Page:Popular Science Monthly Volume 1.djvu/557

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and needles have been magnetized just as if a battery had been employed.

There are many other points of similarity which might be enlarged upon; but, if one were to attempt to set down all the strange and various considerations which come under cognizance in this subject, they would soon swell the matter much beyond the limits of a magazine article.—Fraser's Magazine.



AT the last meeting of the Royal Astronomical Society, Dr. Huggins, the eminent spectroscopist, made an extraordinary statement respecting the motions taking place among the stars. The results he announces are so wonderful that it will be well briefly to explain how they have been obtained, as well as their relation to what had formerly been known upon the subject.

Our readers are doubtless aware that the stars are not really fixed, but are known to be travelling swiftly through space. To ordinary observation the stars seem unmoving; nor indeed can the astronomer recognize any signs of motion save by prolonged observation. But, if the exact place of a star be carefully determined at any time, and again many years later, a measurable displacement can be recognized; year after year, and century after century, the motion thus determined proceeds, until at length the star may be removed by a considerable arc (or what is so regarded by astronomers accustomed to deal with the minutest displacements) from the position it had formerly occupied.

But, in general, these movements afford no means of estimating the real rate at which the stars are travelling through space. In the first place, a star might be moving with enormous rapidity toward or from the earth, and yet seem to be quite fixed on the star-vault—just as the light of a rapidly approaching or receding train seems to occupy an unchanging position if the train's course is at the moment in the direction of the line of sight. It is only what may be called the thwart-motion of the star that the astronomer can recognize by noting stellar displacements. But even this motion he cannot estimate—in miles per second, say—unless he knows how far off the sun is; and astronomers know in truth very little about stellar distances.

Now, it seems, at first sight, altogether hopeless to attempt to measure the rate at which a star is approaching or receding. No change of brightness could be looked for, nor indeed could any observed change be trusted as an evidence of changed distance, since stars are liable to real changes of brilliancy, much as our own sun is liable to be more or less spot-marked. But the distances of the