432 THE WORLD MACHINE 



We have never run across as yet such a runaway planet, 

 nor have we any actual evidence that they exist. But the 

 possibility is one of the plain implications from our recently 

 acquired knowledge of twin suns. For aught we know this 

 may be the origin of one or more of the planets of our own 

 system, though the striking uniformity in all the motions of 

 our system makes the chances against this perhaps millions to 

 one. It is difficult to understand how a planet coming, on the 

 theory of chance, from any one of the possible directions of 

 space could be swung into line into the general plane of 

 planetary motion and set marching with the rest, all by the 

 sheer power of gravitation. 



Be this as it may, the apparent conclusion which we may 

 draw regarding the stability of our planetary system is precisely 

 the opposite from the conclusions of Laplace and Lagrange. So 

 far as the motions and forces inherent to it are concerned, our 

 system would apparently be stable throughout infinite ranges 

 of time. For anything that we can now perceive this is the 

 case. But the probability that the vast majority of heavenly 

 bodies are not luminous but dark, the consequent implication 

 of great number and increased possibility of approaches and 

 collisions, gives the matter quite another aspect. In another 

 two or three hundred years perhaps we shall know something 

 of the actual number of bodies in space, perhaps of their rela- 

 tive separation as well. Then it would be possible to compute, 

 on the theory of probability, the average chance which every 

 system has of surviving amid the constant clash of the suns 

 as they pursue their interweaving ways. 



How many of the meteoric swarms through which the earth 

 sweeps are of origin foreign to the solar system we do not know. 

 Quite possibly all of them are ; it is fairly certain that some of 

 them are. We have seen our globe and all of the other planets 

 sweeping up hundreds of tons of them per day, the sun possibly 

 thousands of tons. We have, then, in the meteoric showers a 

 steady cosmic contribution to the mass of our system. On the 

 other hand, the far larger part our system may act simply 

 as a temporary carrier ; we may be steadily picking up swarms 

 as we push through space. These swarms take on highly 

 elliptical orbits ; in nearing another system these might be 

 much more readily shed than a planet. In the same fashion 

 we might lift a few swarms from some neighbourly sun. 



