CRYSTALS

New Zealand Times, Volume XXXIII, Issue 7869, 3 August 1911, Page 8

CRYSTALS

Scattered over the earth’s crust, says “ can be found a number of chemiical substances of definite geometrical i figure, bounded by plane faces, and these polyhedral figures are known as crystals. Superficial examination shows that, roughly, each crystalline substance assumes some specific geometric form, characteristic of .that substance, and closer inspection shows that while the crystals vary in size,' and tho bounding planes in relative area, yet the angles between corresponding pairs of faces on any two crystals of the same substance remain the same. This constancy of interfacial angles among crystals of the same substance is as much a law of nature as gravity, aud to detroraino what is the meaning of this striking peculiarity, and of other extraordinary features that have been, brought to light, by diligent examination, is the object of crystallography. It is a subject of absorbing interest, for not only does the crystal exhibit many of the characteristics we connect with living organisms, such as growth and recuperative power after injury, but the arrangement of the molecules in accordance with a specific architectural plan must be of profound significance in the construction of matter. Yet, continues “ Engineering,” it is a science that has been neglected, or, at least, studied intermittently, notwithstanding tho scope the science oifers for the exercise of experimental ingenuity and the attractiveness of the problems it puts before the physicist, the mathematician, and the chemist. We are _ now passing through a period of activity. There is now- some danger that in the ardour of pursuit siomo of the evidence may bo misinterpreted and some of the deductions prove premature. All crystals can be regarded as structural edifices produced by accretion, in which the arrangement of the parts is uniformly repeated throughout corresponding points having a similar environment, everywhere within the finished edifice. Hence arose a very curious mathematical problem: How many types of homogeneous arrangement of points is it possible to construct in space? There are 230 different points of homogeneous structures, no more and no less. , The whole of these fall naturally into thirty-two classes of crystals, leaving no class unaccounted for.