222 Astronomical Sociely. 



and on the coast of the Lower Boulonnois, occur beneath the equi- 

 valent of the Portland stone. 



At the close of this meeting, which terminated the session, the 

 Society adjourned till Friday evening, the 2nd of November. 



ASTRONOMICAL SOCIETY. 



June 8. — There was read a paper by F. Baily, Esq. "Remarks on 

 the Astronomical Observations of Flamsteed." The object of this 

 communication is to draw the attention of astronomers to the ob- 

 servations of that eminent observer, which the author considers, 

 from their great number, from the care bestowed upon them, 

 and for the very long period elapsed since they were made (nearly 

 140 years), to be deserving of more strict examination than they 

 appear yet to have received. The imperfection of the instruments 

 used by Flamsteed appears to have been one chief cause of this 

 neglect, being in fact only a mural arc of 120° with cross wires in 

 the focus of the telescope fixed in the plane of the meridian, and 

 an uncompensated clock. The arc, though of 80 inches radius, 

 could be read off only to 10", or at most by an estimation of pro- 

 portional parts to 5". With these however, imperfect as they neces- 

 sarily were, he succeeded in constructing a catalogue of the mean 

 right ascensions and declinations of about 3000 stars, which has 

 served as a basis for the observations of all subsequent astronomers. 



This catalogue was of course very inadequately reduced. Aber- 

 ration and nutation were unknown in Flamsteed's time, and refrac- 

 tion very imperfectly ; so that the catalogue, as it stands, cannot be 

 considered as at all fairly representing the observations. It was, 

 however, for manjr years the only catalogue in the hands of astro- 

 nomers, till it gave way to Mayer's, which being deduced from ob- 

 servations made with better instruments, and by an astronomer of 

 great ability, was held more worthy of confidence. But, Mr. Baily 

 observes, the observations of Mayer were made in precisely the 

 same way as Flamsteed's, the right ascensions being determined by 

 the time of the stars passing the vertical wire of the telescope of a 

 mural quadrant. His clock, however, was compensated, and his arc 

 better divided, and no doubt better adjusted. More confidence 

 therefore is to be placed in any one observation of Mayer's than in 

 any corresponding one of Flamsteed's. But the number of Mayer's 

 stars is not above one-third of Flamsteed's ; the greater part were 

 observed only once, and not above fifty so often as six or seven times. 

 Whereas Flamsteed observed most of his stars several times ; above 

 a tenth part more than ten times ; many of them more than fifty, and 

 some even more than 100 : thus v Geminorum was observed 103 times ; 

 Spica 108; y Geminorum 124; Aldebaran 125; Regulus 133; 

 7] Geminorum 163, and jx Geminorum 193 times. It must be evi- 

 dent then, that much that is defective in an instrumental point of 

 view, must be compensated and rectified by the frequency of the 

 observations ; and, although eclipsed by the catalogues of Bradley 

 and Piazzi, the author, considering the great age of Flamsteed's, 

 regards it as possessing a degree of interest, in common with all 

 ancient and authentic records,which ought never to be lost sight of. 



He 



