ADVISOKY COMMITTEE ON ASTRONOMY 153 



ration of which Argelander was aided by Schonfeld and Kriiger. 

 Schoiifeld's Southern Durckmusteriatg , Tiiome's Cordoba Durchmus- 

 terung, and Gill and Kapteyn's Cape Photographic Diirchrmisterung 

 have done a similar and even greater service for the southern 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 v/ere observed. These results are valuable 

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

 ing the years 1852-1S60 with a Steinheil prism photometer by Seidel 

 were of a higher degree of precision. ZuUner'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 Grundziige einer 

 allgemeinen Photometrie 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 betv/een + 40'' and -\- 50°. Wolff's two catalogues (1877 

 and 1884) of stellar magnitude determined with a Zollner photometer 

 contain over i, roo 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 Durchmusienvtg^ 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 T879 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 weli-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. 13S, and Sufi, A. D. 964, 

 were included, also the six catalogues of Sir William Ilerschel, 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 Urancmetria Oxoniensis, which contains the measures of 2,647 

 stars north of declination — ro'', made by Pritchard at Oxford with 



