92 Astronomical Operations at the Pulkova Observatory. 



For the determination of the same constant, Mr. O. Strove 

 employed the comparison of four hundred stars observed at Dor- 

 pat, from 1822, with a meridian circle of Reichenbach and Ertel, 

 with the same stars obtained by Bradley's observations. This 

 comparison gave him the proper motions of these four hundred 

 stars in right ascension and declination. Now, since the remark- 

 able work and research of Argelander, presented to the Academy 

 of St. Petersburg, in 1837, upon the proper motion of the solar 

 system, have made known this motion and direction beyond 

 question, Mr. O. Struve sought to determine by means of the 

 eight hundred equations of condition arising from the four hun- 

 dred proper motions which he obtained, both the correction which 

 should result for the supposed precession of Bessel, and the quan- 

 tity of the solar motion. 



Here a difficulty respecting this motion presents itself; for the 

 effect must be in the inverse ratio of the distances of the stars 

 from the sun, and the parallax and distances of the stars are still 

 unknown, with the exception perhaps of a very small number of 

 cases. To obviate this the author had recourse to the apparent 



§ 



brightness of the stars, which, according to optical principles, is 

 modified with their distances. Struve, the father, in the intro- 

 duction to his catalogue of double stars, established, from inves- 

 tigations based upon the number of stars of different classes scat- 

 tered in the celestial vault, that by taking for unity the distance 

 of the stars of the first magnitude, that of stars of the second 

 magnitude is 1.71, and so on as far as to the stars of the seventh 

 magnitude, whose distance is 11.34. These values though not 

 exact must, according to him, approach near the truth in nearly 

 all cases ; though in particular instances an isolated star may be 

 found at a very different distance from that which its apparent 

 splendor assigns to it* 



The value of the annual precession for 1790 to which Mr. 0. 

 Struve arrived by the resolution of his eight hundred equations 

 of condition, is 50"-23449, with a probable error of 0"-0077l. 



Bessel 



very 



As to the motion of the solar system in space, he found that 

 for a point situated at right angles to the direction of this motion, 

 and placed at the mean distance of the stars of the first magni- 

 tude, the annual angular motion was 0"-321, according to the 



