CHAPTER XXXIII 

 THE LAST RIDDLE 



THERE can never be in human knowledge any such thing as 

 finality. Always at the end there is a mystery ; it will always 

 be there. Still in a relative way we do seem here and there to 

 approach something like finality. We have reached something 

 like finality in the explanation of the planetary mechanism. 

 So far as we are now able to perceive the planets form a system 

 that, internally at least, is stable. So far as we now know, if 

 they were undisturbed by any exterior agency, they would pursue 

 their orbital ways for ever. It may be that subtle causes are 

 at work eventually to disturb this apparent equanimity. If 

 there are, they are too minute in their action to be observed. 

 For all of our human concerns the sun long since will have 

 been snuffed out and life upon any of the planets become im- 

 possible before they would begin to have an appreciable effect. 



The dominating, binding force of the system of the planets 

 we call gravitation or attraction. When we endeavour to con- 

 ceive of a similar system for the stars we are lost. We can 

 imagine no such binding force. Considering their speed, the 

 spaces that intervene between the stars seem insuperable. The 

 force of gravity, the attraction of one particle of matter for 

 another, is practically the weakest force we know. It requires 

 the minutest measurements of which man is capable, to disclose 

 the existence of this attraction between two earthly bodies. 



Even the attracting force of such an enormous mass as the 

 sun, exerted upon the huge bulk of the earth, is representable 

 by very familiar strengths and strains. An ingenious com- 

 parison has been made by Professor Young. He pictures the 

 earth as attached to the sun by means of telegraph wires. 

 Their own weight of course disregarded, it would require a 

 system of wires spaced a half-inch apart, and covering the 

 whole of the surface presented to the sun, to hold the earth in 

 leash. When we consider that each wire would hold a section 



445 



