DISTANCES OF THE STARS. 259 



The first place is due to the star 61 Cygni, which 

 Bessel has rendered so celebrated. The astronomer of 

 Konigsberg determined, in 1812, the large proper motion 

 of this double star, (below the 6th magnitude,) but it was 

 not until 1838, that, by means of the heliometer, he dis- 

 covered its parallax. Between the months of August, 1812, 

 and November, 1813, my friends Arago and Mathieu institu- 

 tuted a series of numerous observations, for the purpose of 

 finding the parallax of the star 61 Cygni, by measuring its 

 distance from the zenith. In the course of their labours they 

 arrived at the very correct conclusion that the parallax of 

 this star was less than half a second. 19 So late as 1815 and 



19 Arago, in the Connaissance des Temps pour 1834, p. 281: 

 " Nous observames avec beaucoup de soin, Mr. Mathieu 

 et moi, pendant le mois d'Aout, 1812, et pendant le mois de 

 Novembre suivant, la hauteur angulaire de Tetoile audessus 

 de Thorizon de Paris. Cette hauteur, a la seconde epoque, 

 ne surpasse la hauteur angulaire a la premiere que de 0"*66. 

 Une parallaxe absolue d'une seule seconde aurait neces- 

 sairement amene entre ces deux hauteurs une difference de 

 l"-2. Nos observations n'indiquent done pas que le rayon 

 de 1'orbite terreste, que 39 millions de lieues soient vus de 

 la 61 e du Cygne sous un angle de plus d'une demi-seconde. 

 Mais une base vue perpendiculairement soutend un angle d'une 

 demi-seconde quand on est eloigne de 412 mille fois sa lon- 

 gueur. Done la 61 e du Cygne est au moins a une distance de 

 la terre egale a 412 mille fois 39 millions de lieues." 

 " During the month of August, 1812, and also during the fol- 

 lowing November, Mr. Mathieu and myself very carefully 

 observed the altitude of the star above the horizon, at Paris. 

 At the latter period its altitude only exceeded that of the 

 former by 0"-66. An absolute parallax of only a single second 

 would necessarily have occasioned a difference of 1"*2 be- 

 tween these heights. Our observations do not therefore 

 show that a semi-diameter of the earth's orbit, or 39 millions 

 of leagues, are seen from the star 61 of Cygnus, at an angle 

 of more than 0"-5. But a base viewed perpendicularly sub- 



s2 



