158 G. H. KNIBBS. 



this number gave no certain result, Bessel concluded that a con- 

 siderable period must elapse before the true theory of solar motion 

 can be made out. The Besselian method depended upon the 

 principle that the poles of the proper motions give a reliable 

 indication of the sun's path in reference to the stars considered. 



(24) Others, 1821.— In 1821 Olbers calculated the direction of 

 the path in space of our system from the proper motion of 82 

 stars. 1 This was published in connection with his correspondence 

 with Bessel. 



(25) Argelander, 1837. — Argelander's great memoir " On the 

 proper motion of the solar system," presented to the Academy of 

 St. Petersburg in 1837 2 may be said to be the first systematic 

 attempt to discuss the problem with anything like the thoroughness 

 it deserved ; 390 stars with proper motions sufficiently large were 

 available, by comparing Bessel's reductions of Bradley's observa- 

 tions with Argelander's own '1830' catalogue. 3 These stars were 

 divided into classes as follows, and with the following results for 

 the year 1792-5 : — 



Class i. P.M.>1" 4 21 Stars R.A. 260-°8 D. + 31°3 



„ ii. „ l-"0-0-"5 50 „ „ 255-°2 „ 37-6 



„ in. „ 0-5-0-09 319 „ „ 261-°2 „ 31-0 



The general result corrected to the beginning of this century 

 (1800-0) was RA _ 25SK9) D = + 32 .o 5 „ 



Argelander's fundamental assumption was that the distances 

 of the stars varied inversely as their proper motions. His reduc- 



1 Point vers lequel se dirige le systeme solaire, d'apres les mouvements 

 propres de 82 etoiles. Olbers u. Bessel. — Briefwechsel, herausg. von A. 

 Erraan n., 1852, p. 220. 



' z Ueber die eigene Bewegung des Sonnensystenis. — Mem. d. sav. etr. 

 de l'acad. imper. St. Petersb., t. in., pp. 561 -605. 



3 DLX Stellarnm fixarum positiones mediae, ineunte anno 1830. Ex 

 observationbus Abose habitis deduxit — Kelsingforsiae, 1835. 



4 P.M. denotes as usual, proper motion. 



5 The values given for the second calculation and final result are in the 

 St. Petersburg Memoirs— i. 255-°9 ; 37-°8) 



ii. 258-2; 39 2 [ 1792-5 

 in. 262-0 ; 29-2 ) 

 For mean, 1 800 -260-°8 ; 31-°3.— Vide pp. 589 - 590. Argelander corrects 

 these in the memoir published in the Astron. Nach.: the corrected values 

 are those above given. 



