62 NATIONAL ACADEMY OF SCIENCES 



It turns out that this one object has exactly the radial velocity 

 of the helium stars in the first stream; that is, we find exactly 

 the motion we must expect in these nebulae, if it were the birth- 

 place of the stars. We will not, of course, on this single fact 

 find far-reaching conclusions ; but we have a right, in my opinion, 

 to say that here is a fact that singularly strengthens what has 

 already been concluded from other facts. 



We see, moreover, that the observation of the radial velocity 

 of other irregular nebulae must, ere long, furnish us with a crucial 

 test of the theory. 



There is another problem involved in our observations which 

 might seem to be of no less importance than the one just men- 

 tioned. How have we to explain the fact that the internal 

 velocity of the stars gradually increases with age? The astron- 

 omer who, in the study of the motion of the heavenly bodies, has 

 found hardly a trace of any other force than gravitation, will 

 naturally turn to gravitation for such an explanation, and it 

 really seems a necessity, that under the influence of the mutual 

 gravitation, bodies which at the outset have little or no relative 

 motion must get such motion, and they must come to fall toward 

 each other, and this velocity must increase with time. 



Thus far, there is no great difficulty, but now let us look 

 farther back in time, back to the time in which the stars had not 

 yet been formed, and in which matter was still in its primordial 

 state. If it be true that mutual attraction of the stars has gen- 

 erated such an enormous amount of internal motion in the time 

 needed by the helium stars to develop from the helium stars 

 to second and third class stars, how have we to explain that we 

 find that same matter nearly at rest at the first stage of evolution 

 at which we meet it? How have we to explain that in pre- 

 helium ages gravitation has produced no effect? 



He that believes in the creation of matter at a finitely remote 

 epoch may find no difficulty in the question ; but to him who does 

 not, it is simply astonishing to see matter behaving as if there 

 were no gravitation at all. What may be the explanation? Is 

 there no gravitation in primordial matter, or is there another 

 force exactly counterbalancing its effects? 



