236 
MR. J. C. AV. HUMFREY OX THE EFFECTS OF STRAlX 
specimen gets gradually less in each photograpli; this was due to the etching, which 
had to he fairly severe in order to entirely eat away the old pits and exhibit the new 
structure, and which v'as sufficient, when repeated several times, to produce a con¬ 
siderable change in the size of the specimen. 
If we examine this series it will be seen that when once a patch with a new 
orientation is formed, and is surrounded l)y other new ones, it remains practically 
unaltered when subjected to further annealing. There is a sliglit change of outline 
in some cases, but this can be accounted for if we consider that the boundaries need 
not be at right angles to the surface, and will, therefore, change slightly as the etching 
solution eats down to successive depths. The structural change is entirely confined 
to the original orientation, wdiich is gradually split up into numerous different ones, 
and when once these are formed they persist. 
The slight differences of orientation which appear after straining, when the 
specimen is first etched, appear to some extent upon these photographs as bright 
bands across the original orientation. They are, however, far more clearly illustrated 
in the next series. Fig. 20 shows the crystal after straining in tension and re-etching 
mao’nified 5 diameters. It exhibited no sioms of re-crvstallisation before annealing, 
but the “ strain hands ” (as they may be called) were particularly well developed 
and can he clearly seen in the photograph. Fig. 21 shows the same specimen after 
annealing for 20 minutes at 100° C. It is evident that the strain bands have no 
influence on the re-crystallisation, but are swallowed up in an exactly similar manner 
as the original orientation. A remarkably fine develoj^ment of etched pits was 
obtained on this specimen, and these are clearly visible even under the low magnifi¬ 
cation at wliich the photographs were taken. 
The next experiment was to see whether any change took place in a strained 
crystal of lead at atmospheric temperatures. The specimen was strained in tension, 
and is shown (magnified to 4 diameters) in fig. 22 after this straining and re-etching. 
The stress liad been applied until local contraction had commenced, and the strain 
thus produced was sufficient to cause a certain amount of re-crystallisation to be 
visible immediately upon re-etching. The band of patches of new orientations 
can he seen running diagonally across the specimen at one end. The photograph 
reproduced in fig. 23 was taken from the same specimen after three weeks. The 
specimen was kept in a small glass jar, and was simply subjected to the slightly 
varying temperature of the room. In fig. 23 it will be seen that re-crystallisation 
has continued until nearly the whole of one end has clianged, the band widening out 
in iDoth directions so as to fill in the light-hand bottom corner and extend further 
upwards. 
It is clear from this series tliat, althoiioli a further re-crvstallisation occurs at 
ordinary atmospheric temperature, yet it is much slower than when the temperature 
is slightly increased, as had been the case in the former series. It has been found 
in all cases that the higher the temperature at which the strained piece is kept the 
