Mid-ocean

“ These birds, which flock into the city in vast numbers at the first approach of cold, and, sailing up and down the canals between the palaces, bring to the dwellers in the city a full sense of mid-ocean forlornness and desolation, now rioted on the savage winds, with harsh cries, and danced upon the waves of the bitter brine, with a clamorous joy that had something eldritch and unearthly in it. ”

“ This water was bitterly salt and joined another sea on the other side of the Martian continent. Yet it had a pronounced flow against us eastward, this tide running for three spring months and being followed, I learned, as ocean temperatures varied, by a flow in the opposite direction throughout the summer.
Just at present the current was so strong eastwards, the moisture beaded upon my rowers' tawny hides as they struggled against it, and their melancholy song dawdled in "linked sweetness long drawn out," while the swing of their oars grew longer and longer. ”

“ Let us, therefore, the more thoroughly to appreciate those agitations of the sea which take place in consequence of the diurnal changes in its temperature, call in the sunshine, the cloud without rain, with day and night, and their heating and radiating processes. And to make the case as strong as, with truth to nature, we may, let us again select one fifth of the Atlantic Ocean for the scene of operation. The day over it is clear, and the sun pours down his rays with their greatest intensity, and raises the temperature of the water two degrees. ”

“ You must understand, then, that all tide takes its rise in the free and open ocean under the action of the moon. No ordinary-sized sea like the North Sea, or even the Mediterranean, is big enough for more than a just appreciable tide to be generated in it. The Pacific, the Atlantic, and the Southern Oceans are the great tidal reservoirs, and in them the tides of the earth are generated as low flat humps of gigantic area, though only a few feet high, oscillating up and down in the period of approximately twelve hours. ”

“ There is a strife between these currents, and on their confines eddies are formed which ships avoid, but there is no danger unless the wind blows strongly against the tide.
Besides the influence of the currents and the tides of the ocean in altering the configuration of the land, the sea is the home of innumerable forms of animal life, which are constantly laboring in the same direction. It has been truly said, that [706] a beef bone, thrown overboard by a sailor on a ship, may form the nucleus of a new continent. ”

“ And, when we reflect how the heat of the sun’s rays was conserved by the ocean waters, and that their circulation during such times was almost wholly performed by the winds, as the difference of temperature between the polar latitudes and the equator was small, it appears that during the eras previous to the glacial age the oceans must have obtained a higher temperature than possessed by the warmest seas of to-day. ”

“ And it is probable the time is yet future when we shall have any theory that will fully account for all the phenomena of the tides. On account of the shallowness of some seas, and the narrowness of the straits in others, there arises a great diversity in the phenomena, only to be accounted for by an exact knowledge of the place. For instance, in the English channel and the German ocean, the tide is found to flow strongest in those places that are narrowest, the same quantity of water being, in this case, driven through a smaller passage. ”

“ When we travel out upon the ocean, and get beyond the influence of the land upon the winds, we find ourselves in a field particularly favorable for studying the general laws of atmospherical circulation. Here, beyond the reach of the great equatorial and polar currents of the sea, there are no unduly heated surfaces, no mountain ranges, or other obstructions to the circulation of the atmosphere — nothing to disturb it in its natural courses. The sea, therefore, is the field for observing the operations of the general laws which govern the movements of the great aerial ocean. ”

“ Yet this is a field of inquiry of very great [662] importance in physical geography, since an accurate determination of the temperature at different depths is certainly the best, and frequently the only means, for determining the depth, the width, the direction and general path of the warm ocean currents, which are the chief agents in diffusing the equatorial heat; and more especially of those deeper currents of cold water which return from the poles to supply their places, and complete the watery circulation of the globe. ”

“ I have heard that these far-away ocean-depths are very quiet and still—no rolling waves ever break their stillness, and this is proved in a very beautiful way. At the bottom of the Atlantic Ocean, where overhead great billows which seem mountain-high are in ceaseless motion, there lie beds of delicate shells, so small that you need a microscope to see their beauty, yet these shells are unbroken; no storm ever reaches their quiet home ”

“ 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. ”

“ 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. ”

“ If an object be set afloat in the ocean, as at the equator, it would, in the course of time, even though it should not be caught up by any of the known currents, find its way to the icy barriers about the poles, and again back among the tepid waters of the tropics. Such an object would illustrate the drift of the sea, and by its course would indicate the route which the surface-waters of the sea follow in their general channels of circulation to and fro between the equator and the poles. ”

“ That the tides may have their full motion, the ocean in which they are produced ought to be extended from east to west 90°, or a quarter of a great circle of the earth, at least; because the places where the moon raises most, and most depresses the water, are at that distance from one another. Hence it appears, that it is only in the great oceans that such tides can be produced, and why, in the large Pacific ocean, they exceed those in the Atlantic. ”

“ If all the intertropical heat of the sun were to pass into the seas upon which it falls, simply raising the temperature of their waters, it would create a thermo-dynamical force in the ocean capable of transporting water scalding hot from the torrid zone, and spreading it, while still in the tepid state, around the poles. The annual evaporation from the trade-wind region of the ocean has been computed, according to the most reliable observation, to be as much as 15 feet, which is at the rate of half an inch per day. ”

“ Upon the sides of mountains, or on their summits, now thousands of feet above the level of the ocean, unquestionable traces of the action of the sea can be found. And the scientific observer of to-day sees all about him evidences that the immense work of the creation of continents, commenced by the sea in the earliest periods of time, is to-day continuing without relaxation or intermission, and with such energy that even during the short course of a single life great changes can be seen to have been produced. ”

“ The circular disc of the earth was crossed from east to west and divided into two equal parts by the “sea,” as they called the Mediterranean, and its continuation, the Euxine.
Around the earth flowed the “River Ocean,” its course being from south to north on the western, and in a contrary direction on the eastern side. It flowed in a steady, equable current, as was supposed, unvexed by storm or tempest. The sea and all the rivers on earth received their waters from it. ”

“ PAGE 149 THE OPEN SEA IN THE ARCTIC OCEAN.
surface, by changes, from whatever cause, in the course or velocity of the surface current, for obviously the under current could not bring more water into the frozen ocean than the surface current would carry out again, either as ice or water.
287. Every winter, an example of how very close warm water in the sea and a very severe climate on the land or the ice may be to each other, is afforded to us in the case of the Gulf Stream, and the Labrador-like climate of New England, Nova Scotia, and Newfoundland. ”

“ For instance, it will happen sometimes that when both the sun and moon are acting conjointly they will both be at their nearest point to the earth, and when this is the case the spring tide will be much higher than usual.
For many years the writer has observed that artesian wells, made by deep borings of small diameter into the earth to a water supply, have a daily period of ebb and flow, as well as a neap and spring tide, the same as the tides of the ocean, except that the process is reversed. ”

“ Another fact that points in the same direction is the existence over the whole floor of the deepest oceans of ice-cold water, which, originating in the polar seas, owing to its greater density sinks and creeps slowly along the ocean bottom to the depths of the Atlantic and Pacific, and is not perceptibly warmed by the internal heat of the earth. ”

“ From these light Observations, I think it may be concluded, First, that in all Places, Currents and Tides have a very great affinity. That it is principally the Formation of the Lands drives them into the one or the other; if contracted between two Shores so as to form a Channel, the diurnal Elevation of the Ocean, by the Attraction of the Moon, will make there a Tide, rapid in proportion to it’s Breadth, Depth, and Sea it is open to: And if an open Coast, as Guinea, those Tides become Currents. ”

“ The time of greatest flow of an artesian well will occur at low tide in the ocean. This might be accounted for from the fact that when the tide is at its height the moon is also pulling upon the crust of the earth, which would tend to take the pressure off the sand rock which lies one or two thousand feet below the surface and through which the flow of water comes, and thus slacken the flow. When the moon is in position for low tide, the crust of the earth would settle back and thus produce a greater pressure upon the water-bearing rock. ”

“ We know that cold ocean-rivers pour from north-polar regions to the south, both in the Atlantic and in the Pacific. A general creeping under-flow of icy waters towards the equator evidently balances the general surface drift of warm waters towards the poles. Since cold water is heavier than warm, it would naturally find its way to lower depths, leaving the warm light liquid to float on the top. ”

“ Contrary to the rule in the Equatorial seas, we find in the Polar-ocean an increase of temperature from the surface downwards, in consequence of the warmer under-currents, flowing from the south northwards, and passing beneath the cold waters of the superficial Arctic current. ”

“ 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. ”

“ A stream of colder water also flows from the Black Sea into the Mediterranean. It must happen in many other parts of the world that large quantities of water raised from one tract of the ocean by solar heat, are carried to some other where the vapor is condensed and falls in the shape of rain, and this, in flowing back again to restore equilibrium, will cause sensible currents. ”

“ 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. ”

“ That in this period our continents as far south as the latitude of 40° were overwhelmed with ice or ice-laden seas is rendered evident by the fact that the whole surface up to several thousands of feet above the sea-level has been bared of its accumulated débris and polished and grooved by ice, and laden with boulders and other glacial deposits, while in many places at heights of even 1,000 or 1,200 feet these deposits contain sea-shells of species now living in the colder parts of the ocean. ”

“ The trade winds prevail about thirty degrees on each side of the equator. This part of the ocean may be called the Elysian Fields of Neptune’s empire; and the torrid zone, notwithstanding Ovid’s remark, “non est habitabilis æstu,” is rendered healthy and pleasant by these gently-blowing breezes. The ship glides smoothly on, and you soon find yourself within the northern tropic. ”