I9I0.] ABOUT THE FIXED STARS. 229 



student of nature. The " Astronomy of the Invisible " thus takes 

 on vastly greater importance than in the time of Laplace and 

 Bessel. And we see that the sagacious suggestions made by these 

 great astronomers nearly a century ago were well founded. And 

 just as there are invisible planets about the luminous fixed stars, 

 so also there probably are countless bodies everywhere in space 

 which are essentially non-luminous. The amount of dark matter 

 in the universe therefore is much greater than has been generally 

 supposed, or heretofore considered probable. 



U. S. Naval Observatory, 

 Mare Island, California, 

 March 28, 1910. 



