Notices respecting New Books, 467 



until it is sufficient to produce a change of state, so that it is 

 not taken in at one particular temperature, as occurs in the case 

 of allotropic phosphorus, but throughout a long range. If we 

 could define the point where the change referred to takes place, 

 we might, by keeping carbon near this temperature, change it 

 partially into diamond. But all these questions must remain 

 without any decisive answer until we know with certainty the 

 heat of combustion of graphite and diamond. 



LVI. Notices respecting New Books, 



The Strains in Trusses computed by means of diagrams : with twenty 

 examples drawn to scale. By Francis A. Ranken, M.A., C.E., 

 Lecturer at the Hartley Institution, Southampton, formerly Assistant 

 Engineer on the Cambrian Railways, S^c. London : Longmans, 

 Green, and Co. 1872. (Pp. 64, 8vo.) 

 n^HE object of this work is to illustrate, by a variety of examples, 

 ■*- the solution of the following problem : — Given that a number of 

 points in one plane are joined two and two by straight lines in such 

 a way as to form a rigid system, and that forces act in the same 

 plane at these points in such a way as to hold the system in equili- 

 brium, to determine the forces transmitted along the lines, and 

 whether they tend to stretch or compress them severally. It is 

 scarcely necessary to add that this is the question presented for solu- 

 tion when trussed roofs are designed and all considerations of trans- 

 verse strain are put on one side. The book consists mainly of ex- 

 amples ; and the solutions are effected entirely by means of the tri- 

 angle and polygon of forces, without calculation, merely by means of 

 a construction made with scale and compasses. The general ques- 

 tion is one which lends itself very readily to the method of solution 

 adopted ; and though in some rtises, where the truss is of a compli- 

 cated form, the diagram giving the solution is intricate, yet the 

 result is obtained by very simple means, and does away with the 

 need of a most laborious though not otherwise difficult calculation. 

 The number of cases actually solved is very considerable ; in fact 

 all the ordinary forms of trusses are discussed, and the diagrams 

 which yield the solution drawn carefully to scale. 



The book will doubtless prove useful to students of Engineering, 

 and might be studied with advantage by all who are going through 

 a course of Theoretical Mechanics. While fully recognizing the 

 great care that has been bestowed upon the diagrams, we may 

 perhaps add that it would have been of service to beginners if Mr. 

 Ranken had shown (say in one diagram) all the forces which actu- 

 ally keep each joint in ecjuilibrium. To have done this throughout 

 the book would have made the diagrams unnecessarily complicated ; 

 but it might have been done, for instance, in the diagram on p. 18, 

 and would have helped the student to understand the action of the 

 forces in this and other cases. When several forces are shown, a 

 beginner is very apt to think that they are all he is concerned with. 



2H2 



