Astronomers have still another name for the Horse and its Rider. To them it is a "naked-eye double," the tiny star being called "Alcor," and the one on the Dipper's handle just below it, "Mizar." A 3-inch telescope discloses a still closer companion to Mizar which has a decided greenish tinge in its light. Of the two stars composing Mizar, each one is itself composed of two, which revolve around a common center of gravity in a period to be counted in thousands of years. This wonderful law of gravitation which holds not only planets in their orbits, but also stars, was discovered by Sir Isaac Newton, an English philosopher and mathematician. Two stars revolving around a common center of gravity in this manner are called a "binary"; in the case of Mizar and its companion, each of the two visual components is called a "spectroscopic binary." The brighter component was discovered to be a binary in 1889 by E. C. Pickering with the aid of a spectroscope and the fainter component was found to be a spectroscopic binary in 1908 by Frost and Lee. Alcor is also a spectroscopic binary. The stars are such an exceedingly great distance from the earth that even though they are in constant motion, they do not seem to change their relations to other stars through long periods of time. The whole configuration of the Big Dipper will some day be changed because its stars are traveling in various directions. Through the skill of various scientists this infinitesimal difference in motion is detected and recorded,--not only that a star is moving, but which way and how fast! Thus the spectroscope exploded the old idea that the stars were "fixed." The facts, however, are amazing and one must immediately readjust his ideas of what constitutes big and little, fast and slow, for in studying astronomy the small distances on our earth and the vast distances in space, and man-made speed and God-made speed, can hardly even be compared. [Figure 12] The stars of the Big Dipper are an exceptional group for they are all bright stars of the second magnitude, with the exception of Megrez at the junction of the handle to the bowl. These seven stars, and the "Rider," were given names by the Arabian astronomers, and although modern astronomers prefer for the most part a Greek letter prefixed to the genitive case of the Latin name of the constellation--such as β Ursae Majoris--these names are rather interesting to know. Starting from the top of the Big Dipper's handle, the Arabian names are as follows: Benetnasch, Mizar, Alioth, Megrez, Phaed, Merak, and Dubhe. THE LITTLE DIPPER [Illustration]