cannon, due to echo from the clouds and the earth. Thunder is
ordinarily much more prolonged and impressive in a mountainous country
than in a region of plains, because the steeps about the hearer
reverberate the original single crash.

The distribution of thunderstorms is as yet not well understood, but
it appears in many cases that they are attendants on the advancing
face of cyclones and hurricanes, the area in front of these great
whirlstorms being subjected to the condensation and irregular air
movements which lead to the development of much electrical energy.
There are, however, certain parts of the earth which are particularly
subjected to lightning flashes. They are common in the region near the
equator, where the ascending currents bring about heavy rains, which
mean a rapid condensation and consequent liberation of electrical
energy. They diminish in frequency toward the arctic regions. An
observer at the pole would probably fail ever to perceive strong
flashes. For the same reason thunderstorms are more frequent in
summer, the time when the difference in temperature between the
surface and the upper air is greatest, when, therefore, the uprushes
of air are likely to be most violent. They appear to be more common in
the night than in the daytime, for the reason that condensation is
favoured by the cooling which occurs in the dark half of the day. It
is rare, indeed, that a thunderstorm occurs near midday, a period when
the air is in most cases taking up moisture on account of the swiftly
increasing heat.

There are other forms of electrical discharges not distinctly
connected with the then existing condensation of moisture. What the
sailors call St. Elmo's fire--a brush of electric light from the mast
tops and other projections of the ship--indicates the passage of
electrical energy between the vessel and the atmosphere. Similar
lights are said sometimes to be seen rising from the surface of the
water. Such phenomena are at present not satisfactorily explained.
Perhaps in the same group of actions comes the so-called
"Jack-o'-lantern" or "Will-o'-the-wisp" fires flashing from the earth
in marshy places, which are often described by the common people, but
have never been observed by a naturalist. If this class of
illuminations really exists, we have to afford them some other
explanation than that they are emanations of self-inflamed
phosphoretted hydrogen, a method of accounting for them which
illogically fi