able state of a
cloud, going up or down according as it was heated or cooled.

When the formation of the drop of water or snowflake begins, the mass
is very small. If in descending it encounters great thickness of
cloud, the bit may grow by further condensation until it becomes
relatively large. Generally in this way we may account for the
diversities in the size of raindrops or snowflakes. It often happens
that the particles after taking on the form of snowflakes encounter in
their descent air so warm that they melt into raindrops, or, if only
partly melted, reach the surface as sleet. Or, starting as raindrops,
they may freeze, and in this simple state may reach the earth, or
after freezing they may gather other frozen water about them, so that
the hailstone has a complicated structure which, from the point of
view of classification, is between a raindrop and a snowflake.

In the process of condensation--indeed, in the steps which precede the
formation of rain and snow--there is often more or less trace of
electrical action; in fact, a part of the energy which was involved in
the vapourization of water, on its condensation, even on the dust
motes appears to be converted into electrical action, which probably
operates in part to keep the little aggregates of water asunder. When
they coalesce in drops or flakes, this electricity often assumes the
form of lightning, which represents the swift passage of the electric
store from a region where it is most abundant to one where it is less
so. The variations in this process of conveying the electricity are
probably great. In general, it probably passes, much as an electric
current is conveyed, through a wire from the battery which produces
the force. In other cases, where the tension is high, or, in other
words, where the discharge has to be hastened, we have the phenomena
of lightning in which the current burns its way along its path, as it
may traverse a slender wire, vapourizing it as it goes. In general,
the lightning flash expends its force on the air conductors, or lines
of the moist atmosphere along which it breaks its path, its energy
returning into the vapour which it forms or the heat which it produces
in the other parts of the air. In some cases, probably not one in the
thousand of the flashes, the charge is so heavy that it is not used up
in its descent toward the earth, and so electrifies, or, as we say,
strikes, some object attached to the earth, through which