April 7, 1899.] 



SCIENCE. 



515 



The Elements of Graphic Statics. By L. M. Hos- 



KiNs, Professor of Applied Mechanics in the 



Lelaud Stanford Jr. University. New York, 



The Macmillau Company. 1S99. Revised 



Edition. Pp. viii + 199, and eight plates. 



The character of works under the head of 



Graphical Statics varies between that extreme 



of which Cremona's treatise may be regarded as 



typical, in which the name can be regarded as 



scarcel5'' more than a peg on which to hang a 



large amount of theoretical projective-geometry 



matter, and the opposite extreme, where we 



may place the work before us, characterized, 



as it is, by intense practicality and general 



avoidance of everything of merely theoretic or 



historic interest. The favorable impression 



made upon one by the mechanical excellence 



of Professor Hoskins' book is further confirmed 



by a careful examination of the text. 



Avoiding the error of Culmanu in presuppos- 

 ing too much information on the part of his 

 students as to projective relations and graphic 

 methods, the author lays his own foundation on 

 which to build, treating the subject more, how- 

 ever, as a branch of mechanics than of geometry. 

 To this his Part I. is devoted, and it would seem 

 impossible to set forth the fundamentals more 

 clearljr and concisely than in the fifty pages de- 

 voted thereto. 



Familiarity with analytics and the calculus 

 is assumed for the remainder of the work. 

 Bow's convenient system of notation is em- 

 ployed throughout. 



Excluding entirely from the book any con- 

 sideration of structures whose discussion in- 

 volves the theory of elasticity, the hundred 

 pages constituting Part II. are devoted to the 

 usual problems of beams and of bridge and roof 

 trusses. We have not at hand a copy of the 

 original edition for comparison with the 

 revision, but as Professor Hoskins' preface in- 

 dicates that the principal changes are in this 

 section we state them in this connection in his 

 own words: "In the present revised edition 

 no change has been made in general plan, and 

 few changes in the treatment adopted, except 

 in the portions relating to beams and trusses 

 carrying moving loads. These portions have 

 been wholly re-written. It is believed that a 

 substantial improvement has been made upon 



the methods hitherto used, particularly in the 

 criterion for determining the position of a given 

 load-series which causes maximum stress in any 

 member of a truss. The improvement consists 

 in generalization, which is believed to be gained 

 without sacrifice of simplicity. The gra^jhical 

 method of applying the criterion in the case of 

 trusses with parallel chords has been fully 

 treated by Professor H. T. Eddy. The method 

 here given applies without the restriction to 

 parallel chords. The algebraic statement of 

 the same criterion, as given in Art. 152, is also 

 believed to be a useful generalization of the 

 methods hitherto used. Whether the algebraic 

 or the graphical treatment is preferred, a method 

 is useful in proportion to its generality, pro- 

 vided this does not involve a loss of simplicity. 

 There is a decided advantage in the use of a 

 single general equation applicable to any mem- 

 ber of any truss, instead of several particular 

 equations, each applicable to a special rnember 

 or to a special form of truss." That this general- 

 ization will be cordially welcomed and availed 

 of by the profession may safely be predicted. 



Part III. gives graphic methods of determin- 

 ing centers of gravity and the moments of in- 

 ertia of plane areas, with a discussion of inertia- 

 curves, carried as far as the practical engineer 

 will ordinarily need. Eight clear, double-page 

 plates complete the work, and one's only re- 

 gret in viewing them is that they cannot face 

 the text describing them, to the saving of the 

 student's time and temper. 



We notice that the author uses a term, 

 ' complanar ' (whether he suggests it or not is 

 not evident), Avhich we trust will not supplant 

 the generally accepted 'con-plane,' which is con- 

 sistent with the other equally self-explanatory 

 terms con-focal, con axial, etc., and needs no 

 modification. 



The book is a thoroughly good one preem- 

 inently for the class-room, and a course in it 

 should be a pleasure alike to pupil and in- 

 structor. Fred'k N. Willson. 



Princeton University. 



GENERAL. 



Professor Martin's books on The Human 

 Body are in many ways models in the presenta- 



