IMPORTANCE OF CATALOGUES. 153 



cosmical bodies which change their positions, moving as it were 

 between fixed boundaries. Another circumstance proves even 

 more distinctly the importance of very complete catalogues of 

 the stars. If a new planet be once discovered in the vault of 

 heaven, its notification in an older catalogue of positions will 

 materially facilitate the difficult calculation of its orbit. The 

 indication of a new star which has subsequently been lost sight 

 of, frequently affords us more assistance than, considering the 

 slowness of its motion, we can hope to gain by the most careful 

 measurements of its course through many successive years. 

 Thus the star numbered 964 in the catalogue of Tobias Mayer 

 has proved of great importance for the determination of Uranus, 

 and the star numbered 26266 in Lalande's catalogue 18 for that 

 of Neptune. Uranus, before it was recognized as a planet, had, 

 as is now well known, been observed twenty-one times ; once, 

 as already stated, by Tobias Mayer, seven times by Flamstead, 

 once by Bradley, and twelve times by Le Monnier. It may be 

 said that our increasing hope of future discoveries of planetary 

 bodies rests partly on the perfection of our telescopes (Hebe, 

 at the time of its discovery in July, 1847, was a star of the 8'9 

 magnitude, while in May, 1849, it was only of the llth mag- 

 nitude), and partly, and perhaps more, on the completeness of 

 our star-catalogues, and on the exactness of our observers. 



The first catalogue of the stars which appeared after the 

 epoch when Morin and Gascoigne taught us to combine tele- 

 scopes with measuring instruments, was that of the southern 



1 Baily, Cat. of those stars in the " Histoire Celeste" of 

 Jerome de Lalande.for which tables of reduction to the epoch 

 1800 have been published by Prof. Schumacher, 1847, p. 1195. 

 On what we owe to the perfection of star catalogues see the 

 remarks of Sir John Herschel in Cat. of the British Assoc., 

 1845, p. 4, 10. Compare also on stars that have disap- 

 peared Schumacher, Astr. Nachr., no. 624, and Bode, Jahrb. 

 fur 1817, s. 249. 



