146 Observations on the Tails of Halley’s Comet. 
sky neither rendered opake by vapors, nor bright by the = 
rays of the sun. 
Oct. 8., P. M—The comet seen, but so near the horizon, that 
nothing but the envelope was visible. 
Oct. 9, 5h. 30m. A. M.—Thin clouds, the moon, and the dawn, 
conspired to render the tail invisible. 
7 P. M.—The moon was below the horizon, but the comet being 
only about 18° above it, the distinctness of the tail, as seen with 
the naked eye, was not greater than on the morning of the 4th, yet 
by myself and several others, it was seen distinctly with the same 
telescope which was before used, as also with one of a less magni- 
fying power, and greater comparative aperture. With the latter, 
which showed it more distinctly, it appeared as a faint brush of light 
extending about half way to 4 of Ursa Major, and was directed 
nearly towards that star. With the larger telescope, the nucleus 
was distinct. 
Oct. 10th, 7h. 30m. P. M-—The moon had not risen, nor was 
any sensible portion of its light reflected from that part of the at- 
mosphere which was in the direction of the comet. This body was 
about 4° farther from the horizon than at 7 o’clock on the preceding 
evening, and the tail more distinct; and, although this distinctness 
was afterwards diminished by the rising of the moon, and by the 
descent of the comet, in its diurnal revolution, yet there had been 
in 24 hours, an evident increase of brightness and length, as seen 
under similar circumstances as to sebrastyial atmosphere. By indi- 
rect vision, it was about 3° in length. When the eye was fixed 
steadily on it, it nearly disappeared, as other faintly luminous objects 
do by direct vision. The length was still more reduced by the 
larger telescope, probably in consequence of the faintness of the 
object, and the smallness of the aperture of the telescope, compared 
pice, its magnifying power. The smaller telescope had not that ef 
cl 
Oct. 11th, Th. 30m. P. M.—The train was very distinct. As 
seen obliquely, it intersected the line connecting « and > Draconis, 
at about one eighth the distance from the former to the latter. Seen 
by direct vision, it was very short. ‘When at some distance from 
the axis of vision, it was usually seen with great distinctness, 8° oF 
9° in length ; but occasionally, when the eye was in the most favor- 
able position, its length Was three times as great, ¢. e. between 2 24° 
