648 



to appreciate the evidence on which it rests will doubt the possibility 

 of detecting such a quantity by such means ; and astronomers, accord- 

 ingly, regard the conclusion as one which, if not absolutely certain, 

 is at least so extremely probable, that it must command assent until 

 disproved by another equally good, and longer continued, series of 

 observations. 



The fruits of the extreme precision which Bessel so greatly con- 

 tributed to introduce into astronomical observations and reductions, 

 have already begun to make their appearance. In an interesting 

 disquisition published in some recent numbers of the ' Astronomische 

 Nachrichten' (514, 515, 516), he seems to have established the 

 existence of a very remarkable phenomenon which had been indi- 

 cated, at different times, by Pond, namely, the variability of the 

 proper motion of two of the principal stars, Procyon and Sirius. 

 It is unnecessary to point to the boundless field of speculation re- 

 specting the constitution of the sidereal heavens which such a dis- 

 covery lays open. 



The annals of astronomy afford many illustrious examples of inde- 

 fatigable industry and prolific labour, but few more remarkable than 

 Bessel. From the date of his first publication in 1804, the astrono- 

 mical periodicals of Germany teem with his productions. Zach's 

 ' Monatliche Correspondenz,' Lindenau's * Zeitschrift,' Bode's * Jahr- 

 buch,' the ' Berlin Ephemeris,* the * Memoirs of the Berlin Acade- 

 my,' and, more especially, Schumacher's 'Astronomische Nachrich- 

 ten,' have all been enriched by his communications. The last-named 

 journal, indeed, contains upwards of 180 bearing his signature, em- 

 bracing almost every subject connected with the science and prac- 

 tice of astronomy, and questions of every order of difficulty. Some 

 of his papers in the ' Berlin Memoirs' are extremely remarkable, 

 not only l3y reason of the results arrived at, but as showing the re- 

 sources and originality of the author, and his skill in the highest 

 departments of analysis and physical astronomy. Among these may 

 be mentioned, in particular, his researches on the great comet of 

 1807 (published in 1810), in which he proposed a method, which is 

 now generally followed, of determining the orbit when it is necessary 

 to take the perturbations into account ; a most important memoir on 

 the precession of the equinoxes '(1815) ; another on the planetary 

 perturbations (1824); and three on the right ascensions of Maske- 

 lyne's 36 stars (1818, 1819, 1825). Among his later productions 

 are two quarto volumes of ' Untersuchungeti ' (or Astronomical Re- 

 searches), and a third is said to have been nearly prepared for the 

 press. Many other titles might be cited, but those now mentioned 

 may suffice to give an idea of the wide extent over which he ranged. 

 Indeed it may be said of Bessel, that there is no department of astro- 

 nomy which he did not handle, and that nothing passed through his 

 hands without receiving extension or improvement. But, perhaps, 

 that which stands out as most remarkable in his writings is his pro- 

 found knowledge of the theory of instruments ; and perhaps also the 

 influence of his example in teaching observers to trust less to the 

 mechanical perfection of instruments, and to bestow more pains in 



