Excerpt from Displacement Interferometry by the Aid of the Achromatic Fringes, Vol. 3 As the achromatic fringes can not (in general) be found without first finding the corresponding spectrum fringes and, conversely, since for each type of spectrum fringes (direct or reversed) a corresponding group of achro matic fringes may be associated, I have devoted Chapter II to spectrum fringes differing in their manner of production. The endeavor here has been to obtain interferences from distant slender luminous objects, without the aid of a slit. Partially at least the work has succeeded, but not as far as I hoped. The experiments are very difficult. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com 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.