718 



SCIENCE. 



[N. S. Vol. III. No. 72. 



the celestial vault, we must observe liow 

 far such a body is separated in two direc- 

 tions from the neighboring stars, and evi- 

 dently we must know where these stars are 

 situated in the heavens. A few thousand 

 stars are sufficient for this purpose provided 

 they are determined in position with the 

 highest precision. 



But the astronomer is also deeply inter- 

 ested in 'the sublime problem of the construc- 

 tion of the heavens ' and many thousands of 

 stars mu.st be exactly located to aid in solv- 

 ing this problem. Moreover, there is need 

 of a general rollcall of all the stars visible 

 in ordinary telescopes. Such a ' rollcall ' 

 or ' index ' gives the positions of the stars 

 with an accuracy less than the highest pre- 

 cision requires, and is mainly useful as a 

 basis of work for the more accurate cata- 

 logues. The work of determining the 

 positions of stars on the sky-dome is the 

 most important and fundamental operation 

 in practical astronomy. During the present 

 century this foundation work of astronomy 

 has been carried on ' with a zeal and suc- 

 cess by which all previous efforts are 

 dwarfed into insignificance.' 



The great German astronomer ' the un- 

 rivalled Bessel' from 1821 to 1833 made 

 some 75,000 observations, by which the 

 number of faii'ly well determined stars was 

 increased to above 50,000. His assistant 

 and successor, Argelander, who gave up 

 finance for astronomy, using a glass only 

 two and a half inches in diameter, recorded 

 324,189 stars down to the 9^ magnitude. 

 This number included all the stars of the 

 magnitude named, visible in the northern 

 hemisphere of the heavens, and in addition 

 a small zone about two degrees wide, south 

 of the celestial equator. Schonfeld con- 

 tinued the survey at Bonn, down to the 

 southern tropic. 



In 1882 a photogi'aph taken of the great 

 comet of that year, by Dr. Gill at the Royal 

 Observatory at the Cape of Good Hope, 



showed so many stars that it was deter- 

 mined to use photograph j^ in completing the 

 Bonn survey to the south pole. The expos- 

 ure of the plates in duplicate required four 

 years from 1885-89. But this was the least 

 laborious part of the great work. These 

 plates had to be measured and the meas- 

 urements reduced so as to obtain the proper 

 positions of the stars on the sky. Prof. 

 Kapteyn, of Groningen, lately completed 

 this task, and the catalogue from the plates 

 is now passing through the press. The 

 catalogue will contain about 350,000 stars 

 to the tenth magnitude. A considerable 

 part of the southern skj^ covered by the 

 surveys of Schonfeld and Gill was examined 

 also \>y Dr. Gould. Through 'unceasing 

 labors during his fifteen years ' residence a 

 Cordoba,' in the Argentine Republic, an ac- 

 quaintance of some 73,160 stars down to 

 the 9^ magnitude was brought about. The 

 Argentine General Catalogue was published 

 in 1886 and contained the accurate places 

 of 32,448 southern stars. These and other 

 catalogues put us in possession of a list of 

 stars fairly well determined in position, 

 numbering nearly 700,000. Catalogues of 

 much greater precision, giving the positions 

 of a smaller number of stars with the high- 

 est accuracy, have been prepared after 

 many years of observation and calculation 

 by the noted observatories of the world. 



As an example of cooperation in modern 

 science, I ought to mention that the first 

 organized effort for determining star posi- 

 tions with the highest precision was made 

 by the German Astronomical Society in 

 1865. The scheme, now practically fin- 

 ished, was to fix the positions accurately of 

 about 100,000 stars on Argelander's list 

 and some 30,000 from Schonfeld's. Thir- 

 teen observatories were interested in this 

 great work, each being assigned a 'zone;' 

 two in this country — Harvard College Ob- 

 servatory and the Dudley Observatory at 

 Albany. 



