576 Royal Astronomical Society. 



Correction of the Epoch of Mean Long. = + 2"' 13 



Aphelion = + 225 



— — Inclination = -f- 3 *23 



Long, of the Node . . = — 21 -40. 



And Lindenau's elements corrected, for the epoch Jan. 1, 1836, 

 are — 



Epoch of Mean Long. = ll 9 2° 1' 35"23 



Aphelion.. = 10 9 15 3 



Node = 2 15 12 3 '60 



Eccentricity = 0-00684568 



Inclination = 3°23'34'\33. 



April 7. — The following communications were read : — 

 Occultations of Stars by the Moon, observed at Ashurst and 



Dulwich, in the year 1840. By Robert Snow, Esq. 



Observations on the Variability of the Star a Cassiopeia? during 

 the years 1839 and 1840. By Robert Snow, Esq. 



Description of the Observatory erected at Starfield, by W. Las- 

 sell, Esq. 



The author states that this observatory was erected in the sum- 

 mer of the year 1839 at Starfield, near Liverpool, in latitude 53° 

 25' 7" north, and longitude h ll m 41 s west of Greenwich. The 

 account of the building and instruments is accompanied by drawings 

 and a model, giving a very distinct idea of the ground-plan and ele- 

 vation of the building, and of the relative position of the instruments. 

 The building consists of one circular apartment, of 14 feet 6 inches 

 diameter, surmounted by a dome, and is based upon a structure of 

 undisturbed clay. The two instruments contained within it are a 

 transit instrument and an equatoreal instrument, both supported on 

 parts of the same pier, which is 1 1 feet in length, the part support- 

 ing the transit instrument being 3 feet 6 inches broad, and that 

 supporting the equatoreal, 2 feet 8 inches broad ; and the whole of 

 the pier is kept quite separate from the walls, to avoid any commu- 

 nication of tremor. The dome revolves on eight rollers of 6 inches 

 in diameter, placed at equal distances, and the friction is so small, 

 that the strength of a boy of twelve years of age is quite adequate 

 to turn it. The transit instrument is placed a little to the west of 

 the meridian line, passing through the centre of the dome, and by 

 revolution of the dome commands the whole 180° of sky. 



The telescope of the equatoreal is a Newtonian reflector of 9 

 inches clear aperture, and of 112 inches focal length. The object- 

 ■airror the author believes to be of very great perfection of figure, 

 showing the stars in the most favourable states of the atmosphere 

 with perfect roundness, and answering very well to the severe test 

 recommended by Mudge in the Phil. Trans., of alternately exposing 

 different portions of its surface to the rays from the object. The 

 penumbra of a star seen out of focus is truly round, and equal in 

 brightness in its various parts, presenting also the same form on 

 both sides of the place of distinct vision. 



The mirror is mounted in a copper tube, 9 feet long and of 9^- 

 inches in diameter, and there is a peculiar contrivance, by means 



