The third volume of the Mémoires presentés par divers Savans of the Imperial Academy of St. Petersburg, published in 1837, contains a paper by Professor Argelander, in which that distinguished astronomer has discussed the question of the proper motion 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 Bradley’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 considered, perhaps, to have been determined with as great an approximation to accuracy as can be attained in the present state of our 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 astronomers 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 obtained by Argelander, Lundahl and Struve, or favoured the hypothesis of a displacement 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 displacements among the fixed stars was first announced, and the probable direction of the sun’s motion first indicated. Independently of theoretical considerations, the subject 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 accounted for by theory, mix themselves up with the determination of the precession and other fundamental elements; and the first step towards acquiring any knowledge of their laws, quantities, or directions, is obviously to distinguish between what is real and what is only apparent, and to separate from the whole observed displacement the effect due to the motion of our own system. Before proceeding to describe the data and results of the present investigation, it will be desirable, perhaps, to give a brief notice of the principal inquiries that have heretofore been undertaken with reference to the same subject.
A New Proper Motion Survey of the Pleiades Cluster