INORGANIC EVOLUTION. 



23 



temperature are simply due to the smaller bodies having cooled 

 more rapidly than the larger ones. In fact, one may with 

 probability suppose that they all formed part of one very large 

 and diffused collection of matter, either gaseous or meteoric, 

 which extended at least as far out from the centre as the orbit of 

 Neptune. And this conclusion is rendered all the more probable 

 by the fact that the spectroscope informs us that the Sun is 

 composed of very much the same materials as those which we 

 iind upon our earth. 



Let us now glance at the innumerable multitude of Stars and 

 Nebulae. 



It has been said that our Sun is a star, and that is doubtless 

 true ; and it is also true that every star is a sun. But the great 

 majority of the Stars differ fi'om our Sun in many very important 

 respects. Indeed, probably no two stars are exactly alike. Nature 

 does not repeat herself. Everything that comes from her work- 

 shop possesses its own peculiarities. No two leaves are exactly 

 alike ; no two men are exactly alike ; and, so far as we can judge, 

 no two stars are exactly alike. The number of the stars is 

 exceedingly great. It has been estimated that the stars visible 

 in the most powerful telescopes number at least 100 millions, 

 and possibly even double that niunber ; and they vary extremely 

 in size and brilliancy, many far surpassing our Sun in magnitude 

 and light, and many being very much smaller. For example, 

 Canopus is probably not less than 15 to 20 millions of miles in 

 diameter, and has been estimated to give at least 22,000 times 

 the light of the Sun. On the other hand, one of the sun's 

 nearest neighbours, a small star in the constellation of the 

 Grreat Bear, is estimated to emit only sio part of the sun's light, 

 and to have a mass smaller in proportion. Indeed, the great 

 majority of the stars which are nearest to us, with the exceptions 

 of Sirius, Procyon, and Alpha Centauri, are much smaller and 

 less luminous than oiu- Sun. And yet on the whole our Sun is 

 rather a small star than otherwise. The stars are not scattered 

 through space with any approach to uniformity. In that region 

 of the universe which we occupy, the stars are comparatively 

 very sparsely distributed, our nearest stellar neighbour being 

 Alpha Centauri, whose light takes four years and four months to 

 reach us, travelling at the rate of 185,000 miles a second, across 

 a distance of about 25 billions of miles. But in some other 

 regions the stars are situated very much nearer to each other, 

 especially in star clusters and in the Milky Way. As I have 

 said, the great majority of the stars are very unlike our Sun in 



