One of the most curious discoveries of modern times, in reference to the solar spectrum, is that of Fraunhofer of Munich--one of the most distinguished artists and opticians on the Continent.[13] He discovered that the spectrum is covered with dark and coloured lines, parallel to one another, and perpendicular to the length of the spectrum; and he counted no less than 590 of these lines. In order to observe these lines, it is necessary to use prisms of the most perfect construction, of very pure glass, free of veins--to exclude all extraneous light, and even to stop those rays which form the coloured spaces, which we are not examining. It is necessary also to use a magnifying instrument, and the light must enter and emerge from the prism at equal angles. One of the important practical results of this discovery is, that those lines are fixed points in the spectrum, or rather, that they have always the same position in the coloured spaces in which they are found. Fraunhofer likewise discovered in the spectrum produced by the light of Venus, the same streaks, as in the solar spectrum; in the spectrum of the light of Sirius, he perceived three large streaks which, according to appearance, had no resemblance to those of the light of the sun; one of them was in the green, two in the blue. The stars appear to differ from one another in their streaks. The electric light differs very much from the light of the sun and that of a lamp, in regard to the streaks of the spectrum--‘This experiment may also be made, though in an imperfect manner, by viewing a narrow slit between two nearly closed window-shutters, through a very excellent glass prism held close to the eye, with the refracting angle parallel to the line of light. When the spectrum is formed by the sun’s rays, either direct or indirect, as from the sky, clouds, rainbow, moon, or planets, the black bands are always found to be in the same parts of the spectrum, and under all circumstances to maintain the same relative position, breadth and intensities.’