———— eee Se 
4 
#44) 
Bartow—A Mechanical Cause of Homogeneity of Orystals. 567 
necessarily one of gradual change from the moment when the first 
indications of orderly arrangement present themselves till the most 
perfect symmetry is achieved. And if the opposing forces, the 
arranging force and the disturbing force which produces fluid 
motions, are subject to any ebb and flow, it is conceivable that 
after some amount of orderly arrangement has been achieved the fluid 
motions, instead of uniformly subverting this symmetry, will merely 
so far break up the partially-arranged mass as to reduce it to frag- 
ments which roll upon and round-off one another; these fragments 
"preserving internally the degree of symmetrical arrangement which 
has been already imposed, and the space between them being 
occupied by less-regularly arranged aggregates of particles of the 
same or of some different composition. 
_ The rounded crystalline grains whose presence in many cases 
marks an intermediate stage of crystallization from solution, and 
which have been called giobulites and crystallites,) may be men- 
tioned in this connection as furnishing a possible parallel to the 
condition just traced, but the composition of the bodies referred 
to is very possibly, in some cases, due to impaired homogeneity, the 
nature of which we are about to consider.” 
Where a homogeneous assemblage in which, under slow change 
of conditions, a very gradual spread of solidification is taking place, 
is continuous, and but little disturbed by outward influences, we 
shall expect the accretion at the growing surfaces to proceed with 
‘much uniformity, and especially that at every surface throughout 
which the conditions are uniform the growth or increase will also 
be uniform. And it is obvious that the extremely regular progress 
of crystallization in continuous masses subject to very uniform 
conditions and very slow change is entirely in harmony with this 
_ expectation. 
Further, if the general conditions change but slowly, consider- 
_ able disturbing movements of the liquid portion of a homogeneous 
assemblage may not prevent the accretion to the solid portion from 
being extremely uniform so Jong as the slowness of the change of 
1 See ‘‘ Die Krystalliten’’ von H. Vogelsang. Bonn, 1874. 
2 See p. 568. Compare Heinrich Vater “‘ Ueber den Einfluss der Lésungsgenossen auf 
die Krystallisation.’? Zeitschr. f. Kryst. 27, p. 477. 
