ADVISORY COMMITTEE ON ASTRONOMY 1 53 



ration of which Argelauder was aided by Schonfeld and Kriiger. 

 Schonfeld's Southern Durchmustening , Thome's Cordoba Durchmus- 

 teru7ig, and Gill and Kapteyn's Cape Photographic Diirchmusteriing 

 have done a similar and even greater service for the sonthern heavens. 

 But neither visual estimates nor photographic determinations can 

 supply the precise measures of stellar magnitudes obtainable with 

 the aid of a suitable photometer. 



Reference has already been made to Herschel's stellar photometer, 

 with which 69 stars were observed. These results are valuable 

 mainly as pioneer efforts. But the measures of 208 stars made dur- 

 ing the years 1 852-1860 with a Steinheil prism photometer by Seidel 

 were of a higher degree of precision. ZoUner' s photometer, in which 

 an artificial star is reduced to the intensity of the observed star by 

 the aid of a polarizing prism, is described in his Grundzuge einer 

 allgemeine7i Photo inetrie des Himmels, published in 1861. This work 

 also contains photometric observations of over 200 stars, which were 

 made more for the purpose of testing the photometer than for the 

 formation of a catalogue of magnitudes. Zollner's photometer was 

 first systematically used for this purpose at the Harvard College 

 Observatory by Peirce, whose catalogue gives the magnitudes of 495 

 stars lying between -|- 40° and + 50°. Wolff's two catalogues ( 1877 

 and 1884) of stellar magnitude determined with a ZoUner photometer 

 contain over i, 100 stars. Reference should also be made to the ex- 

 cellent work of Lindemann on the magnitudes of stars in the Pleiades 

 and his revision of the magnitudes of the Bonn Durchimisteruiig, and 

 to that of Ceraski on the magnitudes of circumpolar stars. 



The first observatory which made the measurement of the light 

 of the stars an important part of its work was that of Harvard Col- 

 lege. In 1879 the meridian photometer, an instrument devised with 

 special precaution for the elimination of systematic errors, was used 

 to measure the light of 4,260 stars. Among them were included all 

 stars which were of the sixth magnitude or brighter, according to 

 any well-known authority, and north of declination — 30°. When 

 published in 1884 it included the reduction to the photometric scale 

 of the magnitudes of all the stars contained in the principal cata- 

 logues preceding it. The Almagest, A. D. 138, and Sufi, A. D. 964, 

 were included, also the six catalogues of Sir William Herschel, which 

 furnish determinations of the light of 2,785 stars a century ago with 

 an accuracy not again attained for more than fifty years. 



The Uranomelria Oxome?isis, which contains the measures of 2,647 

 .stars north of declination — 10°, made by Pritchard at Oxford with 



