The Ocean and its Wonders | Page 9

burst upon the calm ocean with
such sudden violence that for a time the waves cannot lift their heads.
The instant they do so, they are cast down and scattered in foam, and
the ocean in a few minutes presents the appearance of a cauldron of
boiling milk! Such squalls are extremely dangerous to mariners, and
vessels exposed to them are often thrown on their beam-ends, even
though all sail has been previously taken in. Generally speaking,
however, the immediate effect of wind passing either lightly or
furiously over the sea is to raise its surface into waves. But these waves,
however large they may be, do not affect the waters of the ocean more
than a few yards below its surface. The water below their influence is
comparatively calm, being affected only by ocean currents.
The tides of the sea--as the two great flowings and ebbings of the water
every twenty-four hours are called--are caused principally by the
attractive influence of the moon, which, to a small extent, lifts the
waters of the ocean towards it, as it passes over them, and thus causes a
high wave. This wave, or current, when it swells up on the land, forms
high tide. When the moon's influence has completely passed away, it is
low tide. The moon raises this wave wherever it passes; not only in the
ocean directly under it, but, strange to say, it causes a similar wave on
the opposite side of the globe. Thus there are two waves always
following the moon, and hence the two high tides in the twenty-four
hours. This second wave has been accounted for in the following way:
The cohesion of particles of water is easily overcome. The moon, in
passing over the sea, separates the particles by her attractive power, and
draws the surface of the sea away from the solid globe. But the moon
also attracts the earth itself, and draws it away from the water on its
opposite side thus causing the high wave there, as represented in the

diagram, figure 1.
The sun has also a slight influence on the tides, but not to such an
extent as the moon. When the two luminaries exert their combined
influence in the same direction, they produce the phenomenon of a very
high or spring-tide, as in figure 2, where the tide at a and b has risen
extremely high, while at c and d it has fallen correspondingly low.
When they act in opposition to each other, as at the moon's quarter,
there occurs a very low or neap-tide. In figure 3 the moon has raised
high tide at a and b, but the sun has counteracted its influence to some
extent at c and d, thus producing neap-tides, which neither rise so high
nor fall so low as do other tides. Tides attain various elevations in
different parts of the world, partly owing to local influences. In the
Bristol Channel the tide rises to nearly sixty feet, while in the
Mediterranean it is extremely small, owing to the landlocked nature of
that sea preventing the tidal wave from having its full effect. Up some
gulfs and estuaries the tides sweep with the violence of a torrent, and
any one caught by them on the shore would be overtaken and drowned
before he could gain the dry land. In the open sea they rise and fall to
an elevation of little more than three or four feet.
The value of the tides is unspeakable. They sweep from our shores
pollution of every kind, purify our rivers and estuaries, and are
productive of freshness and health all round the world.
------------------------------------------------------------------------
The gentlemen here referred to are agreed as to the fact of systematic
arrangement of currents, though they differ in regard to some of the
causes thereof and other matters.
CHAPTER FOUR.
THE GULF STREAM--ITS
NATURE--CAUSE--ILLUSTRATION--EFFECT OF SMALL
POWERS UNITED--ADVENTURES OF A PARTICLE OF
WATER--EFFECT OF GULF STREAM ON CLIMATE--ITS
COURSE--INFLUENCE ON NAVIGATION--SARGASSO

SEA--SCIENTIFIC EFFORTS OF PRESENT DAY--WIND AND
CURRENT CHARTS--EFFECTS ON COMMERCE-- CAUSE OF
STORMS--INFLUENCE OF GULF STREAM ON MARINE
ANIMALS.
Of the varied motions of the sea, the most important, perhaps, as well
as the most wonderful, is the Gulf Stream. This mighty current has
been likened by Maury to a "river in the ocean. In the severest droughts
it never fails, and in the mightiest floods it never overflows. Its banks
and its bottom are of cold water, while its current is of warm. It takes
its rise in the Gulf of Mexico (hence its name), and empties into the
arctic seas. Its current is more rapid than the Mississippi or the Amazon,
and its volume more than a thousand times greater."
This great current is of the most beautiful indigo-blue colour as far out
as the Carolina coasts;