galvanized iron is
used, it should be exposed to the weather two or three months
before painting, or the paint will come off, spoiling its
appearance.

[Illustration: Detail of Paddle Boat]

** Peculiar Properties of Ice [100]

Of all the boys who make snowballs probably few know what occurs
during the process. Under ordinary conditions water turns to ice
when the temperature falls to 32 degrees, but when in motion, or
under pressure, much lower temperatures are required to make it a
solid. In the same way, ice which is somewhat below the freezing
point can be made liquid by applying pressure, and will remain
liquid until the pressure is removed, when it will again return to
its original state. Snow, being simply finely divided ice, becomes
liquid in places when compressed by the hands, and when the
pressure is removed the liquid portions solidify and unite all the
particles in one mass. In extremely cold weather it is almost
impossible to make a snowball, because a greater amount of
pressure is then required to make the snow liquid.

This process of melting and freezing under different pressures and
a constant temperature is well illustrated by the experiment shown
in Figs. 1, 2 and 3. A block of ice, A, Fig. 1, is

[Illustration: Experiment with a Block of Ice]

supported at each end by boxes BB, and a weight, W, is hung on a
wire loop which passes around the ice as shown. The pressure of
the wire will then melt the ice and allow the wire to sink down
through the ice as shown in Fig. 2. The wire will continue to cut
its way through the ice until it passes all the way through the
piece, as shown in Fig. 3. This experiment not only illustrates
how ice melts under pressure, but also how it solidifies when the
pressure is removed, for the block will still be left in one piece
after the wire has passed through.

Another peculiar property of ice is its tendency to flow. It may
seem strange that ice should flow like water, but the glaciers of
Switzerland and other countries are literally rivers of ice. The
snow which accumulates on the mountains in vast quantities is
turned to ice as a result of the enormous pressure caused by its
own weight, and flows through the natural channels it has made in
the rock until it reaches the valley below. In flowing through
these channels it frequently passes around bends, and when two
branches come together the bodies of ice unite the same as water
would under the same condi