Note 5 — THE CIRCLE OF THE SCIENCES.

“Spectroscope.” The name given to the apparatus used for the study of the spectrum. “When a ray of sunlight admitted through an aperture in a dark room is concentrated upon a prism of rock salt”—or glass—“by means of a lens of the same material, and then after emerging from the prism is received on a screen, it will be found to present a band of colors, in the following order: red, orange, yellow, green, blue, indigo, and violet.”—Ganot. This band is called the spectrum. That there are other but invisible lines than those mentioned in the spectrum, is proven by the use of the thermopile, oftener called thermomultiplier, mentioned in the article on “Home Studies in Chemistry.” This is a complicated instrument used for detecting minute differences in the degrees of heat; its description without an accompanying illustration would be of no benefit to any one. So delicate is it that the heat of the hand held at a distance of three feet is sufficient to deflect the needle. The spectroscope is composed of three telescopes, mounted on a common foot, whose axes converge toward a glass prism. One of the telescopes is movable, and can be adjusted so as to give the observer the clearest view of the spectrum. The ray of light is admitted through the telescope and falls upon the prism, which decomposes it, and the spectrum is formed on the opposite side of the prism. In the telescope which the observer uses a powerful magnifying glass is placed. The third telescope is used for measuring the relative distances between the lines.