University and School Extension

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Excerpt from University and School Extension: Spherical Trigonometry § I. The student should construct his spherical triangles on a globe. He will thus get a good idea of the meaning of each problem, and the unknown parts of the triangle may be fairly well measured, and a good check against large errors in his calculations will be obtained. A cylindrical cup, whose depth is half its diameter, or a hemispherical cup, should be provided with a flat rim graduated to degrees. To this cup should be fitted a slated globe, so it will turn easily in any direction. The rim of the cup is the ruler used for drawing and measuring the arcs of great circles. Dividers may also be used for laying off the lengths of arcs, their measures being taken from the globe or from the graduated rim of the cup. An angle is measured by laying off on each of its including sides, or on those sides produced, 90°, the arc joining these two points thus found will be the measure of the angle. Two equal triangles may be made to coincide by direct superposition, and two symmetrical triangles by turning one of them inside out, and then superposing it on the other. [A piece of tin-foil may be fitted to a sphere and figures cut out from it as they are cut out of paper in plane geometry to make this superposition.] 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.