222 Proceedings of the Koval Society of Edinburgh. [Sess. 
it will be noticed that the induction changes become more rapid the higher 
the compression, but that this becomes less and less pronounced as the 
current is increased. This is shown by the decrease in the slopes of the 
curves on proceeding from IV to I. 
The same thing is noticeable in the curves of fig. 7, but here another 
feature requires to be noted. After compressing to 40 tons per square 
inch, and the induction curve obtained, it was noticed that this curve had 
higher inductions in the initial stages than the curve obtained after a 
compression of 35 tons per square inch. In other words, the curves crossed, 
this occurring at a current of 3'5 amperes. After 45 tons per square 
inch, this efiect was still present but to a lesser degree, the two curves 
crossing at a current of 2'85 amperes. Then at 50 tons per square inch 
the effect was absent. The result of this is shown in the curves of fig. 7. 
From these it would seem that the irregularity of the curves becomes less 
at the high currents. This would seem to indicate that some change of 
structure is taking place in the metal which can be observed at the low- 
current values, but which becomes masked by the effect of the higher 
currents. 
It will be seen from the figures given in Tables II and III for the 
dimensions of the pieces after the various compressions that the deforma- 
tions are fairly regular. The cross-sectional area of the pieces in all cases 
is practically constant, as obtained from the product of the two dimensions. 
It will be noticed also that the deformations increase as the load increases. 
The reason for this is as follows. At all the compression values, when the 
particular load had been applied to the test piece, it was necessary to wait 
until the pointer on the compression machine became steady, i.e. until 
plastic flow of the material had stopped. At the higher values 45 and 50 
tons per square inch this plastic flow lasted quite an appreciable time, and 
this accounts for the increase of deformation with increment of load. In 
other words, the higher the load, the longer the duration of the period of 
plastic flow. 
In figs. 8 and 9 the curves are shown giving the relationship between 
induction and deformation. The same remarks apply here as in the case 
of the curves in figs. 6 and 7 showing the relationship between induction 
and load. Here the irregularity before referred to is still more pronounced. 
Generally speaking, increase of deformation decreases the induction except 
at the points previously indicated. It may be stated here that there is 
very slight probability of this irregularity being due to any errors of 
observation. All the induction curves were obtained from at least four 
separate series of figures, in some cases six, and in no case was there any 
