Stcr. XXXVII. PROPER MOTIONS OF THE STARS. 369 



is poorer than the northern in close double stars above 

 the tenth magnitude. He observes, that if Mr. Dunlop's 

 measures can be depended upon, 6 Eridani is perhaps 

 the most remarkable of all the binary systems in the 

 heavens. The revolution of the satellite star being at 

 the rate of 10-67 per annum, it consequently must 

 accomplish a revolution in a little more than thirty years. 

 The motion of Mercury is more rapid than that of any- 

 other planet, being at the rate of 107,000 miles an hour ; 

 the perihelion velocity of the comet of 1680 was no less 

 than 880,000 miles an hour ; but if the two stars of 6 

 Eridani or Ursae be as remote from one another as the 

 nearest fixed star is from the sun, the velocity of the 

 revolving stars must exceed the powers of imagination. 

 The discovery of the elliptical motion of the double stars 

 excites the highest interest, since it shows that gravita- 

 tion is not peculiar to our system of planets, but that 

 systems of suns in the far distant regions of the uni- 

 verse are also obedient to its laws. 



Besides revolutions about one another, some of the 

 binary systems are carried forward in space by a motion 

 common to both stars, toward some unknown point in 

 the firmament. The two stars of 61 Cygni, which are 

 nearly equal, and have remained at the distance of about 

 15" from each other for fifty years, have changed their 

 place in the heavens during that period, by 4' 23", with 

 a motion which for ages must appear rectilinear : be- 

 cause, even if the path be curved, so small a portion of 

 it must appear a straight line to us. The single stars 

 also have proper motions, yet so minute that the trans- 

 lation of p Cassiopeiae, of 3"'74 annually, is the greatest 

 yet observed : but the enormous distances of the stars 

 make motions appear small to us which are in reality 

 very great. Sir William Herschel conceived that, 

 among many irregularities, the motions of the stars have 

 a general tendency toward a point diametrically oppo- 

 site to that occupied by the star Herculis, which he 

 attributed to a motion of the solar system in the contrary 

 direction. Should this really be the case, the stars, 

 from the effects of perspective alone, would seem to 

 diverge in the direction to which we are tending, and 

 would apparently converge in the space we leave, and 

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