which form Binofiy Systems^ 93 



" In the present imperfect state of the data, it would be use- 

 less to enter into any minute investigations respecting the ele- 

 ments of the orbit ; but when twenty or thirty years observa- 

 tions shall have enabled us to trace precisely the variation of 

 the angular motion up to the aphelion, and to ascertain by di- 

 rect observation the periodic time and mean motion, the princi- 

 ples of physical astronomy may be applied." 



These are the observations in Messrs South and Herschel's 

 memoir of 1826. After comparing the preceding observations 

 with the latest by Mr South in 1825.S2, Mr Herschel re- 

 marks : 



** Nothing can be more satisfactory than the confirmation 

 these observations afFord of the rapid motion ascribed to 

 this remarkable star. In the interval of 1.97 year since the 

 epoch 1823.29, the motion has amounted to no less than 

 13°.55 in the direction np, sf or — 7''.025 per annum. The 

 sudden diminution of velocity is however not confirmed. 

 Indeed, it rested on too short an interval, and on too few 

 observations (from four very close stars) to deserve great con- 

 fidence. We cannot do better than recommend this star for the 

 next ten or twenty years to the constant and careful measure- 

 ment of astronomers ; nor can we too strongly inculcate here 

 the indispensable necessity of multiplying extremely their 

 measures of position to eliminate those errors of judgment to 

 which the most experienced observers are liable in measures 

 of this sort. This done, there is no doubt of our arriving at 

 a precise knowledge of the elements and positions of the orbit 

 described by each about their common centre of gravity, and 

 the question of the extension or non-extension of the Newto- 

 nian law of gravity to the sidereal heavens— the next great 

 step which physical astronomy has yet to make-*will be effec- 

 tually decided," 



6. y Virginis, R. Asc. 12^ 32^ Decl. S. O** 27'. 



The two stars which compose this double star are both 

 white, and of the 8th and 8f magnitude. Both the angle of 

 position, and the distance of these stars have undergone a 

 great change. The following are the results :— • 



