yo SPECIAL RESULTS IN THE TJRANOLOGICAL PORTION 



of the existence of great concentric rings filled with millions 

 of stars, forming the Galaxy. The knowledge of the num- 

 ber and relative position of the fainter stars, as has been 

 shown by Galleys prompt and happy discovery of Neptune, 

 and by that of several of the smaller planets, facilitates 

 the discovery of planetary bodies which change their place, 

 moving amidst fixed points. Another circumstance shows, 

 in a still clearer light, the importance of very complete star- 

 catalogues. When once a new pk.net has been discovered 

 in the celestial vault, the difficult calculation of its path is 

 aided by its rediscovery in a catalogue of older date. The 

 fact of a star having been formerly registered, and being 

 now missing in the position assigned to it, has thus often 

 effected more, than, from the slowness of the planet's motion, 

 could be gained by the most carefully-repeated measure- 

 ment during several successive years. Thus for Uranus, 

 the star "No. 964 in the Catalogue of Tobias Mayer, 

 and for Neptune, the star 26266 in the Catalogue of 

 Lalande, ( 184 ) have been of great importance. "We now 

 know that Uranus was observed 21 times before it was 

 known to be a planet : once by Tobias Mayer, 7 times by 

 Elamsteed, once by Bradley, and 12 times by Le Monnier. 

 We may say, that the increasing hope of future discoveries of 

 planetary bodies rests partly on the excellence of our present 

 telescopes (Hebe, when discovered in July 1847, was equal 

 to a star of between the 8th and 9th magnitudes, but in May 

 1849 was only of the llth magnitude), and partly, and 

 perhaps still more, on the completeness of our catalogues 

 and the care of our observers. 



Subsequent to the epoch when Morin and Gascoigne com- 

 bined telescopes with measuring instruments, the first star- 



