42 



NATURE 



{Nov. i6, 1871 



The illustrations are also unusually good in both books, 

 but while Wernicke's is professedly a mathematical 

 treatise, the work of Buff leans more to the physical 

 aspects of mechanics. There is, however, considerable 

 reference to mathematics in Buff, in fact, he makes free 

 use of the calculus when necessary. 



The book consists of thirteen sections : — Section I. is on 

 Rest and Motion ; Section II. on Movement in Space and 

 Time : this contains, in addition to the usual theorems on 

 the motion of a point, a useful article on harmonic motion. 

 Section in. introduces the Composition of Movements ; in 

 this will be found a discussion of experiments upon the 

 trajectory of the bullet from the needle-gun. Section v. 

 commences the subject of Mechanical Work ; we are glad 

 to see in this book the principle of work receives that 

 prominence which it unquestionably deserves. Section 

 \II., on Friction, discusses, among other subjects, Pam- 

 boui-'s experiments upon the friction of railway carriages. 

 Section IX., upon the Efficiency of Machines, is admirable, 

 the theory being properly proportioned to the experiments. 

 We find here a full discussion of the subject, without that 

 deluge of formulic which is so often repulsive to those in 

 searchof distinct physical conceptions. Section X. contains 

 what is familiar to us by the term Mechanism ; Section 

 XII. is the most complete account of Centrifugal Force which 

 we have met with in any work ; we have here a physical 

 explanation of the permanent axes, of precession and 

 nutation, of the mode of finding the masses of the heavenly 

 bodies, and of various other matters. Section xill., upon 

 the Motion of the Pendulum, is a collection of interesting 

 subjects, among them Foucault's pendulum, and a far 

 better account of Cavendish's experiments than is to be 

 found in any English book on mechanics. We are also a 

 little surprised to find the weighing scales treated in this 

 section. The arrangement is novel, and though doubtless 

 much might be said in favour of it, yet we think, on the 

 whole, it is not convenient. 



We cordially recommend Buff's treatise to the notice of 

 teachers of natural philosophy. 



Mr. Wormell's book, which appears to have been 

 specially intended for the London University examination 

 for B.A. and B.Sc, contains practical and experimental 

 illustrations, in addition to the usual matter. We should 

 gladly welcome a thoroughly good work on the general 

 plan which has been adopted by Mr. Wormell, but the 

 book before us ought to receive careful revision before it 

 is placed in the hands of students. We shall indicate 

 some of the points that we have noticed which require 

 correction. We do so in the belief that a future edition 

 of the work might be made really valuable, and supply a 

 much felt want. Seine of the errors are common to this 

 work and other text-books. We can, therefore, only accuse 

 Mr. Wormell of reproducing them, but we cannot allow 

 this excuse on every occasion. 



On page 14, we find as follows : — " Any two forces 

 F',F' apphed at a point jif may be transferred parallel to 

 themselves to any other point HI' in the line of direction 

 of the resultant." 



This proposition, if true, would assert that the attractions 

 of the earth and sun upon the moon might be transferred 

 to any heavenly body in space which happened to be in 

 the line of direction of the resultant of the forces. The 

 geometrical proof of the composition of parallel forces (p. 



33) is meaningless, until the proposition referred to has 

 been properly stated. This blunder is extremely common, 

 it arises from enunciating as a property of forces what is 

 really the definition of a rigid body. 



On page 112 we find the following passage : — 



" I. When the materials composing the surfaces in 

 contact remain the same, the friction varies as the pres- 

 sure. Suppose, for example, that a block of wood, having 

 a hole bored in it, rests on a plane inclined at the angle of 

 repose, if lead be poured in the hole, the sc?-ciu may be 

 turned so as to incline the plane at a greater angle with- 

 out causing the body to slide. By increasing the pressure 

 we increase the friction." 



This is very bad ; the statement we have italicised in 

 the second paragraph is entirely erroneous. So serious 

 an error would be quite inexcusable even in one of those 

 for whose use the book has been written. 



We should have liked to have seen more experiments 

 upon the mechanical powers cited. A student who reads 

 (p. 94) that in the three sheave pulley-block the power 

 is one-sixth of the load, will naturally be surprised when 

 he finds by trial that the power must be one-fourth of the 

 load ; nor can we find a single word in the book which 

 would enlighten his difficulty. We should also have ex- 

 pected that the author would have replaced the antiquated 

 and useless pulley systems which only exist in manuals, by 

 some compact and useful machines like the differential 

 pulley. 



Such are some of the points which we consider to require 

 careful revision before Mr. Wormell's book can be pro- 

 nounced suitable for the use of students. 



OUR BOOK SHELF 



Contributions to Botany, Iconographic and Descriptive. 

 By John Miers, F.R.S., F.L.S. Vol. 3, containing a 

 complete Monograph of the Menispermaceje. Sixty- 

 six litho plates. (London : WiUiams and Norgate, 

 1S64— 1S71.) 

 Mr. Miers's long-promised Monograph of the Meni- 

 spcrmacea; forms the third volume of his valuable " Con- 

 tributions to Botany." The intimate acquaintance of this 

 veteran botanist with South American plants, and his 

 long study of this particular family, extending over more 

 than twenty years, render his obser\-ations peculiarly 

 valuable to all systematic botanists. Although in some 

 important particulars Mr. Miers combats the views of 

 such high authorities as the authors of the " Flora Indica," 

 and those of the " Genera Plantarum," he adduces reasons 

 for his dissent, which will, at least, need careful considera- 

 tion from all who hereafter write on these plants. Mr. 

 Miers retains, with some modifications, his views of the 

 structure of the different organs in this order published 

 in the Annals of Natural History in 1851, and classifies 

 the genera which constitute it into seven tribes, on cha- 

 racters dependent mainly on the structure of the fruit, and 

 on the position of the cotyledons relatively to the radicle, 

 whether incumbent or accumbent. The establishment of 

 sixty-four distinct genera in the order, instead of the 

 thirty-one admitted by Bentham and Hooker, may be 

 open to criticism, but several of them contain only single 

 species now for the first time described, which appear to 

 be altogether aberrant types of the order. Good plates 

 are always valuable ; and we have here sixty-six, drawn 

 on stone by the author himself, containing careful dissec- 

 tions to illustrate the salient characters of the genera and 

 more important species. This concluding volume of Mr. 



