PHOTOGRAPHY IN THE SERVICE OF ASTRONOMY. 479 



catalogue was not published till 1847), comprises more than •17,000 stars. 

 The Paris observatory has devoted itself, for a long time, to determin- 

 ing them anew with the greatest care, for the purpose of forming a 

 new catalogue, which is being gradually accomplished under the skill- 

 ful direction of Mr. Gaillot. The first two volumes, comprising 7,245 

 stars, appeared in 1887, and this brings to view the astonishing precision 

 to which Lalande and his co-workers attained with instruments on the 

 whole very defective. 



The catalogue which Weisse has deduced from the "zones" of Bessel 

 contains about 62,000 stars. That of Argelanuer, founded on the 

 "northern zones" observed at Bonn, contain 324,000, to which Mr. 

 Schoenfeld, the successor of Argelander, has recently added more than 

 133,000 stars, derived from his "southern zones." The Bonn zones fur- 

 nish positions, rapidly determined, of stars of the northern sky and of 

 a part of the southern sky, to the nint^i or tenth magnitude. We have 

 already said that Mr. Gill has undertaken, at the Cape of Good Hope, 

 to complete this inventory for the remainder of the southern sky, by 

 the means of photography ; we have besides also now, for this part of 

 the sky, the zones which Mr, Gould observed at Cordoba (Argentine 

 Republic). To this must be added that in 1867, the International Astro- 

 nomical Society has taken the initiative in a general revision of the Bonn 

 zones which was distributed among fifteen observatories, and which 

 will furnish the material for a new catalogue. The matters concerned 

 here are careful summaries which do not admit of a very great precision 

 in the observed places; for the stars more brilliant, which do not sur- 

 pass the eighth magnitude and which are less numerous, we possess a 

 series of catalogues prepared with more rigor and founded upon the 

 mean of frequently repeated observations. It is from these astronomers 

 derive the fundamental stars, stars of reference to which others are 

 referred in order to correct their absolute positions. These vast works, 

 which have cost so much effort and employed so many human lives, is 

 it necessary to believe that they will lose their value \iheu the great 

 photographic chart shall be completed! We do not think thus. Not 

 only the catalogues of high precision, founded upon meridian observa- 

 tions, will remain indispensable for the exact determination of absolute 

 positions; but the zone catalogues will serve to control the relative 

 positions of the stars determined by photography. 



The comparison of plates taken at two different epochs will permit 

 the undertaking upon a vast scale of the research of proper motions, 

 which at present can be entered upon only for some thousands of stars. 

 These small i)rogressive disj'lacements which, in the mean, do not 

 exceed one-tenth of a second in the space of a year (in some cases it 

 attains to seven or eight seconds a year) proceed only in part from real 

 movements of the stars, which are thus seen to change in position. 

 These are, in a certain degree, apparent displacements which have for 



