LESSON XVI.-SHIP AMONG THE ICEBERGS.

1. A FEARLESS shape of brave device,

Our vessel drives through mist and rain
Between the floating ships of ice,

Those navies of the northern main;
Those arctic ventures blindly hurled,
The proofs of Nature's olden force,
Like fragments of a crystal world

Long shattered from its skyey course.
2. These are the hurricanes that fright

The middle sea with dream of wrecks,
And freeze the south winds in their flight,
And chain the Gulf Stream to their decks.
At every dragon prow and helm

There stands some viking as of yore,
Grim heroes from the boreal realm,
Where Odin rules the spectral shore.
3. Up signal there! and let us hail

Yon looming phantom as we pass;
Note all her fashion, hull and sail,
Within the compass of your glass.
See at her mast the steadfast glow

Of that one star of Odin's throne;
Up with our flag, and let us show

The constellation on our own.
And speak her well; for she might say,
If from her heart the words could thaw,
Great news from some far frozen bay,
Or the remotest Esquimaux.

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.

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The floor is of sand, like the mountain-drift,

And the pearl-shells spangle the flinty snow;
From coral rocks the sea-plants lift

Their boughs, where the tides and billows flow;
The water is calm and still below,

For the winds and waves are absent there;
And the sands are bright as the stars that glow
In the motionless fields of the upper air.

There, with its waving blade of green,

The sea-flag streams through the silent water,
And the crimson leaf of the dulse is seen

To blush like a banner bathed in slaughter;
There, with a light and easy motion,

The fan-coral sweeps through the clear deep sea,
And the yellow and scarlet tufts of ocean

Are bending like corn on the upland lea;
And life in rare and beautiful forms

Is sporting amid those bowers of stone,
And is safe when the wrathful spirit of storms
Has made the top of the waves his own.

And when the ship from his fury flies

Where the myriad voices of ocean roar,
When the wind-god frowns in the murky skies,

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 twigs 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.

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LESSON XVIII.-OCEAN WAVES.

ROLL on, thou deep and dark blue ocean-roll!
Ten thousand fleets sweep over thee in vain;
Man marks the earth with ruin-his control
Stops with the shore; upon the watery plain
The wrecks are all thy deed, nor doth remain

A shadow of man's ravage, save his own,

When, for a moment, like a drop of rain,
He sinks into thy depths with bubbling groan,
Without a grave, unknelled, uncoffined, and unknown.
And I have loved thee, ocean! and my joy

Of youthful sports was on thy breast to be
Borne, like thy bubbles, onward: from a boy
I wantoned with thy breakers-they to me
Were a delight; and if the freshening sea
Made them a terror, 'twas a pleasing fear,
For I was, as it were, a child of thee,
And trusted to thy billows far and near,
And laid my hand upon thy mane-as I do here.-BYRON

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 wayes 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.

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6. There is no more magnificent sight than the roll of the breakers as they dash upon some rock-bound coast. The 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!

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Bear'st thou not from distant strands
To my heart some pleasant token'?
Tales of mountains of the south,
Spangles of the ore of silver,
Which with playful singing mouth,
Thou hast leaped on high to pilfer'?
Mournful wave! I deemed thy song
Was telling of a mournful prison,
Which, when tempests swept along,
And the mighty winds were risen,
Foundered in the ocean's grasp,

While the brave and fair were dying.
Wave! didst mark a white hand clasp
In thy folds as thou wert flying?
Hast thou seen the hallowed rock

Where the pride of kings reposes,
Crowned with many a misty lock,

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!
When this soul's last joy or mirth
On the shore of time is driven,

Be its lot like thine on earth,

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, à 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 causes. Constant currents are produced by the combined action of the ro tation of the earth, the heat of the sun, and the trade-winds; periodical currents are occasioned by tides, monsoons, and other long-continued

vinds; 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."