SUBJECT TO LAW
“Thou rulest the raging of the Sea.”--PSALM lxxxix. 9.
“Nothing useless is or low,
Each thing in its place is best,
And what seems but idle show
Strengthens and supports the rest.”--LONGFELLOW.
Things are what they are in this world very largely because of the pull
of opposing forces, and among such forces not one is more universal
than that of Gravity. Many causes beside Weight have their share in
making our Earth what it is; but if Weight were banished from our
midst, the Earth as we know it would exist no longer.
The only way to get rid of weight would be by getting rid of Gravity.
And since no force in Nature acts more steadily and incessantly than
this, we are no more likely to get rid of it than we are to get rid of
the world itself.
Gravity, or Gravitation, or Attraction--it is known by all these names.
Sometimes it is called a Law; sometimes a Force. Neither term may be
counted amiss. No law is worth anything without a sufficient force to
back it up; and no force is worth anything unless it acts according to
law. But we might almost as reasonably call this behaviour of things
“an Obedience” as “a Law.”
Each particle of each substance draws and is drawn by each other
particle of every substance. And each body in the Universe, from a
grain of sand to a sun, draws and is drawn by each other body, whether
far or near. All these drawings are in obedience to that mysterious
something--that force, or power, or influence--which has been named
Attraction or Gravitation. So much we know; and beyond it we know very
little as to the nature of the said “Attraction;” but we find that the
outcome of it is Weight.
By means of weight, the sun, the moon, the planets, yes, and even the
countless multitudes of stars, are kept in their paths; in each case
the inward pulling being counterbalanced by the impetus and outward
pulling of a rapid rush. By means of weight, houses, rocks, stones rest
firmly on the earth; by means of weight, the atmosphere is bound to
the earth, the Ocean to its bed. Had sea-water no weight it might be
scattered as fine water-dust through Space.
A larger and heavier Earth would bind down the ocean yet more strongly,
while a smaller and lighter Earth would have a weaker grip. Easily
as the sea is now stirred by every passing breeze, an ocean such as
ours on a little world like the Moon or Mercury would be more rapidly
agitated. The waves would leap higher with less cause.
So the Ocean, like the Land, is subject to law, knowing neither repose
nor action except in obedience to Nature’s forces.
When ocean-waters lie still as a mill-pond, they do so through an
exact _poise_ of contending powers. When waves rush high and currents
pour strongly, each movement is still in strict obedience to governing
forces, which are themselves governed by law. Each movement is due to
a long series of past movements; and each in turn helps to bring about
a long series of future movements. There are no breaks in the chain.
Every effect is also a cause.
Currents here and drifts there; breezes here and hurricanes there; all
these disturb the calm of the sea. Only for a brief spell, in one part
or another, is the pull of opposing forces so far balanced that the
water can lie still. And at most the stillness is comparative. Even
in a so-called “dead calm” gentle heavings to and fro will be found.
Absolute placidity in the ocean is a thing unknown.
Even when the waters are at their stillest they are always being drawn
steadily towards Earth’s centre. A perfectly level ocean would mean
each portion of its surface being equally distant from that centre.
The ocean ever strives after this ideal, but never attains to it; yet,
century after century that aim is pursued, with a perseverance which
might afford a lesson to ourselves.
Despite all this change and restlessness, we talk of the ocean having a
“level” surface. We picture it to our minds as being in outer shape the
same as that of the Earth--a sphere. But this is not strictly true to
fact.
If we could look upon the Earth, with large far-seeing eyes, from a
few thousands of miles off, we should find curious irregularities in
the watery outline. Instead of showing all round a smooth surface, the
ocean would be found to rise here and sink there, to be in one part
higher, in another part lower. A man roving over the ocean, all about
the Earth, would have in places to ascend undulations like hills,
almost high enough sometimes to be called mountains, in other parts to
descend declivities.
Most of us have noticed in a cup filled with water, that the
water-surface is not perfectly flat. Close to the sides of the cup may
be noticed a distinct rise. It is the same in a tumbler, in a basin,
in a slender glass tube. For the sides of the cup or tumbler or tube
attract the water, drawing it upward; and this is known as Capillary
Attraction.
With the ocean the very same thing is seen. If high land borders on
deep water, the extra attraction of mountain-masses will act just as
the sides of a cup or tumbler will act. They draw upward the water of
the ocean to a higher level. When I say that this is “seen,” I do not
mean that any careless looker-on will be aware of the fact. It has to
be discovered by careful measurement.
In some cases a marked difference has been found. The enormous masses
of the Himalayas, for instance, exert a powerful drawing upon the
neighbouring sea; and at the delta of the Indus the ocean-level, in
consequence of that attraction, is actually three hundred feet higher
than on the coast of Ceylon.
Besides land attraction, winds have an extraordinary power to heap up
waters in one place more than in another. To some slight extent this
may be seen upon English shores, when a strong gale happens to blow
landward at high tide. On such occasions the waters often rise far
beyond their usual mark.
Mention was made earlier of those Phenicians who, having known an
eastern ocean with tides, and a Mediterranean Sea without tides, must
have been perplexed to find a western ocean which corresponded with the
eastern in its ebb and flow.
We all know for ourselves in these later days, how the tides rise and
fall around our coast, twice in twenty-four hours. Each high-water
is twelve hours and twenty-five minutes later than the last; so each
succeeding day sees a difference of fifty minutes in the time of high
or of low tide.
To a very large extent Tides are due to the attractive power of the
moon. They are due also to the sun, but in a much less degree, which at
first sight seems singular, since the attraction of the sun, by reason
of its greater size, far exceeds that of the moon. From the fact,
however, that the powerful drawing of the sun comes from an immense
distance, it follows that it has much less effect than the small
attraction of the moon, which comes from very near at hand.
Her influence over our earth is exerted far more strongly with respect
to those ocean-waters lying just under herself, and far less with
respect to those waters on the farther side of the globe. The effect of
these different pullings is to raise a double wave or swell,--one on
the surface of the ocean just below the moon, and one on the opposite
side of the earth. The waves mean high tides; and low tides occur at
places half-way between them.
Were the whole Earth covered by one continuous sheet of water, these
tidal waves would travel round and round the globe, in a fashion
easy and pleasant for students of the subject. Unfortunately for the
said students, their motions are very complicated. In the northern
hemisphere, where land is abundant, the tidal waves are greatly
interfered with by continents and islands. Often the most that each can
do, as it sweeps along, is to send side-waves and currents journeying
northward into channels and bays, estuaries and lesser seas.
Through the open ocean the tidal wave has no great height. Probably in
central regions of the Pacific it rises only some three or four feet
above the usual sea-level. But when the flow enters narrowing bays and
channels, a very different result is seen; and the waters are often
piled up in a wonderful manner,--as in the Bristol Channel, where the
level at high tide is sometimes nearly forty feet above that at low
tide.
A marked contrast to this is seen in the Mediterranean. There, as
already said, practically no tides exist. The rise and fall amount at
most to only a few inches. Instead of a wide entrance and a narrowing
estuary, we have just the opposite--a narrow entrance and a widening
sea beyond. Connection with the outside ocean is too restricted to
admit of any full flow of the tidal wave.
Solar tides, or tides brought about by the sun’s attraction, are much
the same in cause and effect as lunar tides, only far smaller in
degree. When Sun and Moon happen to be on the same side of the Earth,
or on different sides but in the same line, so that their combined pull
is exerted in one direction, we have Spring Tides. These are always at
the time of New Moon and Full Moon. Sun and Moon then work together,
each helping the other in a common aim; and the ocean-waters rise
higher and sink lower than at other times.
When Sun and Moon are so placed with regard to the Earth, that they
exercise their pull in a cross direction, Neap Tides result,--that
is tides which have small ebb and flow. In this case the sun hinders
instead of helping the moon, and the moon does the same for the sun,
each tending to counteract the work of the other.
Connected with and partly caused by the rise of the tide is the curious
phenomenon known as a “Bore”--a single high wave, moving onward like a
wall of water, with great rapidity and a roaring noise. More usually
this belongs to a river, and thus it has not much connection with
the subject of the ocean; but it is also sometimes seen in sharply
narrowing estuaries or ocean inlets.
[Illustration: BORE OF THE TSIEN TANG KIANG
_Face page 34_
]
To the inhabitants of a flat and unprotected country, bordering on
river or estuary, the bore is often a thing of terror, for its advent
is uncertain and abrupt, and in its upward rush it sweeps everything
before it. The entering of such a wave into the Severn is an almost
daily event, and it reaches often a height of many feet. Bores are
usual, too, in the River St. Lawrence, in the Hoogly, in an estuary
of the Bay of Fundy, and in other places innumerable; and they vary in
height from two or three feet to over twelve feet. The effect of such
a wall of water as this, deluging low lands, carrying away trees and
houses and living creatures, may be easily imagined.