It has been said “The easiest method is the one that was first learned.” That is true for the person who is contented to keep in the rut, but for those who are inquisitive, progressive, or not satisfied with what they know, but want to know more, it is not true.
It is also said there is nothing new in navigation. This is true if it refers solely to the solution of the astronomical triangle, but when it comes to the methods of solution and the application of the parts found to the practice of navigation then it is not true.
Captain Sumner, as we all know, discovered the fact that if in working a time sight for longitude two or more latitudes were assumed, the resulting positions, if plotted on a Mercator chart, would all lie on the same straight line. This was really a discovery for it came when he was trying to fix his position, entering the English Channel during foggy weather. This method is now known as the chord method of finding a line.
The French Admiral Marcq St. Hilaire brought into general use in the French Navy his method of finding a line, which we now know as the tangent method.