THE EXTENT OF THE UNIVERSE 33S 



as of the sixth, and so on indefinitely. Now, it is actually 

 found that while this ratio of increase is true for the 

 brighter stars, it is not so for the fainter ones, and that the 

 increase in the number of the latter rapidly falls off when 

 we make counts of the fainter telescopic stars. In fact, it 

 has long been known that, were the universe infinite in 

 extent, and the stars equally scattered through all space, the 

 whole heavens would blaze with the light of countless 

 millions of distant stars separately invisible even with the 

 telescope. 



The only way in which this conclusion can be invalidated 

 is by the possibility that the light of the stars is in some 

 way extinguished or obstructed in its passage through space. 

 A theory to this effect was propounded by Struve nearly a 

 century ago, but it has since been found that the facts as he 

 set them forth do not justify the conclusion, which was, in 

 fact, rather hypothetical. The theories of modern science 

 converge towards the view that, in the pure ether of space, 

 no single ray of light can ever be lost, no matter how far 

 it may travel. But there is another possible cause for the 

 extinction of light. During the last few years discoveries 

 of dark and therefore invisible stars have been made by 

 means of the spectroscope with a success which would have 

 been quite incredible a very few years ago, and which, even 

 to-day, must excite wonder and admiration. The general 

 conclusion is that, besides the shining stars which exist 

 in space, there may be any number of dark ones, forever 

 invisible in our telescopes. May it not be that these bodies 

 are so numerous as to cut off the light which we would 

 otherwise receive from the more distant bodies of the uni- 

 verse ? It is, of course, impossible to answer this question 

 in a positive way, but the probable conclusion is a negative 

 one. We may say with certainty that dark stars are not so 

 numerous as to cut off any important part of the light from 

 the stars of the Milky Way, because, if they did, the latter 

 would not be so clearly seen as it is. Since we have reason 

 to believe that the Milky Way comprises the more distant 

 stars of our system, we may feel fairly confident that not 

 much light can be cut off by dark bodies from the most dis- 

 tant region to which our telescopes can penetrate. Up to this 



