e salt-petre in water, and allow the solution to
evaporate slowly, you may obtain large crystals, for no portion of the
salt is converted into vapor. The water of our atmosphere is fresh
though it is derived from the salt sea. Sugar dissolved in water, and
permitted to evaporate, yields crystals of sugar-candy. Alum readily
crystallizes in the same way. Flints dissolved, as they sometimes are
in nature, and permitted to crystallize, yield the prisms and pyramids
of rock crystal. Chalk dissolved and crystallized yields Iceland spar.
The diamond is crystallized carbon. All our precious stones, the
ruby, sapphire, beryl, topaz, emerald, are all examples of this
crystallizing power.

[Illustration: SNOW-STAR.]

You have heard of the force of gravitation, and you know that it
consists of an attraction of every particle of matter for every other
particle. You know that planets and moons are held in their orbits by
this attraction. But gravitation is a very simple affair compared to
the force, or rather forces, of crystallization. For here the ultimate
particles of matter, inconceivably small as they are, show themselves
possessed of attractive and repellent poles, by the mutual action of
which the shape and structure of the crystal are determined. In the
solid condition the attracting poles are rigidly locked together; but
if sufficient heat be applied the bond of union is dissolved, and in
the state of fusion the poles are pushed so far asunder as to be
practically out of each other's range. The natural tendency of the
molecules to build themselves together is thus neutralized.

This is the case with water, which as a liquid is to all appearance
formless. When sufficiently cooled the molecules are brought within
the play of the crystallizing force, and they then arrange themselves
in forms of indescribable beauty. When snow is produced in calm air,
the icy particles build themselves into beautiful stellar shapes, each
star possessing six rays. There is no deviation from this type, though
in other respects the appearances of the snow-stars are infinitely
various. In the polar regions these exquisite forms were observed by
Dr. Scoresby, who gave numerous drawings of them. I have observed them
in mid-winter filling the air, and loading the slopes of the Alps. But
in England they are also to be seen, and no words of mine could convey
so vivid an impression of their beauty as the annexed drawings of a
few of them, executed at