then the angle between the webs is recorded. Double stars are thus measured, first in distance, and second, their position. After this, if any movement of the stars takes place, the tell tale micrometer at once detects it. In 1780, Sir Wm. Herschel measured double stars and made catalogues with distances and positions. Within twenty years, he startled intellectual man with the statement that many of the fixed stars actually move--one great sun revolving around another, and both rotating about their common center of gravity. If we look at a double star with a small telescope, it looks just like any other; using a little larger glass, it changes appearance and looks elongated; with a still better telescope, they become distinctly separated and appear as two beautiful stars whose elements are measured and carefully recorded, in order to see if they move. Herschel detected the motion of fifty of these systems, and revolutionized modern astronomy. Astronomers soared away from the little solar system, and began a minute search throughout the whole sidereal heavens. Herschel's catalogue contained four hundred double suns, only fifty of which were known to be in revolution. Since then, enormous advance has been made. The micrometer has been improved into an instrument of great delicacy, and the number of doubles has swelled to ten thousand; six hundred and fifty of them being known to be binary, or revolving on orbits--Prof. S. W. Burnham, the distinguished young astronomer of the Dearborn Observatory, Chicago, having discovered eight hundred within the last eight years. This discovery implies stupendous motion; every fixed star is a sun like our own, and we can imagine these wheeling orbs to be surrounded by cool planets, the abode of life, as well as ours. If the orbit of a binary system lies edgewise toward us, then one star will hide the other each revolution, moving across it and appearing on the other side. Several instances of this motion are known; the distant suns having made more than a complete circuit since discovery, the shortest periodic time known being twenty-five years. Wonderful as was this achievement of the micrometer, one not less surprising awaited its delicate measurement. If one walks in a long street lighted with gas, the lights ahead will appear to separate, and those in the rear approach. The little spider lines have detected just such a movement in the heavens. The stars in Hercules are all the time growing wider apart, while those in Argus, in exactly the opposite part of the Universe, are steadily drawing nearer together. This demonstrates that our sun with his stately retinue of planets, satellites, comets, and meteorites, all move in grand march toward the constellation Hercules. The entire universe is in motion. But these revelations of the micrometer are tame compared with its final achievement, the discovery of parallax.