Bartow—A Mechanical Cause of Homogeneity of Crystals. 581 
which, since crystals are homogeneous structures,’ resembles that 
arranging of the ultimate parts of a body, and stereotyping of the 
arrangement, which constitute crystallization. 
IT.—Partial dissolution in a symmetrical manner of the ties 
which attach the parts of a linked assemblage, and subsequent 
partial destruction of the homogeneity, so that the assemblage 
breaks up into groups in each of which the parts are symmetrically 
placed with respect to one another, while the arrangement of the 
groups has become irregular, the groups thus resembling the 
theoretical molecules of stereo-chemistry. 
III.—Symmetrical intercalation of homogeneous assemblages 
whose forms are identical or appropriately related, comprising 
formation of twin assemblages, including under this head the 
symmetrical fitting together of enantiomorphous assemblages as 
well as that of identical assemblages; the formation of isomorphous 
assemblages and their intermixture, and the symmetrical inter- 
locking of unlike assemblages. Comparison to crystal-twinning, 
isomorphism, isogonism, and crystalloid structure, also to some 
kinds of diffusion. 
TV.—Interlacing of different kinds of groups or individuals, 
converting a fortuitous assemblage into an assemblage which 
approximates to homogeneity, but does not reach it, because the 
arrangements for closest-packing are not homogeneous ones. 
V.—Combination of two or more homogenous or approximately 
homogeneous assemblages to form a single homogeneous or approxi- 
mately homogeneous assemblage; an effect which, (a) in its most 
perfect form finds a parallel in that highly symmetrical inter- 
mixture of the combining atoms or complexes which must, it is 
evident, accompany or precede a chemical synthesis,’ and which 
1 Homogeneous, that is to say, according to the definition given by the writer in 
his memoir: ‘‘ Ueber die geometrischen Higenschaften homogener starrer Structuren,’’ 
&e. Zeitschrift fiir Krystallographie, &c., 28, p. 1. 
Comp. Mineralogical Maz., vol. xi., p..120; or Zeitschr. fiir Kryst. 27, p. 450. 
* This effect is very closely related to that defined in I.; indeed these two effects 
may be said to overlap. Under head I., however, the salient point before us is the 
symmetry of arrangement which succeeds a more or less chaotic state, while under 
head V. it is the uniform intermingling of. different kinds of particles or elements in 
precise proportions which claims our attention. The latter condition is a result of the 
former which may survive the symmetry to which it owes its origin; it may exist 
continuously while the symmetry productive of it is intermittent and fluctuating. 
