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SCIENCE 



!N. S. Vol. XXVII. No. 682 



sarily employed an exposure of four min- 

 utes was necessary with the use of the dark 

 blue line of hydrogen {H^). This degree 

 of insensitiveness of the films made it un- 

 desirable to spend time on such photo- 

 graphs. 



In 1876 he made the first use of a grating 

 spectroscope in astronomical work, and 

 measured the rate of rotation of the sun 

 by the displacement of the lines at the east 

 and west limbs. 



Professor Young successfully observed 

 the transit of Venus of 1874 at Peking, 

 and went to Russia for the eclipse of 1887, 

 but was prevented from work by clouds. 

 He had clear skies at the eclipse of 1878 

 at Denver, and in 1900 at Wadesboro, N. C 

 He also particularly studied the chromo- 

 spheric lines, and made a list of 190 which 

 he had noted with the spectroscope at- 

 tached to the Dartmouth nine-inch tele- 

 scope. The advantage of a high elevation 

 becoming evident, he made an expedition 

 in the summer of 1872 to Wyoming, where 

 with the apparatus taken from Hanover, 

 at an elevation of 8,000 feet, he added 

 another hundred lines to his list. The sub- 

 sequent increase in these lines, aside from 

 those found in eclipse photographs, has 

 been chiefly due to his own observations at 

 Princeton. 



In 1877 he accepted a call to Princeton, 

 where much larger instrumental facilities 

 were offered to him, with less confining 

 teaching duties. He gave, however, much 

 time to the organization and equipment of 

 the students' observatory, making it then 

 probably the best in this country. A 

 powerful spectroscope was provided for the 

 23-inch equatorial of the Halsted Observa- 

 tory, and with this he made important 

 observations of the chromosphere and sim- 

 spots. He discovered in 1883 that the ab- 

 sorption spectrum of the sunspot umbra 

 may be resolved into "countless and con- 

 tiguous" dark lines, a difficult observation 



later amply confirmed by others. With the 

 Halsted refractor he also made micrometrie 

 observations of planets and satellites. He 

 carried out an extensive program of ob- 

 servations of the transit of Venus in 1882 

 at Princeton. 



His admirable work "The Sun," of the 

 International Scientific Series, appeared in 

 1881 and presented in a clear and interest- 

 ing manner the known facts and theories 

 of solar physics. It includes many of his 

 own interpretations of difficult points and 

 is the authoritative work on the subject. 

 It is characteristic of his modesty that 

 many of his own discoveries (such as that 

 of the reversing layer) are there given 

 without mention of his own name, and 

 would only be recognized as such by those 

 familiar with the circumstances, who could 

 read between the lines, or by those who 

 happened to consult the index. Several 

 editions of this work appeared, and it was 

 translated into several foreign languages. 

 The last, thoroughly revised, edition was 

 published in 1895. 



His "General Astronomy," the first of 

 his important series of text-books which 

 have been used by more than a hundred 

 thousand students, was issued in 1888. It 

 represents much more than a mere text for 

 students, and has been widely used as a 

 work of reference. The "Elements of 

 Astronomy" and "Lessons in Astronomy," 

 adapted for more elementary students, 

 were published a little later. The "Man- 

 ual of Astronomy," comprising most of 

 what was in the General Astronomy, but 

 with more illustrations and with the in- 

 clusion of the latest data, was issued in 

 1902. 



The fundamental idea in Professor 

 Young's text-books, popular articles and 

 lectures, was that statements should be 

 accurate as far as they go. He was no 

 special pleader, and in his public utter- 

 ances always fairly stated both sides of dis- 



