J. 0. Thompson — Laiu of Elastic Lengthening. 49 



of india rubber has been observed by Miller* These facts 

 and the results of my experiments justify the conclusion that 

 in every case the modulus of elasticity of a body is a function 

 of the molecular distance, and that every agency, whether it be 

 heat or mechanical force, which increases this molecular dis- 

 tance, produces a diminution of the modulus of elasticity. 



This relation which is enunciated here for the first time as a 

 general law has, as far as I am aware, no exception which can- 

 not be explained by the necessary errors of observation. 



It is interesting to notice that in many instances the theory 

 of probabilities is able to deduce from the measurements of 

 Wertheim results similar to mine. The following values for 

 the moduli of pure gold (Wertheim, 1. c. p. 30), and pure 

 silver (p. 45) show on their face an evident diminution as the 

 stretching weight increases. 



rg- 



gold. 



silver. 



3 



7030 





4 



6391 





5 



5021 



7701 



6 



5492 



7578 



7 



5340 



6476 



8 



5291 



7555 



9 



4972 



7213 







5140 



7123 



In other cases, for instance in the measurements made with 

 copper (p. 35) and silver (p. 31) where consecutive values of 

 the modulus differ by as much as 10 per cent it is necessary to 

 apply the theory of probabilities. 



In the previously mentioned measurements with annealed 

 platinum the opposite tendency can probably be explained by 

 curvature of the wire. 



"Whether in the method of flexure it is possible to detect a 

 dependence of the modulus on the amount of the load I have 

 not had time to investigate. Since however the compression 

 on one side of the neutral layer is equal to the extension on 

 the other, and consequently the density remains either exactly 

 or very nearly the same, it is probable that in this case no 

 change in the modulus of elasticity could be observed. 



A number of relations and applications of this true law of 

 elastic lengthening to other physical laws, and other phenomena 

 observed in the course of my experiments, I shall discuss at 

 some future time. 



* Miller, 1. c. 



Am. Jour. Sci. — Third Series, Yol. XLIII, No. 253.— January, 1892. 

 4 



