July 12, 1906J 



NATURE 



243 



.1 mineral in a slate of fusion below its ordinary 

 mclting^-point may allow of the previous crystallis- 

 ation of another, which cannot sustain such con- 

 ditions, and thus the normal order of crystallisation 

 may be reversed. This fact is used to explain the 

 crystallisation of augite before the felspar in basic 

 roclvs, which, in normal circumstances, so frequently 

 show ophitic structure. 



.Ml through the book the influence of personal ex- 

 periment remains manifest, and we must not com- 

 plain if the genesis of the sedimentary rocks is treated 

 in a somewhat rapid fashion. Flints thus receive 

 far less than their due (p. 232), considering how much 

 tlirv have been discussed. Guppy's observations on 

 >ilicificd corals in the Fiji Islands raise, for instance, 

 new questions in themselves. But references to recent 

 work, such as Linck's on the separation of calcium 

 carbonate from sea-walcr, will lead the reader for- 

 ward ; and we turn back contentedly from these 

 scantier pages to the fine account of the problems of 

 contact-metamorphisiri. and thank the author again 

 and again for his clear and stimulating treatise. 



.\s is natural in so wide a field, we miss mention 

 of some memorable work, such as that of Harker on 

 mixed rocks in the Inner Hebrides; on the other hand, 

 we hail with delight the name of MacGrcgory (p. 31), 

 who appears to be Prof. J. W. Gregory in the glory 

 of a -Scottish title. Grenville .A. J. Cole. 



STRUCTVRES AXn ytATERIAl^S. 



Tlicory of Sfnictiircs and Strcngtii of Materials. By 



Prof. Henrv T. Bovey. Fourth edition. Pp. xiii-l- 



(-)68. (New York : John Wiley and .Sons ; London : 



Chapman and Hall, 1005.) Price i/. 11.';. 6rf. not. 



THIS well-known text-book has been largely re- 

 written and enlarged for the present fourth 

 edition. In the preface Prof. Bovev states that a 

 number of fresh examples, mostlv drawn from actual 

 practice, have been added to the various chapters, and 

 that all tables of strengths, elasticities, and weights 

 of materials have been brought up to date. 



In chap. i. a description of Bow's method of nota- 

 tion is given, and the author has now adopted this 

 system throughout the book when dealing with 

 stresses developed in framed structures. The treat- 

 ment of the three-hinged braced arch for station 

 roofs and for sheds of wide span is a new piece of 

 work in this chapter. In chap. ii. there is a new 

 series of paragraphs dealing with the graphical de- 

 termination of the maximum bending moment at anv 

 point of an arbitrarilv loaded girder, and several 

 examples illustrating the author's methods are worked 

 out in full. Chap. iii. of the older editions has wiselv 

 been broken up into two chapters, one (chap, iii.) 

 dealing with momentum, energv, and balancing, and 

 the other (chap, iv.) with stress, strain, and elas- 

 ticity. In the older editions this chapter was a very 

 difficult one for the student to follow, and the author, 

 in rewriting and dividing it, has brought the various 

 steps of the work into their true relation one with the 

 other. The whole of the material in chap. x. of 

 NO. 191 5, VOL. 74] 



the oldfer editions, which dealt with thick-walled, 

 hollow cylinders, has now been incorporated into 

 chap, v., which treats of the more dilTicult work on 

 stress and strain^ and undoubtedlv it follows more 

 naturally in this position after the discussion of the 

 general equations of stress. 



In chap, vii., in dealing with the relation of the 

 neutral plane to the stress at any point in a beam, 

 Prof. Bovey has incorporated the results of his own 

 experimental work, which was carried out with the 

 view of determining within the limits of elasticity 

 the changes of fibre length at different depths of a 

 beam when loaded transversely. In this chapter there 

 are also additional paragraphs dealing with the design 

 of reinforced concrete beams, the position of the 

 neutral axis, and the strength of such beams ; ad- 

 ditional graphical methods are given for determining 

 the slope and deflection in loaded beams, and in 

 connection with the theory of continuous girders 

 fresh matter has been introduced. 



In chap, viii., which deals with the theory and the 

 bending of struts, the results of the most recent ex- 

 periments have been incorporated, and, as the chapter 

 has been rearranged, it is now much more useful to 

 engineers engaged in the difficult problem of strut 

 design. In chap. ix. the stresses in non-circular 

 shafts are discussed, and there is also much new- 

 matter in the paragraphs on the efficiency of shaft- 

 ing and the whirling of shafting, and open coil 

 springs are dealt with, as well as the ordinary helical 

 springs. Chap, x., which is devoted to bridges, ha- 

 been entirely rewritten and greatly improved. Graphical 

 methods are used throughout for the determination 

 of stresses in the piers, and the most recent types 

 of bridges are discussed and explained. Excellent 

 tables are given of the loads upon, and the weights 

 of, bridges, and several examples of fairly large 

 bridges are worked out in complete detail. This 

 chapter is now a most valuable one for those who 

 are concerned with the design of bridges of all 

 classes, and the examples have been made thoroughly 

 practical. We have no hesitation in saving that Prof. 

 Bovey in thus practically rewriting his book has con- 

 siderably improved its value both to the engineering 

 student and to the civil engineer engaged in the 

 design of all classes of structures in steel and iron. 



T. H. B. 



RATIONAL DAIRYIXG. 

 Dairy Chemistry. By Harry Snyder. Pp. x-l-igo. 

 (London: Macmillan and Co., Ltd.; New York: 

 The Macmillan Co., 1906.) Price 4s. 6d. net. 



PROF. SNYDER'S work as agricultural chemist 

 in the University of Minnesota is well known. 

 This State, with a population less than that of Kent 

 and Essex, possesses a University Agricultural De- 

 partment in which are 800 students most of whom 

 arc attending a three years' course. The majority 

 arc students who during the summer months have to 

 work fcir .1 living, and at the close of their academic 

 training n-lurn to rural employment. Thus Min- 



