HARDENED BY OVERSTRAIN. 
31 
The specimen whose history is given by Diagram 8 was ultimately heated to 
800° C., and Curve 18 was obtained. The successive overstrains illustrated Ijy 
Curves 19, 20, 21, and 22 were then apjdied, and the material was left in a 
condition of hardness, the tempering from whicli could be made the sul)ject of further 
investigation. 
In conclusion, it may be stated that many experiments other than those described 
above were performed during the course of tliis researcli. The preliminary experi¬ 
ments, which showed qualitatively the tempering of iron hardened by tensile over¬ 
strain, were performed in the Engineering Laboratory of the Uiiiversity of Glasgow, 
Professor Barr having kindly placed his laboratory and all necessary apparatus at 
the author’s disposal. All the experiments described in this paper were carried out 
in the Engineering Laboratory of the University of Cambridge, and the author 
desires to express his indebtedness to Professor Ewing for suggestions and advice 
given from time to time as the work was in progress. 
