Wish could ser LESSON XVI.-SHIP AMONG THE ICEBERGS. 1. A FEARLESS shape of brave device, Our vessel drives through mist and rain Those navies of the northern main; Long shattered from its skiey course. The middle sea with dream of wrecks, There stands some viking as of yore, Yon looming phantom as we pass; Of that one star of Odin's throne; The constellation on our own. If from her heart the words could thaw, 4. No answer: but the sullen flow Of ocean heaving long and vast; An argosy of ice and snow, The voiceless North swings proudly past. LESSON XVII.—THE DEPTHS OF OCEAN. DRUMMOND. 1. NOTHING can be more beautiful than a view of the bottom of the ocean during a calm, even round our own shores, but particularly in tropical climates, especially when it consists alternately of beds of sand and masses of rock. The water is frequently so clear and undisturbed that, at great depths, the minutest objects are visible; groves of coral are seen expanding their variously-colored clumps, some rigid and immovable, and others waving gracefully their flexile branches. Shells of every form and hue glide slowly along the stones, or cling to the coral boughs like fruit; crabs and other marine animals pursue their prey in the crannies of the rocks, and sea-plants spread their limber leaves in gay and gaudy irregularity, while the most beautiful fishes are on every side sporting around. 2. The floor is of sand, like the mountain-drift, And the pearl-shells spangle the flinty snow; Their boughs, where the tides and billows flow; For the winds and waves are absent there; There, with its waving blade of green, The sea-flag streams through the silent water, To blush like a banner bathed in slaughter; The fan-coral sweeps through the clear deep sea, Are bending like corn on the upland lea; Is sporting amid those bowers of stone, And when the ship from his fury flics Where the myriad voices of ocean roar, And demons are waiting the wreck on shore, Then far below in the peaceful sea The purple mullet and gold-fish rove, Where the waters murmur tranquilly Through the bending twig, of the coral grove. PERCIVAL. 5. The allusion to the "peaceful sea," below the reach of the storms which agitate the surface, has reference to the well-known fact that the effects of the strongest gale do not extend below the depth of two hundred feet: were it not so, the water would be turbid, and shell-fish would be destroyed. 1. 2. LESSON XVIII.-OCEAN WAVES. ROLL on, thou deep and dark blue ocean-roll! When, for a moment, like a drop of rain, Of youthful sports was on thy breast to be 3. The three great movements of the ocean are waves, caused by the winds, tides, caused by the attraction of the sun and moon, and currents, caused by the earth's rotatory motion and the unequal heating of the waters. 4. There is a kind of wave or undulation called a ground swell, occasioned by the long continuance of a heavy gale. This undulation is rapidly transmitted through the ocean to places far beyond the direct influence of the gale that caused it, and often it continues to heave the smooth and glassy surface of the sea long after the wind and surface waves have subsided. 5. The force of waves in severe gales is tremendous. Mr. Stephenson has estimated the force of waves which were twenty feet high as being three tons to each square foot against perpendicular masonry. Waves vary in magnitude, from a mere ripple to enormous billows, but their height in storms is from ten to twenty-two feet. From the bottom of the hollow, or "trough of the sea," the height will be double that of the wave, or from twenty to forty-four feet. The distance between one "storm wave" and another is about five hundred and sixty feet, and the velocity of the waves about thirty-two miles an hour. 6. There is no more magnificent sight than the roll of the breakers as they dash upon some rock-bound coast. The 66 roar of the surf" after a storm is often tremendous, and may be heard at the distance of many miles. The spray is sometimes thrown as high as one hundred and fifty feet; and light-houses more than a hundred feet in height are often literally buried in foam and spray, even in those ground swells where there is no wind. 7. But when an ocean wave has exhausted its force, and breaks in a gentle ripple on the shore, nothing can be more peacefully beautiful, and no music falls with sweeter cadence on the ear. How different the picture from Byron, which we have placed at the head of this lesson, from the one with which we close! 10. 11. 12.. Bear'st thou not from distant strands Was telling of a mournful prison, While the brave and fair were dying. Where the pride of kings reposes, Wreathed with sapphire green and roses? Or with joyous playful leap, Hast thou been a tribute flinging, Up that bold and jutty steep, Pearls upon the south wind stringing? Faded wave! a joy to thee, Now thy flight and toil are over! Oh may my departure be Calm as thine, thou ocean rover! To be lost away in heaven-Anonymous. LESSON, XIX.-TIDES AND CURRENTS. 1. THE alternate elevation and depression of the waters of the ocean twice every twenty-four hours, was formerly considered one of the greatest mysteries of nature. The first man who clearly explained the cause and phenomena of tides was Sir Isaac Newton. Their true cause he demonstrated to be the attraction of the sun and moon, particularly the latter on account of her proximity to the earth. 2. The average height of the tides will be increased by a very small amount for ages to come, on account of the decrease of the mean distance of the moon from the earth; but after they have reached their greatest height, a reverse movement will take place. Thus there are great tides of tides, or oscillations between fixed limits, requiring immense periods of time for their accomplishment. The tidal wave extends to the very bottom of the ocean, and moves with great velocity. 3. "Currents of various extent, magnitude, and velocity," says Mrs. Somerville, "disturb the tranquillity of the ocean; some of them depend upon circumstances permanent as the globe itself, others on ever-varying Constant currents are produced by the combined action of the rotation of the earth, the heat of the sun, and the trade-winds; periodical currents are occasioned by tides, monsoons, and other long-continued causes. winds; temporary currents arise from the tides, melting ice, and from every gale of some duration. A perpetual circulation is kept up in the waters of the main by these vast marine streams; they are sometimes superficial and sometimes submarine, according as their density is greater or less than that of the surrounding sea. 4. The most constant and most important of all these currents, and one which exerts a modifying influence on all the others, is that produced by the rotation of the earth on its axis. As the waters descend from the poles, where they have no rotatory motion, the earth's surface revolves more and more rapidly, until, at the equator, it has acquired an easterly motion of a thousand miles an hour; and as the waters do not fully partake of this motion, they are left behind, and consequently seem to flow westward in a vast stream nearly four thousand miles broad. This stream, being broken, and its parts changed in various directions by the islands and continents which it meets in its course, gives rise to numerous smaller currents, which in their turn are again modified by the general westerly flow, and by winds, rivers, and melting ice. 5. Among these smaller currents is the "Gulf Stream," occasioned chiefly by the constant flow of the waters of the tropics westward across the Atlantic Ocean. A part of this vast heated current is directed into the Gulf of Mexico; issuing thence, it proceeds in a northeasterly direction along the coast of the United States, and being deflected still farther eastward by the great island of Newfoundland, it crosses the Atlantic, and spreads its warm waters around the coasts of the British Isles. "It is the influence of this stream upon climates," says Lieutenant Maury, "that makes Erin the Emerald Isle, and clothes the shores of Albion with evergreen robes; while, in the same latitude on the other side, the shores of Labrador are fast bound in fetters of ice." Any convulsion of the globe that should open a broad channel through the isthmus of Panama would direct this stream into the Pacific, and change the British Isles into a scene of sterility and desolation. 6. It is very important for navigators to study the course and velocity of the ocean currents, as the length and safety of the voyage depend upon them. So much does this circulation of the ocean resemble the circulation of fluids in the human system, that our distinguished countryman, Captain Maury, who has so successfully studied and described them, has been appropriately called the "Harvey of the seas." |