The Milky Way 



our stellar system, without, however, meaning 

 by this that it controls the motions of the 

 universe, as our sun rules the motions of the 

 planets which circle round it. 



It may therefore be considered probable that 

 the milky nebula revolves as a whole round Alcy- 

 one, and that the galactic circle is, in the stellar 

 system, the analogue of the ecliptic in the 

 solar system. Our sun, in particular, describes 

 a vast orbit, whose radius is approximately 

 192 light-years, with a duration of revolution of 

 twenty-two million years that is to say, about as 

 many terrestrial years as there are seconds in a 

 single year. It must not be forgotten that these 

 figures are only hypothetical and can only be 

 accepted as giving an idea of the magnitude of 

 these motions. In any case they show that the 

 stars of the milky nebula are not independent, 

 and that universal attraction establishes between 

 them the same close connection which unites 

 the bodies of the solar system. 



We have still to show how great is the 

 variety of the types found in the sky, though, 

 at first sight, it presents only a number of 

 bright points. 



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