Ohservat ions of a Comet . 5 7 



28th of September; and the first time T had an opportunity 

 of examining it was the 4th of October, when its brightness 

 to the naked eye gave me great hopes to find it of a different 

 construction from many I have seen before, in which no 

 solid body could be discovered with any of my telescopes. 



In the following observations, my attention has been di- 

 rected to such phaenomena only, as were likely to give us 

 some information relating to the physical condition of the 

 comet: it will therefore not be expected that I should give 

 an account of its motion, which I was well assured would 

 be most accurately ascertained at the Royal Observatory at 

 Greenwich. 



The different parts of a comet have been generally ex- 

 pressed by terms lhat may be liable to misapprehension, 

 such as the head, the tail, the coma, and the nucleus ; for 

 in reading what some authors say of the head, when they 

 speak of the size of the comet, it is evident that they take 

 it for what is often called the nucleus. The truth is, that 

 inferior telescopes, which cannot show the real nucleus, 

 will give a certain magnitude of the comet, which may be 

 called its head ; it includes all the very bright surrounding 

 light ; nor is the name of the head badly applied, if we keep 

 it to this meaning ; and since, with proper restriction, the 

 terms which have been used may be retained, I shall give a 

 short account of my observations of the comet, as they re- 

 late to the above-mentioned particulars, namely, the nucleus, 

 the head, the coma, and the tail, without regarding the or- 

 der of the time when they were made. The date of each 

 observation, however, will be added, that any person who 

 may hereafter be in possession of more accurate elements of 

 the comet's orbit, than those which I have at present, may 

 repeat the calculations in order to obtain a more accurate 



result. 



Of the Nucleus. 



From what has already been said, it will easily be under- 

 Stood, that, by the nucleus of the comet, I mean that part 

 of the head which appears to be a condensed or solid body, 

 and in which none of the very bright coma is included. It 

 should be remarked, that from this definition it follows, that 



when 



