OF ARTS AND SCIENCES. 239 



with it; but tliey turned out very faint, and the removal of the slit did 

 not make them any brighter. 



October 18 and 19, 1876. Experiments were made upon the spec- 

 trum of Venus, both vpith the reflector and refractor, - — the former 

 giving much the stronger pictures. The plates show the lines very 

 Avell, especially those between G and IT. At this time an eyepiece 

 was added for the purpose of watching the lower end of the ppectruni, 

 and so maintaining the adjustments. 



October 25, 187G. Six photographs of the spectrum of Venus were 

 made, which came out very s;itisfactorily. Experiments were made, 

 giving data ibr determining the best width of slit. 



October 27, 187G. Some photographs of the spectrum of Vega 

 were made with the same apparatus, but results were not very satisiac- 

 tory. The air was misty. 



October 29, 187(5. In the afternoon the same stellar spectroscope 

 was attached to the 12-inch refractor, the aperture of which was 

 reduced to 1^ inches. The slit was closed so that b appeared distinctly 

 triple, in the spectrum of the sun, and a series of photographs was made 

 with exposures of 4 minutes, 1 minute, 5 seconds, and 1 second, respect- 

 ively. The last proved just about the proper exposure, and indicates 

 that the necessary exposure for Venus is 19(') times that for the Sun. 



During 1877 Dr. Draper was occupied mainly with work connected 

 with his reseai'ch upon the existence of oxygen in the Sun. In 1878 

 the season was occupied with the Transit of Mercury in May, and 

 with the Solar Eclipse on July 29th; -so that during these two years 

 nothing was done with stellar spectra. 



While in England, in June, 1879, he obtained some of Wratten and 

 Wain Wright's dry plates, and on his return resumed his stellar work 

 with them. As the 28-iiich mii-ror had not been resilvered since the 

 removal of the film at the time of the Transit of Mercury, he used 

 the 12-inch refractor for all his experiments, in connection with the 

 Iluggins star spectroscope, witli two prisms, instead of only one, as in 

 1876. In October, he read before the National Academy of Sciences 

 a i)aper upon the subject, which was published in the American 

 Journal of Science for December, 1879. 



The plates made by the collodion process up to and including 1876 

 were, of course, of no value for measurement, and have all been lost or 

 destroyed, except about half a dozen " strippings " of the earliest ones, 

 which still remain gummed into the note-books. For this reason it 

 has seemed desirable to present the note-book data respecting them in 

 the way which has been adopted. 



