58 Observations of a Comci. 



when the nucleus is-very small, no telescope, but what has 

 light and power in an eminent degree, will show it di- 

 stinctly. 



Observations. 



Oct. 4, 1807 . IO-feet reflector. The comet has a nu- 

 cleus, the disk of which is plainly to be seen. 



Oct. 6. I examined the disk of the comet wit-h a proper 

 6et of diaphragms, such as described in a former paper*, 

 iu 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 was 

 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 mag- 

 nitude. 



Illumination of the Nucleus. 



Oct. 4, 6h. \o. The nucleus is apparently round, and 

 equally bright all over its disk. I attended particularly to 

 its roundness. 



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 

 defined, and equally luminous. Its brilliant colour in 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. 20. In order to see the nucleus as small as it really 

 Isj we should look at it a long while, that the eye may gra- 



* See Phil. Trans, for 1805, p. 53. Use of :he Criterion, 

 f See Phil Tram, kn 1800, p. 78. 



dually 



