Now picture to yourselves that all the particles of those
substances which form crystals have poles like our magnets, then
you can imagine that when the heat which held them apart is
withdrawn and the particles come very near together, they will
arrange themselves according to the attraction of their poles and
so build up regular and beautiful patterns.

So, if we could travel up to the clouds where this fairy power of
crystallization is at work, we should find the particles of
water-vapour in a freezing atmosphere being built up into minute
solid crystals of snow. If you go out after a snow-shower and
search carefully, you will see that the snow-flakes are not mere
lumps of frozen water, but beautiful six-pointed crystal stars, so
white and pure that when we want to speak of anything being
spotlessly white, you say that it is "white as snow." Some of
these crystals are simply flat slabs with six sides, others are
stars with six rods or spikes springing from the centre, others
with six spikes each formed like a delicate fern. No less than a
thousand different forms of delicate crystals have been found
among snowflakes, but though there is such a great variety, yet
they are all built on the six-sided and six-pointed plan, and are
all rendered dazzlingly white by the reflection of the light from
the faces of the crystals and the tiny air-bubbles built up within
them. This, you see, is why, when the snow melts, you have only a
little dirty water in your hand; the crystals are gone and there
are no more air-bubbles held prisoners to act as looking-glasses
to the light. Hoar-frost is also made up of tiny water-crystals,
and is nothing more than frozen dew hanging on the blades of grass
and from the trees.