n8 Dr. Herschel’s Observations of a Comet, 
case the bright point to the globules, and in the other the 
globules to the bright point. * 
The apparent and real Magnitude of the planetary Body. 
The size of the bright point being much more like the 
smallest of the two globules, I shall add one quarter of their 
difference to o",^, and assume the sum, which is 0^,775 as 
the apparent diameter of the planetary disk. 
Then by a calculation from some corrected elements of the 
comet's orbit, which, though not very accurate, are however 
sufficiently so for my purpose, 1 find that the distance of the 
comet from the earth, at the time of observation, was nearly 
114 millions of miles; from which it follows that the bright 
point, or what we may admit to be the solid or planetary body 
of the comet, is. about 428 miles in diameter. 
The Eccentricity and Colour of the planetary Body. 
The situation of the bright point was not in the middle of 
the head, but was more or less eccentric at different times. 
The ibth of October that part of the head, which was to- 
wards the sun was a little brighter and broader than that to- 
wards the tail, so that the planetary disk or point was a little 
eccentric. 
The 17th 1 found its situation to be a little beyond the centre, 
reckoning the distance in the direction of a line drawn from 
the sun through the centre of the head. 
The 4th of November it was more eccentric than I had ever 
seen it before. 
* A similar method was used with the comet of 1807. See Phil. Trans, for 1808, 
page 145 • 
