1873-] Notices of Books. 255 



The investigation of transverse strains may be reduced to the 

 three following fundamental laws in mechanics, viz., the resolu- 

 tion of forces, the law of the lever, and the equality of mo- 

 ments, upon which are founded all the investigations given of 

 the strength of materials when subject to transverse strain. 



After an introductory chapter, our author enters upon a con- 

 sideration of the circumstances of flanged girders with braced or 

 thin continuous webs, when subjected to six different conditions 

 of weight or strain. In this part of the work the formulas inves- 

 tigated refer to transverse strains only, the horizontal strains in 

 braced or thin continuous webs being so inconsiderable that they 

 may be practically neglected. All girders have what is called a 

 neutral surface and a neutral axis, the former being that surface 

 along which the resultant of the horizontal components of all 

 the diagonal forces equal cipher, and the latter the line of de- 

 marcation between the horizontal elastic forces of tension and 

 compression exerted by the fibres in that particular section of 

 the girder. The sum of the moments of the horizontal elastic 

 forces in any transverse section round any point whatsoever is 

 the moment of resistance of that particular section, or, as it is 

 also called, the moment of rupture. The coefficient of rupture 

 varies, of course, with different materials, and, in order to enable 

 the formulas given on the above subject to be the better applied, 

 a table of coefficients is given. 



As the result of several investigations, it is laid down as a rule 

 that the strength of similar girders varies as the square of their 

 lineal dimensions, but the weight of the girder itself varies as 

 the cube of its lineal dimensions. 



Space will not admit of our following Mr. Stoney's book in 

 such detail as the interest of the subject would otherwise justify. 

 The calculations given respecting one class of girders are con- 

 tinued to girders of various sections, to girders with parallel 

 flanges but having webs formed of various-shaped bracings, to 

 girders with oblique or curved flanges, &c. The chapter on 

 " Deflection of Girders " is an important one, showing, as it 

 does, that girders of uniform section throughout are often de- 

 fective from a scientific point of view. In all properly constructed 

 girders each part is duly proportioned to the maximum strain 

 which can pass through it, so that no material is wasted ; and 

 when this occurs in a girder with horizontal flanges and a 

 uniformly distributed load, that is, the load which produces the 

 maximum strain in the flanges, these latter will taper from the 

 centre, where their section is greatest, towards the ends as the 

 ordinates of a parabola. 



Having considered and given rules for the quantity of mate- 

 rials, and the angle of economy for braced girders, there follow 

 chapters on torsion, the crushing strength of materials, and rules 

 for the strength of pillars, whether circular or braced. These, of 

 course, have reference to the construction of piers and abut- 



