Author: D. H. Mahan

Publisher:

Published: 2015-07-13

Total Pages: 358

ISBN-13: 9781331332275

Excerpt from Summary of the Course of Permanent Fortification: And of the Attack and Defence of Permanent Works, for the Use of the Cadets of the U. S. Military Academy 3... References. The numbers which express the distances of the lines from the plane of comparison, are termed references. The unit in which these distances are expressed, is usually the linear foot and its decimal divisions. As the position assumed for the plane of comparison is arbitrary, it may be taken either above or below every point of the surface to be projected. In the French military service, it is usually taken above; in our own, below the surface. The latter seems the more natural and is more convenient, as vertical distances are more habitually estimated from below upward than in the contrary direction. Each of these methods has the advantage of requiring but one kind of symbol to be used, viz: the numerals expressing the references; whereas, if the plane of comparison were so taken that some of the lines projected should lie on one side of it and some on the other, then it would be necessary to use, in connection with the references, the algebraic symbols plus or minus, to designate those lines above the plane from those below it. This method of representing objects has given rise to a very useful modification of the ordinary one of orthogonal projections on two planes, and has been denominated one plane descriptive geometry; the plane of comparison being the sole plane of projection; the references taking the place of the usual projections on a vertical plane. By this modification, the number of lines to be drawn is greatly decreased; the complication of the drawing lessened; the graphical operations required in the solution of problems, presented by the drawing, simplified; and the relations of the parts more readily seized upon, as the eye is confined to one plane of projection alone. 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.