Currents in the ocean arise from various causes. They may be produced by
long-continued gales of wind, by the melting of polar ice, or by any
cause that may give rise to onward movements of limited portions of the
great mass of waters. Other currents, and of these only is it necessary
to speak in this connection, are permanent. The most remarkable of these
are the polar currents and the equatorial currents.
POLAR CURRENTS are produced by the perpetual movement of the waters from
the poles to the equator. In accordance with the laws of mechanics, an
accumulation of the waters takes place on that part of the globe which
has the greatest velocity of motion; and as the earth in turning on its
axis moves with far greater velocity at the equator, the waters
continually flow toward that line from the poles.
EQUATORIAL CURRENTS. This accumulation of the waters at the equator
tends to produce the equatorial currents, which consist of the
continuous progression of the tropical seas in a westerly direction.
When the wave brought by the polar currents arrives--coming as it does
from regions where it naturally has less velocity--it does not at once
acquire the velocity of the earth’s motion at the equator; and since
the rotation of the earth is from west to east, this portion of the
water lagging behind forms a stream or current which has an apparent
motion from east to west, that is to say, apparent as regards the earth,
but real in relation to the adjacent land and water. The trade winds,
which in this zone blow constantly in the same direction, lend their aid
in maintaining the equatorial current.