y the heat
energy that is stored in the water. And when this energy is given up to
a certain degree the power that holds the spring wound up is suddenly
released, when it unwinds and occupies a larger space. There is a force
that we may call polar force, which is constantly tending to push the
molecules of water into an arrangement such as we see when
crystallization takes place--as it always does in the act of freezing.
These polar forces cannot act so long as the energy in the form of heat
is sufficient to hold the water in the fluid state. But the moment this
energy, which tends to hold it in the fluid state, falls below that
which tends to rearrange it into the crystalline form, it is overcome by
the superior power of the latter force, and we have the phenomenon of
solidified water.

A very interesting experiment may be performed with a block of ice by
anyone when the ice is near the melting point. If a wire is put around
the ice and a sufficient weight is suspended to it, the pressure of the
wire on the ice will gradually liquefy that portion immediately under
the wire, which allows it to sink into the ice slowly, and as this
process goes on the ice freezes together again behind the wire, so that
in time the wire will pass entirely through the block and leave it still
a solid block, as it was before the experiment began.

This is an interesting fact which it will be well to remember when we
come to explain glacial action, or rather the law that governs glacial
action. If we take two pieces of melting ice and bring them together
they immediately congeal at the point of contact. This phenomenon is
called "regelation." Ice has some of the properties of a viscous
substance. It will yield slowly to pressure, especially when near the
melting point, but if put under a tensional strain it will break, as any
brittle substance will, so that it has the properties of both viscosity
and brittleness. Ordinarily we are in the habit of treating water as a
fluid and ice as a solid, but from what has gone before the reader must
understand that in a certain sense ice should be treated as having
semi-fluidic properties.

CHAPTER XXIV.

WHY DOES ICE FLOAT?

Nature is full of surprises. By a long series of experimental
investigations you think you have established a law that is as
unalterable as those of the Medes and Persians. But once in a while you
stumble upon phenomena that seem to contradict all that has gone before.