KEAL MOTION OF THE SUN. 



more extensively and accurately observed, and calculations of the* 

 motions of the sun which they indicate, have been made by 

 several astronomers. The following points have been assigned as- 

 the direction of the solar motion in 1790: 



R. A. K. P. D. 



260 34' 63 43' Sir W. Herschel. 



256 25' 

 255 10' 

 261 n' 

 252 53' 



26l 22' 



51 23' Argelander. 



5' *6' 



59 ' 



75 34' Luhndahl. 



62 24' Otto Struve. 



The first estimate of Argelander was made from the proper motions 

 of 21 stars, each of which has an annual motion greater than 1" ; 

 the second from 50 stars having annual proper motions between 1" 

 and 0'5", and the third from those of 319 stars having motions 

 between 0-5" and O'l". The estimate of M. Luhndahl is based on 

 the motions of 147 stars, and that of M. Struve on 392 stars. 



The mean of all these estimates * is a point whose right ascen- 

 sion is 259 9', and north polar distance 55 23', which it will be 

 seen differs very little from the point originally assigned by Sir 

 W. Herschel. 



All the preceding calculations being based on observations 

 made on stars in the northern hemisphere, it was obviously 

 desirable that similar estimates should be made from the observed 

 proper motions of southern stars. Mr. Galloway undertook and 

 executed these calculations ; and found that the southern stars 

 gave the direction of the solar motion for 1 790, to be towards a-point 

 whose right ascension is 260 1', and north polar distance 55 37'. 



No doubt, therefore, can remain that the proper motion of the 

 stars is produced by a real motion of the solar system, and that the 

 direction of this motion in 1790 was towards a point of space which 

 seen from the then position of the system had the right ascension 

 of about 260, and the north polar distance of about 55. 



67. It follows from these calculations, that the average dis- 

 placement of the stars requires that the motion of the sun should 

 be such as that if its direction were at right angles to a visual 

 ray, drawn from a star of the first magnitude of average distance, 

 its apparent annual motion would be 0-3392" ; and taking the 

 average parallax of such a star at 0'209", if B express the 

 semi-axis of the earth's orbit, the annual motion of the sun 

 would be 



, = 1-623!,. 



Herschel, Ast., 2nd Ed., p. 583. 



