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ally withdrawn, the antagonist to their union being re-.
moved, the molecules prepare for new arrangements and
combinations. Like the particles of iron in our magnetic
experiment, the water molecules are endowed with attractive
and repulsive poles, and they arrange themselves together
in accordance with these attractions and repulsions. Solid
crystals of water are thus formed, to which we give the fa-
miliar name of ice. To the eye of science these ice-crystals
are as precious as the diamond—as purely formed, as deli-
cately built. Where no disturbing causes intervene, there
is no disorder in this crystalline architecture. By their own
constructive power molecule builds itself on to molecule
with a precision far greater than that attainable by the
hands of man. We are apt to overlook the wonderful when
it becomes common. Imagine the- bricks and stones of
this town of Dundee endowed with locomotive power. Im-
agine them attracting and repelling each other, and arrang-
ing themselves in consequence of these attractions and re-
pulsions to form streets and houses and Kinnaird Halls;
would not that be wonderful? Hardly less wonderful is
the play of force by which the molecules of water build
themselves into the sheets of crystal which every winter
roof your ponds and lakes.

If I could show you the actual progress of this molecu-
lar architecture, its. beauty would delight and astonish you.
A reversal of the process may be actually shown. The
molecules of a piece of ice may be taken asunder before
your eyes, and from the manner in which they separate, you
may to some extent infer the manner in which they aggre-
gate. When a beam is sent from our electric lamp through
a plate of “glass, a portion of the beam is intercepted, and
the glass is warmed by the portion thus retained within it.
When the beam is sent through a plate of ice, a portion
of the beam is also absorbed; but instead of warming the
ice, the intercepted heat melts it internally. It is to the

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