1809.] 
gained, because the exertion of a power 
_depending on the quantity of hivht was 
obstructed, which I found was here of 
greater consequence than the increase of 
magnitude, 
Illumination of the Nucleus. 
Oct. 4, 6h. 15’. The nucleus is appa- 
rently round, and equally bright all over 
its disk. 1 attended particularly to its 
roundness. 
Oct 18. The nucleusis not only round, 
but also every where of equal brightness. 
Oct. 19. [see the nucleus again, per- 
fectly round, well defined, and equally 
luminous. Its brilhant colourin my ten- 
feet telescope is a little tinged with red; 
but less so than that of Arcturus to the 
naked eye. 
Magnitude of the Nucleus. 
Oct. 26. In order to see the nucleus 
as small as it really is, we should look at 
it a long while, that the eye may gradually 
lose the impression of the bright coma 
which surrounds it. This impression will 
diminish gradually; and when the eye has 
got the better of it, the nucleus will then 
be seen most distinctly, and of a deter- 
mined magnitude, : 
Oct. 4... With a-seven-feet reflector 1 
estimated the diameter of the nucleus of 
the comet at first to be about five seconds; 
but soon after It called it four, and by look- 
ing at it longer, I supposed it could not 
exceed three seconds. 
Oct. 6. ‘Ten-feet reflector, power 221. 
‘The apparent disk of the comet is much 
less than that of the Georgian planet, 
which being an object I have seen so 
often with the same instrument, and mag- 
nifying power, this estimation, from me- 
mory cannot be very erroneous, 
Oct. 5. Micrometers for measuring 
very small diameters, when high magaify- 
ing powers cannot be used, being very lit- 
tle to be depended upon, | erected aset of 
sealing-wax globules upon a post at 2422 
anches from the object mirror of my ten- 
feet reflector, and viewed them with an 
eye glass, which gives the instrument a 
power of 221, this being the same which 
J had found last night to shaw the nucleus 
af the comet well. 1 kept them in their 
place all the day, and reviewed them from 
time to tune, that their magnitudes might 
- be more prectsely remembered in the 
evening, when I intended to compare the 
appearance of the nucleus with them. 
On examining the comet, I found the 
diameter of its nucleus to be certainly loss 
than the’largest of my globules, which, 
Being *0466 of an inch, subtended an an- 
gle of 3-97 atthe distance of the tele- 
gcope in the day time, 
Proceedings of Learned Societies. ~ 165 
Comparing the nucleus also with the 
impressions which the view of the second 
and third had left in my memory, and of 
which the real diameters were °0325 and - 
-0290 of an inch, and magnitudes at the 
station of the mirror 2°77 and 2: 47, i 
found, that the comet was almost as large 
as the second, and a little larger than the 
third. 
Oct. 18. The nucleus js Jess than the 
globule which subtends 2:77. 
Oct 19. 
clear, I saw the comet forty minutes after 
five; and being now at a considerable al- 
titude, examined it with 289, and having 
but very lately reviewed my ‘globules, i 
judged its diameter to be not only less 
than my second globule, but also less than 
the third ; that is, less than 2°47. 
Oct. 6. 
withstanding its great light, does not ‘show 
the nucleus of the comet larger than the 
ten-feet, with an equal magnifier, makes. 
1, 
Oct. 98, My large 
with the mirror of twenty- four inches in 
diameter, does not increaseshe size of the 
nucleus. : 
Oct. 6: Being fully aware of the obt 
Jections that may “be made against the me= 
thod of comparing the magnitade of the 
nucleus of the comet with, objects that 
-cannot be seen together, [ had reconrse* 
to the satellites of P Jupiter fora more de- 
cisive result, and with my seven-feet te- 
lescope, power 202, I viewed the disk of - 
the third satellite and of the nucleus ef 
the comet alternately. They were both 
already too low te be seen very distinctly ; 
the diameter of the nucleus however ol ae 
peared to be less than twice that of the 
satellite. 
Oct. 18. With the ten-feet reflector, 
and the power 221, a similar estimation 
was made; but the light of the moon 
would not permit a fair comparison. 
Oct. 19.. I had prepared a riew ten- 
feet mirror, the delicate polish of my for~ 
mer one having suffered a little from be- 
ing exposed to eae air in n-cturnal ob 
servations, ‘This new one being-wncon- 
monly distinct, and the air also ‘remarka- 
bly clear, I turned the telescope from the 
comet to, Jupiter’s third satellite, and saw 
its diameter very distinctly larger than 
the nucleus of the comet. I turned the 
telescope again to the comet, and as soon 
as I saw it distinctly round and well de- 
fined, I was assured that its diameter was 
less than that of the satellite. 
6h. 20’. I repeated these alternate 
observations, and always found the same 
result, The night is beautifully clear, and 
the 
The air being uncommonly 
The twenty-teet reflector, nots » 
e ten-feet telescope, : 
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