594 



SCIENCE. 



[N. S. Vol. XII. No. 303. 



spectroscopic Durchmusterung, alone con- 

 tains the spectra of 10,351 stars down to 

 the 7-8 magnitudes, and this has further 

 been extended by work at Arequipa, whilst 

 Vogel and Miiller, of Potsdam,* made a 

 spectroscopic survey of the stars down to 

 7.5 magnitude between — 1° and + 20° 

 declination. This has again been supple- 

 mented by Scheinerf (' Untersuchungen 

 liber die Spectra helleren Sterne '), and by 

 Vogel and Wilsing J ( ' Untersuchungen 

 liber die Spectra von 528 Sternen ') . Lock- 

 yer § in 1892 published a series of large- 

 scale photographs of the larger stars, and 

 more recently McClean|| has completed a 

 spectroscopic survey of the stars of both 

 hemispheres down to the '6h; magnitude. 

 For the study and investigation of special 

 types of stars, the researches of Duner on 

 the red stars made at Upsala, and those of 

 Keeler and Campbell on the bright line 

 stars made at the Lick Observatory, de- 

 serve mention. For the study of stellar 

 spectra the use of prisms in slit or object- 

 ive prism spectroscopes has predominated, 

 though more recently the use of spec- 

 ially ruled gratings has been attended by 

 some degree of success at the Yerkes Ob- 

 servatory. 



Several new stars have also been dis- 

 covered by their spectra by Pickering in his 

 routine work of charting the spectra of the 

 stars in diiferent portions of the sky. 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 an- 

 other field of inquiry, viz, that of the 

 motion of the stars in the line of sight, 

 based on the process of reasoning due to 



* Astro-Phys. Obs. zu Pohdam, Vol. III., 1882-83. 



tibid., Vol. VII., 1895. 



Jlbid., Vol. XII., 1899. 



iPhil. Trans., Vol. CLXXXIV., A, 1893. 



\\Pliil. Trans., Vol. CXCI., A, 1898. 



Doppler, and accordingly named Doppler's 

 Principle.* 



The observatories of Greenwich and Pots- 

 dam were among the first to applj' 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 cer- 

 tain classes of stars having a large com- 

 ponent velocity in the line of sight, which 

 changes its direction from time to time, and 

 in many such cases orbital motion has been 

 proven, as in the case of Algol. 



Another case of binary stars has also 

 been discovered spectroscopically and ex- 

 plained 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 from the 

 other source of light, according as one is 

 moving towards or away from the earth. 

 This displacement of the spectrum lines 

 led to the discovery of the duplicity of /? 

 Aurigse, and C Ursee Majoris by Pickering.f 



Several other such stars have now been 

 detected, notably /? Lyrse, and lastly Capella 

 discovered independently by Campbell J at 

 Lick, and Newall§ at Cambridge. 



The progress of the new astronomy is so 

 closely bound up with that of photography 

 that I shall briefly call to mind some of the 

 many achievements in which photography 

 has aided the astronomer. 



Daguerre's invention in 1839 was almost 

 immediately tried with the sun and moon, 

 J. "W. Draper and the two Bonds in 

 America, Warren de la Rue in this coun- 

 try, and Foucault and Fizeau in France, 

 being among the pioneers of celestial photog- 



* ' XJeber das farbige Licht der Doppelsterne, "... 

 Abhandl. der K. Bohmischen Ges. d. Wiss. V. Folge, 

 2. Bd. 1843. 



■fAm. Jour. (3), 39, p. 46 (1890). 



t Astro-Phys. Jour., Vol. X., p. 177. 



i Monthly Notices, Vol. LX., p. 2 (1899). 



