Observations on the Tails of Halley's Comet. 147 



and 27°. After being dilated for a few (perhaps two or three) de- 

 grees from the head, it appeared to continue nearly of the same 

 width to the extremity, the remoter half appearing to be rather 

 narrower, and very faint. All the eye pieces were tried ; also the 

 finder, and the other small telescope. With the last, its apparent 

 length was 8° ; with the five feet telescope and lowest power, 1° 

 in length, and still less, or invisible, with the higher powers. To 

 the eye, there appeared to be a nucleus ; but with the telescope, 

 this seemed to be more like a vapor, still denser than the outer va- 

 por, and to have a diameter about one eighth that of the whole 

 head ; but with the small telescope, from one fourth to one sixth. 

 With the highest magnifying power, nothing but this central part 

 could be seen, and that appeared rather as a mass of vapor, than 

 a solid nucleus. 



At 10 o'clock, some time after the' moon had risen, and when the 

 comet had descended nearer to the horizon, the tail was not seen 

 by direct vision, and by indirect vision, its length was but 2°. 



Oct. 12, 8A. oOtn. P. M. — The tail appeared to be directed to- 

 wards /3 Ursae Minoris, and seemed to the naked eye about 9° in 

 length. There was one remarkable circumstance in relation to its 

 length, this evening, as compared with the preceding ; which was, 

 that when viewed directly and intently, its length, brightness and 

 constancy, were found to have increased, whilst the total length, as 

 seen by iiidirect vision, was not half as great as on the preceding 

 evening. That long, faint, white, and straight beam of equable 

 width, which on the preceding evening, had stretched across the 

 heavens like an auroral streamer, was now, as it were, cut off near 

 the place where it joined the more obvious part. These were the 

 phenomena of simple vision; and nothing remarkable was seen with 

 the portable telescope. 



But at 8h. 40m. on directing the larger telescope, furnished with 

 the eye piece of lowest magnifying power, I discovered a kind of 

 supernumerary tail. The nebulous matter seemed to have been in 

 in a great measure, accumulated on the lower side of the brightest 

 part, or nucleus, and to have formed a very distinct and regular 

 conical brush of light, the axis of which was directed downwards, 

 and a little to the right, making an angle of about 120° with the 

 long tail before described. The length of this new tail was equal 

 to about three times the diameter of what I have called the nucleus, 

 having the breadth of the nucleus at the part next to it, and about 



