THE LAST RIDDLE 447 



five hundred million suns like ours. The telescopes reveal the 

 existence of stars distant possibly thirty thousand light-years 

 or more. Let us conceive this mass distributed over an equivalent 

 extent of space. Conceive that a star is drawn from an infinite 

 distance towards the centre of this system : what is the utmost 

 speed which it may acquire ? The very surprising answer is 

 twenty-five miles per second. 



But we have seen that Arcturus and 1830 Groombridge move 

 at two or three hundred miles per second. Of course if one sun 

 approached very close to another, the case would be quite 

 different. For example, a body approaching the sun may 

 acquire a velocity of nearly four hundred miles per second. For 

 such a mass as that of Arcturus, still more of Canopus, this 

 velocity would be very much greater. It may be that it is 

 from their occasional approach one to another that the stars 

 acquire some of the speeds that they are known to possess. 

 This would obviate one difficulty ; but not its correlative. 



If such a stellar universe as Professor Newcomb imagines is 

 incapable of generating a velocity like unto that of Arcturus or 

 Groombridge, it is obvious that it could not hold a star or sun 

 with such a speed in leash. If Arcturus is moving at three 

 hundred miles or more per second, it would require a mass one 

 hundred and forty-four times that of five hundred millions suns 

 to keep this speeding sun from dashing away into the depths 

 of space. If our stellar system were finite, and of less mass 

 than this, Arcturus would be lost to it. 



Arcturus is but probably one case in many. There may be 

 hundreds and thousands of suns, for aught we know, moving 

 very much more rapidly than this. If ever the stars formed a 

 relatively compact system, they might, in this view, have been 

 steadily losing one sun after another. In so doing the system 

 would be steadily losing mass, with the result that it would 

 progressively lose whatever power it may originally have pos- 

 sessed to hold together. 



Of course all this is merely the vaguest conjecture. We 

 know absolutely nothing about the mass of the universe save 

 perchance one thing. Seeliger of Munich has pointed out that 

 the idea of an infinite universe is incompatible with the notion 

 that the law of gravity is absolute and invariable. Seeliger 

 assumes that the law is not absolute, and that the force of 

 gravitation does not increase or decrease in perfect conformity 



