THE ASTROPHYSICAL JOURNAL, VOL. 55

An International Review of Spectroscopy and Astronomical Physics, January-June, 1922The 40-inch refractor at Yerkes Observatory, although designed only for visual observations, has been available for astronomical photography since 1900 by means of a method perfected by G. W. Ritchey and described by him in the Astrophysical Journal for December of that year. The method c0nsists of the use of a ray-filter which absorbs those waves of short lengths for which the objective is uncorrected, combined with photographic plates which are especially sensitive to the yellow, a color which the ray-filter transmits freely, and which comes in the region for which the color-curve of the 40-inch objective is very nearly flat.About the PublisherForgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.comThis 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.