OF ARTS AND SCIKNCES. 237 



Sulijniiied are certain notes which seem to be of interest, and ina- 

 jtoriant to a proper underr^tanding of the manner in which the research 

 was carried on and developed. They are condensed from tlie original 

 note-book records. 



" May 2W, 1872. Two ()hotographs of the spectrum of ^'ega were 

 taken with collodion plates. The first was with an exposure of 3 

 miiuites, the next of 30 seconds. iS'o slit was used and no lenses. A 

 quartz prism was placed inside of the i'ocus of the telescope [the 28- 

 iiich Cassegrain], and a sensitive plate at the focus. The piiotographs 

 showed no lines." It was tlien deemed better to reduce the magnify- 

 ing power of the telescope, by using a flat mirror in place of the small 

 convex. A flat mirror ot IG inches diameter was therefore orround 

 and polished. When this was finished and put in place in tl-.e tele- 

 scope, the three hooks liy which it was supported caused it to deform 

 the image of a star into a triangular form. Dr. Diaper then tried 

 supporting the fiat by an iron plate cemented to its back, bnt with no 

 better result. lie then decided to try a 9-inch concave mirror of 1 1 

 inciies focus, adapting to it a spectroscope formed l)y placing a slit 

 at tlie focus, followed by a one-inch microscope objective, next a 

 Hoffman direct-vision prism, sm-ceeded by an eyepiece, and finally the 

 sensitive plate. This apparatus gave too faint a spectrum, and he 

 returned to the original arrangement, with which, on August 1, 1872, 

 he obtained for the first time a photograph of the spectrum of Vega 

 showing four lines. The width of the spectrum was obtained by 

 eiving the telescope a slight motion in declination, during the ex- 

 posure. On August 8th and Dth lie took several other photographs, 

 the exposures ranging from 5 to 10 minutes. Of course with this 

 arrangement no reference spectrum could be obtained. 



Recurring to the suhject in the summer of 1873, he took a spectrum 

 of a AipiiLx', half an inch long and .^ inch wide. It does not appear 

 from the notes that it showed any lines: exposure 10 minutes. 



During the same season Dr. Draper arranged a spectroscope con- 

 sisting of a (juartz prism combined with a cylindrical lens. It was 

 abandoned because it gave the spectrum the form of an elongated 

 image of the nnrror, instead of a narrow l)and. 



He next combined a heavy flint-glass prism of G0° with a quartz 

 piism. This made nearly a direct vision spectroscope of good dis- 

 persive power, and with it he obtained the spectrum of a AquiUe as a 

 narrow band, in 5 minutes' exposure. 



In 1874 Transit of Venus work occupied all his time. In October, 

 1875, several photographs of the spectrum of Vega were taken with 



