The wondrous use of electricity as an agent for the production of light, heat, and power is no greater achievement, in its way, than is Spectrum Analysis in bringing to our earthly laboratories the work of the Divine Hand performed in distant regions of space. Yet the story of the spectroscope is easily told. In its essential elements it is merely this: A ray of light, entering a darkened room through a hole in the window shutter, produces a bright beam on the opposite wall. A triangular glass prism held close to the crevice turns this beam into a band of rainbow hues. If the hole can be changed into a small slit, say one fourth of an inch high and one fiftieth of an inch wide, and if the light can further be made to pass in succession through several prisms, instead of through one, the band will be so elongated thereby that its various and surprising markings can be thoroughly traced and fully studied. [Illustration: THE SPECTROSCOPE.] To this band of bright colors Sir Isaac Newton gave the name of the solar spectrum. The image formed by the light of any luminous body, after it has passed through a prism, is said to be the spectrum of that body. VIII. THE SPECTROSCOPE AND ITS TRIUMPHS. The spectroscope consists essentially of three tubes joined in the form of the letter Y, one of which is a small telescope, in the focus of which a narrow slit is placed to admit the ray of light that is to be examined; a prism, or a ruled grating that disperses the light, so as to form a spectrum; and a view telescope, with which to observe the various parts of the spectrum. By using a small telescope to view the spectrum of the sun, Fraunhofer, a German optician, in 1814, discovered that the whole length of the spectrum was crowded with dark lines, very narrow, indeed, but scattered all through the seven hues. He found that sunlight, whether taken directly or reflected from clouds or from the moon or planets, invariably gave the same spectrum; but in no case did light from the stars give a spectrum of the same sort as that from the sun. [Illustration: YERKES TELESCOPE, UNIVERSITY OF CHICAGO. Largest in the World.] Dr. Kirchhoff, of Heidelberg, in 1859, explained the origin of the dark lines, and showed that there are three kinds of spectra: first, that of an incandescent solid or liquid, which is always perfectly continuous, showing neither dark lines nor bright; second, the spectrum of a glowing gas, which consists of bright lines or bands separated by dark spaces. These lines are characteristic of the chemical elements that cause them; and so, from the composition of the bright lines in a spectrum, it is possible to tell their origin. Third, a spectrum crossed by dark lines; which occurs when an incandescent solid is viewed through absorbent vapors.