lash jumping from
the cloud to the earth or from one cloud to another.

"The rumble of the thunder--which used to be thought the rolling of a
chariot in the sky, is due to the different distances of various
portions of the discharge, to the echo of the explosions from the
projecting hills and valleys of the cloud forms, and to the irregular
shape of the earth, when the sound waves strike the ground."

"Hail is electric, too, isn't it?" said Anton. "In a hail-storm the
other day I noticed that the hail jumped up a lot higher from an old
piece of iron that lay on the ground than from a stone right beside it.
I tried the iron and the stone with a marble, after the storm was over,
and the marble bounced higher from the stone. I figured that there must
be some kind of electric repulsion and that the hail must be
electrified."

"It is, very often," the Forecaster answered. "In some very violent
electric storms, you'll see hail jump up as if it were alive, when it
strikes the earth. Of course, boys, there's some slight elasticity in a
hail-stone, too, because a good many of them are made like an onion or a
pearl, with a number of layers round each other."

"But why in the world should a hail-stone be made like an onion?" said
Fred, with a puzzled stare. "Isn't hail just frozen rain?"

"No," answered the Forecaster, "frozen rain is sleet, which is never
seen in summer. It is caused by the rain in the upper air falling
through a cold layer of surface air and becoming frozen on the way.
Sleet is ice, and transparent.

"Hail never falls in winter, only in summer, and almost always in
connection with a thunderstorm. It is made by drops of moisture, like
very fine rain, being carried by the strong upward currents of a
thunderstorm to altitudes where the air is very cold, there becoming
coated with a layer of snow, and becoming heavier, falling through the
less active upward currents on the edge of a storm. As these
snow-covered frozen raindrops fall through the clouds, they grow bigger,
because on their cold snow surfaces the moisture condenses and is frozen
to a skin of ice. At the base of the cloud, they are often sucked in by
the upward current and carried up again for another layer of snow,
falling again through the clouds and being covered with another skin of
ice. This may happen a dozen or a hundred times, the hailstones growing
in size with every successive layer of snow and ice, until at last they
become so heavy tha