes of their distances are 

 proportional to the squares of their periodic times. The 

 problem before us is to prove that these phenomena are 

 incidental to the normal operation of the principle of the 



