HERSCHEL THE DISCOVERER. 25 



terested in comets, and attentively studied them, 

 introducing the terms of " head," " nucleus," and 

 "coma." Herschel anticipated the view that 

 comets are not lasting, but are partly disin- 

 tegrated at their perihelion passages. He was 

 of opinion that they travelled from star to star. 

 The extent of their tails and appendages he 

 thought to be a test of their age. 



We have now completed our sketch of 

 Herschel's important labours regarding our 

 Solar System. As Miss Clerke says, "A whole 

 cycle of discoveries and successful investigations 

 began and ended with him." But through ob- 

 serving the stars he made a further discovery 

 in connection with the Solar System; indeed, 

 one of the greatest discoveries in the history 

 of astronomy the movement through space of 

 the Sun, carrying with it planets and comets. 



"If the proper motion of the stars be ad- 

 mitted," said Herschel, "who can deny that of 

 our Sun?" Of course it was plain that the 

 motion of the Sun could only be detected 

 through the resulting apparent motion of the 

 stars. Thus, if the Sun is moving in a certain 

 direction, the stars in front will appear to open 

 out, while those behind will close up. But the 

 problem is by no means so easy as this. The 

 stars are also in motion, and, before the solar 



