Ocean wave

“ A tidal wave coming up the Atlantic coast meets the ocean wave from the east, and, entering the bay with their combined force, they raise the water at the head of it to the height of sixty or seventy feet. ”

“ A LIFE ON THE OCEAN WAVE.
Epes Sargent. Henry Russell.
1. A life on the o - cean wave, A home on the roll - ing
2. Once more on the deck I stand Of my own swift-glid-ing
3. The land is no longer in view, The clouds have be - gun to
deep, Where the scat - tered wa - ters rave, And the ”

“ Progress of the Tide-wave over the Ocean and in the British Seas.—Sufficient tidal data would give the state of the tide at every part of the world at the same instant of time, and if the tide wave is a progressive one, like such wave as we may observe travelling along a canal, we should be able to picture mentally the motion of the tide-wave over the ocean and the successive changes in the height of water at any one place. ”

“ This rise and fall of the waters along the coast, accompanied frequently by strong currents, are produced directly by the arrival in the shoal water of a pulsation of the ocean, which becomes a true onward-moving gravity wave as it nears the land. In the open sea the amplitude of the tidal undulations is but two or three feet, and their rate of travel in general 700 to 800 miles per hour. ”

“ The motion of the tide-wave is not a progressive motion, but a mere undulation, and is to be carefully distinguished from the currents to which it gives rise. If the ocean completely covered the earth, the sun and moon being in the equator, the tide-wave would travel at the same rate as the earth revolves on its axis. ”

“ An assumption that the basic tidal movement in the open ocean consists of a system of stationary wave oscillations, any progressive wave movement being of secondary importance except as the tide advances into tributary waters. ”

“ We may conceive the moon's tide-generating force as making a wave in the canal and continually outstripping the wave it generates, for the moon travels along the equator at the rate of about 1000 miles an hour, and the sea is less than 13 miles deep. The resultant oscillation of the ocean must therefore be the summation of a series of partial waves generated at each instant by the moon and always falling behind her, and the aggregate wave, being the same at each instant, must travel 1000 m. ”

“ To raise a tidal wave the sun and moon require not merely an ocean of wide extent to act upon, but an ocean so placed that there is a great diversity in their pull on various parts of it; for it is the difference between the pull exerted on various parts, and not the pull itself, which creates the tidal wave. Now the Polar sea has not the required extent, and is not in the proper position, for this diversity of pull to exist in sufficient degree to produce a tidal wave which could be recognized. ”

“ We know how, as the circles widen, the height of the wave grows less and less, until, at no great distance from the centre of disturbance, the wave can no longer be discerned, so slight is the slope of its advancing and following faces. How tremendous, then, must have been the upheaval of the bed of ocean by which wave-circles were sent across the Pacific, retaining, after travelling 5000 miles from the centre of disturbance, the height of a two-storied house! ”

“ As they pass up the narrowing spaces the waves become compressed—that is, an equal volume of moving water has less horizontal room for its passage, and is forced to rise higher. We see a tolerably good illustration of the same principle when we observe a wind-made wave enter a small recess of the shore, the sides of which converge in the direction of the motion. With the diminished room, the wave gains in height. It thus comes about that the tide throughout the Atlantic basin is much higher than in the southern ocean. ”

“ The tides of the Atlantic Ocean are of great complexity. The tidal wave of the Southern Ocean, which sweeps uninterruptedly round the globe from the east to west, generates a secondary wave between Africa and South America, which travels north at a rate dependent only on the depth of the ocean. With this “free” wave is combined a “forced” wave, generated, by the direct action of the sun and moon, within the Atlantic area itself. Nothing is known about the relative importance of these two waves. (H. N. D.) ”

“ That this wave ‘does work,’ no one can doubt who has watched its effects. The mere rise and fall in open ocean may not be strikingly indicative of ‘work done;’ but when we see the behaviour of the tidal wave in narrow channels, when we see heavily-laden ships swept steadily up our tidal rivers, we cannot but recognise the expenditure of force. Now, where does this force come from? Motion being the great ‘force-measurer,’ what motion suffers that the tides may work? We may securely reply, that the only motion which can supply the requisite force is the earth’s motion of rotation. ”

“ Some observers have claimed to see them over one hundred feet high, but from twenty to fifty feet is about the average of observations on the Atlantic. The breadth of a wave is calculated as fifteen times its height. Thus, a wave four feet high is sixty feet broad. The inclination of the sides of the waves varies however with the force of the wind, and with the strength of the secondary vibrations in the water, which may interfere with the primary ones. The speed of the waves is only apparent like the motion in a length of cloth shaken up and down. ”

“ Again, waves are formed by a force acting horizontally; but in the case of the tide wave, that force acts uniformly from the surface to the lowest depths of the ocean, and the breadth of the wave is that curved surface which, commencing at low water, passes over the summit of the tide down to the next low water—this is a wave of the first order. ”

“ The semi-synchronous oscillation of the Southern Ocean raises the magnitude of oceanic tides somewhat above these directly generated values.
Oceanic tides are true waves, not currents. Coast tides are currents. The momentum of the water, when the tidal wave breaks upon a continent and rushes up channels, raises coast tides to a much greater height—in some places up to 50 or 60 feet, or even more. ”

“ Alone I walked the ocean strand;
A pearly shell was in my hand:
I stooped, and wrote upon the sand
My name—the year—the day.
As onward from the spot I passed,
One lingering look behind I cast:
A wave came rolling high and fast,
And washed my lines away. ”

“ and, clambering down a crag, I find myself at the extremity of a long beach. How gladly does the spirit leap forth, and suddenly enlarge its sense of being to the full extent of the broad, blue sunny deep! A greeting and a homage to the Sea! I descend over its margin, and dip my hand into the wave that meets me, and bathe my brow. That far-resounding roar is Ocean's voice of welcome. His salt breath brings a blessing along with it. ”

“ Now imagine this sea of uniform temperature to be suddenly stricken with the invisible wand of heat and cold, bringing its waters to the various temperatures at which they at this instant are standing. This change of temperature would make a change of specific gravity in the waters, which would destroy the equilibrium of the whole ocean; upon this a set of currents would immediately commence to flow, namely, a current of cold and heavy water to the place of the warm, and a current of warm and lighter to the place of the cold. ”

“ Light and heat differ as much as the short, choppy waves of the ocean and the slow, long swell of the ocean, but not more so. The sailor handles his boat in one way in a choppy sea and in a different way in a rolling sea, for he knows that these two kinds of waves act dissimilarly. The long, slow swell of the ocean would correspond with the longer, slower waves which travel out from the sun, and which on reaching us are interpreted as heat. The shorter, more frequent waves of the ocean would typify the short, rapid waves which leave the sun, and which on reaching us are interpreted as light. ”

“ Winds exercise but little influence constant currents.—More water cannot run from the equator or the pole than to it. If we make the trade-winds to cause the Gulf Stream, we ought to have some other wind to produce the Polar flow; but these currents, for the most part, and for great distances, are submarine, and therefore beyond the influence of winds. Hence it should appear that winds have little to do with the general system of aqueous circulation in the ocean. ”

“ But with regard to the sea, it is not known what office is performed by electricity and magnetism, in giving dynamical force to its waters in their system of circulation. The chief motive power from which marine currents derive their velocity has been ascribed to heat; but a close study of the agents concerned has suggested that an important — nay, a powerful and active agency in the system of oceanic circulation is derived from the salts of the sea water, through the instrumentality of the winds, of marine plants, and animals. These give the ocean great dynamical force. ”

“ No such waves are found in the trade-winds; for, though the S.E. trades are quite as constant, yet they have not the force to pile the water in such heaps, nor to arrange the waves so orderly, nor to drive them so rapidly as those "brave" winds do. There the billows, chasing each other like skipping hills, look, with their rounded crests and deep hollows, more like mountains rolling over a plain than the waves which we are accustomed to see. Many days of constant blowing over a wide expanse of ocean are required to get up such waves. ”

“ Our investigations go to show that the roaring waves and the mightiest billows of the ocean repose, not upon hard or troubled beds, but upon cushions of still water; that everywhere at the bottom of the deep sea the solid ribs of the earth are protected, as with a garment, from the abrading action of its currents, and that the cradle of its restless waves is lined by a stratum of water at rest, or so nearly at rest that it can neither wear nor move the lightest bit of drift that once lodges there. ”

“ On no other supposition can we reasonably account for the fact that our barometric records fail to afford us any very distinct evidence as to the existence of tides in the atmosphere. For you will, of course, remember that our atmosphere may be regarded as a deep and vast ocean of air, which embraces the whole earth, extending far above the loftiest summits of the mountains.
It is one of the profoundest of nature's laws that wherever friction takes place, energy has to be consumed. ”

“ Now we may judge how exceedingly small a current this would produce when we consider that there is a rise of about two feet in the open ocean at one place and a fall of the same amount at another every six hours, caused by the tides, and yet the flowing of the water from the one place to the other place to produce this rise at one place, and fall at the other, it is well known does not produce any sensible currents in the open sea. ”

“ Indeed the reason of this seems sufficiently obvious, if we consider that constant currents are, in all probability, produced by constant winds, the wind driving before it, though with a slow and imperceptible motion, a large body of water, which being accumulated upon any coast that it meets with, must escape along the shore by the endeavours of its surface to reduce itself to the same level with the rest of the ocean. ”

“ Beneath it lay the sea, like a copper shield, smooth and glowing, seething like a boiling caldron, with its level foam, for the long, low-rolling billows lifted themselves but lazily from Ocean's breast, and assumed no distinctness of form or motion. Not the faintest breeze came to relieve the stifling closeness of the atmosphere, or lift the collapsed sail, or furled flag, that clung around our mast. The air shimmered visibly around us, as though undergoing some transformation from the heat, some culinary process, through which it was to be rendered unfit for human lips to breathe. ”

“ Heat the top of an iron plate, and the bottom becomes warm; but heat the top of a sheet of water, as in a pool or basin, and that at the bottom remains cool. The heat passes through iron by conduction, but to get through water it requires to be conveyed by a motion, which in fluids we call currents.
235. Therefore the study of the climates of the sea involves a knowledge of its currents, both cold and warm. They are the channels through which the waters circulate, and by means of which the harmonies of old ocean are preserved. ”

“ Temperature, barometric pressure, attractive force of the moon, have all been advanced as bringing about ocean currents. Seamen believe that it is the wind that brings about certain oceanic movements. ”

“ It is true that the moon in its attraction of the sea-water produces a vastly greater sum total of effect than the wind does in raising the surface-waves, but reckoning only that part of the ocean energy which might conceivably be made available for service it is safe to calculate that the waves offer between two and three thousand times as much opportunity for the capture of natural power and its application to useful work as the tides could ever present. ”

“ For it is the calorific waves emitted by the sun which heat our air, produce our winds, and hence agitate our ocean. And whether they break in foam upon the shore, or rub silently against the ocean's bed, or subside by the mutual friction of their own parts, the sea-waves finally resolve themselves into waves of ether, and thus regenerate the motion from which their temporary existence was derived. This connexion is typical. Nature is not an aggregate of independent parts, but an organic whole. ”