i6 THE EVOLUTION OF THE UNIVERSE 



know from our shooting-stars, which are fragments 

 of metal (from grains to large blocks) that shoot 

 rapidly into our atmosphere at night, and are burned 

 up by friction, soace is far from empty. Countless 

 myriads of these solid particles or blocks travel 

 through it at a great speed. The "ocean of ether" 

 is as full of them as the sea is of fishes. A great 

 cloud of dust billions of miles in extent would capture 

 countless numbers of them. 



So there would be sure to be denser centres in our 

 imaginary dust cloud. These would draw the sur- 

 rounding dust by the same law of gravitation as the 

 earth gathers the dust in your room. They would 

 grow larger and denser. The spaces between the 

 thick centres would grow thinner and thinner. More- 

 over, as these centres would be, so to speak, sus- 

 pended in space, they would draw particles freely 

 from all sides, and would take the shape of large 

 loose globes. If you imagine this going on for mil- 

 lions of years, you see at once that in the end prac- 

 tically all the dust of the cloud will be gathered 

 into so many large globes, with great empty spaces 

 between them. You will also see that the heavier 

 particles, the metals, will go to the centre, and the 

 lighter particles, the gases, will remain at the fringe. 

 You will have gaseous atmospheres round globes of 

 metal. 



The mathematician can tell us a good deal more 

 about what would happen. We understand him well 



