1911-12.] Effect of Vibration upon the Structure of Alloys. 319 
years of quiescence. No change in the structure of any of the specimens 
during the latter period could be detected. Hence, even if distortion did 
facilitate growth during vibration, the conclusion that the chief factor in 
the change was the vibration itself is not invalidated. The atmospheric 
temperature during the period of vibration varied between 50° and 70° F. 
(10° and 21° C.), but the limits may have been somewhat wider during the 
succeeding three years. As regards the heat developed during rotation, 
the rise of temperature shown by an ordinary thermometer after the 
tumbling box had run for several hours was less than 1° F. ; it follows 
from this that any local rise of temperature at a point just receiving a blow 
must have been small. It was clearly impossible to make any measure- 
ment of local heating, but, with a weight of less than ^ lb. falling 
through a height of about 6 inches, a local rise of more than 10° C. is 
extremely unlikely. 
The preliminary experiments, therefore, without being regarded as in 
any way conclusive, may be held to indicate a change in the structure of 
chill cast gun-metal under the influence of vibration. If this be really the 
case, the remarkable result is the growth of inhomogeneous skeletons in 
preference to the formation of a uniform solid solution — a result which 
would show that the forces due to the physical instability are of greater 
effect than those due to lack of chemical equilibrium. So far as can be 
judged from examination of the few specimens available, the apparent 
growth of a crystal grain takes place as the result of a piecemeal change in 
the orientation of surrounding grains — an action which would involve not 
merely the rotation of molecules, but the migration of appreciable masses 
in order that a larger and continuous dark-etching skeleton should be 
formed. It is true that a similar process occurs to some extent during 
annealing, though this aspect of the matter does not appear to have been 
remarked hitherto ; the change in the direction of chemical uniformity is 
more marked in annealing, but the increase of crystal size proceeds whether 
the aggregates are homogeneous or not. 
For most of the apparatus used in preparing and examining the speci- 
mens the author is indebted to the Earl of Moray Endowment of the 
University of Edinburgh. 
