82 
MR. GALLOWAY ON THE PROPER 
and ventured to assign the precise point in the heavens towards which our system is 
actually borne, was Sir William Herschel. The paper containing this investigation 
was published in the Philosophical Transactions for 1783 ; and it is remarkable not 
only by reason of its giving the first determination of the kind, but on account of the 
confirmation which the result, though deduced from very insufficient data, has re- 
ceived from subsequent investigations — a circumstance, however, by no means rare 
in respect of the cosmical speculations of Sir W. Herschel. 
After some general considerations respecting the a priori probability of the sun’s 
proper motion, Sir W. Herschel, in the paper alluded to, proceeds to describe the phe- 
nomena to which it would give rise, namely, a general parallactic motion of the stars, 
the amount of which, in respect of any star, will depend both on the star’s distance 
from the sun and its situation in the sphere with reference to the point towards which 
the sun is moving. It is manifest that if we suppose the sun to move in the direction 
of any assumed point, all the stars which are near enough to our system to be sensibly 
affected by such a motion, will appear to move towards the point diametrically oppo- 
site ; and that on one side of the sphere all the right ascensions will appear to in- 
crease, while all those on the other side will appear to diminish. He selected seven 
stars — Sirius, Castor, Procyon, Pollux, Regulus, Arcturus, and a Aquilse — all of 
which appeared from comparisons made by Dr. Maskelyne to have proper motions 
in right ascension, and two of them — Sirius and Arcturus — also in declination; and 
finding that the right ascensions of all of them, with the exception of a Aquilse, ap- 
peared to diminish, he assumed the direction of the sun’s motion to be from a point 
“ somewhere not far from the 77th degree of right ascension to its opposite 257th 
degree,” the effect of which would be to produce apparent changes of right ascension 
agreeing with the observed ; and he adds, “ supposing the sun to ascend at the same 
time towards some point in the northern hemisphere, for instance towards the con- 
stellation of Hercules, then will also the observed change of declination of Sirius and 
Arcturus be resolved into a single motion of the solar system.” In order to test this 
conclusion he selected twelve stars, quoted by Lalande from Mayer’s table above 
referred to, the motions of which were assigned both in right ascension and decli- 
nation ; and adding the motions in right ascension of three other stars, he thus 
obtained twenty-seven changes of position to be accounted for by the hypothesis. By 
assuming the sun’s motion to be directed towards a point “ somewhere near X Her- 
culis,” he found that twenty-two of these motions were satisfied, there being only two 
exceptions in right ascension, and three in declination. The point thus indicated is 
situated at 257° of right ascension, and 25° of north declination ; but he observes that 
with respect to the changes of declination the point X Herculis is not, perhaps, the 
best-selected, as a somewhat more northern situation may agree better with the 
changes of declination of Arcturus and Sirius, “ which capital stars,” he thinks, “ may 
be the most proper to lead us in this hypothesis.” 
In a Postscript to his paper, Sir W. Herschel compares the above conclusion with 
