OF ARTS AND SCIENCES. 269 



X. 



SIR WILLIAM HERSCHEL'S OBSERVATIONS OF 

 VARIABLE STARS. 



By Edward C. Pickering. 



Presented January 9, 1884. 



The discovery last summer of two additional catalogues of the 

 Light of the Stars by Sir William Herschel has been announced else- 

 where. At the same time a Journal was found, which gives the dates 

 of observation for the individual comparisons contained in the six 

 catalogues. The suggestion was made by Mr. Chandler, that the 

 observations of variable stars contained in tliese catalogues would thus 

 be rendered of value. The observations contained in Table I. were 

 kindly forwarded by Lieut. Col. Herschel, who has taken much trouble 

 in furnishinfj me with all the material available for the following dis- 

 cussion. The successive columns of Table I. give a current number, 

 the number of the catalogue of Herschel in which the star is con- 

 tained, the usual designation of the star, and its Flamsteed number. 

 The next columns give the date, the observation, and the resulting 

 magnitude. The latter is derived from the photometric observations 

 made in 1879-82 at Harvard College Observatory with the meridian 

 photometer, and will appear in the Annals of the Observatory, Volume 

 XIV. The values assumed for the intervals employed by Herschel 

 are obtained from a discussion of all his catalogues, and will appear 

 in the same volume; they are 0.1 for a period, 0.2 for a comma, and 

 0.4 for a dash. 



The scale employed may be defined as that in which a magnitude 

 corresponds to the ratio whose logarithm is four tenths, and which 

 coincides with the scale of Arijelander for the ma<xnitude 5. It is 

 best illustrated by the statement that the magnitudes 3, 4, 5, and (J on 

 the scales of the Uranoraetria Nova, Heis, and the Durchmusterung 

 would be expressed by 3.1, 4.2, 5.0, and 5.8 on the photometric 

 scale. 



