82 PRESSURE OF LIGHT 



less and less elliptic orbits, the smaller particles 

 yielding sooner to this tendency than the larger. 

 And all would tend to lessen their orbits and 

 finally to pass into the sun. There are very good 

 grounds for the supposition that some of the 

 periodic meteor showers are comets which have 

 been disintegrated and spread along their orbits. 

 We may perhaps make the additional supposition 

 that we witness examples of the further disintegra- 

 tion into orbits differing widely from the original 

 ones in the casual meteors which flash across the 

 sky and which cannot be assigned to any known 

 group. 



But the end of all must be the same. The Sun 

 cannot tolerate dust. With the pressure of his 

 light he drives the finest particles altogether away 

 from his system. With his heat he warms the 

 larger particles. They give out this heat again 

 and with it some of that energy which enables 

 them to withstand his attraction. Slowly he 

 draws them to himself, and at last they unite 

 with him and end their separate existence. 



