

SCIENCE PROGRESS 



ON THE STRUCTURE OF THE UNIVERSE 



Bv H. SPENCER JONES, M.A., B.Sc. 



Fellow of Jesus College, Cambridge ; Chief Assistant, Royal Observatory, Greenwich 



It may be said with a good deal of truth that the ultimate object 

 of stellar astronomy is to discover the solution to the problem 

 of the structure and the evolution of the universe. The many 

 recent researches upon the distances and distribution of stars, 

 upon the relative distances of stars of different types, upon the 

 numbers of stars of different magnitudes, and upon allied topics, 

 have all contributed in throwing some light on this problem, 

 which, because of its complexity and baffling nature, because 

 also it is the most far-reaching with which the mind has to deal, 

 has fascinated and engaged the attention of men almost from 

 the dawn of civilisation. The Greek philosophers supposed the 

 world on which they lived to be the centre of the universe, and 

 that the sun, the planets, and the stars all rotated around it, 

 and they devised ingenious theories to account for the observed 

 motions of the planets. Our knowledge has advanced a great 

 distance since their time, yet, although many facts have been 

 accumulated, we have so far taken only the first few steps 

 towards a solution. This is not surprising when it is remem- 

 bered that for much of our knowledge we are dependent upon 

 photography, the application of which to astronomy is still of 

 quite a recent date. Except for the nearest stars, the refined 

 measurements necessary for determining stellar distances have 

 only been made possible by the development of photographic 

 methods. The problem of the present structure of the universe 

 is indeed, as Kapteyn has pointed out, the problem of the 

 distances. If the distance of each star were known in addition 

 to its position in the sky, its position in space would be 

 determined, and our knowledge of the present structure would 

 be complete. To fix the change in the structure, it would then 

 i 



