1825.] 



Astronomical Society* 



467 



of y Draconis, the other, in the measure of the distance of that 

 star from the pole. 



After the new mural circle was erected in 1812, another 

 attempt was made to determine this important element, the 

 result was 38° 2V 2V\b\ a result, however, in which it was 

 thought probable that an error of half a second might exist. 



In the year 1822 a new method of observing was introduced 

 at Greenwich, by means of the reflected images of stars from 

 an artificial horizon. To apply this to the determination of the 

 element in question, by comparing two catalogues, one formed 

 by direct vision, the other by reflection ; that co-latitude being 

 assumed to be the true one which made the sum of the small 

 positive and negative differences equal to 2:ero; and that was found 

 to be 38° 3 F 21'', differing by one second from the determi- 

 nation furnished by Bradley's observation. This result, how- 

 ever, may involve an error of from a quarter to half a second, 

 which subsequent observations may diminish. 



The same paper includes some remarks on observations upon 

 the pole-star, and an interesting circumstance, which is this :— 

 The undulation to which a mass of mercury is hable, even 

 with the greatest care, is, in itself considered, unfavourable to the 

 exact bisection of an image ; but a circumstance occurs in the 

 formation of the image in the telescope, which, in some mea- 

 sure, compensates the inconvenience. The vibrations of the 

 mercury in a longitudinal trough, occasion an elongated image 

 of the star in the direction of the wire, appearing like a suc- 

 cession of stars which become smaller and smaller, as they 

 recede from the central undefined mass, exhibiting an appearance 

 like beads threaded on the wire, which is extremely favourable 

 to bisection. 



The elements of one of the comets above-mentioned, were 

 announced to the Society, as computed by Mr. Taylor, sen., 

 and Mr. Taylor, jun. of the Royal Observatory, and M. Ca- 

 preci, of Naples. They are respectively, as below. 



Passage of perihelion < 



Longitude of ditto . . . . 



Longitude of g3 



Inclination of orbit. . , . 

 Perihelion distance. . . . 

 Motion 



Taylor, sen. 



Dec. lOa-9338 



Greenwich. M.T, 



3 ISO 3/ 57// 



35 46 58 



33 20 40 



1-22951 



Retrogade. 



From 3 observ. 



Taylor, jun. 



Dec. lOd-4559 



Greenwich. M.T, 



319" 10' 26" 



35 45 36 



33 30 42 



1-24633 



Retrograde. 



From 3 observ. 



Capreci. 



Dec. 8d-895 

 Naples. M.T. 

 317° 24' 40" 



35 19 50 



32 44 20 

 1-20808 



Retrograde. 

 From 4 observ. 



A letter was read from Mr. R. Cornfield, a member of the 

 Society, to Dr. Gregory, describing an appearance noticed by 

 him with a Gregorian reflector, power 350, and by Mr. J. 

 Wallis, the lecturer on astronomy, with a Newtonian tele- 



2 h2 



