22S Astronomical Society. 



p. | r close 0" and below 1" 



1 not close 1 and below 2 



Class II 2 and below 4 



Class III 4 and below 8 



Class IV 8 and below 16 



Class V 16 and below 32 



Class VI 32 and below 64 



So that the limit of distance of stars of the nth class shall be 2" x 1". 



The author then subjoins a list of stars common to his two former 

 Catalogues, and to that of Professor Struve, 86 in number ; after 

 which he proceeds to describe some singular phenomena observed in 

 the course of his examination of these objects, which explain certain 

 discrepancies between the results of observations of their angles of 

 position on different nights, and which tend to throw light on some 

 obscure points in the theory of vision. He considers it as rendered 

 very probable, by some of the facts adduced, that time is required for 

 light to make an impression on the retina, as well as for the impres- 

 sion made to wear off j and that this time is the less, the brighter the 

 object ; and explains by this principle a remarkable degree of unstea- 

 diness and fluctuation observed in the limb of the planet Mars, while 

 small stars in the field remained perfectly tranquil, as well as certain 

 other curious phenomena. 



He then adds some observations on the contrasted colours so fre- 

 quently observed in double stars, and regards them as (at least) in 

 many cases referable to the laws of vision -, in virtue of which, a strong 

 light having an excess of the less refrangible rays, will cause a feebler 

 one, in which no such excess exists, to appear of the complementary 

 hue ; instances of which, in artificial lights, are adduced. He notices 

 especiallv the extremely intense red colour of a star of the 8th mag- 

 nitude, R. A. 4 h 41". N.P.D. 61° 47' (1828.) 



These prefatory remarks are terminated by some observations of 

 the 5th star in trapezio nebula Ononis, pointed out by M. Struve. 

 The author adducevS evidence, which he considers as satisfactory, that 

 no such star existed in that situation on the 13th March, 1826. It 

 was observed, however, by M. Struve, to be conspicuous on the 1 1th 

 Nov. of that year. It is now readily seen in the Slough telescope , 

 and at the time of drawing up the present paper, it was so bright as 

 not to be overlooked with the most ordinary degree of attention. He 

 considers it therefore, if not as a new star, at least as a variable 

 one of very singular character. 



The Catalogue, which follows, is arranged in all respects like the 

 preceding ones published in the Memoirs of this Society, and is fol- 

 lowed by a list of about 200 double stars, for the most part found in 

 the same sweeps with the others ; but which, occurring in M. Struve's 

 Catalogue, cannot now be regarded as new double stars. Their ob- 

 served places and estimated angles of position, distances, and mag- 

 nitudes, are however given, in order to afford ground of comparison 

 between the two Catalogues, of which comparison the Tesults are 

 stated. 



PROCEEDINGS 



