OCTOBEK 24, I 901] 



NA TURE 



62- 



in many European fields, as well as in America. Some 

 tentative efforts are now being made to introduce the 

 photo-theodolite to India, but the results are hardly 

 mature enough to justify any opinion as to their success. 

 In France photo-topography has been chiefly applied to the 

 field of that which we should term in England "revenue" 

 or " cadastral " survey ; and in Canada (a fact which is 

 not recognised by Colonel Laussedat) a still wider open- 

 ing has been afforded by the Geological Survey, which is 

 practically a small scale topographical survey leading to 

 the first general map of the country. There are, at any 

 rate, records sufficient to enable us to bring the test of 

 actual experience in other countries than France to bear 

 on Colonel Laussedat's estimate of the capabilities of the 

 system. That estimate appears to be absolutely favour- 

 able, but it must be contended that the illustrations 

 which support Colonel Laussedat's opinion are not in 

 themselves comprehensive enough to justify the con- 

 clusions at which he arrives, which would apparently 

 include all classes of reconnaissance, or survey, in all 

 conditions of ground as suitable for its application. 



An official examination into the results of a photo- 

 theodolite survey was conducted in Paris as long ago as 

 the year 1859, and the report of the commissioners 

 nominated by the Academy of Sciences was so favourable 

 that in 1863 a "photo-topographic brigade" was formed, 

 under the direction of Laussedat, which executed surveys 

 on comparatively large scales (from i/iooo to 1/20000)^ 

 and which lasted for a period of eight years. The 

 brigade was broken up in 1S71, and whilst Colonel 

 Laussedat refrains from commenting on the reasons for 

 its suppression, he clearly indicates that it was for no 

 reason which implied technical failure. 



Various modifications of the original system are dis- 

 cussed or recommended, and one or two excellent illus- 

 trations of the resulting surveys are given at the end of 

 the book. But it must be noted that the field of survey 

 to which this process has been applied in France is after 

 all but local, and the scale of mapping is comparatively 

 large. For instance, we find in Plate xiii. a reproduction 

 of about 15 square miles of country, originally surveyed 

 on a scale approximating to 12 inches per mile (reduced 

 to one-fourth in reproduction), to which the foUowmg 

 ■details are appended. The survey was completed in ten 

 days in the field, supplemented by two and a half months 

 of subsequent work in the drawing ofifice (bureau). It 

 involved the use of fifty-two photographs, which were 

 taken at thirty-one stations. Of these stations eighteen 

 were stations of triangulation, and the rest "sup- 

 plementary." The map itself is fully contoured 

 and apparently quite up to the standard, in detail, of 

 maps on a similar scale executed by the English 

 Ordnance Survey. The time (and consequently the 

 expense) involved in its production will of course com- 

 pare favourably with that of any other known system of 

 surveying ; but it would be rash to infer therefrom 

 that photo-topography is under all conditions either a 

 cheap or a rapid method of surveying. In Canada good 

 work has been done by this process on the smaller 

 scales of one inch or two inches per mile, and the 

 system generally is well established. But Canadian 

 surveyors are not prepared to advocate it in entire 

 supersession of the more widely known system of plane 

 NO. 1669, VOL. 6<l] 



table topography based on triangulation, maintaining 

 that itsadvantages are confined to comparatively restricted 

 conditions of surface conformation. Thirty-one stations 

 of observation in fifteen square miles of country (giving 

 an average of two " fixings" per square mile) may under 

 certain conditions be sufficient, to enable a surveyor to 

 see into the topographical detail of ridge and furrow, 

 plain and gully, that the country presents, and result in a 

 creditable map. But in a vast proportion of the broken 

 and rugged districts presented by the varied physio- 

 graphy of Asia, Africa, or America two stations per mile 

 would certainly not be sufficient, and the accumulation 

 of photographs would rapidly become an unwieldy 

 burden. When we consider the requirements of geo- 

 graphical surveys on yet smaller scales 'say i, 500000) 

 it is impossible to concede that the recognised systems 

 of rapid plane tabling in experienced hands, which 

 result in daily outturns which may be reckoned in scores 

 of square miles of finished mapping (no " bureau" work 

 is required by a really well-trained topographer), can be 

 surpassed in rapidity by any more complicated process 

 which has yet been invented. 



Possibly the discussion of the application of photo- 

 graphy to this most important field of geographical 

 survey may be reserved for a future volume, although it 

 might certainly have been usefully included in the present 

 one. The author is at any rate on perfectly sound ground 

 when he recommends every explorer who makes use of 

 photography for illustrative purposes to fix the position 

 of his views and the direction (or azimuth) of them with 

 careful exactness on his route map ; with the assurance 

 that in scientific hands they will prove of immense value 

 in elucidating the topography of the country which they 

 illustrate if they are thus registered. 



There is no work in the English language equal to 

 that of Colonel Laussedat as a comprehensive and up-to- 

 date review of the history and development of topo- 

 graphy ; in the value of its scientific deductions and 

 illustrations ; or in the interest which is sustained by the 

 literary skill exhibited. It should find a place in every 

 library of civil or military engineering institutions which 

 professes to maintain an efficient stock of standard 

 works for reference. T. H. H. 



EUCLID REVISED. 

 Euclid's Eleuients of Geometry. Books i.-iv., vi. and 

 xi. By Charles Smith, M.A., and Sophie Bryant, 

 D.Sc. Pp. viii-l-460. (London: Macmillan and Co., 

 Ltd., 1901.) Price 4^. bd. 



IF Euclid is to continue as the foundation of geome- 

 trical teaching in our schools, this work must be 

 very warmly welcomed. The exact order of Euclid is 

 followed, but (as the editors inform us) with no special 

 regard to the exact words of the translation of Simson 

 (who for a moment becomes " Simpson " in the foot-note 

 on p. 79). There is also a complete absence of the 

 mechanical chopping up of each proposition into separate 

 blocks under the heads of "general enunciation," 

 "particular enunciation," "hypothesis," "construction," 

 " to prove," " proof," "conclusion," which in some text- 

 books, and in the minds of many boys, has reduced the 

 whole subject to an artificial jargon. 



