clxxx GENERAL SUMMARY OF SCIENTIFIC AND 



test piece, when the unexpected discovery was made that the 

 resisting power of the specimen had actually become greater 

 during the period of rest under strain, and the pencil of the 

 register, instead of descending, rose until it indicated an in- 

 crease of about twenty per cent, in the strength of the 

 sample, when it traced a path parallel with, but above, that 

 of the previous day. This remarkable observation was con- 

 firmed by repeated experiments. The phenomenon here dis- 

 covered is the elevation of the limit of elasticity by a con- 

 tinued strain. Professor Thurston at once communicated 

 his discovery to the American Society of Civil Engineers, 

 in whose Transactions and the Journal of the Franklin Insti- 

 tute it appeared simultaneously shortly afterward. By one 

 of those coincidences that are of such frequent occurrence in 

 the annals of scientific discovery, where many independent 

 observers are experimenting in the same field of investigation, 

 Commander Beardslee, IT. S. N., in experimenting upon the 

 tensile strength of iron left under stress, made precisely the 

 same discovery, without the knowledge that it had but a 

 short time previously been published by Professor Thurston. 

 The interesting feature of this independent observation, how- 

 ever, resides in the fact that it was made by a perfectly dis- 

 tinct method and apparatus. Professor Thurston's experi- 

 ments were made with his "Autographic Testing Machine," 

 and those of Commander Beardslee upon the ordinary form 

 of Tensile Lever Machine. In the memorandum of Com- 

 mander Beardslee containing his first publication on the sub- 

 ject, the test piece (bloom iron turned approximately to one- 

 half square-inch section) exhibited a gain of resistance at a 

 position of earliest set, i. e., an elevation of the elastic limit, 

 from 23,075 to 26,100 pounds per square inch, or 13.1 per 

 cent, in seventeen hours. Continuing these experiments by 

 direction of the Navy Department, Commander Beardslee 

 made the further discovery that metal (iron) which had been 

 submitted to strain until it had taken a set, and then removed 

 entirely from the machine and laid aside for intervals of va- 

 rious lengths, when again replaced under strain increased in 

 power of resistance as in the first instance. 



The important fact therefore is established by these inves- 

 tigations that metal strained so far as to take on a permanent 

 set gains in power of resistance within certain limits of time 



