1882.] t)OJ [Barker. 



ture or pressure, or both, which enable it to radiate more light than the 

 contiguous portions of the solar mass. This view of the case however, 

 required radical modification in the then accepted view of the constitution 

 of the sun ; a modification which he pointed out and advocated. So ex- 

 ceptional were these results, and especially the conclusions from them, 

 that it was hardlj^ to be expected that they should be at once accepted. 

 Dr. Draper, however, in this, as in all his work, was his own severest 

 critic. Increasing constantly his appliances and perfecting his methods he 

 produced, in 1879, another photograph on a much larger scale, which 

 showed the coincidences which he claimed, especially of groups of lines, 

 so unmistakably as to leave no question of the fact in a mind free from 

 bias. To strengthen still more the evidence on the subject, he had 

 planned for execution the present winter, a research upon the spectra of 

 other non-metallic gases, in the hope that some of these, too, would be 

 found represented as bright lines in the sun spectrum. 



In 1878, he was the director of a party organized by himself to observe the 

 total eclipse of the sun of the 29th of July. His familiarity with the lo- 

 cality led him to select Rawlins, "Wyoming, an important station on the 

 Union Pacific Railway, as the objective point. The result justified his 

 selection. The expedition was entirely successful, and the observations 

 which were made were of great value. By means of his splendid appa- 

 ratus, Dr. Draper himself obtained an excellent photograph of the corona 

 and also a photograph of its diffraction spectrum which was apparently 

 continuous. In 1880, he obtained a number of spectra of Jupiter in con- 

 nection with stellar work. On examining one of these spectra, the pho- 

 tograph appeared to him to show that the planet really furnished a cer- 

 tain amount of intrinsic light. The exposure on Jupiter was fifty minutes, 

 the spectrum of the moon being taken in ten. The original negative was 

 sent over to his friend, Mr. A. C. Ranyard, who presented it to the Royal 

 Astronomical Society. In June, 1881, he took several excellent photo- 

 graphs of the comet, and also of its spectrum. With a slit and two prisms 

 he obtained three photographs of the spectrum, with exposures of 180, 

 196, and 228 minutes, respectively. On each plate, a comparison spectrum 

 was also photographed. 



Upon the organization of the United States Commission to observe the 

 Transit ot Venus in 1874, Dr. Draper's great attainments in celestial pho- 

 tography pointed him out at once as the man best suited to organize the 

 photographic section, and he was accordingly appointed Director of the 

 Photographic Department. He went at once to Washington, entered 

 heartily into the work, and during three entire months devoted himself 

 to the labor of organizing, experimenting and instructing ; declining sub- 

 sequently all compensation for the time thus spent. Although his duties 

 at home prevented him from joining any of the expeditions, yet so instru- 

 mental had he been in making the transit observations a success, that 

 upon the recommendation of the Commission, Congress ordered a gold 

 medal to be struck in his honor at the Philadelphia Mint. This medal 



PROC. AMER. PHILOS. SOC. XX. 113. 4e. PRINTED MAY 5, 1883. 



