March io, 192 i] 



NATURE 



39 



the space that can be devoted to each is very 

 limited, and, as the author himself points out in 

 his preface, many details which may assume 

 considerable local importance, but are rela- 

 tively insignificant from a more general point 

 of view, have perforce been omitted. The salient 

 features of each field have, howiever, been care- 

 fully studied, and are stated in such a way as to 

 give a sufficiently clear view of their various 

 characteristics ; perhaps it might have been pre- 

 ferable to have subdivided the coalfields of Scot- 

 land, and to have devoted at least two chapters 

 to these, instead of dealing with all of them in 

 one, although no doubt that chapter is rela- 

 tively a long one. Whilst there are necessarily 

 omissions here and there, partly for lack of 

 space, as has already been pointed out, and partly 

 because no two geologists are at all likely to agree 

 as to the relative importance of certain features, 

 actual mistakes are decidedly rare. 



It might have been desirable to devote more 

 care to the sketch-maps of the coalfields, for they 

 are by no means so clear as they might have been 

 made; for example, in the map of the North- 

 umberland and Durham coalfield it is doubtful 

 whether a certain line lettered as a dyke of igne- 

 ous rock is intended to represent the author's idea 

 of the course of a possible dyke of such rock, 

 or whether it is meant for the approximate 

 line of the great fault known as the Ninety 

 Fathom Dyke. At the same time, it is 

 only right to admit that the representation 

 of geological maps in black-and-white upon 

 a very small scale is by no means an easy 

 matter. The author may fairly be congratu- 

 lated on having compressed so much useful in- 

 formation within the limits of a small but well- 

 balanced volume, and it is fortunate that it 

 appears at a moment when the importance of an 

 accurate knowledge of the coalfields of the 

 country is becoming generally recognised. 



H. L. 



Practical Aeroplane Photography. 



Airplane Photography. By Major H. E. Ives, 

 U.S. Army. Pp. 422. (Philadelphia and 

 London: J. B. Lippincott Co., 1920.) 185. 

 net. 



MAJOR IVES was formerly officer in charge 

 of the experimental department of the 

 photographic branch in the American Air Service, 

 and as such he and his collaborators have had 

 access to the information, photographs, and draw- 

 ings supplied by the Allies to the United States. 

 He has therefore had a unique opportunity of com- 

 piling a book describing the practice of air photo- 

 NO. 2680, VOL. 107] 



graphy in the war and the apparatus employed, 

 an opportunity which has probably not been 

 afforded to any other individual. The work under- 

 taken has been, on the whole, well done, and an 

 interesting book results. The numerous well- 

 printed illustrations form one of the most 

 noteworthy features ; they include not only photo- 

 graphs of apparatus, diagrams, and interesting 

 air views, but also many reproductions from the 

 secret official publications of the Intelligence 

 Branch of the British War Office, which have not 

 hitherto been available in England. When look- 

 ing through the 208 figures, one notices that in 

 a few cases their source is acknowledged, but in 

 the majority of cases figures are copied from 

 English, French, or Italian sources without 

 acknowledgment. Whatever may be said of this 

 free use of English official photographs, the direct 

 reproduction of five well-known diagrams drawn, 

 we believe, by Capt. Durward, R.A.F., and of two 

 tables copied from M. Clerc, without reference to 

 their authors, can scarcely be passed without com- 

 ment. 



The sections of the book dealing with apparatus 

 and materials are distinctly good. The author has 

 selected his material well, and the only inaccuracy 

 noted is in the description of the Williamson film 

 camera. In describing tilt-recorders, the Goerz 

 type only is figured and mentioned, though the 

 Zeiss type was more commonly employed by the 

 Germans. In his account of aerial photographic 

 methods and the utilisation of photographs, the 

 author is less fortunate, probably having little 

 first-hand knowledge. His treatment of stereo- 

 scopy seems somewhat superficial, while his 

 chapter on map-making is quite unsound. He 

 has adopted the untenable view that a series of 

 overlapping prints taken by a plane flying level 

 at a constant altitude constitutes a complete pic- 

 torial map of the ground. This view may pos- 

 sess an element of truth when the ground is flat, 

 but it cannot be used as a basis for aerial survey. 

 It has already called down the contempt of sur- 

 veyors, and in 19 16 led the General Staff of the 

 French Army to prohibit the use of photo-mosaics 

 and squared maps made from them. Under the 

 impression that an assemblage of photographs — 

 or a photo-mosaic, to use a more precise term — 

 is a map, the author goes on to give a useful 

 description of the method by which such a mosaic 

 is made, but is, in consequence, confused when 

 he tries to introduce the work and suggestions of 

 Bagley. Aerial map-making can be developed 

 only by recognising that, while a photograph 

 may seldom itself be regarded as a map, it does 

 give a representation of the ground from which 

 an accurate map can be compiled (so long as 



