1 6 THE LESSON OF EVOLUTION 



a time must come when all energy will be equi- 

 librated ; and when, possibly, the visible Universe 

 may resolve itself into invisible, motionless ether. 



In the Solar System we can study the development 

 of a rneteoritic swarm in greater detail. Here we 

 find that the whole of the meteorites did not collect 

 into a single mass, but that several planets, as well 

 as the sun, were formed simultaneously. It has 

 been shewn by Professor G. H. Darwin that the effect 

 of many collisions among a swarm of meteorites would 

 be to gradually eliminate orbits of great eccentricity, 

 until in time a regular system would be developed, 

 when the whole of the meteorites would travel nearly 

 in the mean plane of their aggregate motions. The 

 larger of the meteorites would tend to settle towards 

 the centre, while other aggregations might easily occur 

 at different distances from the centre. And of these 

 the outer planets would be larger than the inner ones, 

 because in the more distant regions, where the attrac- 

 tion of the central sun was less, the movements of the 

 meteorites would be slower, and there would be a 

 greater tendency to agglomeration than where the 

 movements were more rapid. As meteorites contain 

 but little oxygen, hydrogen, carbon, silicon and alkalies 

 substances which are all abundant on the surface 

 of the earth large numbers must have been fused 

 together to form the earth, and the lighter substances 

 must have collected near the surface. Consequently, 

 the collisions between these meteorites must have 

 occurred with sufficient rapidity to melt the whole 

 mass. For, after a solid crust had been formed, all the 

 meteorites which fell on the earth would remain on 

 the surface, as they do now. 



