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LXIII, 
ARRANGEMENT OF THE CRYSTALS OF CERTAIN 
SUBSTANCES ON SOLIDIFICATION. By FRED. T. 
TROUTON, D.Sc., F.R.S. 
[Read NovemBer 17; Received for Publication NovemBer 19; 
Published January 31, 1898.] 
In the case of certain substances, an arrangement of the crystals on 
solidification would appear probable from the following conside- 
rations :— 
The substances are those whose conductivity for heat varies 
with the direction the heat is travelling in the crystal. 
Suppose a mass of the molten substance beginning to solidify 
in consequence of heat escaping through its boundary, crystals 
will begin to form at the boundary. The axes of these incipient 
erystals may, in the first instance, lie equally in every direction. 
However, those crystals whose axes of best conductivity lie parallel 
to the flow of heat will now allow heat to pass out faster than 
those in any other direction, and, consequently, at these points 
more rapid solidification will take place than elsewhere. 
Now it would appear to be a justifiable assumption to make, 
that this solidifying matter will, in general, add itself to these parti- 
cular crystals, or at least take up sensibly the same axial direction 
through the well recognized tendency of substances, on crystal- 
lizing, to follow any example ready to hand. If this be so, those 
crystals with their best conducting axes normal to the isothermal 
surfaces, or surfaces across which the heat is flowing, will grow the 
fastest by a kind of “survival of the fittest”; and under suitable 
conditions an arrangement of the crystals may prevail with the 
axes lying parallel. Such an arrangement of a mass crystallised 
from fusion is often to be observed on fracture. 
Though the relative conductivities, in different directions, of a 
SCIEN. PROC. R.D.S., VOL. VIII., PART VI. 3E 
