190 COSMOS 



mid FlamsteaJ believed that they had discovered parallaxei 

 ef several seconds, whereas they had confounded the proper 

 motions of the stars with the true changes from parallax. 

 On the other hand, the ingenious John Michell [Phil. Trans. 

 1767, vol. Ivii., p. 234-2G4) was of opinion that the paral- 

 laxes of the nearest fixed stars must be less than 0' -02, and 

 in that case could only " become perceptible when magnified 

 12,000 times." In consequence of the widely-difiused opin- 

 ion that the superior brilliancy of a star must invariably in- 

 dicate a greater proximity, stars of the first magnitude, as, 

 for instance, Vega, Aldebaran, Sirius, and Procyon, were, 

 M^th little success, selected for obserA-ation by Calandrelli 

 and the meritorious Piazzi (1805). These observations must 

 be classed with those which Brinkley published in Dublin 

 (1815), and which, ten years afterward, were refuted by 

 Pond, and especially by Airy. An accurate and satisfactory 

 knowledge of parallaxes, founded on micrometric measure- 

 ments, dates only from between the years 1832 and 1838 



Although Peters,* in his valuable work on the distance? 

 of the fixed stars (184G), estimates the number of parallaxes 

 liitherto discovered at 33, we shall content ourselves with re 

 ferring to 9, which deserve greater, although very different, 

 degrees of confidence, and which we shall consider in .the 

 probable order of their determinations. 



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

 has rendered so celebrated. The astronomer of Koniofsbers: 

 determined, in 1812, the large proper motion of this double 

 star (below the sixth magnitude), but it was not until 1838 

 that, by means of the heliometer, he discovered its parallax. 

 Between the months of August, 1812, and November, 1813, 

 my friends Arago and Mathieu instituted a series of numer 

 ous observations for the purpose of finding the parallax oi 

 the star 61 Cygni, by measuring its distance from the zenith. 

 In the course of their labors they arrived at the very correct 

 conclusion that the parallax of this star was less than half a 

 second.! So late as 1815 and 1816, Bessel, to use his own 



* Struve, Astr. Stell., p. 104. 



t Arago, in the Connaissance des Temps four 1834, p. 281 : " Noua 

 obsei-vAmes avec beaucoup de soin, M. Mathieu et moi, pendant le 

 mois d'Aofit, 1812, et pendant le mois de Novembre suivant, la hauteur 

 augulaire de I'etoile audessus de I'horizon de Paris. Cette hauteur, k 

 la secoude epoque, ne surpasse la hauteur angulaire sL la premiere que 

 de 0"*66. Une parallaxe absolue d'une seule seconde aurait necessaire- 

 inent amene entre ces deux hauteurs unc difference de l"-2. Nos ob* 

 eervations n'indiquent done pus que le I'ayon de I'orbite terreste, que 



