Excerpt from A Treatise on Plane and Spherical Trigonometry, Vol. 1 of 12: With Their Most Useful After the time of Ptolemy and his commentator Theon, little more is known on this subject till about the close of the eighth century after Christ, when the ancient method of computing by the chords was changed for that of the sines, which were first intro duced into the science by the Arabians; to whom we are also indebted for the several axioms and theorems which are at present considered as the foundation of our modern Trigonometry, as well as for some other propositions which such an alteration in the system naturally required. 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.