188 SPECIAL RESULTS IN THE TJRANOLOG1CAL PORTION 



measurements, only commenced between the years 1832 

 and 1838. 



Although Peters, ( 3 7 ) in his important work on the dis- 

 tances of fixed stars (1846), gives the number of cases of 

 parallax already discovered at 33, I will content myself with 

 citing nine, which deserve, though in very unequal degrees, 

 the greatest amount of confidence, giving them nearly in the 

 order of time of their determinations. 



The first place belongs to the Star 61 Cygni, which Bessel 

 has rendered so celebrated. As early as 1812, the Konigs- 

 berg astronomer determined the large proper motion of this 

 double star (below the sixth magnitude) ; but it was only 

 in 1838, that he ascertained its parallax by the employment 

 of the heliometer. My friends Arago and Mathieu made a 

 series of numerous observations, from August 1812 to No- 

 vember 1813, for ascertaining the parallax of 61 Cygui by 

 measuring its Zenith distance. They arrived at the very just 

 conjecture, that the parallax of the Star must be less than 

 half a second.( 308 ) As late as 1815 and 1816, Bessel, as 

 he himself expresses it, " had not arrived at any admissible 

 result." ( 309 ) Observations from August 1837 to October 

 1838, in which he availed himself of the large heliometer 

 established in 1829, first led him to infer a parallax of 

 0"-3483, corresponding to a distance of 592200 semi- 

 diameters of the Earth's orbit, and to a passage of light of 

 9| years. Peters, in 1842, confirmed this result, by find- 

 ing 0' x '3490 ; subsequently, however, Bessel's result was con- 

 verted by a temperature correction into 0"*3744. ( 31 ) 



The parallax of the finest double Star in the Southern 

 Heavens, a Centauri, has been determined by observations 

 at the Cape of Good Hope, by Henderson in 1832, and by 



