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We publish in this week's issue of the SUPPLEMENT an illustrated article by Prof. Richard A. Proctor, on charts for great circle sailing, which is a very interesting development of the law of least force. The chart brought forward by Prof. Proctor is a stereographic projection --one in which each point on the sphere is projected on a tangent plane by a line joining the point and the outer end of the tangential diameter; and since it gives the entire globe, except a small area within the Antarctic Circle, on one sheet, it is well adapted for plotting a great circle . course. By the method given in connection with the chart, a seaman may lay down without any difficulty the shortest track between two ports, that is, the arc of a great circle joining those ports, or the shortest distance between any point reached during the journey and any desired haven, and can calculate the distance. Ordinarily, vessels follow what is called the rhumb course, or that in which the same compass bearing, apart from magnetic variation, is maintained throughout the journey, but a great saving of distance is effected by sailing on the arc of a great circle; thus the distance from Melbourne to Cape Town is 6,154 miles on the rhumb course, but is 587 miles shorter on a great circle. It is the purpose of Prof. Proctor's article to make this more advantageous course practically attainable. The advantages of great circle sailing have been known for many years, but hitherto the difficulties of calculating and plotting the course have been so great that it never came into more than exceptional use. The gnomonic projection suggested by Mr. Hugh Godfray, for charts to be used in great circle and composite sailing, was some advance, but the area represented on one chart being of necessity limited, it was impossible to lay down a ship's course of any extent on one chart, and the process of calculation was too complicated. The chart and methods suggested by Prof. Proctor are very simple, and may be readily grasped by navigators of even small mathematical knowledge. They promise to bring great circle sailing into general use, and by the notable saving of time effected, to be a valuable contribution to the progress of an age which is prone to rank speed among its greatest attainments.
