Excerpt from The Elements of Non-Euclidean Plane Geometry and Trigonometry IN this little book I have attempted to treat the Elements of non-euclidean Plane Geometry and Trigonometry in such a way as to prove useful to teachers of Elementary Geometry in schools and colleges. Recent changes in the teaching of Geometry in England and America have made it more than ever necessary that the teachers should have some knowledge of the hypotheses on which Euclidean Geometry is built, and especially of that hypothesis on which Euclid's Theory of Parallels rests. The historical treatment of the Theory of Parallels leads naturally to a discussion of the non-euclidean Geometries and it is only when the logical possibility of these non-euclidean Geometries is properly understood that a teacher is entitled to form an independent Opinion upon the teaching of Elementary Geometry. 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.