TRANSACTIONS OF SECTION A. 663 



Tlie study of stellar spectra was taken up by Huggins, Rutherfurd, and Secchi. 

 Kutherfurd ^ published in 1862 bis results upon a number of stars, and suggested 

 a rough classification of tbe white and yellow stars ; but Secchi deserves the high 

 credit of introducing the first systematic differentiation of the stars according to 

 their spectra, he having begun a spectroscopic survey of the heavens for the purposes 

 of classification,'- whilst Huggins devoted himself to the thorough analysis of the 

 spectra of a few stars. 



The introductinn of photography marks another epoch in the study of stellar 

 spectra. Sir William ituggins applied photograpliy as early as 1863,^ and secured 

 an impression of the spectrum of Sirius, but nearly another decade elapsed before 

 Professor If. Draper'* took a photograph of the spectrum of Vega in 1872, which 

 was the first to record any lines. With the introduction of dry plates this branch 

 of the new astronomy received another impetus, and the catalogues of stellar 

 spectra have now become numerous. Among them may be mentioned those of 

 Harvard College, Potsdam, Lockyer, McClean, and Huggins. The Draper 

 Catalogue ^ of the Harvard College, which is a spectroscopic Durchmusterung, 

 alone contains the spectra of 10,351 stars down to the 7-8 magnitudes, and this has 

 further been extended by work at Arequipa, whilst Vogel andMiiller of Potsdam" 

 made a spectroscopic survey of the stars down to tho 7"5 magnitude between —1° 

 and + 20° declination. This has again been supplemented by Scheiner" ('Unter- 

 suchungen fiber die Spectra der helleren Sterne '), and by Vogel and "Wilsing * 

 ('Untersuchungen fiber die Spectra von 528 Sternen '). Lockyer'' in 1892 published 

 a series of large-scale photographs of the brighter stars, and more recently 

 McClean '" has completed a spectroscopic survey of the stars of both hemispheres 

 down to the 3^ magnitude. For the study and investigation of special types of 

 stars, the researches of Dun^r on the red stars made at Upsala, and those 

 of Keeler and Campbell on the bright fine stars made at the Lick Observatory, 

 deserve mention. For the study of stellar spectra the use of prisms in slit or 

 objective prism spectroscopes has predominated, though more recently the use of 

 specially ruled gratings has been attended by some degree of success at the Yerkes 

 Observatory. 



Several new stars have also been discovered by their spectra by Pickering in 

 his routine work of charting the spectra of the stars in different portions of the 

 skj-. The photographic plate containing their peculiar spectra was, however, not 

 examined in many cases until the star had died down again. 



Spectrum analysis also opened up another field of inquiry, viz., that of the 

 motion of the stars in the line of sight, based on the process of reasoning due to 

 Doppler, and accordingly named Doppler's Pri)icip]e." 



The observatories of Greenwich and Potsdam were among the first to apply 

 this to the stars, and more recently Campbell at Lick, Newall at Cambridge, and 

 Belopolsky at Pulkowa have made use of the same principle with enormous 

 success. 



It was also discovered that there are certain classes of stars having a large 

 componeut velocity in the line of sight, which changes its direction from time to 

 time, and in manv such cases orbital motion has been proven, as in the case of 

 Algol. 



Another class of binary stars has also been discovered spectroscopically and 

 explained by Doppler's principle. I refer to the stars known as spectroscopic 

 binaries, in which the spectrum lines of one luminous source reciprocate over those 



' A7n. Jcnirn., vol. xxxv. 18G2, p. 77. - Comptes Rendus, t. Ivii. 1853. 



» Phil Trans., 1864, p. 428. 



■* Ajii. Journ. of S"c. and AHs., vol. xviii. 1879, p. 421. 

 ^ Annals Ilarrard Cull., vol. xxvii. 1890. 

 « Astrn-Phys. Ohs. zu Potsdam, vol. iii. 1882-8.3. 



' lUd., vol. vii. 1895. « Hid., vol. xii. 1899. 



" Phil. Trans., vol. clxxxiv. A, 1893. 

 '" Phil. Trans., vol. cxci. A, 1808. 



" ' Ueber das farbige Licht der Doppclsterne," . . . Ahliaiidl. der K. Pohmi3cIic?i 

 Ges. d. Wiss. V. Folge, 2. Bd. 1843. 



