Excerpt from Diffraction by an Aperture IThe present treatment of diffraction of a wave by an aperture in a thin screen is based upon a new theory of wave propagation. This theory is called 'the geometrical theory of because it is an extension of geometrical optics which describes diffraction phenomena. It is like geometri cal optics inasmuch as it postulates that fields propagate along certain lines or curves called rays. However, it goes beyond geometrical optics, by intro ducing various new kinds of rays, called 'diffracted rays', in addition to the usual optical ones. It also assigns a field value to each point on a ray in a quantitative way and postulates that the total field at a point is the sum of the fields on all rays through that point. Thus the new theory not only provides a qualitative description of diffraction in terms of the diffracted rays, but it permits a quantitative determination of the field as well.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.