316 
Proceedings of the Koyal Society of Edinburgh. [Sess. 
In the light of later knowledge the older observations, of little value 
individually, when taken collectively give ground for supposing that 
vibration favours an increase in the size of metallic crystals, so that a piece 
after long-continued vibration may be expected to have a coarser structure 
than it possessed originally. This is no matter for surprise, for in a body 
not in a state of perfect internal equilibrium any molecular agitation tends 
in the direction of equilibrium. With a pure metal, not subject to 
allotropic change, there can be no lack of chemical equilibrium, and there 
is only the physical instability of crystal size upon which the effect of 
vibration may be manifested. Experience strongly suggests that in any 
mass of uniform metal there is a tendency for all the crystals to assume 
a parallel orientation — that is, to become a single crystal. In ordinary 
circumstances there is sufficient resistance to prevent the accomplishment 
of such a rearrangement, even when a practically unlimited time is available, 
but every shock to which the piece is subjected, by producing a momentary 
reduction of the resistance, may allow of some slight rearrangement. 
The general effect of vibration in increasing the scale of the structure 
of a metal being considered, though not proved, as highly probable, it 
seemed useful to the writer to investigate, in a preliminary manner, the 
effect upon alloys in which there was a chemical, or physico-chemical, as 
well as a purely physical instability, so as to determine whether an 
appreciable change of structure could take place in a reasonable time for 
experiment. To this end a bar of gun-metal, containing 90 per cent, of 
