Excerpt from The Development of Great Circle Sailing Suppose the vertex Of the great circle passing through two places, A and B, is to be found; with a pair of dividers take out their differ ence of longitude from the scale of differences of longitude, and, if the latitudes of A and B have the same name, set one point of the dividers in the division of the diagram nearest to the right hand on that curve whose number corresponds to the latitude of either A or B, whichever is the nearer to the equator, and keeping the line joining the points Of the dividers horizontal, follow the curve up or down till the other point meets the curve corresponding to the latitude of the other place. The index line passing through the points of the dividers in this position will indicate the latitude of the vertex. If that point of the dividers which stands on the curve corresponding to the latitude Of departure be kept fixed, and the other he moved in a horizontal direction until the nearest meridian of vertex is reached, the dividers, being applied to the scale, Will indicate the longitude of the point of departure from the vertex. With the latitude Of the vertex and longitude from the vertex, thus found, the tables are entered and the distance from the vertex and the course are picked out. If the latitudes of A and B are of different names, the vertical line named Equator in the linear index must be kept between the points of the dividers in finding the latitude of the vertex, but the rest of the Operation remains the same as before described. 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.