XI 



THE STAES AND NEBULAE 



T" T E made the stars also" is the curt phrase with 

 I I which the Mosaic cosmogony dismisses these 

 *- * wonderful diadems of the sky, and, milleniums 

 later, the great Newton himself knew nothing to add 

 about them in the way of definite knowledge. During the 

 past century, however, beginning with BessePs and 

 Henderson's successful determinations of the parallaxes 

 of Alpha Centauri and 61 Cygni in the 1830 's, the dis- 

 covery of the principle of spectrum analysis by Kirchhofr" 

 in 1859, and Sir William Huggins' application of the 

 Doppler principle to the study of spectra for determining 

 the radial velocities of stars, in 1868, immense progress 

 has been made but, only, be it frankly said, in the way 

 of gathering material, rather than in the work of actual 

 construction. Let me particularize: 



STELLAR MOTIONS 



First, as to stellar motions. I trust I am not mis- 

 judging the aims of astronomers in supposing that their 

 detailed study of individual stars and of their several 

 proper and radial motions is not esteemed by them an 

 end in itself, but a stepping stone, merely, to an ultimate 

 understanding of the organic constitution of the universe 

 as a unit and a system. Indeed, if the latter be not the 

 true purpose, and if the mere multiplication of unclassifi- 

 able and unintelligible data of such things as, observa- 

 tions on variable stars, star spectra, radial motions of 



