400 ELLIPTICAL MOTION OF DOUBLE STARS. SECT. XXXVI. 



exceed that of Uranus. It is very "probable that an occultation of 

 one of the suns by the other will take place in 1867, or a very 

 close appulse of the two stars. 



Singular anomalies have appeared in the motions of 70 Ophiuchi, 

 which was discovered to be a binary system by Sir William 

 Herschel in 1779, and which has since nearly accomplished a re- 

 volution. Various orbits have been computed : those which best 

 represent the angles of position fail with regard to' the distances of 

 the stars from one another, and vice versa. But it is a very re- 

 markable fact that the errors are periodical, being for considerable 

 periods of time alternately in excess and defect. Captain W. S. 

 Jacob, who determined the periodic time of the revolving star to 

 be 93 years, attributes this anomaly to the disturbing action of 

 an opaque body revolving round the lesser star. Assuming .that 

 to be the case, and computing, he found that the errors were con- 

 siderably diminished both in the angle of position and distance. 

 It is a subject of the highest interest, and well worthy of the 

 attention of such astronomers as have the means of making the 

 necessary observations. Among the triple systems, as Cancri, 

 two of the stars revolve about one another in 58 -9 years ; but 

 the motion of the third and most distant is so slow, that it has 

 only accomplished a tenth part of its revolution about the other 

 two since the system was discovered. 



It appears from the calculations of Mr. Dunlop that a- Eridani 

 accomplishes a revolution in little more than 30 years. The 

 motion of Mercury is more rapid than that of any of the planets, 

 being at the rate of 107,000 miles an hour. The perihelion 

 velocity of the comet of 1680 was 880,000 miles an hour; but, if 

 the two stars of a- Eridani, or of Ursse Majoris, be as remote 

 from one another as the nearest fixed star is from the sun, the 

 velocity of the revolving star must exceed the power of imagina- 

 tion to conceive. The elliptical motion of the double stars shows 

 that gravitation is not confined to the planetary motions, but that 

 systems of suns in the far distant regions of the universe are also 

 obedient to its laws. The stellar systems present a kind of 

 sidereal chronometer, by which the chronology of the heavens 

 will be marked out to future ages by epochs of their own, liable 

 to no fluctuations from such disturbances as take place in our 

 system. Some stars are apparently double, though altogether 

 unconnected, one being far behind the other in space, as a Lyrse, 



