Excerpt from Practical Remarks on Near Sight, Aged Sight, and Impaired Vision: With Observations Upon the Use of Glasses, and on Artificial Light The point to which rays converge is called their focus, or focal point. That from which they proceed, their radiant or radiating point. The distance of the focus from the re ecting or refracting surface is termed the focal dis tance or focal length. 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."