Excerpt from A Manual of the Principal Instruments Used in American Engineering and Surveying, Manufactured by W. And L. E. Gurley BY focus at the cross telescope wires, and there forms a minute, inverted image, which may be seen by placing a piece of ground glass at that point to receive it. The eyepiece magnifies this image, restores it to its natural position and conveys it to the eye. 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.