STELLAR DISTRIBUTION. 225 



from the inner border of the zone to be 500 

 times the distance of Sirius, while the external 

 border is 1100 times that distance. The Uni- 

 verse is finite in extent, its limits being about 

 9000 light years from the Solar System. In 

 Seeliger's opinion the extinction of light may 

 come into play beyond our Universe, and pre- 

 vent us seeing other collections of stars. 



The question of external universes is purely a 

 hypothetical one, although there is undoubtedly 

 much to be said in its favour. These universes 

 have never been seen, and we can only speculate 

 as to their existence. The last word on the 

 subject is by Gore, in 1893, in his elaborate 

 work, * The Visible Universe/ He regards the 

 Solar System as a system of the first order, 

 and the Galaxy and its fellow-universes of the 

 second. He makes a calculation of the possible 

 distance of an external universe of his second 

 order. He assumes the distance of the nearest 

 universe from our Galaxy as proportional to 

 that separating the Sun from a Centauri, 

 and reaches the amazing conclusion that the 

 distance of the nearest Galaxy is no less than 

 520,149,600,000,000,000,000 miles, a distance 

 which light, with its inconceivable velocity of 

 186,000 miles a second, would take almost 

 ninety millions of years to traverse. 



p 



