LIFE IN THE PRIMITIVE OCEAN 23 



be a great central globe and a number of smaller 

 globes (or planets) connected with it. 



These smaller globes would, of course, be sucked 

 by gravitation into the central globe unless they 

 moved round it at a great speed. There are several 

 ways in science of showing how this circulation of 

 the planets round the sun might be caused, but they 

 are too advanced for this little primer. If the reader 

 will look at the photograph of a spiral nebula in some 

 astronomical book, he will see the fiery matter con- 

 densing into a large central sun and a large number 

 of smaller fiery masses all round it. We know that 

 they are moving round it. The whole structure is 

 turning round. 



But how do the planets come to follow orderly 

 paths round the central sun, at such distances and 

 such speeds that the system may last for millions of 

 years? Natural selection gives the answer. At first 

 there were probably far more planets circling round 

 our sun than there are now. Those which followed 

 unsuitable paths were drawn in by the others or by 

 the sun until only the "fittest" survived. Our eight 

 planets are the survivors of a mighty struggle for life. 



We have every reason to suppose that the other 

 stars were formed in the same general way as our 

 sun. It is therefore probable that they have, unless 

 there v^ere special conditions, planets of their own. 

 These planets are made of the same material as ours. 

 The spectroscope can tell us what even the most 



