62 Astronomical Society. 



ASTRONOMICAL SOCIETY. 



May 9. — A paper was read, entitled " Approximate Places of 

 Double Stars in the Southern Hemisphere, for 1827, as observed at 

 Paramatta, N.S.Wales. By Mr. James Dunlop." 



After the departure of Sir T. M. Brisbane from the Colony of New- 

 South Wales, the author, finding himself in the possession of re- 

 flecting telescopes capable of adding considerably to our knowledge 

 of the nebulae and double stars of that portion, resolved to remain, 

 for the purpose of making a general survey, of the heavens, from the 

 south pole to 30° of south declination. The dark nights in the 

 absence of the moon were devoted to observations of the nebulae, 

 and the moonlight to those of double stars, of which however only 

 a part could be subjected to exact micrometrical measurement. 

 The apparatus employed for. this purpose consisted of a 46-inch 

 achromatic telescope, equatorially mounted, and furnished with two 

 micrometers ; — one a parallel-line micrometer, the author's own 

 workmanship ; the other, a double-image micrometer, on Amici's 

 principle. Those which could not be micrometrically measured, 

 had their positions and distances noted by estimation while passing 

 the field of the 9-feet reflector, with which they were discovered in 

 the sweeps for nebulas, and their places are given as determined in 

 the sweeps. 



The author prefaces his catalogue with the details of the microme- 

 trical measures of about 30 principal Southern double stars, the most 

 remarkable of which are a Crucis and a Centaury the former bear- 

 ing a great resemblance, both in the magnitudes and the mutual di- 

 stance of its individuals, to Castor; the latter being a star of the first 

 magnitude, accompanied by one of the fourth, at about 20" di- 

 stance, — a remarkable combination, such as does not occur in our 

 hemisphere. 



A Catalogue of 254 double stars arranged in order of right as- 

 cension follows, in which the right ascension to seconds of time, 

 and declination to the nearer minute of space, — the position, qua- 

 drant, distance, the differences of right ascension and declination 

 when observed, and the magnitudes, are set down in separate co- 

 lumns. They comprise double stars of all classes and of every 

 variety. One very remarkable is the star 1 k Argus^ JR. 8 h 4 m , 

 declin. —42° 7', which consists of individuals of the sixth and 

 eighth magnitudes, the large star being blue, and the small one 

 dusky red. This affords almost the only instance known of a com- 

 bination of two considerably bright stars differing decidedly in mag- 

 nitudes, where a marked excess of the less refrangible rays enters 

 into the composition of the light of the smaller star, and of the 

 more refrangible into that of the larger. Among the double stars 

 is set down also one of the seventh magnitude, right ascension 

 l tl 19 m 43 s , declin. —33° 31', of that singular deep red purple co- 

 lour of which examples are not wanting in our own hemisphere. 



An extract of a letter was read from Professor Harding, of Got- 

 tingen, to Dr. Tiarks, in which he alludes to a phenomenon which 

 had recently been observed by several astronomers on the conti- 

 nent, relative to an inequality of the dark space between the body 



of 



