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The Astrophysical Journal, Vol. 20

Excerpt from The Astrophysical Journal, Vol. 20: An International Review of Spectroscopy and Astronomical Physics Plate II shows the spectrograph mounted on its laboratory stand and surrounded by the other parts of the equipment. The order to Mr. Brashear was for the best spectrograph he could make. In consequence, he consulted those using his spectrographs in order to obtain any suggestions which might assist in designing and building an instrument, the efficiency of which would be the highest attainable. In design and mechanical construction it is similar to the Mills spectrograph of the Lick Observatory. It differs however, in having a collimator truss of three rods instead of four, a Huggins guiding device, and a prism-train equipped with a minimum deviation device. In planning and building the instrument, care was taken to insure great rigidity throughout, and particularly in the prism-box, and the construction is sufficiently massive to insure against flexure. The large refractor for which the spectrograph was designed and with which it is used has an objective, by Clarks, with a clear aperture of 61 cm and a focal length of 983 cm for the photographic rays. This ratio of aperture to focus - 1 to 16 - had to be satisfied by the collimator lens in order that it might transmit all the cone of rays from the large objective. The length of the collimator depended upon what seemed to be the most feasible aperture and dimensions to give the spectroscope. The amount of weight that might be added to the telescope tube without danger of flexure, and the additional length of tube that the dome could well accommodate, together with a consideration of the efficiency of the instrument for planetary work, led to the adoption of a collimator of about 490 mm focal length. This gave the lens an aperture of 30.5 mm, and defined the size of the prisms and the dimensions of the spectrograph. The spectrograph was mounted in the autumn of 1901. Complete, with the necessary counterbalances at the upper end of the telescope, it added 450 pounds to the weight of the telescope tube, which required a corresponding increase in the counterbalances on the declination axis. The mounting of the refractor is massive, and this considerable increase in the weight upon the bearings has not influenced the running of the driving-clock. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.
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