September i6, 1920] 



NATURE 



77 



"Popular Oil Geology," has produced a remark- 

 ably neat and illuminating little volume which 

 m&v be confidently recommended to all interested 

 in the subject of petroleum technology. 



Prof. Ziegler has condensed a very large subject 

 into a comparatively small space, and it must 

 be admitted that in but few instances have the 

 principles of the science suffered from this treat- 

 ment. The author has the obvious knack of 

 extracting the real substance of the various 

 branches of oil geology, and of presenting this 

 without unnecessary "padding," so that the book 

 really achieves its purpose of being an introduc- 

 tion to larger volumes dealing in more detail with 

 the principles of the subject. 



The chapters on the laws of the migration and 

 accumulation of oil and gas, on oil structures and 

 oil fields, and on prospecting are particularly good, 

 while the final remarks on oil investments, cul- 

 minating in a parody of John Hammond's rules 

 for investors, are quite as amusing as they arc 

 apposite. 



The book is profusely illustrated, a great many 

 of the maps and diagrams being taken from the 

 U.S. Geological Survey publications, as acknow- 

 ledged in the preface. While this practice of re- 

 production is useful within limits, it is one that 

 can be very easily overdone. To say that it shows 

 lack of originality is possibly an exaggeration, but 

 when such diagrams as that included on p. 77 

 occur again and again in various American publi- 

 cations we have examined, it seems disappointing 

 that a new rendering of the same subject cannot 

 be invented. But for that and the price (which 

 for a book of this description is rather excessive), 

 this little volume deserves a place on the book- 

 shelf of the layman, student, and expert alike. 



H. H. MiLNEK. 



Our Bookshelf. 



Oeone. By Prof. E. K. Rideal. (A Treatise of 

 Electro-chemistry.) Pp. ix+198. (London: 

 Constable and Co., Ltd., 1920.) Price 12s. net. 



In recent years ozone has attracted increasing in- 

 terest on account both of its value as an aid to 

 research in organic chemistry, and of its actual 

 or possible applications on the industrial scale. 

 The literature of the subject is, however, widely 

 scattered, hence in compiling this monograph, 

 which forms a section of the treatise on electro- 

 chemistry in course of production under the editor- 

 ship of Sir. Bertram Blount, the author has done 

 good service to chemists. 



An interesting introductory portion, which deals 

 with the early history, the general properties, and 

 the occurrence of ozone, is followed by five 



NO. 2655, VOL. 106] 



chapters in which the methods of production — 

 chemical, thermal, and electrolytic — and in par- 

 ticular production by means of ultra-violet radia- 

 tions and of the silent electric discharge, are ade- 

 quately described. These are succeeded by a 

 summary of the principal investigations on the 

 catalytic decomposition of ozone, and in the next 

 chapter its more important industrial applications 

 — e.g. in the sterilisation of water, the "purifica- 

 tion " of air, the bleaching- of oils and fats, and 

 the manufacture of vanillin — are discussed in some 

 detail. The last chapter contains an account of 

 the methods of detecting and estimating ozone. 



The author has been distinctly successful in his 

 effort to collect and correlate tlie various refer- 

 ences to ozone which occur in chemical literature, 

 and his monograph will be welcomed if only for 

 that reason. In addition, it contains a valuable 

 summary of what is known- — after all not very 

 much — about ozone, and by indicating problems 

 which remain to be solved should also serve to 

 promote investigation. It is therefore all the more 

 regrettable that several of the pages of an other- 

 wise praiseworthy book are disfigured by gram- 

 matical errors, or by sentences so carelessly con- 

 structed as to be obscure in their meaning. 



Microscopy: The Construction, Theory, and Use 

 of the Microscope. By Edmund J. Spitta. Third 

 edition. Pp. xxviii -1- 537 ■+ xxviii plates. 

 (London : John Murray, 1920.) Price 255. net. 



The first edition of this work was reviewed 

 in Nature for February 6, 1908. The work has 

 gained a well-deserved popularity, and two further 

 editions have since been called for. In each of 

 these the opportunity has been taken to bring the 

 subject-matter so far as possible up to date, and 

 to indicate important new developments. In the 

 present edition may be noted especially the 

 reference to low-power objectives designed to give 

 great depth of focus and a flat field, valuable 

 especially for the photography of relatively large 

 specimens of appreciable thickness, where good 

 definition has to be obtained of parts lying in 

 different planes. To illustrate the use of these, a 

 considerable number of new plates have been 

 added, which include some admirable reproduc- 

 tions of photographs obtained with modern ob- 

 jectives of this type. 



Mention must also be made of the photographs 

 added to illustrate the use of the term "critical 

 definition." Unfortunately, the term, though no 

 doubt convenient, is not one to which a precise 

 significance can be given, and it thus always pre- 

 sents difficulties to the learner, who comes to 

 appreciate only by experience the sense in which it 

 is employed. 



The "Addenda," amounting to more than 

 twenty pages, contain useful notes of some recent 

 improvements, with a few convenient tables. 

 Attention is directed especially to the use of the 

 newer Kodak filters for obtaining blue light with 

 a powerful illuminant, details being given. The 

 index has been improved and additional references 

 have been inserted, notably those to the pages of 



