SOLAR SYSTEM, MOTION OF THE, IN SPACE. One of the most interesting results of modern astronomical research consists in the discovery of the fact, that many stars of the class styled fired stars, are in reality subject to a minute movement, in virtue of which their positions in the celestial sphere are slowly shifting from year to year. This proper motion was originally found to he applicable only to a few of the principal stars, but as the observations of astronomers have acquired a greater degree of precision, the number of stars which appear to be slowly changing their position continues to increase, and the probability is, that there is no star in the celestial sphere whose position is absolutely fixed. But the results at which astronomers have arrived with respect to the paralLax of the stars, combined with the relative intensities of the light of the sun and the stars, as determined by photometric experiments, tend strongly to confirm the idea that the sun is neither more nor less than a star. It is rcasouable then to suppose that the sun, like the stars, should be subject to a motion of translation in space. This idea seems to have first suggested itself to Foutenelle, who refers to it in a notice on the labours of Cassini. Bradley also, at the close of his paper in which he announces the discovery of the nutrition of the earth's axis, has remarked that the apparent motion of the stars may arise either from a real motion of the stars themselves, or from a motion of the solar system in space. But he was of opinion, that ages would elapse before astronomers would arrive at a definitive conclusion on this subject.
Thomas Wright, in his `Theory of the Universe,' published in 1750, suggests, as very probable, that the sun, with his attendant planets, may be circulating round some other centre. Mayer was the first astronomer who endeavoured to deduce a trustworthy result from an examination of the proper motions of the stars. His researches were based upon a comparison of the places of eighty stars, as observed by Romer in the year 1706, with the corresponding places as determined by Locale and himself about the middle of the same century. The conclusion at which he arrived Was, that the proper motions of the stars do not afford any evidence of a motion of the solar system in space. A remark made by Mayer on this occasion is worthy of mention. He states, that if the solar system is advancing to any par ticuLar region of the heavens, the stars in this direction will necessarily be gradually receding to a greater distance from each other, while, again, those in the opposite direction will appear to be drawn closer together. In 1783 the elder Herschel having been induced to examine
the subject, arrived at a result quite different from that obtained by Mayer. His investigation was founded on the proper motions of seven of the brightest stars, as determined by Maskelyne. The result of his inquiry indicated a motion of the solar system towards a point in the heavens near the star A Hercules, which he found to be situated in 257° of right ascension, and 25° north declination. In 1805 he subse quently resumed the subject, and obtained for the point towards which the solar system is moving, the following co-ordinates : right ascension; 245° 52' 30"; north declination, 49° 38'.
The same subject was considered about the same time by Prdvost and Klitgel, whose results agreed tolerably well with those obtained by Herschel. On the other hand, Biot and Bessel, who examined the subject, arrived at the conclusion that the present state of our know ledge respecting the proper motions of the stars is insufficient to afford any trustworthy indication of the existence of a motion of the solar system in space. In receut times, however, the researches of Arge lander, Lundahl, and Otto Struve, have confirmed the views of Sir William Herschel. The researches of these astronomers were based upon an examination of the proper motions of stars chiefly in the northern hemisphere. The late Mr. Galloway, however, obtained very nearly the same result by an examination of the proper motions observed in the southern hemisphere by Lacaille about the middle of the last century, and again by Johnson and Henderson iu recent times. By combining his own result with the results arrived at by Argelauder and Lundahl, he obtained the following values for the co-ordinates of the point in the heavens towards which system is advancing :— these numbers referring to the equinox of 1792.
The most recent examination of this subject is due to Mr. Airy, who by a method totally different from that employed by previous inquirers has obtained a result agreeing very nearly in right ascension, but differing considerably in declination, from that hitherto arrived at.