this May morning—a wind from the warm
regions which has come over the sea loaded
with vapour. Though violent, it felt warm
to the fac; but in the sky were scattered
clouds, and the wind veered frequently towards
the north, with sudden showers, one of
which pelted upon Tom. It was a contest
between the south-west current, and a current
from the north, which now and then forced a
way down, and, where it did so, cooled the
atmosphere, and obliged it to part with some
of its vapour, either in the form of clouds or
rain. The winds are quiet now, and if you
look out, you will see that the fight is over,
and the south-west beaten after all its crowing;
north wins. You see by the smoke that
there is a north wind, which, being a cold
polar current, cannot hold, in an expanded
state, one half of the vapour brought into our
atmosphere by the south-west. The north
wind, therefore, marks its victory by a general
precipitation; the whole sky is uniformly
clouded, and a steady rain falls, and will fall,
until the balance is restored. When the
north wind has turned out of the sky all the
vapour that it cannot manage, we shall have
fine weather, until a warm wind interferes.
The warm wind, then, must bleed some drops
before it gains possession, but, having
conquered, will possess a sky containing less than
its due quantity of vapour; therefore precipitation
will not be continued. The south-
west wind, however, soon brings moisture
with it; and then, if the noon be fine, clouds
form at evening, when the temperature falls,
and it may rain at night. Everything contains
its regulated quantity of latent heat—a body in
the form of air more than a liquid, and a liquid
more than a solid. Latent heat is sensible heat
mysteriously transformed, used in the processes
of nature, swallowed up, become insensible.
Water contains more of this, then, in the state
of a thin vapour than in the condensed form.
When, therefore, clouds form, heat that was
used up and made latent is restored and rendered
sensible; that is one reason why cloudy
weather is warm. After a shower, the whole
earth is moist, and evaporation takes place on
the entire surface. Water, to become vapour,
seizes, appropriates, and thrusts into the
latent form some of the sensible heat lying in
its neighbourhood, and, therefore, a coolness
or a chill, succeeds the rain. But there is
chill, also, during the rain-fall, when the
condensation is at its greatest; how is that?
Doubtless you know that air and water conduct
heat but badly. You could not heat a
tub of water from the top, and the sea retains
through all seasons a remarkable imperturbability
as to its temperature. So you, or the
sun, cannot heat any amount of air from the
top; but the sun's rays that reach the earth
warm that, and it retains the warmth, and
radiates it back again; and so it is the heat
of the sun sent from our own earth which fills
the air about us. If we walked on such high
stilts as to raise our mouths and noses far
above the sod, we should be very glad to have
our stilts cut shorter; for the radiant heat
lessens as we rise from the earth's surface, in
proportion no less rapidly than light lessens
as we quit a candle; and at any distance from
the earth the atmosphere is very cold. So
rain descending from the cold heights brings
a chill with it. So clouds that cover over the
earth and prevent its heat from radiating into
space, but rather reflect it back again, act as
a blanket does over a man's warm body when
he is in bed, and so we have a second reason
why it is warm—close— in cloudy weather.

Since water retains in a remarkable degree
an even temperature, and land heats and cools
in correspondence with all changes of the sun,
it follows that where land and water are
commingled, inequalities of temperature will be
various and frequent; every inequality being
the cause of a wind, and the water supplying
copious material for clouds and rain. Therefore
our island is so often clouded. Every
one who walks by the sea-side, knows the sea-
breeze produced by difference of temperature
between the land and water. The water
being uniform in heat, is colder than the earth
during a summer's day, and the air, cooled
upon its surface, blows in from the sea to fill
the space left by the lighter current. But at
night the earth has cooled down, till at length
sea is the warmer of the two, and the cold
current furnished by the earth blows to the
sea. The moist wind from the ocean, flowing
over continent, precipitates its moisture near
the coasts, especially on steep and rugged
hills; so that, far inland, clouded skies are
rare. The earth in summer, therefore, lies day
after day unsheltered from the sun, and stores
up heat continually;—you know the heat of
continental summers. In the comparatively
cloudless winter nothing impedes radiation—
out into space the heat all streams. You
know the severe cold of a winter on the
Continent. At Astrakhan the summer heat is
that of Bordeaux, and fine grapes grow; but
the winter cold is below zero.

Rain being elicited by heat from water, will,
of course, abound most where the sun is
hottest. The average yearly fall of rain between
the tropics is ninety-five inches, but in
the temperate zone only thirty-five. The
greatest rain-fall, however, is precipitated in
the shortest time—tropical clouds like to get
it over, and have done with it. Ninety-five
inches fall in eighty days on the equator,
while at St. Petersburgh the yearly rain-fall
is but seventeen inches, spread over one
hundred and sixty-nine days. Again, a tropical
wet day is not continuously wet. The morning
is clear; clouds form about ten o'clock, the
rain begins at twelve, and pours till about
half-past four; by sunset the clouds are gone,
and the night is invariably fine. That is a
tropical day during the rainy season.

What does the "rainy season" mean? At a
point twenty-three and a half degrees north
of the equator, at the tropic of Cancer, the