t these mimic lightnings. (Goethe is the
authority for this.) To atmospheric electricity we doubtless owe the
coruscations of the Aurora, one of the most beautiful of our meteors.

The usual forms of lightning are the zigzag or forked sharply
defined,--the sheet-lightning, illuminating a whole cloud, which it
seems to open,--heat-lightning, not emanating from any cloud, but
apparently diffused through the air and without report. There are also
fireballs which shoot across the sky, leaving a train often visible
for seconds and minutes. These last, when they project any masses to
the earth, are termed aerolites.

Atmospheric electricity has much to do with the distribution of rain,
the precipitation of vapor, the condition of our nervous system, and,
according to Humboldt, with the circulation of the organic juices.
Atmospheric electricity has heretofore been a great obstacle to the
success of the Magnetic Telegraph, and curiously disturbs its
operation; but there has recently been invented an instrument called a
Mutator, which is connected with the wires, and carries off all the
disturbing influences of the atmosphere without interfering with the
working current. On the other hand, artificially created electricity
has led to important advances in many of the arts and sciences.

Ice is water frozen under a very curious and peculiar law. Hail is the
congelation of drops of rain in irregular forms, always sudden,--by
some attributed to electricity and currents of air violently rarefied
by it, and by others to rain-drops falling through a cold stratum of
air and suddenly congealed. Snow, the ermine of the earth, is the
crystallized moisture of the air, and is in subjection to unchanging
laws.

Water contracts as it grows colder, until it falls in temperature to
42 deg.. It then expands till it reaches 32 deg., when it becomes solid,
though its density is actually diminished, and its specific gravity is
reduced to .929, while that of unfrozen water is 1.000. Of course it
is much lighter, and it floats. This admirable arrangement prevents
our rivers being frozen up and our lakes becoming solid. Ice thickens
because it is porous, and allows the heat of the water to pass up and
the cold to descend; but this is happily a slow process, as ice is a
bad conductor. Salt water freezes at the temperature of 7 deg., 25 deg. below
freezing-point. There are many things to be said about ice, whether as
glaciers, or Arctic bergs, or, as