148 



NATURE 



[June i8, 1903 



The translators say that, as the course of elementary 

 plane geometry will be shortened on account of recent 

 changes, teachers will be able to introduce solid geo- 

 metry at an earlier period than formerly. The choice 

 ■of the best complete school course of geometry is a 

 very important matter at the present time. We should 

 like to see solid geometry taught in connection with 

 projection, and think that the elementary geometry ol 

 vectors should be introduced. 



SHIP'S MAGNETISM. 

 Elementary Manual for the Deviations of the Compass 

 in Iron Ships. By E. W. Creak, C.B., F.R.S., Re- 

 tired Captain R.N. Pp. xii+150; with 4 charts. 

 (London : J. D. Potter, 1903.) 

 T N his preface the author explains that the present 

 work aims at being the successor of the " Elemen- 

 tary Manual " by the late Sir F. J. Evans. It is 

 ■" intended for the use of seamen of the Royal 

 Navy and Mercantile Marine and Navigation Schools, 

 and as an introduction to the Admiralty Manual for 

 the Deviations of the Compass." 



After a table of contents, there is a short introduc- 

 tion embodying some elementary definitions. Sections 

 1. and ii., pp. 1-25, give an elementary description of 

 the properties of magnets, with illustrations intended 

 to supply a general idea of the action of the earth as a 

 magnet, followed by a brief account of the phenomena 

 of terrestrial magnetism which are of most importance 

 to navigators. Section iii., pp. 26-42, describes the 

 •ordinary " Thomson " and liquid compasses and 

 various auxiliary instruments. It also describes that 

 temple of accuracy the Compass Observatory at 

 Deptford, and gives valuable advice on such practical 

 matters as the storage of compass cards, and the 

 choice of a site for the standard compass on board 

 ship. Sections iv. to vi., pp. 43-108, are mainly 

 technical. 



Section iv. treats of the " swinging " of ships to 

 determine the deviations of the compass. It describes 

 the sources of change in the deviation, more especially 

 the effects due to " heeling " of the ship and to change 

 of geographical position. It also gives some interest- 

 ing particulars as to the large changes of deviation 

 produced by the firing of heavy guns in warships. 

 Section v. describes the effects of " soft " and " hard " 

 iron. It introduces the reader to semicircular and 

 quadrantal deviation by describing experiments where- 

 by analogous effects can be produced by magnets or 

 by soft iron situated near a compass. 



Section vi. associates different constants in the 

 ordinary mathematical theory of ship's magnetism — 

 which the reader of the work is apparently intended 

 to consult in the Admiralty Manual — with the action 

 of imaginary magnets occupying specified positions 

 in the ship. It then takes the actual results obtained 

 in swinging certain warships, and shows how to con- 

 struct deviation tables from them. This is done with 

 great minuteness, and should be specially valuable to 

 those who are unable to master the theoretical part of 

 the subject. Section vii., pp. 109-13 1, treats of hollow 

 iron spheres, Flinders bars, and other means of 

 NO. 1755, VOL. 68] 



mechanical correction of the compass. There is a 

 short account of the Peichl quadrantal corrector, which 

 the author considers specially adapted for the case of 

 compasses in conning towers of warships, where the 

 earth's horizontal force is generally much reduced by 

 the action of the ship's own magnetism. Amongst 

 some concluding notes the author mentions the highly 

 magnetisable and the nearly unmagnetisable alloys 

 of iron recently discussed by Prof. Barrett and Mr. 

 Hadfield as having a possible future in connection 

 with compass work. 



At the end of the book are some tables and a copious 

 index. Table i. serves to facilitate the calculation of 

 deviation tables. Table ii. tabulates some elementary 

 trigonometrical functions. Tables iii. and iv. embody 

 recommendations as to the dimensions of soft iron 

 spheres and Flinders bars most suitable for the correc- 

 tion of deviation errors of assigned magnitude. At 

 the end are charts of the earth's isogonal and isoclinal 

 lines, and the lines of equal horizontal and vertical 

 force, calculated for the epoch 1905. 



So far, at least, as warships are concerned, the 

 author's practical knowledge of the subject is prob- 

 ably unrivalled, and the value of the book as a mine 

 of experience is hardly likely to be questioned. On 

 the theoretical side there is more room for two opinions. 

 The author takes a very humble — it is sincerely to be 

 hoped too humble — view of the mathematical attain- 

 ments of British navig^ators. His attitude to theory 

 is the very antithesis of that of Mascart in his recent 

 " Magnetisme Terrestre " (chapter xiv.). Mathe- 

 matical results are occasionally introduced by a state- 

 ment which does not amount to a complete proof, but 

 might be mistaken for one, when a proof could be 

 given without assuming advanced mathematical know- 

 ledge. Various of the references to magnetic and 

 general theory scattered throughout the book are also 

 capable of more exact statement from a physical 

 standpoint. 



The fact that the author defines the C.G.S. units in 

 his introduction, but sticks to inches and other British 

 or wholly arbitrary units In his text and charts, affords 

 food for reflection. In one or two sections of the book 

 there seem an appreciable number of minor misprints, 

 more especially in one or two of the numerical ex- 

 amples, and attention might usefully be given to their 

 elimination in the probable event of a second edition 

 of the work being called for. C. C. 



OUR BOOK SHELF. 



Encyclopaedia Biblica, a Critical Dictionary of the 

 Literary, Political and Religious History, the Archae- 

 ology, Geography and Natural History of the Bible. 

 Edited by the Rev. T. K. Cheyne, D.Litt., D.D., and 

 J. Sutherland Black, M.A., LL.D. Vol. iv. Q to Z. 

 Pp. xxxii + cols. 3989 to 5444. (A. and C. Black, 

 1903-) 

 This work, now completed, contains, as the publishers 

 inform us, about as much printed matter as twelve 

 volumes of the " Dictionary of National Biography." 

 They have also published a thin-paper edition, which 

 when bound in one volume is only about three inches 

 thick. This encyclopaedia has commanded for its 



