252 COSMOS. 



7th magnitudes. 5 Seven stars have revealed an unusually 

 great motion, namely : Arcturus, 1st magnitude (2"*25) ; 

 a Centauri, 1st magnitude (3"'58); 6 p Cassiopeia?, 6th mag* 

 nitude (3'" 74); the double star, ^ Eridani, 5*4 magnitude 

 (4"'08); the double star 61 Cygni, 5'6 magnituae, (5"-123), 

 discovered by Bessel in 1812, by means of a comparison with 

 Bradley's observations; a star in the confines of the Canes 

 Venatici, 7 and the Great Bear, No. 1830 of the catalogue of 

 the circumpolar stars by Groombridge, 7th magnitude (ac- 

 cording to Argelander, 6"'974); i Indi (7"'74. according to 

 D' Arrest); 8 2151 Puppis, 6th magnitude (7"'871). The 

 arithmetical* mean of the several proper motions of the fixed 

 stars in all the zones into which the sidereal sphere has been 

 divided by Madler, would scarcely exceed 0"-102. 



An important inquiry into the " Variability of the proper 

 motions of Procyon and Sirius," in the year 1844, a short 



6 Bessel, in the Jahrbuch von Schumacher fur 1839, s. 38. 

 Arago, Annuaire pour 1842, p. 389. 



6 Centauri, see Henderson and Maclear, in the Memoir* 

 of the Astron. Soc., vol. xi. p. 61 ; and Piazzi Smyth, in the 

 Edinburgh Transact., vol. xvi. p. 447. The proper motion 

 of Arcturus, 2"'25 (Baily,inthe same Memoirs^ vol. v. p. 165), 

 considered as that of a very bright star, may be called very 

 large in comparison with Aldebaran, 0"* 185 (Madler, Central- 

 sonne, s. 11), and a Lyra?, 0" - 400. Among the stars of the 

 1st magnitude, a, Centauri, with its great proper motion of 

 3"*58, forms a very remarkable exception. The proper motion 

 of the binary system of Cygnus amounts, according to Bessel 

 (Schum. Astr. Nachr., bd. xvi. s. 93), to 5"- 123. 



7 Schumacher's Astr. Nachr., no. 455. 



8 Op. cit., no. 618, s. 276. D'Arest founds this result on 

 comparisons of Lacaille (1750) with Brisbane (1825), and of 

 Brisbane with Taylor (1835). The star 2151, Puppis, has a 

 proper motion of 7"'871, and is of the 6th magnitude. 

 (Maclear, in Madler's Unters. uber die Fixstern-S^steme, til. 

 ii. s. 5.) 



* Schum. Astr. Nachr., no. 661, s. 201. 



