Excerpt from Elementary Treatise on Natural Philosophy, Vol. 4 of 4: Sound and Light This Part, even in its original form, contained large portions which were re written rather than translated. And the last two chapters had no place at all in the original French. In the sixth edition the numbering of the chapters and sections was altered, to make it consecutive with the other three parts, and additional matter was introduced under several heads. In the seventh edition two pages on Concave Diffraction Gratings were added. The tenth edition contains additions relating to beats, recent measures of the velocity of light, goniometers, convex mirrors, and nodal points of lenses. 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.