134 Prof. J. A. Ewing. On Measurements of small [May 10, 



modulus so far as very small strains are concerned is scarcely 

 changed. But if the modulus be calculated by reference to the effects 

 of higher loads, it will be much smaller in the overstrained bar. 

 This has been noticed by Bauschinger, who has also observed the 

 tendency, illustrated in tests to be described below, which iron and 

 steel show to recover their elasticity with the lapse of time, after 

 overstrain has taken place.* 



On resuming the above experiment, 45 minutes after the previous 

 load had been removed, the influence of the overstrain was still 

 conspicuous. 



Load in tons. Extensometer. Difference per ton. 



208 



1 304 96 



2 402 98 



3 501 99 



4 602 101 



5 708 (106) 

 710 After 20 seconds. 108 



6 833 



850 After 1 minute. 

 244 



240 After 1 minute. 



The bar was then taken out of the testing machine and left to itself 

 for 5 days. On the fifth day the following readings were taken ; they 

 show in a striking way the effect of this interval of rest : 



(3c.) Same piece after resting for 5 days. 

 Load in tons. Extensometer. Difference per ton. 



200 



1 296 96 



2 392 96 



3 490 98 



4 588 98 



5 685 97 



6 782 97 

 200 

 6 782 



200 



* See also a paper by the present writer (" On certain Effects of Stress," ' Hoy. 

 Soc. Proc.,' No. 205, 1880), which gives instances of the rise of the yield-point 

 with lapse of time, a phenomenon evidently having a close relation to the rise of 

 the modulus. 



