NATURE 



ZZ1 



THURSDAY, AUGUST 9, 1900. 



PRACTICAL NAVIGATION. 

 Self-instruction in the Practice and Theory of Navigation. 

 By the Earl of Dunraven, Extra Master. Two 

 volumes. Pp. xxv + 354 + 388. (London : Macmillan 

 and Co., Ltd., 1900.) 



THE science of navigation, apart from the practical 

 art of seamanship, stands on a very curious footing. 

 Based mainly on mathematical results, it presents pro- 

 bably 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 sys- 

 tematised 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 produc- 

 tion 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 acquaint- 

 ance with the various methods and formulae that they 

 will have to put into practice. The effect, if not the ob- 

 ject, 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 responsi- 

 bility. 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 determina- 

 tion 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 leger- 

 demain, 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 de- 

 tail, 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 

 NO. 1606, VOL. 62] 



"of a dimly-lit 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. 



But if our methods of teaching are as far asunder as 

 the poles, it is impossible to escape the influence of the 

 cheerful, breezy style in which the book is written — a 

 model for those who attempt to substitute teaching by 

 written description for oral explanation. The author 

 appears to be sitting at the same table with the student, 

 giving him of his best, and actually pushing him through 

 the examination. If any one has failed to satisfy the 

 examiner that he is competent to do " a day's work," let 

 him take Earl Dunraven for his guide, and he will become 

 fully persuaded of the easiness of the problem, rather than 

 of its difficulty, and will pass the ordeal with success. 



The author supposes his pupil to be conversant with 

 the multiplication table, but with practically nothing else, 

 so he gives first a chapter on arithmetic, followed by one 

 on the application of logarithms ; the theory is dismissed 

 in a page, and of this short summary the student is told 

 " don't bother to read it unless you have a mind to." This 

 is the keynote of the whole book, only those problems 

 which can have an immediate practical significance, or 

 can be broached in the examination room, are pressed on 

 the student's notice. But to make amends for the lack 

 of theory, on the practical side, the detail is very full and 

 complete. From logarithms we pass to the description 

 of the instruments used at sea, and so arrive at the 

 "sailings" and that troublesome problem of the "day's 

 work," which proves such a stumbling block for so many 

 aspirants for certificates. At this point the author thinks 

 it time to introduce a little algebra and trigonometry, 

 though he advises only extra masters to read it, and we 

 must admit that it contains some hard things, and that 

 we should have some difficulty in solving some of the 

 simple equations proposed by following the rules laid 

 down for our guidance. The author is not seen at his 

 best in these chapters, which are better taught in the 

 schoolroom than on the ship's deck. Tides and charts, 

 so far as their investigation and construction are needed 

 for the examination room, are fully explained. The first 

 volume concludes with the solution of simple problems 

 connected with the determination of latitude, longitude, 

 and azimuth. 



We cannot get very far into the second volume without 

 some knowledge of spherical trigonometry, and here, 

 again, we do not find the chapters devoted to this subject 

 altogether satisfactory. Spherical trigonometry covers a 

 very small but well recognised subject of inquiry, and can 

 without much difficulty be made complete. The methods 

 are simple and easily applied, except in one point, and 

 that is the determination of the quadrant in which the 

 various arcs fall. Earl Dunraven has not much assist- 

 ance to offer on this vexed point. He pins his faith to 

 Haversines, and as a rule keeps free from the employ- 

 ment of auxiliary angles. In this he is no doubt well 

 advised, for the advantages of the method so long insisted 

 upon in elementary treatises are by no means so apparent 

 in actual work. Through the intricacies of the ingenious 

 method known as Sumner Lines, Earl Dunraven con- 

 ducts us with care, especially dwelling on the use of the 



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