OBSERVATIONS OF A COMET. 



II. 



Observations of a Comet, made with a view to investigate its 

 Magnitude, and the Nature of its Illumination. By Wil- 

 liam Herschel, LL. Z>. F.R.S*. 



JL HE comet, which we have lately observed, was pointed Comet when 

 out to me by Mr. Piggot, who discovered it at Bath the 

 28th of September, and the first time I 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 differ- 

 ent construction from many I have seen before, in which no 

 solid body could be discovered with any of my telescopes. 



Jn the following; observations, my attention has been di- Examined 



, & / ,., i • with respect f 



rected to such phenomena only, as were likely to give us - lts physical 



some information relating to the physical condition of the condition, 

 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- Terms relating 

 pressed by terms that may be liable to misapprehension, q Uen tlymisap* 

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

 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 oi- 

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



* Philosophical Transactions for jSo$, Part II, p. 145. 



B % observation, 



