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IX. On the Proper Motion of the Solar System. 
By Thomas Galloway, Esq., M.A., F.R.S., Sec. R.A.S. 
Received March 4, — Read April 15, 1847. 
The third volume of the Memoires presentes par divers Savans of the Imperial Aca- 
demy of St. Petersburg, published in 1 83/, contains a paper by Professor Argelander, 
in which that distinguished astronomer has discussed the question of the proper mo- 
tion of the solar system, and determined the probable situation in space of the point 
towards which the sun is at present advancing. This determination was founded on 
the proper motions of 390 stars situated between the north pole and the tropic of 
Capricorn, as shown by a comparison of their positions in 1775 according to Brad- 
ley’s observations, reduced by Bessel, with their positions in 1830 computed from 
the observations made by Argelander himself at Abo ; every star being taken into 
account which appeared to have a proper motion amounting to a tenth of a second 
in space annually. Two other investigations of the same question have since been 
published; one by Lundahl, founded on the proper motions of 147 stars, as shown 
by a comparison of the observations of Bradley and Pond, and the other by Otto 
Struve, based on 392 stars, whose proper motions were determined by a comparison 
of Bradley’s observations with those made at the observatory of Dorpat. From 
these three investigations the direction of the sun’s motion in space may be con- 
sidered, perhaps, to have been determined with as great an approximation to accu- 
racy as can be attained in the present state of > pur knowledge of the proper motions 
of the stars in the northern hemisphere. The recent catalogues of Mr. Johnson and 
the late Professor Henderson, deduced from the observations made by those astro- 
nomers respectively at St. Helena and the Cape of Good Hope, on being compared 
with the Cape observations of Lacaille made about the middle of the last century, 
show that a considerable number of the southern stars have also very appreciable 
proper motions ; and it appeared to me to be a matter of some interest to inquire 
whether the proper motions so determined afford any confirmation of the results ob- 
tained by Argelander, Lundahl and Struve, or favoured the hypothesis of a dis- 
placement of the solar system. The result of this inquiry I have now the honour of 
submitting to the Royal Society, in whose Transactions the existence of relative dis- 
placements among the fixed stars was first announced, and the probable direction of 
the sun’s motion first indicated. Independently of theoretical considerations, the sub- 
ject is of much importance in astronomy. The proper motions of the stars, which 
may be said to be the only residual astronomical phenomena now remaining to be 
