240 OX THE EFFECTS OF STRAIN OX THE CRYSTALLINE STRUCTURE OF LE.YD. 
explanation in both cases. To quote from ErviXG and Eosexhaix’s paper : “ When 
a metal solidifies from the licpiid state it does so by the formation of skeleton crystals 
starting from a great number of centres, and the arms of these skeletons continue to 
grow until arrested by meeting with other growths. From these arms other arms 
again shoot out, and so on until the entire metal is solidified; but each crystalline 
element as it settles into place on any of these arms must assume the proper orientation 
to enable it to fit in, and in the process of filling space by lueans of such a system of 
many meeting and interlacing arms the formation of a twin would be almost 
impossible. But when the metal crystallises after severe strain it does so by the 
growth of skeleton arms that must often start from a cleavage plane of an actual 
solid crystal, and probably the new elements deposited upon such a plane would find 
it as easy to assume the twin orientation as the normal.” 
In the present case it is exceedingly probable that practically all the jratches of new 
orientation start from a cleavage plane, and hence the formation of twin crystals 
won Id be exceedingly comm on, as in fact it is. 
In conclusion, the autlior would like to express his thanks to Professor Ewix’G for 
the great help and many suggestions which he has given. The research has been 
carried out, under his direction, in the Engineering Laboratory at Cambridge. 
