EVOLUTION OF THE STARS 



221 



the next approach to the Sun carries the scattering process a step 

 further. Kepeated returns to the Sun dissipate the individual consti- 

 tuents of the comet more widely. The intensity of the comet's light 

 is reduced, and eventually it becomes too faint for discovery and obser- 

 vation. There is little room to doubt that this process is responsible for 

 the total disappearance of several periodic comets. 



Meteor Steeams 

 The argument is strongly supported by the meteor streams. It is 

 well known that on certain nights of the year we see an unusually large 

 number of meteors, which come from certain definite directions in space. 

 These meteors have been extensively observed and their orbits have 

 been computed. The illustration shows the orbits of four such swarms. 



Fig. 3. Orbits of Meteoric Swarms, which are known to be associated with comets. 



They intersect the Earth's orbit at certain computed points. We pass 

 through those points on certain nights of the year and the meteoric 

 materials moving in the one orbit collide with the Earth in the other 

 orbit. Xow, it has been shown that the orbits of these four meteor 

 streams and of one other stream are the orbits of five periodic comets 

 which have disappeared from sight. Clearly, the cometary materials 

 had been gradually scattered by the disintegrating effect of the Sun's 

 attraction, and the separate particles were compelled to move in orbits 

 differing slightly from each other, and from the recognized orbits of 

 the comets. The meteoric collisions with the Earth are such as to 

 show that we are dealing with widely separated small masses moving 

 in orbits nearly identical with each other. 



In the case of these five swarms there is certainly a close connection 

 between meteors and comets. Whether all meteoric matter has come 

 from the disintegration of comets can not be answered now. We can 



