THE EVOLUTION OF THE UNIVERSE 17 



enough when he says that this coming together, or 

 condensation, of the particles of dust would cause 

 heat. Compression always causes heat. And when 

 you are thinking of a mass of metal dust weighing 

 trillions of tons, as a star does, the heat will in the 

 end be prodigious. The concentrated dvist would 

 become a star. We need only say further that these 

 great centres of fiery concentrated dust would tend to 

 turn round on their axes; and that, although they 

 were tens of millions of miles apart, they would be 

 sucked into each other and destroyed unless they 

 travelled rapidly through space in orderly' paths. At 

 first, we suppose, they would be a disorderly crowd. 

 Then ** natural selection" would set in. The small 

 irregular masses would be sucked into the larger. 

 No doubt some of the giant suns I have mentioned 

 have fed on others in this way. In the end the great 

 cloud of dust would be a collection of fiery globes 

 travelling in circular paths at a safe distance from 

 each other. 



That is how we understand the origin of stars. 

 Such clouds do exist in the heavens in great numbers. 

 Astronomers call them *' nebulae," which is the Latin 

 for clouds. They already have heat enough to be 

 visible to us. One large class of them, which we call 

 the "spiral nebula," are much disputed. Some 

 think that, as I said on an earlier page, they are 

 separate imiverses at a prodigious distance from us. 

 I do not share this view. Most astronomers believe 



