About 1600 A. D., Kepler placed a prism in a beam of sunlight and saw what had not before been seen—so far as known—the first solar spectrum. A century later Newton darkened a room, admitted solar rays through a round aperture in a shutter, passed them through a prism and obtained a clearer spectrum than Kepler's. Little was thought of these things, however, until, when in 1802, Wollaston made a slit in a shutter, projected a spectrum, in which he was surprised to see a few dark lines. In 1814 Fraunhofer made a spectrum in the same way, but happened to look at it with a telescope. This act changed the course of the science of optics for all time; it was the origin of Spectrum Analysis, one of the chief products of the human mind, one of the corner-stones upon which rests the structure of modern science. Men's minds immediately began to expand, and a period of mental activity set in, the like of which was never known before. Fraunhofer saw hundreds of lines, but the great spectroscope in the Mount Lowe Observatory shows thousands, in width from that of a spider-web to one-tenth of a millimeter. They are the most valuable set of lines known. They enable finite man to tell what the earth, sun and stars, meteors, comets and nebulÆ are composed of. The prism of Newton and Fraunhofer is now displaced by the diffraction grating—ruled by Rowland 14,438 lines to the inch. These striÆ break up light into its elements, reflect them to the eye, and in solar and stellar light reveal the absorption lines. The spectroscope of the Lowe Observatory made by that accomplished optician Brashear is one of the finest.