“PHOTOGRAPHIC MAP OF THE SOLAR SPECTRUM / MADE BY PROF. H. A. ROWLAND, JOHNS HOPKINS UNIVERSITY.” The scale extends from 44.8 to 49.4 units.
Henry A. Rowland, the first professor of physics at Johns Hopkins University in Baltimore, Md., produced a photographic map of the solar spectrum using concave diffraction gratings made with his own ruling engine. This is a section of the first edition, published in 1886.
Ref: “Photograph of the Normal Solar Spectrum. Made by Professor H. A. Rowland,” Johns Hopkins University Circular 5 (1886).
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