^ and positions of s6 double and triple stars, ^c. 369 



No. XXVI. R. A. 17^ 56"^ ; Decl. 2° ss' N. 



70 p Ophiuchi ; II. 4 ; H. and S. 258. 

 continued, 

 this star can hardly be doubted. But as it is inconsistent 

 with the laws of central forces that this should take place 

 without a corresponding increase of distance ( for the angular 

 velocity is inversely as the square of the distance in the ap- 

 parent as well as in the real orbit, whatever be its position 

 with regard to the line of sight), it becomes necessary to ex- 

 amine more minutely into the distances at the different epochs. 

 It will be observed, however, that in all the interval from 

 1781 to 1819 we find no measure of the distance, and that 

 the maximum of angular velocity must have taken place 

 somewhere in this interval. (See Phil. Trans. 1824. iii. p. 

 290-291.) In such a case we must recur to estimations in 

 diameters, though necessarily less to be depended on than 

 positive measures. On re-examining Sir W. Herschel's 

 MSS., we fortunately find the following observations, which 

 throw considerable light on this point, and in some measure 

 supply the deficiency of measures. It will be recollected 

 that his measures of distance are always supposed to include 

 both diameters of the stars measured. 



" October 27, 1779. 3".593. They are very difficult to 

 " measure, and for that reason I join also an exact 

 " estimation by the eye. The vacancy between them 

 " is 2|- diameters of the largest — certainly more than 

 " two and less than 3. The smallest may be about i 

 " or I of the diameter of the other. They are exactly 

 " in the equatorial motion ; the largest goes first. The 

 " situation I took by letting them run along the hair." 



MDCCCXXVI. s b 



