52 Astronomical Society. 



"These powers are not exaggerated, but have been measured. with 

 scrupulous care ; so that you may be assured no future trial will give 

 them less than the numbers here quoted." 



II. A communication from the Astronomer Royal, containing the 

 results of all the observations, which have been made at the Royal 

 Observatory at Greenwich, of the sun's zenith distance, at or near 

 the solstices, from the time of Bradley to the present time. 



Mr. Pond states the latitude of the Royal Observatory, which re- 

 sults from Bradley's observations, to be 51° 28' 40",323 ; and that 

 which is obtained from his own observations to be 51° 28' 38",077 j 

 the difference being 2",256. 



III. A communication from Sir Thomas Brisbane, consisting of ob- 

 servations of the moon, and moon-culminating stars, during the years 

 1829 and 1830, made at Makerstoun with a four-feet transit. Sir 

 Thomas Brisbane states in the letter accompanying his paper, that 

 " the observations were almost entirely made by Mr. Dunlop." The 

 paper contains the observed differences in jR between the moon 

 and the moon-culminating stars, observed before and after her culmi- 

 nation, and also the number of wires used in each observation. 



IV. On the theory of the eye-glasses of telescopes j by Professor 

 Littrow, Associate of the Society. 



V. The reading of a paper by Francis Baily, Esq., " On Lacaille's 

 Catalogue of 398 principal Stars," was begun. 



May 13. — The following communications were read : — 



I. Mr. Baily's paper, " On Lacaille's Catalogue of 398 principal 

 Stars," was concluded. 



In this paper Mr. Baily has entered into the merits of this cele- 

 brated catalogue. The method adopted by Lacaille for determining the 

 right ascensions was that known by the name oi equal altitudes: for 

 when he commenced his astronomical career, the transit instrument 

 was but little known, and not fully appreciated ; and although it had 

 been introduced into the observatory by Roemer, yet it was soon 

 abandoned for the mural quadrant, which at that time was consi- 

 dered a more manageable and accurate instrument, and capable of 

 giving at one view both the right ascensions and the declinations. 

 The instrument used for this purpose was a 3-feet quadrant : and he 

 usually took about 14 or 16 altitudes on each side of the meridian. 

 The culmination of the stars being thus determined, he compared 

 them with a Lijrce or Sirius (whose absolute right ascension had been 

 ascertained by frequent comparisons with the sun), and thus computed 

 their right ascensions relatively to those stars. The declinations were 

 determined with two different instruments : one a 6-feet sector, and 

 the other a 6-feet sextant ; the divisions of which were examined 

 with great care by himself, and the trifling discrepancies noted and 

 allowed for. 



By the help of these instruments, Lacaille determined the positions 

 of nearly 400 of the principal stars in the northern and southern he- 

 misphere : and the catalogue which he thus produced, and which is 

 the subject of the present memoir, is worthy of being placed in com- 

 petition with those of his distinguished contemporaries. Mr. Baily 



has 



