WAVES--SYSTEM IN ALL THINGS--VALUE OF SCIENTIFIC KNOWLEDGE--ILLUSTRATIVE
ANECDOTE--HEIGHT OF WAVES--DR. SCORESBY--SIZE, VELOCITY, AND AWFUL POWER
OF WAVES--ANECDOTES REGARDING THEM--TIDES.
When a man stands on the deck of some tight-built ship, holding on to
the weather bulwarks, and gazing with unphilosophic eye through the
blinding spray at the fury of the tempest--by which the billows are made
to roll around him like liquid mountains, and the ship is tossed beneath
him like a mere chip, the sport and plaything of the raging waters--he
is apt to think, should his thoughts turn in that direction at all, that
all is unmitigated confusion; that the winds, which blew west yesterday
and blow east to-day,--shifting, it may be, with gusty squalls, now
here, now there, in chaotic fury,--are actuated by no laws, governed by
no directing power.
Yet no thought could be more unphilosophical than this. Apart
altogether from divine revelation, by which we are informed that "all
deeps, fire, and hail, snow, and vapour, and stormy wind," are
"fulfilling God's word" (which information we are bound to receive as a
matter of faith if we be Christians, and as a matter of necessity if we
be men of common sense, because it is mere absurdity to suppose that the
"stormy winds," etcetera, are _not_ fulfilling God's word--or will), we
now know, to a great extent from practical experience and scientific
investigation, that the winds blow and the waters of the ocean flow in
grand, regular, uninterrupted currents. Amongst these there are
numberless eddies, which, perhaps, have tended to fill our minds with
the idea of irregularity and confusion; but which, nevertheless, as well
as the grand currents themselves, are subject to law, and are utterly
devoid of caprice.
In regard to these matters there is much about which we are still in
ignorance. But the investigations of late years--especially those
conducted under the superintendence of Captain Maury of the American
Navy, and Doctors Carpenter and Thompson of England--have shown that our
atmosphere and our ocean act in accordance with a systematic
arrangement, many facts regarding which have been discovered, and
turned, in some cases, to practical account. See Note 1.
A very interesting instance of the practical use to which scientific
inquiry can be turned, even in its beginnings, is given by Maury. After
telling us of the existence and nature of a current in the ocean called
the Gulf Stream, he gives the following account of the manner in which
upon one occasion be made use of his theoretical knowledge.
In the month of December 1853, the fine steam-ship _San Francisco_
sailed from New York with a regiment of United States troops on board,
bound for California by way of Cape Horn. She was overtaken, while
crossing the Gulf Stream, by a gale of wind, in which she was dreadfully
crippled. Her decks were swept, and, by one single blow of those
terrible seas that the storms raise in the Gulf Stream, more than in any
other part of the Atlantic, one hundred and seventy-nine souls, officers
and soldiers, were washed overboard and drowned.
The day after this disaster she was seen by one vessel, and again, the
next day, December 26th, by another; but neither of them could render
her any assistance.
When these two vessels arrived in the United States and reported what
they had seen, the most painful apprehensions were entertained by
friends for the safety of those on board the steamer. Vessels were sent
out to search for and relieve her. But where should these vessels go?
Where should they look?
An appeal was made to know what light the system of researches carried
on at the National Observatory concerning winds and currents could throw
upon the subject.
The materials they had been discussing were examined, and a chart was
prepared to show the course of the Gulf Stream at that season of the
year. Two revenue cutters were then appointed to proceed to sea in
search of the steamer, and Maury was requested to "furnish them with
instructions."
It will be observed here that the gentleman thus appealed to was at the
time engaged in his study at Washington, utterly ignorant of all that
had occurred within the previous few weeks on the stormy Atlantic,
except through the reports brought thence by ships. These reports
furnished him with meagre data to proceed upon--simply that a crippled
steamer had been seen in a certain latitude and longitude on a
particular day.
But this information was sufficient for the practical man of science.
Proceeding upon the supposition that the steamer had been completely
disabled, he drew two lines on the chart to define the limits of her
drift. This his previous knowledge of the flow of the Gulf Stream at
all seasons of the year enabled him to do. Between these two lines, he
said, the steamer, if she could neither steam nor sail after the gale,
had drifted. And that she could neither steam nor sail he had good
reason to suppose from the account of her brought in by the vessels
above mentioned. A certain point was marked on the chart as being the
spot where the searching vessels might expect to fall in with the wreck.
While these preparations were being made, two ships fell in with the
wreck and relieved the crew. This, however, was not known at the time
by the anxious friends on shore. The cutters sailed on their mission,
and reached the indicated spot in the sea, where, of course, their
assistance was now unnecessary. But when the vessels that had relieved
the crew of the wreck arrived in harbour and reported where the wreck
had been last seen, it was found to be within a few miles of the spot
indicated by Maury!
Thus, upon very slight data, a man of science and observation was
enabled, while seated in his study, to follow the drift of a wrecked
vessel over the pathless deep, and to indicate to a rescue party, not
only the exact course they ought to steer, but the precise spot where
the wreck should be found.
The waves of the ocean are by no means so high as people imagine. Their
appearance in the Atlantic or Pacific, when raised by a violent storm,
is indeed very awful, and men have come to speak of them as being
"mountains of water." But their sublime aspect and their tumultuous
state of agitation have contributed much to deceive superficial
observers as to their real height. Scientific men have measured the
height of the waves.
Not many years ago a vessel, while crossing the Atlantic, was overtaken
by a violent storm. The sea rose in its might; the good ship reeled
under the combined influence of wind and waves. While the majority of
the passengers sought refuge from the driving spray in the cabin, one
eccentric old gentleman was seen skipping about the deck with unwonted
activity--now on the bulwarks, now on the quarter-deck, and anon in the
rigging; utterly regardless of the drenching sea and the howling wind,
and seeming as though he were a species of human stormy petrel. This
was the celebrated Dr Scoresby; a man who had spent his youth and
manhood in the whale-fishing; who, late in life, entered the Church,
and, until the day of his death, took a special delight in directing the
attention of sailors to Him whose word stilled the tempest and bade the
angry waves be calm. Being an enthusiast in scientific research, Dr
Scoresby was availing himself of the opportunity afforded by this storm
to _measure the waves_! Others have made similar measurements, and the
result goes to prove that waves seldom or never rise much more than ten
feet above the sea-level. The corresponding depression sinks to the
same depth, thus giving the entire height of the largest waves an
elevation of somewhere between twenty and thirty feet. When it is
considered that sometimes the waves of the sea (especially those off the
Cape of Good Hope) are so broad that only a few of them occupy the space
of a mile, and that they travel at the rate of about forty miles an
hour, we may have some slight idea of the grandeur as well as the power
of the ocean billows. The forms represented in our illustration are
only wavelets on the backs of these monster waves.
Waves travel at a rate which increases in proportion to their size and
the depth of water in which they are formed. Every one knows that on
most lakes they are comparatively small and harmless. In some lakes,
however, such as Lake Superior in North America, which is upwards of
three hundred miles long, the waves are so formidable as to resemble
those of the ocean, and they are capable of producing tremendous
effects. But the waves of the sea, when roused to their greatest
height, and travelling at their greatest speed, are terrible to behold.
Their force is absolutely irresistible. Sometimes waves of more than
usually gigantic proportions arise, and, after careering over the broad
sea in unimpeded majesty, fall with crushing violence on some doomed
shore. They rush onward, pass the usual barriers of the sea-beach, and
do not retire until horrible devastation has been carried far into the
land.
Maury gives the following anecdote from the notes of a Russian officer,
which shows the awful power of such waves.
"On the 23rd of December 1854, at 9:45 a.m., the shocks of an earthquake
were felt on board the Russian frigate _Diana_, as she lay at anchor in
the harbour of Simoda, not far from Jeddo in Japan. In fifteen minutes
afterwards (10 o'clock) a large wave was observed rolling into the
harbour, and the water on the beach to be rapidly rising. The town, as
seen from the frigate, appeared to be sinking. This wave was followed
by another; and when the two receded, which was at fifteen minutes past
ten, there was not a house, save an unfinished temple, left standing.
These waves continued to come and go until half-past two p.m., during
which time the frigate was thrown on her beam-ends five times; a piece
of her keel, eighty-one feet long, was torn off; holes were knocked in
her by striking on the bottom, and she was reduced to a wreck. In the
course of five minutes the water in the harbour fell, it is said, from
twenty-three to three feet, and the anchors of the ship were laid bare.
There was a great loss of life; many houses were washed into the sea,
and many junks carried up--one two miles inland--and dashed to pieces on
the shore. The day was beautifully fine, and no warning was given of
the approaching convulsion: the sea was perfectly smooth when its
surface was broken by the first wave."
Monster waves of this kind occur at regular intervals, among the islands
of the Pacific, once and sometimes twice in the year; and this without
any additional influence of an earthquake, at least in the immediate
neighbourhood of the islands, though it is quite possible that
earthquakes in some remote part of the world may have something to do
with these waves.
One such wave is described as breaking on one of these islands with
tremendous violence. It appeared at first like a dark line, or low
cloud, or fog-bank, on the sea-ward horizon. The day was fine though
cloudy, and a gentle breeze was blowing; but the sea was not rougher, or
the breaker on the coral reef that encircled the island higher, than
usual. It was supposed to be an approaching thunder-storm; but the line
gradually drew nearer without spreading upon the sky, as would have been
the case had it been a thunder-cloud. Still nearer it came, and soon
those on shore observed that it was moving swiftly towards the island;
but there was no sound until it reached the smaller islands out at sea.
As it passed these, a cloud of white foam encircled each and burst high
into the air. This appearance was soon followed by a loud roar, and it
became evident that the object was an enormous wave. When it approached
the outer reef, its awful magnitude became more evident. It burst
completely over the reef at all points, with a deep, continuous roar;
yet, although part of its force was thus broken, on it came, as if with
renewed might, and finally fell upon the beach with a crash that seemed
to shake the solid earth; then, rushing impetuously up into the woods,
it levelled the smaller trees and bushes in its headlong course; and, on
retiring, left a scene of wreck and desolation that is quite
indescribable.
"Storm-waves," as those unusually gigantic billows are called, are said
to be the result of the removal of atmospheric pressure in certain parts
of the ocean over which a storm is raging. This removal of pressure
allows the portion thus relieved to be forced up high above the ordinary
sea-level by those other parts that are not so relieved.
The devastating effects of these storm-waves is still further
illustrated by the total destruction of Coringa, on the Coromandel
Coast, in 1789. During a hurricane, in December of that year, at the
moment when a high tide was at its highest point, and the north-west
wind was blowing with fury, accumulating the waters at the head of the
bay, three monstrous waves came rolling in from the sea upon the devoted
town, following each other at a short distance. The horror-stricken
inhabitants had scarcely time to note the fact of their approach, when
the first wave, sweeping everything in its passage, carried several feet
of water into the town. The second swept still further in its
destructive course, inundating all the low country. The third, rushing
onward in irresistible fury, overwhelmed everything, submerging the town
and twenty thousand of its inhabitants. Vessels at anchor at the mouth
of the river were carried inland; and the sea on retiring left heaps of
sand and mud, which rendered it a hopeless task either to search for the
dead or for buried property.
We have spoken of waves "travelling" at such and such a rate, but they
do not in reality travel at all. It is the undulation, or, so to speak,
the _motion_ of a wave, that travels; in the same manner that a wave
passes from one end of a carpet to the other end when it is shaken. The
water remains stationary, excepting the spray and foam on the surface,
and is only possessed of a rising and sinking motion. This undulatory
motion, or impulse, is transmitted from each particle of water to its
neighbouring particle, until it reaches the last drop of water on the
shore. But when a wave reaches shallow water it has no longer room to
sink to its proper depth; hence the water composing it acquires _actual_
motion, and rushes to the land with more or less of the tremendous
violence that has been already described.
Waves are caused by wind, which first ruffles the surface of the sea
into ripples, and then, acting with ever-increasing power on the little
surfaces thus raised, blows _them_ up into waves, and finally into great
billows. Sometimes, however, winds 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.
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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.