August 18, 1916] 



SCIENCE 



233 



lications of the von Kuffner Observatory en- 

 titled B, " Die Bestimnmng von Sternhellig- 

 keiten aus Extrafocalen Photographischen 

 Aufnahmen," G, " Beitrage zur Photographi- 

 schen Photometrie der Gestirne." This was 

 pioneer work in the use of extrafocal images, 

 in that it was brought to a successful outcome 

 and applied to various regions of the sky. The 

 Director de Ball published a very appreciative 

 description of Schwarzschild's work in the 

 Bulletin Astronomique for 1905. 



Prom 1899 to 1901 Schwarzschild was 

 " privatdocent " at the University in Munich, 

 and in 1901 was called to the University of 

 Gottingen as director of the observatory and 

 professor of astronomy. He held this position 

 for eight years, which were rich in astronom- 

 ical results, both theoretical and practical. 

 The theoretical work appeared in parts 9-11 of 

 the " Astronomische Mittheilungen der Konig- 

 lichen Sternwarte zu Gottingen." Perhaps the 

 most interesting part relates to the improve- 

 ment of the reflecting telescope by a combina- 

 tion of curves of the two mirrors which would 

 give a field as flat as the refractor used for 

 the " Astrographic Chart." 



The practical part of the work at Gottingen 

 included an improvement on the method of 

 extra-focal images which had been used at 

 Vienna. This consisted in giving a motion to 

 the plate during the exposure, so that the 

 image (itself in focus) was built up into a 

 square area sufficiently large to be measured 

 as an extra-focal image. This attachment was 

 called the " Schraffierkassette," and there re- 

 sulted from its use the " Gottingen Aktino- 

 metrie," which covered the zone 0° to + 20° 

 declination. This appeared as part fourteen 

 of the Gottingen publications, and gave the 

 photographic magnitudes of 3,522 stars, also 

 the visual magnitudes as measured at Potsdam 

 by Miller and Kempf. 



About this time Schwarzschild suggested the 

 use of the difference between the photographic 

 and the visual magnitudes as a measure of 

 the color of the stars. He suggested the term 

 " Farbentonung " (color-index), and gave this 

 quantity for each of the stars in the " Aktin- 

 ometrie." He was also one of the first to 



apply the color-index to the determination of 

 the temperature of the stars. 



During his stay at Gottingen he also devised 

 instruments for determining geographical posi- 

 tions in the navigation of airships. The sex- 

 tant as modified for this purpose was described 

 in " Zeitschrift fur Plugtechnik und Motor- 

 luftschiffahrt," 1913. 



Schwarzschild was called to succeed Vogel 

 as director of the Astrophysical Observatory at 

 Potsdam in 1909. He brought to this trying 

 position a talent exceptionally ripened for a 

 man only thirty-six years of age, and he filled 

 the position with distinguished success. Dur- 

 ing his term the astrophysical work at Pots- 

 dam was carried forward in a way worthy of 

 its first director and his brilliant staff, and 

 the list of publications bears witness not only 

 to the work of the different astronomers, but 

 also to Schwarzschild's ability as a director. 

 Among Schwarzschild's theoretical contribu- 

 tions during this period may be mentioned his 

 work on the distribution of stars in space. 



The remarkable range included in Schwarz- 

 schild's work, from the improvement in the 

 sextant to the distribution of stars in space, 

 showed that he combined theoretical and prac- 

 tical ability in an unusual degree, thus fitting 

 him especially for the directorship of a great 

 astrophysical observatory. 



Schwarzschild's personality was especially 

 pleasing. He was lacking entirely in that stiff 

 formality which renders so many men in high 

 positions unapproachable. He had a great 

 capacity for friendships, and his admiration 

 for Dyson, the English Astronomer Royal, was 

 very pronounced. What could be finer than 

 the simple statement which he made in regard 

 to Dyson, "We nearly always think alike." 

 Schwarzschild's disposition was not in the least 

 jealous. As an example of this may be men- 

 tioned his suggestion to the International 

 Committee, that the magnitudes of the Har- 

 vard System should be taken as the interna- 

 tional standards, and that the other systems 

 should be reduced to this by the application of 

 suitable corrections. 



Schwarzschild was happy in his domestic re- 

 lations and his home was always open to his 



