114 COSMOS. 



sitions will materially facilitate the difficult calculation of 

 its orbit. The indication of a new star which has subse- 

 quently been lost sight of, frequently affords us more assist- 

 ance 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 im- 

 portance for the determination of Uranus, and the star num- 

 bered 26,266 in Lalande's catalogue* 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 al- 

 ready 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 plan- 

 etary 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 

 eleventh magnitude), 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 

 stars compiled by Halley. It was the result of a short resi- 

 dence at St. Helena in the years 1677 and 1678, but, singu- 

 larly enough, does not contain any determinations below the 

 sixth magnitude.! Flamstead had, indeed, begun his great 

 Star Atlas at an earlier period ; but the work of this cele- 

 brated observer did not appear till 1712. It was succeeded 

 by Bradley's observations (from 1750 to 1762), which led to 

 the discovery of aberration and nutation, and have been ren- 

 dered celebrated by the Fundamental Astronomic of our 

 countryman Bessel (1818), % and by the stellar catalogues of 



* Baily, Cat. of those stars in the " Hisloire Cileste" of Jerome de 

 Lalande, for which tables of reduction to the epoch 1800 have been pub- 

 lished 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 disappeared, Schumacher, Astr. Nachr., No. 624, and Bode, Jahrb. 

 fur 1817, s. 249. 



t Memoirs of the Royal Astron. Soc, vol. xiii., 1843, p. 33 and 168. 



I Bessel, Fundamcnta Astronomia pro anno 1755, deducta ex observa~ 

 tionihus viri incomparabilis James Bradley in Specula astronomica Gre- 

 novicensi, 1818. Compare also Bessel, Tabula; Regiomontanm reductio- 

 num observationum astronomicarum ab anno 1750 usque ad annum, 1850 

 computatce ( 1 830). 



