File:The Astrophysical journal (1895) (14778895054).jpg

Identifier: astrophysicaljou09ameruoft (find matches)
Title: The Astrophysical journal
Year: 1895 (1890s)
Authors: American Astronomical Society University of Chicago
Subjects: Astrophysics Spectrum analysis
Publisher: (Chicago) Published by the University of Chicago Press for the American Astronomical Society
Contributing Library: Gerstein - University of Toronto
Digitizing Sponsor: University of Toronto

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the best results in lunar photog-raphy with the great equatorial have been obtained with an apertureof about 12 inches (F;= 48 A). The large concave gratings of Pro-fessor Rowland give full photographic resolution, with F = 44 A.The ratio for the horizontal photoheliograph of the Lick Observatory(F — 96 A) is probably greater than necessary (from the present pointof view), particularly since fine-grained plates are used with thisinstrument. I have seen photographs of the Moon and planets taken with tele-scopes of very great (virtual) focal length, and their appearance was justwhat the foregoing considerations would lead one to expect. Theenlargement had been carried altogether too far. To secure the advantages pointed out by Professor Pickering, itwould be well to give the focal length the benefit of every doubt, butin my opinion it should in no case exceed 100 times the aperture. Ifcarried beyond this limit, nothing would be gained, while the greater » This Journal, 3, 188, 1896.
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bo ^ 3 3 3 3 U OJ U U !J O (J u m ^ u^ in (V 00 r^ MINOR CONTRIBUTIONS AND NOTES 27 I lengtli of exi)osure required, and the increased atmospheric disturb-ances within the instrument, would be positive disadvantages. James P). Keeler. TIIK YERKRS OBSERVATORY OF THE UNIVERSITYOF CHICAGO. BULLETIN NO. 7.SPECTRA OF STARS OF SECCHIS FOURTH TYPE. Some of the results of a photographic study of the spectra of starsof Secchis type IV (VogeFs III/), upon which Mr. Eilerman and thewriter have been engaged for over a year, were presented at the Har-vard Conference last August (see Asirophysical Journal, 8, 237,189S). Since that time, on account of the substitution of a train ofthree prisms and a short camera (/= 10.8 inches) for the single prismand longer camera (/^= 20.0 inches) used with the spectrograph in mostof the earlier work, much better photographs have been obtained withshorter exposures. Four of these spectra are reproduced herewith.The order of arrangement corresponds with that menti

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