back by the resisting shores of the gulf and b y the
volume of cooler water that drains down from the
Mississippi River, and is driven out again through
the Florida Straits to form the Gulf Stream.
This great river of the ocean is in a sense the
product of the West Indian archipelago. Where
the dark blue waters meet the muddy outflow of the
Mississippi, which is cooler and denser, the line of
demarcation is as clear and constant as if the different
coloured barrier were solid; and in their flow
through the straits they are concentrated into a
stream of which the colder and heavier water of the
ocean forms the bed and banks. Here it is thirty-
seven miles wide and 1200 feet deep, and its volume
is 2000 times as great as that which the Mississippi
empties into the gulf as the drainage of a continent,
while it moves with a more rapid flow than the
greatest rivers of the earth. A s it is joined through
the passages north of Cuba b y other parts of the
equatorial current, and finds room to expand farther
on, its volume is increased and its speed lessened,
until the lowered temperature enables it to mingle
with the waters of the North Atlantic. Its wholesome
contribution of West Indian temperature to
the climate of Northern Europe has had incalculable
effects upon civilisation.
T h e currents of the watery ocean and the disturbances
to which they are subject are on or near the
surface, for their causes, in variations of temperature
and of consequent density and pressure, come from
above. T h e currents of the atmospheric ocean and
their disturbances are at or near its bottom, where
it comes in contact with the land and water of the
earth’s surface, and they are liable to greater, more
sudden, and more violent changes, as the fluid air is
more susceptible to variations of temperature and of
density than the liquid water and moves with absolu
t e freedom under the force of pressure or e x pansion
in any direction. W ith this condition of
¡complete mobility, the bottom of the ocean of air is
¡always under the enormous pressure of a superin-
Icumbent mass miles in depth, which is subject to all
■the I skyey influences ” of attraction and of heat.
The meteorology of the West Indies is particularly
¡affected by two results of the uncontrollable action
lo f atmospheric currents,— the steady and beneficent
I trade-winds of the north-east, and sudden spasms of
¡¡storm which sometimes develop into the furious and
idestructive hurricane. T he heat of the equatorial
zone causes the air to expand and rise, and this produces
a pressure from north and south which draws
currents along the surface o f the globe from the
»direction of the poles. T h e rotation of the earth
toward the east, increasing in surface speed with
increase of diameter in its latitude, tends to draw
these currents into one equatorial stream, but the
freedom of expansion and movement characteristic
of air causes it to join the rising mass where the
currents meet in the equatorial belt, and to flow
back in counter currents to the north and south.
I In the northern hemisphere the surface currents,
»drawn from the direction of the A rc tic zone and deflected
to the south-west b y the revolution of the
«earth, constitute the north-east trade-winds. Sweep