146 Observations on the Tails of Halley^s Comet. 



sky neither rendered opake by vapors, nor bright by the reflected 

 rays of the sun. 



Oct. 8., F. M. — The comet seen, but so near the horizon, that 

 nothing but the envelope was visible. 



Oct. 9, bh. 30to. 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 h, the distinctness of the tail, as seen with 

 the naked eye, was not greater than on the morning of the 4lh, 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 h of Ursa Major, and was directed 

 nearly towards that star. With the larger telescope, the nucleus 

 was distinct. 



Oct. loth, 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 terrestrial 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 

 with its magnifying power. The smaller telescope had not that ef- 

 fect. 



Oct. llth, 7A. 30m. P. M. — The train was very distinct. As 

 seen obliquely, it intersected the line connecting 5< and X 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° or 

 9° in length ; but occasionally, when the eye was in the most favor- 

 able position, its length was three times as great, i. e. between 24° 



