NATURE 



\_ncc. 6, 1883 



geological times are doubtful. But Prof. Zittel considers 

 that the climate muit have been damper, the rainfall 

 heavier, and freshwater denudation more active in Pleis- 

 tocene days than now, to account for the erosion that 

 has taken place, the abundance of fulgurites, and the 

 present distribution of the fauna and flora, especially in 

 such ca^es as the occurrence of Central African croco- 

 diles in the marshes and streams of the completely iso- 

 lated Ahaggar Mountains. Reasons are aho given for 

 believing that the Nile was formerly a larger river than 

 it now is. It is probable that Prof Zittel's views 

 on some of these points will be contested, but it is im- 

 possible to deny that his arguments are admirably 

 expressed and clearly reasoned out. 



Some very interesting details are given about the desert 

 sand, and a careful description of its arrangement in the 

 form of sandhills. The sand of the Sahara is considered 

 to have been largely derived from the decomposition of 

 the so-called Nubian sandstone, the original matrix of the 

 well-known silicified wood. In the Libyan desert there 

 are some remarkable anomalies in the arrangement o*^ 

 the sandhills, and it is clear that they cannot have been 

 entirely formed by accumulation through the agency of 

 the prevailing wind as it e.\ists at the present day. It 

 may here be reraarlied that very similar observations 

 were made, a few years since, upon the sand ridges of the 

 Indian desert east of the Indus. Some of the sand 

 ridges, both in .Africa and India, attain an elevation of 

 about 500 feet, and in both areas the largest appear to 

 have undergone no change within the memory of man, 

 although in places, in both continents, moving tracts 

 of sand occasionally overwhelm cultivated land and 

 buildings. 



One mistake in the book deserves notice. In the com- 

 parative table of Upper Cretaceous and Eocene beds in 

 Europe, Asia, North Africa, and North .America the 

 position assigned to some of the Tertiary stages of the 

 Indian rocks requires correction. The lower Nari beds in 

 especial were never supposed to be so old as Middle 

 Eocene (Parisian), and they are now known to be in all 

 probability true Oligocene. But trifling mistakes of this 

 kind are to be expected : it is surprising that more should 

 not have been observed. 



\V. T. B. 



APPLIED MECHANICS 

 Applied Mechanics. By H. T. Bovey, M.A., Professor of 

 Civil Engineering and Applied Mechanics, McGill 

 University, Montreal, Fellow of Queen's College, 

 Cambridge. Part I., pp. 190. Part II , pp. 150. 

 (Montreal : J. Lovell and Son, 1883.) 

 '"P II I S work appears to be designed as a college text- 

 -L book for somewhat advanced students, who have 

 already received good training in mathematics (as far as 

 the elementary parts of the integral calculus) and theo- 

 retical mechanics. 



Part I. treats of the strength of materials, dealing with 

 longitudinal stress, the strength of beams and pillars, 

 torsion, and the strength of hollow cylinders and 

 spheres. 



In Part II. we have chapters on frames, roofs, bridge- 



trusses, suspension bridges, arched ribs, and in con- 

 clusion one on " details of construction," which in- 

 cludes a discussion of the strength of rivets and other 

 fastenings. 



In his exposition of these subjects the author manifests 

 a power of clear and precise statement ; and the treat- 

 ment of the more difficult problems of the first part is 

 perhaps as profound as could be attained without a know- 

 ledge of the general theory of elasticity. The numerous 

 illustrations serve sufficiently well in Part I., where they 

 consist chiefly of diagrams; but in Part II. they are on 

 too small a scale for the complicated structures illus- 

 trated : and in clearness of detail are far below the 

 standard reached in recent English books on the same 

 subjects. Analytical method-i are preferred throughout ; 

 and generally speaking geometry is used merely to illus- 

 trate results previously obtained in a symbolical form. 

 Thus graphical statics is quite subordinate in Part II. ; 

 stress diagrams are introduced, but there are not sufficient 

 instructions in the text to enable a student, who has not 

 studied the subject independently, to construct them for 

 himself. 



In the extended treatment of a parabolic rib of uniform 

 stiffness (pp. 101-17.0) the author follows very closely the 

 lines in Rankine's " Civil Engineering," with some further 

 consideration of the additional terms depending on change 

 of temperature. 



There is no acknowledgment in regard to this and 

 other parts of the work where Rankine's influence is 

 clearly apparent. But as no preface is given to the present 

 volume, perhaps other portions of the great subject of 

 applied mechanics are in course of preparation by our 

 author ; and till the completion of his work he is post- 

 poning the statement of his obligations to those who have 

 gone over the ground before. 



We have referred to the apparent excess of symbolical 

 reasoning: but none of this is due to the introduction of 

 investigations better left to treatises on pure mathematics 

 and theoretical mechanics. 



Difficulties special to the subject of the work, such as 

 the equations of the " neutral axis " (so called) for all the 

 different modes of loading and supporting a beam, the 

 theorem of three moments, the moments of inertia of 

 complicated forms of section, the deflection of struts, are 

 however treated with the fullness of detail required by 

 ordinary students. 



Such investigations constitute the best feature of the 

 book. The detailed application to problems such as occur 

 in actual practice is but slightly touched on ; perhaps 

 for this we are to look to the " E.xamples," of which some 

 few are worked out in the text ; appended to the several 

 chapters, moreover, are close upon 400 proposed for the 

 exercise of the student. 



These form a very important collection. A great num- 

 ber involve numerical results, and unfortunately the 

 answers are not given ; this greatly lessens their value for 

 private students at any rate. Several examples are taken 

 from existing structures, and are liberally furnished with 

 diagrams in illustration of the data. 



Many are new to text-books, and the author has evi- 

 dently taken great pains in collecting and arranging 

 them. 



A. R. Willis 



