150 Dr. Herschel’s Observations of a Comet, 
very distinctly ; the diameter of the nucleus however appeared 
to be less than twice that of the satellite. 
Oct. 18. With the 10-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 new 10-feet mirror, the delicate 
polish of my former one having suffered a little from being 
exposed to damp air in noctural observations. This new one 
being uncommonly distinct, and the air also remarkably clear, 
I turned the telescope from the comet to Jupiter’s third satel- 
lite, 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. 
6 h 20'. I repeated these alternate observations, and always 
found the same result. The night is beautifully clear, and the 
moon is not yet risen to interfere with the light of the comet. 
Nov. 20. With a 7-feet reflector, and power only 75, I can 
also see the nucleus ; it is extremely small, being little more 
than a mere point. 
Of the Head of the Comet . 
When the comet is viewed with an inferior telescope, or if 
the magnifying power, with a pretty good one, is either much 
too low, or much too high, the very bright rays immediately 
contiguous to the nucleus will seem to belong to it, and form 
what may be called the head. 
Oct. 19. I examined the head of the comet with an indiffe- 
rent telescope, in the manner I have described, and found it 
