of a Comet , with Observations thereon . 53 
I think I could not err more than three or four minutes from 
its being on the middle horizontal wire, and about as much 
from the intersection of the vertical, with the middle hori- 
zontal wire. But, after all, it is a vain thing to talk of 
critical exactness in this matter, either in the quadrant or 
transit observations, under the circumstances I am going to 
describe to you. The comet, in the telescopes of these instru- 
ments, had somewhat the appearance of a hen's egg, seen 
obliquely, with the large end towards the eye; of a dull white 
misty light. I could perceive no nucleus, therefore I consi- 
dered the longest diameter, which was nearly directed towards 
the east, (but there was hardly any perceivable difference in 
the diameters) as the line in which, had any nucleus been vi- 
sible, it would have been found ; and I endeavoured, in the 
manner I have described, to bring this line on the middle 
horizontal wire, and the brightest part of it up to the vertical 
wire; and when I thought I had effected this, I read off the 
divisions on the arch, and noted the time by Earnshaw's 
regulator. 
On January 21st, I observed the instantaneous immersion of 
y Tauri, at o h 54/ 22" by my clock; and at 2 h 3' 31" I saw it 
again about a minute's distance from the moon's enlightened 
limb, the moment of emersion having escaped observation. I 
had, on the same day, observed the sun's passage over the me- 
ridian, by a mean of the wires, at 2o h 18' 45^"; the clock had 
been losing a little more than a second a day, for eight or ten 
weeks past.* The mean of ten observations of the first satellite 
* Hence the immersion of the star was at 4 h 34' 48",6, and the first sight of it af- 
ter the emersion at 5 h 43' 46", apparent time. This may perhaps be useful in deter- 
mining the longitude of Mr. Gregory’s observatory. — Note by Dr, Maskelyne, 
