February 24, 19 16] 



NATURE 



701 



hilst he is actually serving an apprenticeship, 

 consideration of stress distribution in struc- 



res, the effect of dead and live loads, etc., to 

 ame only two of many problems in applied 

 nechanics, indicate the type of knowledge which 

 ; is the function of colleges to instil, and the out- 

 line of this method of teaching and procedure 



the volume under notice. 



From the large number of examples appended 



> each chapter it is to be presumed that the 

 olume deals with the work required by the ex- 

 Riinations of the Institution of Civil Engineers 

 Eld the University of London. Therein lies one 

 efect, viz., that the volume, however excellent 

 5s contents may be, is concerned with the attempt 



> cover a syllabus rather than with the educa- 

 ion of a recruit for a live and active industry. 

 lie effect of examinations has often been to 

 arrow and cramp the education of a student, and 

 le aim of a college can easily be turned into 

 Be of passing a maximum number of students 



rough a given examination rather than fitting 

 h men for an industry which is continually 

 iiging in scope and methods. Consider the 

 iiiiinense change in almost every branch of 

 vu^-ineering work in the last ten years, and the 

 1 sequence should be that every syllabus of 

 _;ineering examinations needs revision at least 

 once in a decade. To return, however, to the 

 book under review, the contents are so clearly 

 out and defined that it is evident the author 

 ; sound teacher. Students of mechanism and 

 tlie theory of machines cannot do better than 

 work through the various chapters of this book. 

 At the end of so doing they can face with con- 

 fidence any problems that may arise on such sub- 

 jects as the profile of wheel teeth, acceleration 

 and accelerating forces, the balancing of engines, 

 cams, trains of wheels, frictional resistances in 

 machines, and the like. Chapter xxx. might with 

 advantage have included a description of 'the 

 Froude water dynamometer, a machine which 

 will readily absorb any horse-power up to looo 

 or more, as the limits of the rope-friction brake 

 are so low. /\. J. M. 



MET AM ORPHIC GEOLOGY. 

 Metamorphic Geology : A Text-book. By C. K. 

 Leith and W. J. Mead. Pp. xxiii + 337. (New 

 York: Henry Holt and Co., 1915.) Price 

 2.50 dollars. 



THI.S book is divided into four parts. The 

 first deals with the alteration of rocks by 

 surface agencies (katamorphism), the second with 

 ' cementation and alteration by deep-seated agencies 

 (anamorphism), the third with the general prin- 

 ciples of metamorphism, and the fourth with 

 NO. 2417, VOL. 96] 



laboratory work on the subject. The authors 

 concern themselves rather with results than with 

 the chemical and physical processes by which 

 tho.se results are brought about, and they en- 

 deavour so far as possible to apply quantitative 

 methods. A special feature of the book is the 

 representation, by graphic methods, of the relative 

 gains and losses of the chemical constituents 

 during metamorphism. 



At the conclusion of the first part, after dealing 

 with the weathering of igneous rocks and the 

 nature of the sediments resulting from the erosion, 

 transportation, and redeposition of the weathered 

 material, the authors estimate the amounts of 

 shale, sandstone, and limestone which would be 

 formed by the decomposition and disintegration 

 of an igneous rock of average composition, the 

 assumption being that sedimentary rocks and ocean 

 salts have been derived directly or indirectly from 

 known igneous rocks. We quote the results as 

 illustrating the authors' point of view, and also be- 

 cause of their intrinsic interest. By methods that 

 cannot be here described the conclusion is reached 

 that " 100 grams of average igneous rock yield 1 14 

 grams of end-products, consisting approximately 

 of 87*8 grams of shale, 129 grams of sandstone, 

 67 grams of limestone, and 6"6 grams of ocean 

 salts. Neglecting the ocean salts, these figures 

 correspond to 82 per cent, of shale, 12 per cent, 

 of sandstone, and 6 per cent, of limestone." 



A comparison by volume of the average igneous 

 rock with the sediments assumed to be derived 

 from it also leads to interesting results. The 

 volume of the sediment is greater than that of 

 the igneous rock owing (a) to addition of 

 material, (b) to development of minerals of lower 

 specific gravity, and (c) to porosity. That due to 

 (a) is estimated at 74 per cent., that due to (b) at 

 3-6 per cent., and that due to (c) at 17 per cent, 

 on the average, giving an increase of 28 per cent. 

 If the ocean salts be also taken into consideration 

 the total increase becomes 36"9 per cent. The 

 salts of the ocean correspond to 72,000,000 cubic 

 miles of igneous rock and to 92,000,000 cubic 

 miles of sediment. This would represent a thick- 

 ness of about 0*46 mile over the entire globe, or 

 of I "39 miles over the continental areas. 



The phenomena of " anamorphism " (meta- 

 morphism in the .sense in which that term is 

 generally used in this country) are dealt with in 

 the second part of the book, and the views of 

 Becke and Grubenmann on the origin of the 

 crystalline schists are discussed. Apart from the 

 diagrams already referred to, only two illustrations 

 are given, and it is difficult to understand why 

 these have been selected from 'a host of others of 

 at least equal importance. 



