COMETS 193 



In IsoT Horschel concluded one of hi* paper* in 

 thene words: "I find that out of the sixteen coroeU 

 i I have examined, fourteen have been without 

 le solid bcxly in lh--ir r.-ntr--. un<i 



r two had a very ill-defined small central light. 



i might perhaps be called a nucleus, but did not 

 deserve the name of a disk." In the end of September 



year a comet was discovered by Mr. Pigott to 



ii Herschel at once turned his attention in the 

 , hope of wresting from it information regarding its 



re. By careful observations, continued over five 

 months, he felt himself warranted in < 1 for it 



nible, round and well-defined disk," 538 miles in 



ioter, and "shining in every part of it with equal 



itness," He came also to the conclusion "that 

 the body of the comet on its surface is self-luminous, 



. whatever cause this quality may be derived 1 * 

 He inferred besides that " the changes in the brightness 

 of the small stars, when they are successively im merged 

 in the tail or coma of the comet, or cleared from them, 

 evidently, that they are suffici. -ntly dense to 

 obstruct the free passage of star The ta 



e-omet, three weeks after ite discovery, was more 

 than nine millions of miles in length, and Herschel 

 was inclined to think that it "consisted of radiant 

 matter, such as, for instance, the aurora boreal is." It 

 was not bifid or split in two, as that of the comet of 1769 

 bad been, but it presented a peculiarity seen also mothers 

 of these bodies: "The south-preceding side, in all its 

 length, except towards the end, is very well defined : 

 following side is everywhere hazy and irre- 



; . especially towards the end ; it is also shorter than 

 the south-preceding one, . . . even to the naked eye." 



