ASTRONOMICAL PROBLEMS CURTIS. 331 



sphere and for some distance south of the celestial equator is now 

 practically completed, and the work is advancing favorably for the 

 more southerly portions of the sky at the observatories of Madras, 

 Melbourne, and the Cape. 



One of the most important programs in connection with the 

 astronomy of precision of the Southern Hemisphere is that inaugu- 

 rated in 1908 under the auspieces of the Carnegie Institution of 

 Washington. It has for its object the measurement of the accurate 

 positions of about 25,000 stars in the southern skies in accordance 

 w^itli the system of Prof. Boss, of Dudley Observatory. The instru- 

 ment employed is the meridian circle of the Dudley Observatory, 

 which has been used in the past for exactly similar work in the 

 northern skies. The constants, graduation errors, etc., of this instru- 

 ment have been so thoroughly investigated that doubtless no more 

 efficient instrument exists to-day for this class of work. By the use 

 of the same instrument, the same system of reductions, and to a cer- 

 tain extent even the same observers, it seems probable that the re- 

 sults of this program will afford us a far more exact binding together 

 of the northern and southern skies in one homogeneous system than 

 we possess to-day. The site was selected at San Luis, in the Argen- 

 tine Eepublic. Prof. Tucker, of the Lick Observatory, was in charge 

 of the Carnegie Observatory at San Luis and advices state that the 

 site seems to be a very favorable one for this class of work. The 

 program has been completed as planned and the observers are now 

 (April, 1911) returning to the United States, where the results will 

 be put in final shape for publication. The project involved about 

 3 years' work, and about seven observers and assistants were employed. 



In the years 1885-1891, under the direction of Sir David Gill, the 

 Obser^^atory of the Cape of Good Hope undertook an extensive 

 photographic map of the southern skies from declination —19° to 

 the South Pole. The measurement of the positions of the stars on 

 these plates was carried through by the disinterested and self-sacri- 

 ficing labors of Prof. Kapteyn, and the publication in 1900 of the 

 third and concluding volume of the great " Cape Photographic 

 Durchmusterung " marked the completion of this monumental task. 

 It contains the positions of 454,875 stars, nearly to the tenth magni- 

 tude, and the positions are accurate to about 1 second of arc. It is 

 an epoch-making work in the cartography of the southern heavens; 

 in fact, until the completion of the "Astrographic Catalogue" no 

 such complete and systematic photographic catalogue exists for the 

 Northern Hemisphere. Naturally it can not compete, however, with 

 the accuracy of the "Astrographic Charts"; those from Helsingfors, 

 for example, having the small probable error of 0.11" for the mean 

 of two measured star images. 



