THE NUMBER OF THE STARS. 



Ill 



is very far short of half the total number. To attain that 

 limit, we should have to penetrate down six or seven magnitudes 

 fainter still ; i.e., to the 2ord or 24th magnitude. It is probable 

 that the great 5-foot telescope of the great Mount Wilson 

 Observatory, which is at present the largest telescope in tlie 

 world, could by photography, with very long exposures, just 

 reach down to this limit ; so that half the stars could now be 

 registered if anyone wished to take the trouble to do it. 



The calculations above referred to, lead to the conclusion that 

 the total number of the stars is not less than 1,000,000,000, 

 and that it cannot much exceed twice this amount, so that 

 perhaps we are warranted in saying that it is probably less than 

 3,000,000,000. 



It is interesting to notice that this is comparable with the 

 population of the earth, which is estimated to be about 

 1,500,000,000. This is also about the number of spores which 

 are produced by half-a-dozen mushrooms. 



With these figures before us, we may proceed to enquire what 

 and where are the stars. Omitting details and explanations, 

 the facts that have been already ascertanied may be summarized 

 as follows : — 



The stars are suns, generally similar to our own in structure, 

 but at immensely great distances from us. The nearest star, so 

 far as we know at present, is that known as Alpha Centauri, 

 and is twenty million of million miles aw"ay. In tlie neighbour- 

 hood of the sun, that is to say, within distances not extravagantly 

 greater than this, the stars are probably scattered with some 

 fair approach to uniformity in space, but their brightness varies 

 enormously from one star to another. We know of some stars 

 that are actually one hundred times as bright as the sun, while 

 there are others not nearly so bright, some giving indeed only 

 one ten-thousandth part the light of our sun. On the whole 

 the sun, as compared with other stars, is fairly liigli up in the 

 scale of brightness. 



It can be shown mathematically that if we take any mixture 

 of stars of varying brightness, and repeat this mixture uniformly 

 throughout space, that is to say, if we have throughout all space 

 a uniform distribution of stars, not all of the same biiohtness 

 but the same kind of mixture everywhere, then the total 

 amount of light which these stars would give to us would not 

 be finite but infinite ; the heavens would be one complete blaze 

 of light. And on that basis of a uniform mixture of stars of 

 varying brightness, the relative rate of increase in the number 

 of stars from magnitude to magnitude can Idc calculated, and it 



