MOTION OF THE SOLAR SYSTEM. 
91 
apparent proper motions were not computed, but the variations in rig-lit ascension 
and declination expressed separately in terms of the assumed values of A and D and 
the star’s place, so that each star furnishes two independent equations. For deter- 
mining the relative weights of the equations, he adopts the hypothesis that the 
distances of the stars are inversely as their apparent magnitudes ; and, dividing all 
the stars from the first to the seventh magnitude inclusive into twelve classes, he 
assumes, on grounds given by the elder Struve, in the Introduction to his catalogue 
of double stars, the mean distance of those in the first class =1, of those in the 
second =1*71, and so on to the twelfth class, or seventh magnitude, for which the 
mean distance becomes 1 1 *34 . Weights depending on those distances were assigned 
to the equations furnished by the stars in each of the twelve classes, and the values 
of dA and dD deduced. The result gave the position of Q, for 1790, as follows : — 
A=261° 21'*8±4 0 49'-9; D = +37° 36'-0±4° ll'*8. 
For the sake of comparison, I here subjoin the results of the several investigations 
of Argelander, Lundahl, and Otto Struve. 
Position of the apex of the sun’s proper motion for 1792'5, 
A= 
Argelander I. 258° 25 'Tdtl 2 ° 2l'-3 
Argelander II. 255° 9'7i 8° 34' 0 
Argelander III. 261° 10 ,- 7i 3° 48 ,- 9 
Lundahl IV. 252° 24'-4± 5° 25'-3 
O. Struve V. 261° 23 ,- l+ 4° 49'‘9 
From these five determinations O. Stru 
D= 
+38° 37 f -2±9° 2l'-4 (21 stars). 
+ 38° 34'-3±5° 55'-6 (50 stars). 
+ 30° 58'* 1+2° 3l'*4 (319 stars). 
+ 14° 26'T±4° 29'-3 (147 stars). 
-f37° 35'7±4° 1 1 '* 8 (392 stars), 
deduced the following mean result : — 
A= 259° 9'H, with a probable error =2° 57 , ‘5. 
D=+ 34° 36 L 5, with a probable error =3° 24' 5. 
The proper motions on which the following investigation is grounded are deduced 
from a comparison of the mean positions of eighty-one stars in the southern hemi- 
sphere, as observed by Mr. Johnson and the late Professor Henderson, with the 
positions assigned to them in the catalogues of Lacaille and Bradley. Every star, 
without exception, has been included, which, from the differences of right ascension 
and declination given in the two recent catalogues, appears to have a proper motion 
amounting to 0"T in space, or upwards, annually. 
Mr. Johnson’s catalogue, which was published in 1835, gives the mean positions 
of 606 stars, observed by him at St. Helena, and reduced to the beginning of 1830. 
Of these stars a considerable number are contained in Lacaille’s catalogue, originally 
published in the Astronomise Fundamental 757), and recently by Mr.BAiLYin vol.v.of 
the Memoirs of the Royal Astronomical Society. The epoch of Lacaille’s catalogue 
is 1780, so that the interval is eighty years. In order to compare the two catalogues, 
Mr. Johnson reduced the positions given by Lacaille to the epoch 1830, by applying 
