310 Royal Astronomical Society : — Mr. Snow's and 



also on the 5 th and 6th of the present month, when it was very- 

 bright and easily found. The nucleus was large, but not stellar. 



Occultations of Stars by the Moon to the end of 1839. By Ro- 

 bert Snow, Esq. 



Catalogue of the Pleiades. By Robert Snow, Esq. 



The author states that this catalogue does not lay claim to strict 

 accuracy, but was constructed in order to form a chart, which might 

 be consulted with advantage when occultations^of stars in the 

 Pleiades by the moon take place. Piazzi's stars falling within the 

 limits of the cjiart were taken as standards, and the differences be- 

 tween them and the other stars determined by a wire micrometer. 

 For some stars, too faint to allow of illumination, the ring microme- 

 ter was used ; but they were more usually put down by estimation, 

 which may be done with nicety when many are in the field together. 

 This communication was accompanied by a chart. 



On the Variability of a Cassiopeia. By Robert Snow, Esq. 



In the Monthly Notice for May last (vol. iv. p. 195.), the atten- 

 tion of the Society was directed to the supposed variability of this 

 star ; and it has, accordingly, been watched, with the naked eye, 

 since June 9, 1839, up to the present time, January 8, 1840. The 

 relative brightnesses of a, (3, y Cassiopeia have been registered on 

 sixty-eight evenings. The result at present is that y has been ge- 

 nerally put down as brightest, and never faintest ; j3 generally as 

 faintest ; a faintest twelve times out of sixty-eight, and generally 

 so about the 5th day of the month. In the Society's Catalogue, 

 the order of magnitude is /3, a = y. Mr. Snow remarks that the 

 star a appears to his eye at all times sharper and better defined 

 than y or /3 ; and it is also more readily obscured by fog or haze, 

 although it is a reddish star. 



Observations of a Cassiopeia in 1831 and 1832. By Mr. W. R. Birt, 

 Librarian and Assistant Secretary to the Metropolitan Institution. 

 Communicated by the President. 



These observations were commenced in April 1831, and extend 

 to November 1832 ; eoid the earlier part of them, from April to 

 December 1831, have already, with some others, been communicated 

 to the Society. See Monthly Notices, vol. ii. No. 11. In a letter 

 to Sir John Herschel, Mr. Birt-states, that since 1832 his attention 

 had not been directed to this star until he read the Monthly Notice 

 for May last, when it immediately occurred to him that his obser- 

 vations might probably assist in determining the period in which the 

 brightness of the star completes the circle of its gradations. When 

 Mr. Birt commenced observing the star in April 1831, the lustre 

 appeared to be at its minimum. In December of the same year, 

 he again observed it to be less than j3>. His observations were then 

 discontinued until June 1832, when it again appeared less than j3. 

 Taking the extreme observations, we have thus two periods completed 

 in about fifteen months, or one period in about 225 days. Assuming 

 this as the period of the variation, and computing from April 26, 1831, 

 the number of days elapsed until April 28, 1839, is 2924, which 

 gives thirteen periods of about 225 days each. Sir John Herschel's 



