550 Prof. Trouton and Mr. Rankine: Stretching and 
Rate of Disappearance of Primary Recovery under Constant 
Strain. 
Fig. 8 shows the primary recovery at different times, the 
wire in the intervals being maintained at constant length. 
Fig. 8.—Constant Length. 
Dotted lines show the cmmrmealale recovery at tre lim 
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No great aceuracy could be expected since the loading and 
P=) d 
unloading could not be performed very quickly, for a reading 
had to be taken in the meantime. it will be seen, however, 
that the curve of recoveries is of the same type as the 
decrease of load curve, indicating that the behaviour of the 
wire follows a modified Hooke’s Law, 7. e. the primary re- 
covery at any time is proportional to the weight then on. 
The second part of the curve shows the rate of recovery on 
the final removal of the whole load. 
Arrangement for automatically keeping an Overstressed 
Wire at Constant Length. 
In order to discover whether it is necessary to remove the 
whole load from a wire kept at constant length within a 
finite time (which would be the case if the empirical equation 
given before were true), and at the same time to remove the 
weight more accurately than could be done by hand, a 
method was devised for automatically performing the ex- 
periment. The essence of the method is that contact between 
the wire under test and a plate kept in a constant position 
(except when necessary to compensate for temperature effect) 
electrically opens a valve which removes a small portion of 
the load ; this removal causes the wire to break contact by 
receding a very small distance. The load on the wire 
gradually stretches it again until contact is once more made, 
and this process then repeats itself. 
