154 
EASTMAN. 
The coordinates of the solar apex were found to be— 
From class (a) . . 262° 8'.8; + 39° 25'.2 
“ “ (6) . . 261° 14'.4; +37° 53'.6 
“ f (c) . . 261° 32'.2; +42° 21'.9 
Mean — 261° 38'.5; +39° 53'.6, 
allowing equal weight for each class. 
Madler 19 had already discussed, in 1846, the proper motions 
of a limited number of stars in the constellation Taurus, and 
arrived at the well known conclusion that the Pleiades was 
the central group of the fixed stars, and that the star Alcyone 
was the central sun of that group. 
In 1859, Gr. B. Airy, 20 the Astronomer Royal at Greenwich, 
presented to the Royal Astronomical Society the results of 
his investigation of the movement of the solar system in 
space. He adopted a new method of discussing the linear 
movements of the sun, and of each star, by the use of rec¬ 
tangular coordinates, a device at once complete and inde¬ 
pendent, in which no assumption of the values of the quan¬ 
tities sought was necessary. 
He formed his equations on two widely different suppo¬ 
sitions : First, that the irregularities of proper motions are 
due wholly to chance-error of observation; second, that they 
are due entirely to peculiar motions of the stars themselves. 
He was evidently inclined to believe that the second suppo¬ 
sition was nearer the truth. Like most of the previous in¬ 
vestigators, he sought such a value of the sun’s angular 
motion in space as would be seen from a star of the first 
magnitude, and for that purpose was obliged to assume some 
law of relative distances among the stars. In tllis he was 
guided by the elder Struve’s work, and, dividing the stars 
used into seven groups, according to magnitude, he adopted 
the system in the following table, which is almost identical 
with that of Struve : 
19 Madler, J. H. Astronomische Nachrichten, 566; 213. 
20 Airy, G. B. Mem. Eoy. Ast. Society, XXVIII; 143. 
