Astronomical Society. 389 



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 <rf 

 the element in question, by comparing two catalogues, one 

 formed by direct vision, the other by reflection, that co-lati- 

 tude being assumed to be the true one, which made the sum 

 of the small positive and negative differences equal to zero, and 

 that was found to be 38° 31' 21", differing by one second from 

 the determination furnished by Bradley's observations. This 

 result, however, 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 up- 

 on the pole-star, and an interesting circumstance, which is 

 this : — The undulation to which a mass of mercury is liable, 

 even with the greatest care, is, in itself considered, unfavour- 

 able to the exact bisection of an image ; but a circumstance 

 occurs in the formation of the image in the telescope, which 

 in some measure compensates the inconvenience. The vibra- 

 tions of the mercury in a longitudinal trough occasion an 

 elongated image of the star in the direction of tlie wire, ap- 

 pearing like a succession of stars, which become smaller and 

 smaller as they recede from the central undefined mass, ex- 

 hibiting 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. 



A letter was read from Mr. 11. Comfield, 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- 

 scope, power 160, in reference to the occultation oi Saturn on 

 Oct. 30th. To each of them that part of the ring of Saturn 

 whicli hist emerged from the moon's dark limb (neither of 



them 



