Bartow—A Mechanical Cause of Homogeneity of Crystals. 675 
siderable space, a number of similar but not continuous assemblages 
variously orientated and in a state of fluctuation, but every portion 
of which now and again becomes very homogeneous indeed, and 
these fractional assemblages may consist either of unlinked balls 
(or mutually-repellent particles) or of groups, or partly of each. 
And where the arrangement of the constituents is thus fluctua- 
ting about an ideally symmetrical one, it is evident that some of 
the properties of the ideal arrangement will be wanting, while 
others will be present—those relating to orientation, which depend 
on extensive continuity of a single homogeneous assemblage, will 
not be traceable, while those which depend on local symmetry or 
configuration of the groups apart from orientation, or on mere 
evenness of distribution, will display themselves. 
If no change of state’ occurs to stereotype the arrangement 
reached in the homogeneous condition which from time to time 
recurs in the different parts of the mass, the making and unmak- 
ing of this highly symmetrical disposition may go on continually, 
wherever the materials for it are present; without leaving any 
permanent trace beyond the achievement, where the conditions are 
uniform, of a practically uniform intermixture of the different 
balls, or mutually-repellent particles, or groups, in more or less 
definite average proportions. 
A fluctuating mass, such as is here conceived, will not, however, 
owing to the many irregularities produced by the disturbances, 
attain as a whole the definite combining proportions found in a 
tranquil homogeneous assemblage, but if the particular homogeneous 
arrangement thus momentarily and locally brought about 1s one at 
which a linking together of previously unlinked balls or mutually- 
repellent particles occurs, and this change of state does not occur 
where the regularity falls short of this, the mass may, at least 
partially, notwithstanding the disturbances, pass by degrees, as 
here and there the requisite arrangement is produced, into a new 
permanent combination of a definite symmetrical character. 
A simple assemblage may undergo a change of state analogous 
to that here attributed to a compound assemblage. For suppose 
that a number of grouplets, all of the same kind, are momentarily 
1 This investigation does not explain, but merely premises change of state. 
Compare note 2, p. 687. 
