Abstract
THE SPECTRUM OF THE CHROMOSPHERE.—At the recent meeting of the Astronomical and Astrophysical Society of America, held at Washington, Mr. S. A. Mitchell read a paper on the observations made during the total solar eclipse in Sumatra on May 18, 1901. The spectrum photographs were obtained with an objective grating spectrograph; the grating had a ruled surface 31/2× 5 inches, with 15,000 lines to the inch, the objective being a quartz lens of a little more than 31/4 inches aperture and about 72 inches focal length. Light from the eclipsed sun was reflected into this instrument by a coelostat. The adjustments were such as to ensure a “normal” spectrum, this being the case when grating and photographic plate were each perpendicular to the diffracted beam. The first order was employed, from λ 3000 to λ 6000. Although the sky was never clear during the period of totality of 5 min. 41 secs., eight exposures were made—one before and one just after totality for the cusp spectra, one at first and one at second flash, and four with varying exposures during the total phase. The second flash appeared fully exposed, and the plate has been carefully measured. The dispersion is such that from Hβ to Hɛ occupies a length of 95.4 mm., i.e. 1 tenth-metre correspjnds to about 0.1 mm. In the region mentioned, Hβ to Hɛ, 363 lines have been determined. Of these, 269 have been identified with lines on Rowland's map.
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Our Astronomical Column . Nature 65, 423–424 (1902). https://doi.org/10.1038/065423a0
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DOI: https://doi.org/10.1038/065423a0