But how about ice? Here, you will say, is frozen water, and yet
we see no crystals, only a clear transparent mass. Here, again,
Dr. Tyndall helps us. He says (and as I have proved it true, so
may you for yourselves, if you will) that if you take a
magnifying glass, and look down on the surface of ice on a sunny
day, you will see a number of dark, six-sided stars, looking like
flattened flowers, and in the centre of each a bright spot. These
flowers, which are seen when the ice is melting, are our old
friends the crystal stars turning into water, and the
bright spot in the middle is a bubble of empty space, left
because the watery flower does not fill up as much room as the
ice of the crystal star did.

And this leads us to notice that ice always takes up more room
than water, and that this is the reason why our water-pipes burst
in severe frosts; for as the water freezes it expands with great
force, and the pipe is cracked, and then when the thaw comes on ,
and the water melts again, it pours through the crack it has
made.

It is not difficult to understand why ice should take more room;
for we know that if we were to try to arrange bricks end to end
in star-like shapes, we must leave some spaces between, and could
not pack them so closely as if they lay side by side. And so,
when this giant force of crystallization constrains the atoms of
frozen water to grow into star-like forms, the solid mass must
fill more room than the liquid water, and when the star
melts, this space reveals itself to us in the bright spot of the
centre.