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Constitution and Origin of the Group B of the Solar Spectrum 1


    WHEN a single prism spectroscope is directed towards the sun at the moment when it is in the neighbourhood of the zenith, we perceive near C, at about a fourth of the distance separating it from the extreme red, a strong black line, which Frauenhofer has named B. Under a more powerful instrument of five or six prisms this line becomes a very black broad band, separated from the region of C by what may be described as almost an empty space, the lines which do exist in it being few and faint. On the other side this band is followed by well-marked lines, which appear to be very regularly spaced, and the first of which show some indications of being double. Father Secchi had vainly attempted to resolve the band B; on this subject he writes:—

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      Paper by M. L. Thollon in Bulletin Astronomique, May 1884.

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