The outlines of physics: an elementary text-book . ay uponit two or three small bits of metallic sodium. Mount the wicking justbelow the path of the ray, midway between the lens and slit, and result will be a large flame with the characteristic yellow colorof burning sodium. The rays passing through this mass of sodiumvapor, which is opaque to the yellow light, will suffer absorption. Notethat the spectrum is otherwise continuous and possesses a black line inthe region corresponding to that where the bright line of sodium in theprevious experiment appeared. The identity in the posit
The outlines of physics: an elementary text-book . ay uponit two or three small bits of metallic sodium. Mount the wicking justbelow the path of the ray, midway between the lens and slit, and result will be a large flame with the characteristic yellow colorof burning sodium. The rays passing through this mass of sodiumvapor, which is opaque to the yellow light, will suffer absorption. Notethat the spectrum is otherwise continuous and possesses a black line inthe region corresponding to that where the bright line of sodium in theprevious experiment appeared. The identity in the position of thisblack line and the bright line of sodium may be shown by removingthe sodium flame from between the lens and the slit and introducingone in the place of the light within the lantern, as described in Ex-periment 109. 355. The Fraunhofer Lines. — When, in 1819, the sunsspectrum was observed, using a narrow slit instead of thewide apertures which had been employed by Newton andother earlier students of this subject, it was found that the. Fig. 360. suns spectrum was filled with black lines instead of being,as had been previously supposed, continuous. The firstto notice these lines and to describe them was a Germanphysicist by the name of Fraunhofer, and they are still 388 TBE OUTLINES OF PSTSICS known by his name. He observed the presence of manyhundreds of these lines, and designated the most promi-nent of them by the letters A, B, C, D, U, F, Gr, and location of these lettered lines is shown in Fig. years later it was shown by Kirchhoff and Bunsenthat the bright line of sodium, the position of which cor-responded exactly with the black line D of Fraunhofer,was capable of reversal, that is to say, of being changedinto a black line by the interposition of sodium 112 is a reproduction in the simplest form oftheir experiment. They concluded that the lines of Fraun-hofer, and the innumerable other black lines of the solarspectrum, were pro
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