made with a View to investigate its Magnitude , &c. 147 
Observations . 
Oct. 4, 1807. 10-feet reflector. The comet has a nucleus, 
the disk of which is plainly to be seen. 
Oct. 6. I examined the disk of the comet with a proper set 
of diaphragms, such as described in a former paper,* in order 
to see whether any part of it were spurious ; but when the 
exterior light was excluded, so far from appearing larger, as 
would have been the case with a spurious disk, it appeared 
rather diminished for want of light ; nor w T as its diameter 
lessened when I used only the outside rays of the mirror. 
The visible disk of the comet therefore is a real one. 
Oct. 4. I viewed the comet with different magnifying 
powers, but found that its light was not sufficiently intense 
to bear very high ones. As far as 200 and 300, my 10-feet 
reflector acted very well, but with 400 and 500 there was 
nothing gained, because the exertion of a power depending 
on the quantity of light was obstructed, -f- which I found was 
here of greater consequence than the increase of magnitude. 
Illumination of the Nucleus. 
Oct. 4, 6 h if. The nucleus is apparently round, and equally 
bright all over its disk. I attended particularly to its round- 
ness. 
Oct. 18. The nucleus is not only round, but also every 
where of equal brightness. 
Oct. 19. I see the nucleus again, perfectly round, well de- 
fined, and equally luminous. Its brilliant colour in my 10-feet 
* See Phil. Trans, for 1805, page 53. Use of the Criterion. 
f See Phil. Trans, for 1800, p. 78. 
U 2 
