96 Messrs Herschel and South on Binary Systems. 



1821.30 24*45'^/"^ 



1822.83 18 27 nfV Herschel and South. 



1825.44 12 29 3 



The mean annual angular velocity is about + 3**. The dis- 

 tance is 1".48 at the last epoch. 



In 1782 the distance of the two stars was fully 1^ diameter 

 of the small star, with a power of 227, but Struve observed 

 them with the same power to be only J of a diameter as under. 



12. 21 (L Draconis. R. A. 17'* 8'. N. decl. 54° 43^ 



The two stars are nearly equal, and of the 8th magnitude. 

 The angular position in 1781.73 was 37° 38' sp or nf, and 

 in 1825.25, 61° 2^ sp or nf. Its distance at the last epoch was 

 4".33. Its annual motion is —0° 579, and nearly uniform. 



13. 70 p OphiuchL R. A. 17^ 56/. N. decl. 2° 33^. 



The two stars are of the 7 J and 8 J magnitude. The larg- 

 est is white, and the small one livid. The mean annual motion 

 from 1779 to 1823 is 6° 811. Since 1820, its annual velocity 

 has varied from — 1°. 75, to — 2°. 42. Mr Herschel has 

 shown, what the laws of central forces rendered necessary, that 

 a very considerable diminution of distance accompanied the 

 great increase of angular velocity, some time between 1781 

 and 1819, and that the subsequent diminution of the velocity 

 has also been accompanied with a corresponding increase of 

 distance, which, in 1825.56, was 4" ^6. 



14. 5 LyrcBy R. Asc. 18^ 38', N. decl. 39° 2r. 



The stars are nearly equal, and of the 8th magnitude. The 

 position in 1825.53 was 69"^ 11' np or sf, and the distance 

 3" 34. The annual motion is —0° 325. 



15. 61 Cygni, R. Asc. 20^ 59, N. decl. 37° 52'. 



The two stars are of the 7th and 8th magnitude. The 

 angle of position, as determined by Bradley in 1753.8, 

 was 54° 36^, and in 1825.7 it was 3° 4', as determined by 

 South, and the distance 15" 444. " The mean annual 

 motion," says Mr Herschel, " round their common centre 

 of gravity is 0''.7S0, not far short of that of the two stars of 



