In the PROCEEDINGS OF THE U. S. NAVAL INSTITUTE, No. 3, of September, 1902, an ingenious graphic method for finding progressive bearings, distances, and land marks, in coast navigation is described. The method requires (1) instrumental adjuncts not in daily use by the navigator, namely, cross section paper and protractor, and (2) the transference of positions from the cross section paper to the hydrographic chart.
Since 1874 I have used a simpler and equivalent method, which requires only the plotting instruments in common use by the navigator, namely, chart, parallel rule, pencil, and dividers. I originated the method, for my own use at least, while engaged in deep sea explorations with the U. S. C. S. Steamer Blake; the process is so simple that it would not surprise me to find that it is old. Nevertheless, in showing the method to others, I found but one naval officer who had previous knowledge of it. That officer learned it in the Coast Survey, and subsequently to 1874.
In 1895, while I was in charge of the Hydrographic Office, Navy Department, I caused the method to be published in certain volumes of sailing directions for the great lakes. For example, it is given on page 84 of "Sailing Directions for Lake Huron, Straits of Mackinac, St. Clair and Detroit Rivers, and Lake St. Clair. No. 108—Part III. 1895." The following explanation of the method is quoted bodily from that work:
In Fig. 2, a vessel proceeds in a direction A to B without changing her course. At both A and B she takes a compass bearing of the landmark L, and at B notes the distance run on her course from A to B. A parallel ruler is set to the course AB by means of the compass rose on the chart, and the distance run from A to B is taken from the scale of the chart with a pair of dividers. The parallel rule is then moved to and fro as shown by the dotted lines, and the dividers are applied to its edge until the parallel line AB is found, on which the intercepted distance AB is exactly spanned by the dividers as set by the scale. The line AB then represents upon the chart the course of the vessel. A is the point where she took her first bearing, and B the point where she took her second bearing. Questions of current apply to the above solution in the same manner that they deply to the solution, cited in the first paragraph of this paper, and to the well known solution by means of bow and beam bearings.