THE STARS. 159 



viewed from a distance of a hundred and eighty 

 miles." 



Closely allied to the question of parallax is 

 the determination of the exact positions of the 

 stars and the formation of star-catalogues. In 

 this branch, too, much is due to the genius of 

 Bessel. The observations of Bradley at Green- 

 wich from 1750 to 1762 were reduced by Bessel 

 into the form of a catalogue, which was published 

 in 1818, with the title of 'Fundamenta Astro- 

 nomiae.' During the years 1821 to 1823 Bessel 

 took 75,011 observations, by which he brought 

 up the number of accurately known stars to 

 50,000. At the same time notable catalogues 

 had been constructed, particularly by the Eng- 

 lish astronomer, Francis Baily (1774 - 1844), 

 and by Giovanni Santini (1786-1877), director 

 of the observatory at Padua ; but Bessel's suc- 

 cessor in this branch of research was Friedrich 

 Wilhelm August Argelander (1799 - 1875). In 

 1821 he became assistant to Bessel at Konigs- 

 berg, in 1823 director of the Observatory at Abo, 

 in Finland, and in 1837 of that at Bonn. Here 

 he commenced in 1852 the great * Bonn Durch- 

 musterung,' a catalogue and atlas of 324,198 

 stars visible in the northern hemisphere. The 

 great catalogue was published in 1863. After 

 Argelander's death it was extended so as to 



