CHAPTERS ON THE STARS. 385 



situated in the southern hemisphere were too ill-endowed to permit 

 of their undertaking a complete census of this invisible region. 



The first considerable work emanating from the Cordoba Observa- 

 tory, under Gould, was a catalogue of all the stars from the south 

 pole to 10° of north declination which could be seen with the naked 

 eye. Another work, which was not issued until after Dr. Gould's 

 death, was devoted to photographs of southern clusters of stars. 



The work of the Cordoba Observatory, with which we are more espe- 

 cially concerned in the present connection, consists of a 'Durchmuster- 

 ung' of the southern heavens, commencing at 22° of south declination, 

 where Schonfeld's work ended, and continued to the south pole. This 

 work is still incomplete, but two volumes have been published by 

 Thome, extending to 41° of south declination. It is expected that the 

 third is approaching completion. This catalogue is, in one point at 

 least, more complete than that of Argelander and Schonfeld, as it con- 

 tains all the stars down to the tenth magnitude. The two volumes 

 give the positions and magnitudes of no less than 340,000 stars, and 

 therefore more than the catalogue of Argelander gives for the entire 

 northern hemisphere. If the remaining part of the heavens, from 42° 

 to the south pole, is equally rich, it will contain nearly half a million 

 stars, and the entire work will comprise more than 800,000 stars. 



The Eoyal Observatory of the Cape of Good Hope, under the able 

 and energetic direction of Dr. David Gill, has undertaken a work of 

 the same kind, which is remarkable for being based on photography. 

 The history of this work is of great interest. In 1882 Gill secured 

 the aid of photographers at the Cape of Good Hope to take pictures of 

 the brilliant comet of that year, with a large camera. On developing 

 the pictures the remarkable discovery was made that not only all the 

 stars visible to the naked eye, but telescopic stars down to the ninth or 

 tenth magnitude were also found on the negatives. This remarkable 

 result suggested to Gill that here was a new and simple method of 

 cataloguing the stars. It was only necessary to photograph the heavens 

 and then measure the positions of the stars on the glass negatives, 

 which could be done with much greater ease and certainty than 

 measures could be made on the positions of the actual stars, which were 

 in constant apparent motion. 



As soon as the necessary arrangements could be made and the ap- 

 paratus put into successful operation, Gill proceeded to the work of 

 photographing the entire southern heavens from 18° of south declina- 

 tion to the celestial pole. The results of this work are found in the 

 'Cape Photographic Durchmusterung/ a work in three quarto volumes, 

 in which the astronomers of all future time will find a permanent record 

 of the southern heavens towards the end of the nineteenth century. The 

 actual work of taking the photographs extended from 1887 to 1891. 



VOL. LVII.— 25 



