THE MOVEMENTS OF THE STARS. 263 



trum of the same character. To have demonstrated the 

 material unity of the universe is indeed a notable achieve- 

 ment for that little instrument, the spectroscope. But it 

 seems possible that the services of the prism to science are 

 now taking a direction in which the results to be achieved 

 will outshine in importance and interest even that grand 

 discovery of material unity, to which we have referred. 

 Within the last year or two the spectroscope has made 

 revelations with regard to the movements of certain of the 

 heavenly bodies of a character which have startled the 

 scientific world quite as much as did the fundamental 

 discovery made some thirty years ago of terrestrial ele- 

 ments in the sun. Let me unfold the matter. 



Look at a star such as Sirius or Aldebaran. Bring to 

 bear upon it the meridian circle of the observatory, with 

 all its refinements for exact measurement, and we can 

 determine the exact place of the star in the heavens. We 

 can do so with an accuracy which makes the fixed star a 

 landmark of the universe. Years roll on, and by a 

 repetition of the observations, the place of that star is 

 again determined, and the two places do not agree. They 

 are purged from every source of error, but still a dis- 

 crepancy remains, the place of the star as now observed 

 is not the same as its place was years ago ; it has what we 

 call a proper motion. 



Tested in this way almost all the stars will probably be 

 found to be in motion. We talk of these objects often as 

 fixed, but the word must be used in a relative sense. To 

 our ephemeral glance the stars seem fixed ; but what is 

 indeed fixed when sufficient time is allowed ? The cloud 

 that now caps a mountain summit is obviously unstable ; 



