1881.] The Influence of Stress and Strain. Sfc. 



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April 28, 1881. 



THE PRESIDENT in the Chair. 



The Presents received were laid on the table and thanks ordered for 

 them. 



The following Papers were read : — 



I. " The Influence of Stress and Strain on the Action of 

 Physical Forces." By Herbert Tomlinson. B.A. Com- 

 municated by Professor W. GrRYLLS Adams, M.A., F.R.S. 

 Received April 5, 1881. 



(Abstract.) 



Part I. — Elasticity. 



" Young's Modulus." 



The values of " Young's modulus " were determined for several 

 metals by a method devised by Sir W. Thomson. According to this 

 method wires of the same material and diameter are suspended in 

 pairs about an inch apart from each other, and are attached by one 

 extremity of each to the same support ; the other extremities being 

 fastened in the one case to a scale-pan, and in the other to the centre 

 of a bar of wood or metal carrying constant equal weights at each 

 end : the latter wire is provided with a scale and the former with an 

 index of some sort, which being level with and close to the scale, serves 

 to measure any alteration of length produced by weights placed in the 

 pan. 



In these particular experiments the wires were about thirty feet in 

 length ; a scale divided into half-millimetres and a vernier reading to 

 aijth of a millimetre attached respectively to the two wires, served to 

 measure the temporary alterations of length produced by loading or 

 unloading. The vernier was forked so that, though capable of free 

 up and down motion, it could not readily be dislodged sideways, and 

 by using a compound microscope an alteration = ytroth of a millimetre 

 in the length of the wire could be estimated. 



A large number of experiments with different loads were made, 

 and after a great many unsuccessful attempts to account for certain 

 discrepancies which could not be explained away as errors of observa- 

 tion, the following facts were elicited : — 



(1.) After a wire has suffered permanent extension, the temporary 

 elongation which can be produced by any load becomes less as the 



