STELLAR DISTRIBUTION. 223 



the States in 1853. In 1862 he received an 

 appointment at Washington Observatory, and he 

 retained an official position until 1897. Through- 

 out his scientific career he has been specially 

 attracted by the question of the construction of 

 the heavens, which he fully discussed in his 

 book on 'The Stars' in 1901. Newcomb's in- 

 vestigations have shown that some of the stars 

 are not permanent members of the Sidereal 

 System, among them the swiftly -moving 1830 

 Groombridge. He has shown that the Stellar 

 Universe does not possess that form of stability 

 which is seen in the Solar System. Newcomb 

 considers the Universe to be limited in extent, 

 as opposed to the opinions of Struve and others, 

 who believed it to be infinite. He has brought 

 clearly before his readers a calculation, based on 

 the known law that there are three times as 

 many stars of any given magnitude as of that 

 immediately brighter, the increase of number 

 compensating for the decrease of brilliance. 

 Were the Universe infinitely extended, the whole 

 heavens would shine with the brilliance of the 

 Sun. Newcomb, therefore, concludes that " that 

 collection of stars which we call the Universe 

 is limited in extent." 



Positive evidence that this is the case was 

 obtained by Giovanni Celoria, now director of 



