1944 
CONSTRUCTION OF COMETS, &C. 
Examinations 
with different 
powers. 
The nucleus 
subtended 
seconds. 
velure, would not admit of the idea of a gradual condensation of 
nebulosity, such as I saw in the head of the first comet ; but 
plainly pointed out that the nucleus and its chevelure were 
two distinct objects. 
Jan. 8. The cornet had a pretty well defined nucleus with, 
very faint chevelure. When magnified 1 /O times the nucleus, 
though less bright, was rather better defined. 
Jan. 18 . Within a very faint chevelure I saw the nucleus 
as before. 
Jan. 20, The air being uncommonly clear, I saw the body 
of the comet well defined ; and as the moon was already so 
far advanced in its orbit as to render future opportunities of 
viewing the comet very improbable, I ascertained the magni- 
tude of its body, with a very distinct 10 feet reflector, by the 
following three observations : 
First with a low power, which gave a bright image of the 
nucleus, I kept my attention fixed upon its apparent size ; then 
looking away from the telescope, I mentally reviewed the im- 
pression its appearance had made on the imagination, in order 
to see whether it was a faithful picture of the object and by 
looking again into the telescope I was satisfied of the simi- 
litude. 
In the next place I used a deeper magnifier, and alternately 
viewed and remembered the appearance of the nucleus. It 
was fainter with this power. 
The third observation was made in the same manner with 
a magnifier of 170. This showed the nucleus of a larger 
diameter, but much less bright, and not so well defined. 
The next morning, having recourse to my usual experiment 
with a set of globules, by viewing them at a given distance 
with the same telescope and eye-glasses, I found that one of 
them, on which I fixed, gave me, as nearly as could be esti- . 
mated, the same magnitude with the first eye-glass, and was 
proportionally magni&ed by the second and third, with only 
this difference, that the highest power showed the globule with 
more distinctness than it did the nucleus ; and by trigonome- 
try the angle under which I saw the globule was found to be 
$", 2744 *. 
* j[ prefer this method of ascertaining the small diameter of a 
