The elements of astronomy; a textbook . Fig. 52. — Telespectroscope, fitted for Photography. 194] CONSTRUCTION OF THE SPECTROSCOPE. 135 and there will be three bright lines. If the light comes froma luminous solid, like the lime cylinder of a calcium light, orthe filament of an incandescent lamp, or from an ordinarygas or candle flame (Physics, p. 318), there will be an infinitenumber of these slit images close together, without intervalor break, and we then get what is called a continuous it comes, however, from an electric spark or a so-calledG-eissler tube, or from a Bunsen burn
The elements of astronomy; a textbook . Fig. 52. — Telespectroscope, fitted for Photography. 194] CONSTRUCTION OF THE SPECTROSCOPE. 135 and there will be three bright lines. If the light comes froma luminous solid, like the lime cylinder of a calcium light, orthe filament of an incandescent lamp, or from an ordinarygas or candle flame (Physics, p. 318), there will be an infinitenumber of these slit images close together, without intervalor break, and we then get what is called a continuous it comes, however, from an electric spark or a so-calledG-eissler tube, or from a Bunsen burner flame charged with the Prism-Spectroscope. Grating Direct-Vision SpectroscopeFig. 52.* — Different Forms of Spectroscope. vapor of some volatile metal, the spectrum will consist of aseries of bright lines, or bands. 194*. The Solar Spectrum. — If we look at sunlight, eitherdirect or reflected (as from the moon), we get a spectrum, con-tinuous in the main, but crossed by a multitude of darklines, or missing slit-images. These dark lines are knownas the Fraunhofer lines, because Fraunhofer was the firstto map them (in 1814). To some of the more conspicuous 136 THE SOLAR SPECTRUM. [§ 194* ones he assigned letters of the alphabet which are still retainedas designations : thns A is a strong line at the extreme redend of the spectrum ; C, one in the scarlet ; D, in the yellow ;F, in the blue ; and H and K are a pair at its violet great photographic map of the spectrum containsseveral thousands, each as permanent a feature of the spectrumas rivers and cities are of a geographical chart. Their expla-nation rema
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