all built on the same pattern. The same is true of sugar; and if
you will look at the spikes of an ordinary stick of sugar-candy,
such as I have here, you will see the kind of crystals which
sugar forms. You may even pick out such shapes as these
from the common crystallized brown sugar in the sugar basin, or
see them with a magnifying glass on a lump of white sugar.

But it is not only easily melted substances such as sugar and
salt which form crystals. The beautiful stalactite grottos are
all made of crystals of lime. Diamonds are crystals of carbon,
made inside the earth. Rock-crystals, which you know probably
under the name of Irish diamonds, are crystallized quartz; and
so, with slightly different colourings, are agates, opals,
jasper, onyx, cairngorms, and many other precious stones. Iron,
copper, gold, and sulphur, when melted and cooled slowly build
themselves into crystals, each of their own peculiar form, and we
see that there is here a wonderful order, such as we should never
have dreamt of, if we had not proved it. If you possess a
microscope you may watch the growth of crystals yourself by
melting some common powdered nitre in a little water till you
find that no more will melt in it. Then put a few drops of this
water on a warm glass slide and place it under the microscope. As
the drops dry you will see the long transparent needles of nitre
forming on the glass, and notice how regularly these crystals
grow, not by taking food inside like living beings, but by adding
particle to particle on the outside evenly and regularly.



Week 12