THE EXTENT OF THE UNIVERSE 327 



this question in a somewhat comprehensive way. It is pos- 

 sible only because the universe, vast though it is, shows cer- 

 tain characteristics of a unified and bounded whole. It is 

 not a chaos, it is not even a collection of things, each of 

 which came into existence in its own separate way. If it 

 were, there would be nothing in common between two widely 

 separate regions of the universe. But, as a matter of fact, 

 science shows unity in the whole structure, and diversity 

 only in details. The Milky Way itself will be seen by the 

 most ordinary observer to form a single structure. This 

 structure is, in some sort, the foundation on which the uni- 

 verse is built. It is a girdle which seems to span the whole 

 of creation, so far as our telescopes have yet enabled us to 

 determine what creation is; and yet it has elements of simi- 

 larity in all its parts. What has yet more significance, it is 

 in some respects unlike those parts of the universe which 

 lie without it, and even unlike those which lie in that cen- 

 tral region within it where our system is now situated. The 

 minute stars, individually far beyond the limits of visibility 

 to the naked eye, which form its cloudlike agglomerations, 

 are found to be mostly bluer in color, from one extreme to 

 the other, than the general average of the stars which 

 make up the rest of the universe. 



In the preceding essay on the structure of the universe, 

 we have pointed out several features of the universe showing 

 the unity of the whole. We shall now bring together these 

 and other features with a view of showing their relation 

 to the question of the extent of the universe. 



The Milky Way being in a certain sense the foundation 

 on which the whole system is constructed, we have first to 

 notice the symmetry of the whole. This is seen in the fact 

 that a certain resemblance is found in any two opposite 

 regions of the sky, no matter where we choose them. If we 

 take them in. the Milky Way, the stars are more numerous 

 than elsewhere; if we take opposite regions in or near the 

 Milky Way, we shall find more stars in both of them than 

 elsewhere; if we take them in the region anywhere around 

 the poles of the Milky Way, we shall find fewer stars, but 

 they will be equally numerous in each of the two regions. 

 We infer from this that whatever cause determined the 



