Although he might not detect star-parallax, he sprang a mine upon the older notions of star-fixity. He shook to its very foundations the sidereal astronomy of the day,--the theory, long held, of a motionless universe, motionless stars, and a rotating but otherwise motionless sun. He did away with the mental picture, then widely believed in, of vast interminable fixity and stillness, extending through space, varied only by a few little wandering worlds. As he swept the skies, and endeavored to gauge the fathomless depths, and vainly pursued the search for the parallax of one star after another, he made a great and unlooked-for discovery. This was in connection with double-stars. Double-stars had long been known, and were generally recognized. But whether the doubleness were purely accidental, due merely to the fact of two stars happening to lie almost in the same line of sight, as viewed from earth, or whether any real connection existed between the two, no man living could say. Indeed, so long as all stars were regarded as utter fixtures, the question was of no very great interest. But light dawned as Herschel watched. He found the separate stars in a certain pair to be moving. Each from time to time had slightly, very slightly, changed its place. Then, at least, if all other stars in the universe were fixed, those two were not fixed. He watched on, and gradually he made out that their motions were steady, were systematic, and were connected the one with the other. That was one of the first steps towards breaking down the olden notion, so widely held, of a fixed and unchanging universe. Another double-star, and yet another, responded to Herschel’s intense and careful searching. These other couples, too, were revolving, not separately, but in company; journeying together round one center; bound together apparently by bonds of gravitation, even as our sun and his planets are bound together. Other stars besides binary stars are found to move with a real and not merely a seeming movement. Viewed carelessly, the stars do indeed appear to remain fixed in changeless groups; fixed even through centuries. But, to exceedingly close watching and accurate measurement, many among them are distinctly _not_ fixed; many among them can be actually seen to move. Of course the observed motions are very small and slow. One may be found to creep over a space as wide as the whole full moon in the course of three hundred or four hundred years; and this is rapid traveling for a star in earth’s sky! Another will perhaps cross a space one-tenth or one-twentieth or one-fiftieth of the moon’s width in one hundred years.