SIR WILLIAM SIEMENS, F.R.S. 269 



/,/ tltf (/isriifision of t/w Paper 



"ON THE STRENGTH OF IRON AND STEEL, AND 



ON THE DESIGN OF PARTS OF STRUCTURES 



WHICH CONSIST OF THOSE MATERIALS," 



By GEORGE BERKLEY, M. Inst. C.E. 



MR. C. W. SIEMENS* observed that the paper contained a great 

 deal of valuable practical information ; but he considered enough 

 had not been said, on the one important question which had been 

 raised, viz., whether or not there was a definite limit of elasticity 

 in metals. It was stated in the paper, that a bar of iron 1 inch 

 square would elongate with a strain of 3 tons to the inch, and 

 would, on the load being gradually increased, continue to elongate 

 up to a strain of 9 tons or 10 tons to the inch, beyond which point 

 it was known that a more rapid rate of elongation commenced. 

 These results seemed to imply that there was no definite limit 

 where permanent elongation was produced, but in following up 

 this argument the evident conclusion was, that the bar of metal of 

 1 square inch, if exposed for a great length of time to the moderate 

 strain of 3 tons, must continue to yield, in the same way as though 

 its elastic limit was really exceeded, and must ultimately yield to 

 that force. But all experience went directly against such a suppo- 

 sition. One of the most perfect experiments that could be tried on 

 that point might be found in the old cathedrals of Italy, where 

 heavy chandeliers weighing a ton, or more, had been suspended 

 for hundreds of years, by long rods of not more than f of an inch 

 in diameter. If any permanent injury was produced by such a 

 load, it would no longer be safe to go into these buildings ; and 

 the heavy chandelier in the Pisa cathedral, which swung sug- 

 gestively above the head of Galileo Galilei, must inevitably have 

 long since fallen to the ground. He thought practically that no 

 one had any belief in any such action of time, but he was not 

 disposed, on the other hand, to condemn such experiments as 



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

 XXX. Session 1869-70, pp. 268-209. 



