THE UNIVERSE. OCEANIC DISCOVERIES. 293 



By the precession of the equinoxes the aspect of th 

 starry heavens from every point of the earth's surface is 

 constantly changing. The earlier inhabitants of our high 

 northern latitudes might see magnificent southern constella- 

 tions rise to their view, which, now long unseen, will not 

 reappear for thousands of years. In the time of Columbus, 

 Canopus was already fully 1 20' below the horizon at To- 

 ledo (lat. 39 54') ; it is now about the same quantity above 

 the horizon at Cadiz. For Berlin and the northern lati- 

 tudes the stars of the Southern Cross, as well as a and f> Cen- 

 tauri, are receding more and more ; whilst the Magellanic 

 clouds slowly approach our latitudes. Canopus has had its , 

 greatest northerly approximation during the thousand years 

 which have closed, and is now moving (though, on account 

 of its proximity to the south pole of the ecliptic, with ex- 

 treme slowness) progressively to the south. The Southern 

 Cross began to be invisible in 52j north latitude, 2900 

 years before the Christian era. According to Galle it might 

 previously have reached, in that latitude, an altitude of 

 more than 10; and when it vanished from the horizon of 

 the countries adjoining the Baltic, the great Pyramid of 

 Cheops had already been standing in Egypt for five centu- 

 ries. The pastoral nation of the Hyksos made their inva- 

 sion 700 years later. Former times seem to draw sensibly- 

 nearer to us, when we connect their measurement with me- 

 morable occurrences. 



The extension of a knowledge of the celestial spaces, a 

 knowledge, however, limited to their outward aspect, was 

 accompanied by advances in nautical astronomy ; that is to 

 say, in the improvement of all the methods of determining 

 a ship's place, or its geographical latitude and longitude. 



