NATURE 



481 



THURSDAY, AUGUST 21, 1915. 



NAVIGATION AND NAUTICAL 

 ASTRONOMY. 

 (i) Air Navigation. Notes and Examples. By 

 Instructor Capt. S. F. Card. Pp. vi+140. 

 (London : Edward Arnold, 1919.) Price los. 6d. 

 net. 

 <(2) Navigation. By Prof. Harold Jacoby. 

 Second edition. With a chapter on Compass 

 . Adjusting and a Collection of Miscellaneous 

 !• Examples. Pp. xi + 350. (New York: The 

 Macmillan Co.; London : Macmillan and Co., 

 '■ Ltd., 1918.) Price us. 6d. net. 

 ([i). 'T^HE author of thb^ much-needed Uttle book 

 A may be reg-arded as something of a 

 ijpioneer, for, despite the general interest taken 

 in the subject, this would appear to be the first 

 work formally devoted to the navigation of the 

 ^r. When, some years since, schools of naviga- 



Ition were established at various centres of avia- 

 Jtion, Capt. Card was associated with Brig.-Gen. 

 Briggs, R.A.F., in framing a general plan for 

 .the education of pilots and observers. This fact 

 .^lone is a sufficient proof of the competence of 

 -the author for the work he has taken in hand. 



Nautical readers will be interested to see how 

 closely the navigation of the air is related to the 

 coastal navigation with which they are familiar. 

 We have the same problems, but on a greatly 

 magnified scale. Thus in fixing a position by cross- 

 bearings, it is not a matter of a couple of head- 

 lands three or four miles apart, but Reading and 

 Oxford, or Bedford and Cambridge, are proposed 

 as pairs of bearings suitable for the exercise of 

 the student. 



As stated in the preface, the subject is treated 

 in a very elementary manner, making little 

 demand upon the mathematical knowledge of the 

 student. The explanations are clear and simple, 

 with an abundance of well-executed diagrams. 

 An excellent notion adopted is to add at the end 

 ■of each chapter a blank page for the reception of 

 any notes the student may wish to make upon 

 the contents of the chapter. 



Upon the subject of the navigation of the air 

 Major-Gen. Seely, Under-Secretary for Air, made 

 an important statement in the House of Commons 

 on June 26. He said that the whole system of 

 instruction is being revised, and the schools re- 

 organised, and that endeavours ar= being made to 

 'feet, so far as possible, mechanical aids, such 

 the sextant. He added that there is great 

 t.ope that a satisfactory form of artificial horizon 

 for air use will be brought out, and experiments 

 are in actual progress. Gen. Seely 's remarks 

 ■( appear to refer chiefly to that form of navigation 

 f-over the open ocean with respect to which there 

 f is at present much uncertainty and obscurity. 

 ,\''Capt. Card's manual, on the other hand, is limited 

 I to the type of navigation over the land corre- 

 jjtsponding with what is known as "pilotage" in 

 --dinary marine navigation, in which position is 

 NO. 2599, VOL. 103] 



generally determined by sextant angles and bear- 

 ings of known objects. Let us hope, when more 

 data are available, that the author may supple- 

 ment his very clear exposition of this type by a 

 more general treatise, embracing also ocean air 

 navigation, in which position has to be deter- 

 mined by observations of the heavenly bodies. 

 Some knowledge has been gained Irom the experi- 

 ences of Grieve and Brown, but much remains to 

 be learnt in these matters. 



(2) Prof. Jacoby in his book is somewhat ham- 

 pered by self-imposed limitations. Navigation and 

 nautical astronomy, being mathematical sciences, 

 can scarcely be completely treated upon a non- 

 mathematical basis, whereas in this instance we 

 have it explicitly stated in the preface that "the 

 author has not assumed that the reader possesses 

 formal mathematical and astronomical knowledge, 

 or desires to possess such knowledge." 



Nevertheless, upon the lines so laid down we 

 have a very readable book, calculated to be of 

 interest not only to those unconnected with the 

 sea who would acquire some insight into the pro- 

 cesses of navigation, presented in a chatty, dis- 

 cursive, or, as the author himself puts it, "in- 

 formal," manner, but also to the professional 

 navigator, who, having already some acquaint- 

 ance with the matters dealt with, may like to see 

 the various problems treated m a somewhat dif- 

 ferent fashion from that to which he is accustomed. 

 In a little work of 350 pages, about one-half of 

 which is devoted to tabular matter, we have an 

 account of the leading modern methods employed 

 in position finding at sea, while the various tables, 

 though in somewhat abridged form, suffice for the 

 calculations of actual navigation in ordinary 

 circumstances. Amongst these the Davis table of 

 combined natural and logarithmic haversines, 

 which so greatly simplifies the calculations for 

 the Marcq position lines, is conspicuous. Another 

 useful feature is Table ii., an azimuth table, but 

 with regard to this a word of caution might 

 perhaps be added that, based as it is on the 

 formula, 



sine azimuth _ sine polar distance 

 sine hour angle sine zenith distance 



the slow rate of change in the sine about 90° 

 takes us into troubled waters in the neighbour- 

 hood of the prime vertical, where some other 

 method for azimuth might be employed with 

 advantage. 



One other observation may be offered, with 

 regard to a statement on p. 99 that "the moon 

 is now so rarely observed that we have not given 

 examples of lunar observations." It is quite 

 true that tables of distances are no longer pub- 

 lished, and that the method of finding longitude by 

 measuring lunar distances has in consequence 

 become obsolete. But for position line work an 

 altitude of the moon in the daylight, with a simul- 

 taneous observation of the sun, often enables the 

 navigator to obtain a complete "fix " at one and 

 the same time, an advantage unattainable by any 

 other method in the daytime. Probably more alti- 



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