There are many books on Navigation available for the use of the student, and among them some are exceedingly good. Why, then, add yet another volume to a mass of literature already sufficiently, and more than sufficiently, large? Well, it seemed to me that for many reasons another work designed on somewhat novel principles might be useful. Most writers have treated the subject from the point of view of addressing themselves either to the highly educated or to the totally uneducated, and there is, I think, room for a treatise designed to meet the requirements of those who lie between the two extremes men who, while ignorant of mathematics and astronomy, possess intelligence and a certain amount of rudimentary knowledge.