SECT, xxxvu.] PAEALLAX OF FIXED STARS. 427 



inferred from the comparative velocity of their motions. 

 All the stars have a general motion of translation, which 

 tends ultimately to mix those of the different constellations ; 

 but none that we know of moves so rapidly as 61 Cygni, 

 and on that account it is reckoned to be nearer to us than 

 any other, for an object seems to move more quickly the 

 nearer we are to it. This circumstance induced MM. Arago 

 and Mathieu to endeavour to determine its annual parallax, 

 that is, to ascertain what magnitude the diameter of the 

 earth's orbit would have, as seen from the star, and from 

 that to compute its distance from the earth (N. 223). This 

 has been accomplished with more accuracy by M. Bessel, 

 who has found by observation that the diameter of the 

 earth's orbit, of 190 millions of miles, would be seen from 

 the star under an angle of only one-third of a second, 

 whence 61 Cygni must be 592,200 times farther from the 

 earth than the sun is a distance which light, flying at the 

 rate of 190,000 miles in a second, would not pass over in 

 less than nine years and three months. 



Mr. Henderson found the parallax of Sirius, the brightest 

 star in the heavens, to be less than the third of a second of 

 space ; it is consequently more remote than 61 Cygni ; and 

 a Lyree is 'still farther off, being, by M. Struve's calculation, 

 from his own observations, 789,600 times more remote from 

 the sun than the earth is. By Mr. Maclear's observations, 

 the parallax of a Centauri amounts to nearly a second of 

 space, which makes the distance of that star from the sun 

 200,000 times greater than the radius of the earth's orbit. 



The great gulfs that separate the stars from the sun, and 

 probably from one another, no doubt maintain the stability 

 of the stellar system in the same manner that, in the 

 solar system, the distance of the planets from the sun, 

 and the satellites from their primaries, are so arranged 

 as to preserve their mutual disturbances within due limits. 

 The stars supposed to be nearest to the sun are probably in 

 a great zone, which crosses the Milky Way between rj Argus 



