S/H WILLIAM SIEMENS, F.R.S. 



315 



In the discussion of the Paper 



" ON THE PRESENT STATE OF KNOWLEDGE AS TO 

 THE STRENGTH AND RESISTANCE OF MATE- 

 RIALS," by JULES GAUDARD, Civil Engineer, Lausanne, 



[Translated from the French by WILLIAM POLE, F.R.S., M. last. C.E.] 



MR. C. W. SIEMENS * observed that the author of the paper 

 appeared to base all his calculations, which were very elaborate 

 and valuable in themselves, upon the breaking strain of materials. 

 He thought, for practical information, it would be necessary to 

 follow out a similar investigation, carried only to the limit of 

 elasticity, which the author had entirely ignored. If the limit of 

 elasticity of all materials was proportionate to the breaking strain, 

 the one investigation would cover the two cases ; but materials 

 ditfered greatly in this respect. The ultimate strength and flexi- 

 bility of a metal, such as would be conformable to the calculations 

 of the author, as for instance, lead, was, in its property of yield- 

 ing to moderate force, very different to iron, and in a still greater 

 measure to steel. Steel would yield, within the limit of elasticity, 

 up to a much higher point than, he believed, any other metal. In 

 devising engineering works it was of the utmost importance to 

 know, not merely when a structure would give way, but when any 

 destructive action would commence. 



In dealing with transverse strain, the author illustrated the 

 case by a figure, signifying the strain on every fibre in the beam. 

 That figure was perfectly correct for breaking strains, where the 

 fibres first permanently elongated by the strain brought the next 

 into greater tension, and so on in succession, till the limit was 

 reached where the outer fibres would actually break. But before 

 such a diagram of resisting forces could be true, permanent deflec- 

 tion must have taken place ; and it was of importance to engineers 

 to know what was the distribution of strains before any perma- 

 nent effect had been produced ; and within those limits he main- 



* Excerpt Minutes of Proceedings of the Institution of Civil Engineers, Vol. 

 XXVIII. Session 18o'9-lS70, pp. 32-34. 



