528 Astronomical Society. 



pendicular to the meridian 4579"5 feet. Assuming the compression 

 = -34^, 1" in latitude 33° 56' = 101-739 feet, therefore the differ- 

 ence in latitude = 45"'01 ; and the latitude of the Observatory being 

 33° 56' 3"-25, that of the chimney is 33° 55' lS"-24. The chimney 

 is south-west of Lacaille's Observatory, about 120 feet, or 115 on the 

 meridian, therefore the latitude of his Observatory was 33° 55' 1 7"' 1 1 . 

 Lacaille assumed it to be 33° 55' 15". 



The remainder of the paper is devoted to a descrijjtion of the 

 heights, distances, and bearings of the mountains about Klyp-Fon- 

 teyn, which were ascertained with considerable exactness, and a map 

 constructed, to convey an idea of their form, and pi-obable influence 

 on the zenith sector. The sector, and the repeating circle, for 

 taking the angles, were placed on the corn-floor, on Jacobus Cot- 

 see's foundation, before the foundation of the granary was discovered ; 

 and, as the place was comparatively convenient, and the influence of 

 the surrounding masses nearly the same on both, it was considered 

 unnecessary to remove the instruments. The height of the sector 

 ahove the level of the sea was found, by barometrical comparisons, 

 to be nearly 400 feet. 



May 10. The following communications were read: — 



Occultations of the Pleiades by the Moon, observed at Ashurst, 

 March 19, 1839. By Robert Snow, Esq. 



Occultations of the Pleiades, observed at the Royal Naval Asylum, 

 Greenwich, March 19, 1839. By the Rev. George Fisher, A.M. 



On the suspected Variability of the Star a Cassiopeice. (Extract 

 from a Letter from the President, Sir J. F. W. Herschel, to Mr. 

 Baily, dated Slough, April 28, 1839.) 



" My attention was attracted to the star u Cassiopeia: on the ISth 

 of October last, by noticing that it was on that night very decidedly 

 less than the star y of the same constellation, and that in fact y was 

 then the chief star. On referring to my father's catalogues of com- 

 parative brightness, however, o is found placed above y. It was, 

 therefore, evident that a change had taken place. On two or three 

 subsequent nights the fact was verified, and other eyes than my own 

 were called in to establish its reality. A considerable succession of 

 cloudy nights intervened before other comparisons were procured ; 

 and when a favourable opportunity again occurred, viz. on the beau- 

 tifully clear night of Nov. 12, the order of magnitude was found re- 

 stored to that assigned by my father, viz. a, y, /3. On the 27th and 

 28th of Dec. and the 22nd of Jan. 1839, the observations are posi- 

 tive to this effect. 



" In this state it remained till I began to suspect some illusion in 

 the Octol)er observations ; but, on the 24th inst., being a remarkably 

 clear and beautiful night, y was again the principal star, and a was 

 inferior not only to that, but to /3. And so I observed it to be only 

 about an hour ago. It is true the constellation is now low, but the 

 stars are so near together that the difference of altitude can by no 

 means account for the very marked ditTerence in brightness, though 

 its tendency is certainly in that direction. I should not think of 

 making this observation the subject of a distinct announcement. 



