Self-instruction in the Practice and Theory of Navigation

Abstract

THE science of navigation, apart from the practical art of seamanship, stands on a very curious footing. Based mainly on mathematical results, it presents probably the only, certainly the most conspicuous, instance of the adaptation of pure science to practical ends. As a consequence nautical astronomy, or those portions of it which are indispensable to navigation, has been systematised to such a pitch of perfection that a mechanical system has been substituted for a reasoning process. Many regard this result with satisfaction as a triumph of scientific simplicity, and pride themselves on the production of navigators capable of producing a definite practical result with the least possible expenditure in training. Perhaps it would be unjust to say that this view is shared by the Earl of Dunraven, the author of the latest book on the theory and practice of navigation. But he is not prepared to throw his known experience as a sailor and his great popularity as a successful yachtsman on the side of those who would make the Board of Trade Regulations more stringent, and would demand from applicants for the various certificates some proof that they have acquired more than a rule-of-thumb acquaintance with the various methods and formulæ that they will have to put into practice. The effect, if not the object, of his book is to show with how little knowledge one may pass the Board of Trade Examinations, and be legally entitled to assume positions of enormous responsibility. But admitting that it is desirable to give the practical seaman every chance in the examination room, and that the accurate solution of a problem is the only point to be regarded, is it easier to teach once for all the ordinary methods for the solution of a spherical triangle, or to burden the memory with a variety of rules which are available only for the solution of the particular family of problems to which these rules have been adapted? Take, for example, the case of the determination of an hour angle from the observation of an altitude in a known latitude. The candidate for a certificate, taught on the lines that Earl Dunraven approves and encourages, has to remember first of all a series of rules about declination and latitude being of the same or different names; then he has to write certain quantities down in a particular order, perform sundry acts of legerdemain, take out four different logarithmic functions of angles, add them up, and is landed in a quantity which his lordship calls “the log. of the hour angle.” It is the log. sine squared of half the hour angle, but this is a detail, and if one happens to possess the particular table in which some obliging genius has given this quantity, with argument hour angle, the work is done and it may be, so far as the result is concerned, satisfactorily. To trust to the memory rather than the rigorous process of demonstration is a plan Earl Dunraven thinks admir ably adapted to meet the difficulties introduced by “a wet, slippery, and tumbling deck” and the inconveniences “of a dimlylit cabin, full of confusion and noise.” We fail to perceive the particular advantages of this system, but would express any doubts on this point very modestly, for the author speaks from an actual experience, which we can very inadequately apprehend.

Self-instruction in the Practice and Theory of Navigation.

By Earl of Dunraven, Extra Master. Two volumes. Pp. xxv + 354 + 388. (London: Macmillan and Co., Ltd., 1900.)