Professor Farrar’s observations of the Comet of 1811. 309 
ly round but ill defined. It had very much the colour and nearly the 
apparent magnitude of Saturn. The diameter of the head, including 
the coma, was found by a micrometer Novy. 6, to be nearly three min- 
utes. Around the head for the space of four or five times its diame- 
ter there was a kind of dark ground, and then a luminous appear- 
- ance, somewhat resembling a halo, and very apparent through an 
achromatic telescope, andeven distinguishable by the naked eye. ‘This 
partial ring of light appeared to be of a parabolic form, and after de- 
scribing a curve of nearly 180°, the two parts diverged, and passed on 
in nearly a rectilineal course, making the two branches of the tail, In 
figure it very much resembled a current of water, flowing round a 
stick, or other obstacle placed in it. See Plate HL. Fig. 4. 
~ From Sept. 6th. to Jan. 8, this comet described an arch of 132°, as 
seen from the earth. The apparent motion at first was about one de- 
gree per day; its velocity increased, till it amounted to a little more 
than 13° per day, and then began to decrease till it disappeared ; 
when its daily motion, as refered to the ark, was only about 20’. It 
came within the circle of perpetual apparition, about the 20th of Sept. 
‘and continued within it about 20 days. It reached its greatest appar- 
ent northern declination 50° near the 2d of October, and its greatest 
northern latitude, 632°, about the 17th of the same month. When it 
was first seen, 6th of Sept. its longitude was about 18° less than that 
of the Sun. After continuing for some time at about the same dis- 
tance it gained upon the sun, and on the 11th of Sept. came up with 
it, and passing it arrived at its greatest elongation 53° about the 10th 
of November. From this time it began to fall back with respect to 
the sun, and continued to approach it with an accelerated motion, till it 
was at length lost in the twilight. I began my observations, by taking the 
distances of the comet from Arcturus and Lyra, or Vega, and continued 
