512 



Prof. A. Ewing. 



[June 10, 



the effect when the same stress (35 kilos.) was maintained constant 

 for 5 minntes only. I have also obtained diagrams showing the effect 

 of keeping a load of 35 kilos, on wires for 2 minutes, 10 minutes, 



Fig. 3. 



Showing effect of maintaining a stress of 35 kilogrammes constant for 5 minutes. 



30 minutes, 1 hour, 3 hours, and 141 hours. In all these cases the 

 hardening effect is greater for greater lengths of time, but the increase 

 of the effect is much more rapid at first than it is later. A curve 

 showing the relation of the hardening effect (measured by the length 

 of the straight line in the diagram after the stress has been kept con- 

 stant, and before the wire begins to stretch again) to the time rises 

 rapidly at first, but afterwards becomes nearly parallel to the line along 

 which time is measured. 



Fig. 4. 



Showing effect of removing the load when it reached 35 kilogrammes and replacing 

 it after 19| hours, during which the wire was free from stress. 



An interval of constant stress of even five seconds produces a per- 



