CHAPTER V.

GRAND MOTION of the SUN, AND OF SINGLE STARS. —PROBABLE SYSTEM OF OUR ENTIRE GALAXY.— QUESTION AS TO THE NATURE OF FORCE.

THE

HE investigations explained in last chapter have established a fact of paramount importance. They have confirmed the suspicion of many able and prophetic minds, that wherever we discern among the stars an especial closeness or grouping, there we may safely assert the presence of special system and mechanism, and that the orbs of the group roll around their common centre of gravity, in obedience to the law governing the planetary orbits. And farther, they entitle us to state it as probable, that, even among those larger groups, such as the massive parts of the Milky Way, there is a similar connexion, although the motions which would distinctly manifest it must be too slow and remote, to permit of their courses being recorded during the whole endurance of our race. But, after such truths are accepted, there remain many inquiries unresolved

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MOTION OF OUR SUN.

concerning our scheme of stars: for instance, what is the condition of these single suns-orbs connected apparently with no minor system-individuals only of that complex and marvellous scheme? It is evidently not possible to reach any general conclusion until the point now referred to has been examined; but our investigations will not terminate with its resolution.

I.

The luminary around which our world and its companions circulate is a single star; and as we must know its habitudes best, it is they that should lead us to our earliest acquaintance with the condition of such members of our galaxy. The problem, however, is a very complex one, and we must rise to its full height by steps.

I. If the sun, as a separate orb, had been affected by some peculiar motion in the midst of a cluster of stars at rest, it would be easy to discern, during the lapse of ages, not merely the existence of his motion, but also its precise direction and amount. Suppose, for illustration, a traveller advancing towards any regular arrangement of objects say a line of trees or of columns, and proportionally receding from another; he would detect his motion-even though he did not

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feel it in this wise: the objects in front would gradually widen out-i. e., the intervals separating them would appear larger as he approached them; while for the same reason the group he was leaving would appear closing in. Of this kind, indeed, are the grounds of all our judgments regarding the more familiar celestial motions: we accept the rotation of our world on its axis because of the grand apparent diurnal revolution of the stellar vault; and the fact that the earth is a planet moving through an annual orbit, is a mere deduction— sustained assuredly by many analogies-from the apparent motion, through the ecliptic, of the sun. The safety, indeed, of all such conclusions mainly rests on the number of external and independent phenomena, which the adopted solution avails to explain; and it was because his daring conjecture of a grand solar motion comprehended so many seeming discrepancies, that HERSCHEL first offered it as an astronomical truth. Comparing the best older catalogues of the fixed stars with the most trustworthy of his time, he found that, though not large, there were many apparent displacements; that no star, indeed, which had been long and well observed, could, according to common language, be termed fixed; and it appeared, besides, that the posed motion of the sun towards one district of the heavens, and away from its opposite, accounted for most of the changes of place that had occurred in either

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DISCOVERED BY HERSCHEL.

region. In the neighbourhood of a place within the constellation HERCULES, the stars seemed to have been opening out; while at the opposite point of the sky, their mutual distances were diminishing; so that, as in the case of our rude illustration, it might be fairly concluded that the sun is rolling through some mighty course whose direction, during the entire period of reliable observation, has been towards a determinate point in the sky. But HERSCHEL advanced farther. Seeing that if such a motion exists, not merely the stars in particular regions, but all stars in the heavens must appear to change their places, he occupied himself with the recorded conditions of various orbs scattered over the sky; and on examining the nature and directions of their motions, it appeared that in the main they were all drifting away from the foregoing point in HERCULES. No longer, then, did doubt continue in the mind of our immortal countryman regarding this new revelation concerning the structure of the heavens. And assuredly it was most fitting that to him whose unrivalled sagacity penetrated the secret of the multiple stars, tidings should first come of the perfection, the unity of the whole of our majestic system-the tidings that, among its innumerable hosts, not one is solitary or apart, but an essential element of the universal scheme, exchanging sympathies and action with all, and unfolding what these are by its motions.

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II. It certainly cannot be supposed that amid these innumerable orbs our sun alone is in motion, but rather that his august course is a type of what is inherent in every star. But if the stars around us are in motion, how can we detect the sun's-how are we entitled to infer-in the terms I have been explaining-a motion in the sun, from displacements which, after all, may originate in actual motions of the luminaries surrounding him? Herein indeed lies the true difficulty of the inquiry; it is the difficulty of distinguishing and separating what may be positive motions of the stars, from motions apparent only, or owing to the progression of the sun, which demands for the solution of this problem so much excellent judgment and subtle analysis. But my reader will readily comprehend the principles by whose aid an obstacle so serious has been removed. In the first place, I beg attention to the subjoined diagram -so that the actual nature of the inquiry be apprehended. It is easy to see that if, according to our former hypothesis, these points environing the sun at S, were motionless, the existence of his course towards A would without difficulty appear; but farther, inasmuch as the motions of these various stars, scattered through all the regions of space, must be various, while the steadfast course of the sun must produce a distinct, consistent, and universal effect on their apparent positions, is it not evident, that amid much variety and some apparent

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