366 Scientific Intelligence—Mineralogy. 
and equality of distance preside at the aggregation of layers which 
compose the solid mass. It results from this, that the crystal is 
identical to itself throughout, and that any given particle affects in 
space, and in relation to the neighbouring particles, the same direc- 
tion and the same relations as every other particle in every part of 
the mass. This regularity of interior structure is generally exhi- 
bited on the exterior by characteristic forms, which the practised 
eye can always detect. Varied as they may be, these forms may be 
reduced to a small number of species, which are called the erystal- 
line system, and in which are naturally classed all real and possible 
crystals. Competent judges think nothing is more likely to reveal 
the existence of the elementary particle than the phenomenon of 
crystallization; for if the particle does not exist in the same form 
as that of the smallest sensible crystal, the last particles whose in- 
tegrity seems necessary to the maintenance of the properties of the 
body must have particular and fixed directions, Be this as it 
may, we shall (perhaps) never see the particle itself; but this in 
no way lessens the interest of the phenomena connected with the 
mysterious operation of their free aggregation. It is to this point 
M. Lavalle’s experiments were made. Among a good many curious 
experiments, M. Lavalle took a crystal of alum, a perfect octeed ; he 
destroyed one of the six summits, and so made a square face, parallel 
to one of the faces of the corresponding cube; then, placing it upon 
this face, he abandoned it in the bottom of a box, containing a satu- 
rated solution; the crystal increased as usual, with perhaps what 
may be called the exception, that a face exactly like the square face 
on which it stood, was spontaneously produced on the opposite sum- 
mit. Thus was confirmed by a striking example,—that great law of 
symmetry, which, in natural crystals, always opposes symmetrical 
faces. Another of his experiments was cutting away the angular 
edges of a crystal and the faces, so as to destroy completely all traces 
of its original form. But it must not be supposed that this will 
destroy its original nature; its structure will still remain; the ex- 
perimenter has but to replunge it into the dissolution where it was 
formed, to see it complete itself, and cover again its angles and 
faces. It may happen, however, that this sort of restoration pro- 
ceeds too rapidly, and that numerous small crystals shoot on the 
surface of the altered crystal. This gives a new piece of informa- 
tion; for all these small crystals have a common direction, which 
coincides with that of the mass from which they spring,—thus de- 
monstrating the constancy of structure and the identity of the par- 
ticles of which it is composed. We need not be astonished, then, 
that if a fragment of a crystal in process of formation be broken off, 
this loss will be promptly repaired. Nay, it is further seen, that, 
if a crystal is broken into fragments, each fragment soon reproduces 
in the saturated water an entire crystal, imitating in this respect 
that marvel of organization which, of one polypus, divided into 
