318 ANNUAL OP SCIENTIFIC DISCOVERY. 



assembly of parallel and equi-distant files, so also parallelism and 

 equality of distance preside at the aggregation of layers which com- 

 pose 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 neighboring particles, the same direction and the same 

 relations as every other particle in every part of the mass. This reg- 

 ularity of interior structure is generally exhibited 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 num- 

 ber of species, which are called the crystalline 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 integrity seems necessary to the maintenance 

 of the properties of the body, must have particular and fixed direc- 

 tions. Be this as it may, we shall (perhaps) never see the particle 

 itself; but this in no way lessens the interest of the phenomena con- 

 nected 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 an alum crystal, a perfect 

 octaed ; 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 vase, 

 containing a saturated 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 summit. Thus w T as 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 

 augular 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 

 experimenter has but to re-plunge 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 proceeds too 

 rapidly, and that numerous small crystals shoot on the surface of the 

 altered crystal. This gives a new piece of information ; for all these 

 small crystals have a common direction, which coincides with that of 

 the mass from which they spring thus demonstrating the constancy 

 of structure and the identity of the particles 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 several parts, makes in a few days so many 

 entire polypi- Curious phenomena are produced when a crystal is 

 transferred from one solution to another. 



