226 
Dr. Herschei/s Observations on 
1 . They are celestial bodies, generally of a very small size, 
though how far this may be limited, is yet unknown. 
2. They move in very excentric ellipses, or apparently para- 
bolic arches, round the sun. 
3. The planes of their motion admit of the greatest variety 
in their situation. 
4. The direction of their motion also is totally undetermined. 
5„ They have atmospheres of very great extent, which shew 
themselves in various forms of tails, coma, haziness, &c. 
On casting our eye over these distinguishing marks, it appears, 
that in the first point, relating to size, our new stars agree suffi- 
ciently well ; for the magnitude of comets is not only small, but 
very unlimited. Mr. Pigott's comet, for instance, of the year 
1781, seemed to have some kind of nucleus; though its mag- 
nitude was so ill defined, that I probably over-rated it much, 
when, November 22, I guessed it might amount to 3 or 4" in 
diameter. But, even this, considering its nearness to the earth, 
proves it to have been very small. 
That of the year 1783, also discovered by Mr. Pigott, I saw 
to more advantage, in the meridian, with a 20-feet reflector. It 
had a small nucleus, which, November 29, was coarsely esti- 
mated to be of perhaps 3" diameter. In all my other pretty 
numerous observations of comets, it is expressly remarked, that 
they had none that could be seen. Besides, what I have called 
a nucleus, would still be far from what I now should have mea- 
sured as a disk; to constitute which, a more determined outline 
is required. 
In the second article, their motions differ much from that of 
comets ; for, so far as we have at present an account of the 
