Abstract
SOLAR SPECTROGRAPH FOR THE POULKOVO OBSERVATORY.—Engineering for July 18 contains a detailed description and several photographs of the 7-metre solar spectrograph by Grubb, which has just been erected at the Poulkovo Observatory. The instrument, in which a grating is employed, is of the Littrow type, and is modelled on the 30 ft. tower spectrograph at Mount Wilson. The sun's rays are received on a coelostat, for which a special erection is made at the top. of the south wall of the Observatory, and are reflected into an object-glass, after passing through which they are reflected to the slit of the spectrograph on the ground floor, where they form an image of the sun about 10 cm. in diameter. The main object of the instrument is the study of the sun's rotation by means of the Doppler effect shown by light from the eastern and western limbs. By using a system of four prisms, light from the centre and limbs of the sun is made to fall simultaneously on different parts of the slit, and the spectra are obtained in juxtaposition on a plate 24 cm. long by 4 cm. wide. The spectrograph lens has an aperture of 10 cm. and a focal length of 706 cm. No description of the grating is given, but it is stated that the instrument will give from one spectrogram a velocity measurement of greater accuracy than i/ioth of a kilometre per second in the line of sight. Arrangements are provided for rotating the instrument, the solar image remaining fixed. The coelostat, which has an aperture of 25 cm., has been made adjustable for any latitude between 60° and 370, in order that it may be used at the Simeis Observatory, in the Crimea, if desired.
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Our Astronomical Column . Nature 114, 325 (1924). https://doi.org/10.1038/114325a0
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DOI: https://doi.org/10.1038/114325a0