COMETS. 137 



are very numerous, and a year never passes 

 without one or more being discovered. The 

 ordinary periodic comets, such as Encke's, Faye's, 

 and others, are very faint, and are becoming 

 fainter at each return a clear proof that comets 

 die, as Kepler said three centuries ago. This 

 brings us to the subject of the next chapter, 

 Meteoric Astronomy. 



