76 



NATURE 



[March i6, 191 i 



tjon of the fiauss rcMiforinal meriHionnI pn>jt»clion 

 for the maps of the survey i)f H{iypt. A pneral dis- 

 cussion of the figure of the earth, and the j^eometry 

 of the surface of a spheroid, is then entered upon, 

 leading the way to the theory of the representation of 

 such a surface on a plane sheet and the involved 

 bahincing of errors. These general results are then 

 applied to the standard projections, so that, while 

 special attention is devoted to the Egyptian mapping, 

 the major part of the book is of quite general applica- 

 tion. The methods of investigation are, in many 

 cases, new, and tlic mathematical forms concise and 

 elegant. 



As an interesting example of specialisation, we may 

 note the investigation, on p. 6i, of the Mecca retro- 

 azimuthal projection, which would provide a map 

 giving the true bearing of Mecca at any point. 



The great variety of projections used for the maps 

 of different countries gives rise to certain inconveni- 

 ences, and it is an arguable point whether it would 

 not be possible and desirable to reduce this number 

 to a few standard forms by international agreement. 

 What has already been accomplished in the case of 

 the 1/1,000,000 map of the world might be extended 

 to apply to other scales. We commend the subject to 

 the attention of the next International Geographical 

 Conference. It must always be borne in mind that 

 while the selection of a suitable projection is impor- 

 tant for atlas or general maps upon small scales, it 

 is comparatively unimportant for large-scale survey 

 maps produced in sheets, so long as each sheet is pro- 

 jected separately. The errors due to defects in the 

 projection are always small compared with those due 

 to the distortion of the paper upon which the map is 

 drawn or printed. E. H. H. 



OVERHEAD AND UNDERGROUND ELECTRIC 



LINES. 

 Lignes Electriques Souterraines. Etudes, pose, essais, 



ct recherchcs dc defauts. Pp. 207. 

 Lignes Electriques A^ricnnes et Souterraines. litudes, 



pose et essais. Pp. 181. By C. Giradet and W. 



Dubi. (Grenoble : J. Rey ; Paris : Gauthier-Villars, 



19 10.) Price 5 francs each. 



THE superscription on each of these volumes : 

 " Bibliotheque de I'eleve-ingenieur," seems to 

 indicate that they are written by and for graduates 

 of engineering colleges, and this impression is con- 

 firmed by an introduction contributed by Prof. J. 

 Pionchon, of the Dijon University, in which we are 

 told that the " library " is intended to form a kind of 

 post-graduate instruction to engineering students. To 

 expect students shortly after they have graduated to 

 be able to become authors on technical subjects and 

 write books, which shall be good enough to serve as 

 further instruction to other students which may 

 graduate a year or two later, is hardly reasonable ; but 

 in the present case the difficulty is partly overcome by 

 the circumstance that one of the authors is not a 

 student fresh from college, but evidently a man of 

 considerable practical experience in overhead power- 

 lines and cable work. 



Yet the result of the collaboration is rather dis- 

 NO. 2159, VOL. 86] 



appointing. The books are neither scientific— in tl 

 sense of showing the connection between engineerii) 

 practice and scientific principles — nor are they v< • 

 practical in the sense of containing definite instri 

 tions. There is a little of each, and a good deal 

 what may be described as general talk on the subjet 

 and containing little which is not self-evident to 

 man of average intelligence. Thus, when the autht'i - 

 tell us that overhead power-lines should be so con- 

 structed that copper may be added as the demand f' 

 power increases, everybcxly will agree, but is it nee 

 sarv to labour so obvious a matter? On the otlv 

 hand, some of the general talk is misleading. Tal 

 the statement that cables for verA- high pressure h.-n 

 no practical importance, since cables are only us' 

 within towns, that is, over relatively short distance 

 or the recommendation to earth the middle wire in 

 three-wire system at every juncvion box. Then, agai 

 we find ten pages of what may be called general t.' 

 about various junction boxes, but not a single dm' 

 ing to illustrate the types discussed; whilst the i; 

 portant matter of mechanical protection of cables 

 dealt with on only two pages, and illustrated by tv 

 small scale sections, one showing bricks laid over ti 

 cable longways and the other showing them bro-'i 

 ways. 



The most elaborate technical part of the book < 

 underground lines is that on localisation of faul- 

 and here, by the preface, we are led to expect speci.i, 

 valuable information; for the authors say in it tl'. 

 although the methods given in " some text-book^ 

 are sufiiciently well known, yet their practical ' pp!ii 

 tion under the varying and difficult condition of actu 

 service, demand special elaboration. This is certair 

 true, and one turns with eager expectation to t' 

 chapter in question in order to see what the autht 

 have to say about these special devices. Here ag;i 

 we are rather disappointed; although the author w ! 

 has contributed this part is certainly a man who kno' 

 his subject well, and gives a series of practical a; 

 numerical examples evidently culled from his practii 

 one does not find much which may be considered 

 new methods. Our old friend the loop test crops up 

 various guises, and when we are told that a speci.u 

 wire must be run where no sound cable is available to 

 complete the loop, the advice is, no doubt, quite ser- 

 viceable, but it can hardly be considered as an ad- 

 vance upon the text-book method ; it is simply an 

 obvious way of carrying it out. 



For the localisation of a break in the conductor a 

 method based upon measurement of capacity is recom- 

 mended. This also is old. Most engineers will expect 

 that when a cable parts bodily the insulation at the 

 break will also be destroyed, so that a method based 

 on the measurement of capacity becomes inapplicable ; 

 but, curiously enough, the authors give a case from 

 their experience where the insulation had remained 

 perfect. The history of this breakdown, and of the 

 expedients employed to keep the service up under a 

 variety of great difficulties, is very interesting reading, 

 whilst the fact that the engineers were able to locate 

 the break within a few yards is a striking vindication 

 of a method which at first sight seems of doubtful 

 value. What the authors have to say about the legal 



