Imatges de pàgina
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1. THE depressions on the surface of the earth, caused by earthquakes, volcanoes, or other means, are frequently filled with water, and constitute what are termed lakes. Rivers meeting with obstructions of hills and rocky ridges often form a lake, or chains of lakes, which serve the purposes of navigation, and give variety to the inland landscape.

2. Many lakes are fed by springs, and sometimes they are the sources of large rivers. It is estimated that more than half the fresh water on the globe is contained in the great American lakes, the largest of which is nearly as large in area as England. Lakes are most numerous in high latitudes, where there is abundant rain and but little evaporation.

3. The five great American lakes, Superior, Huron, Erie, Michigan, and Ontario, are much higher than the level of the ocean. Lake Superior has an elevation of more than six hundred feet, and Lake Ontario two hundred and thirty-four feet. The Great Salt Lake, situated in the elevated tableland east of the Rocky Mountains, is about forty-two hundred feet above the level of the sea. Yet it is a curious fact that those great salt-water lakes of Asia, the Caspian Sea, Lake of Tiberias, and the Dead Sea, are each below the sea

level, the first eighty-four feet, the second six hundred feet, and the third more than thirteen hundred feet. The poet Percival, in the following ode, has painted the witching charms of hundreds of our small interior lakes:

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TO SENECA LAKE.

"On thy fair bosom, silver lake,

The wild swan spreads his snowy sail,
And round his breast the ripples break,
As down he bears before the gale.
On thy fair bosom, waveless stream,
The dipping paddle echoes far,
And flashes in the moonlight gleam,
And bright reflects the polar star.
The waves along thy pebbly shore,

As blows the north wind, heave their foam,
And curl around the dashing oar,

As late the boatman hies him home.

How sweet, at set of sun, to view

Thy golden mirror spreading wide,

And see the mist of mantling blue

Float round the distant mountain's side.

At midnight hour, as shines the moon,

A sheet of silver spreads below,

And swift she cuts, at highest noon,

Light clouds, like wreaths of purest snow.
On thy fair bosom, silver lake,

Oh! I could ever sweep the oar,

When early birds at morning wake,
And evening tells us toil is o'er.""

LESSON XXI.-SPRINGS AND RIVERS.

Great Geyser of Iceland.

1. In addition to the common springs, with whose origin every one is familiar, mineral springs of great variety abound in different countries, the waters of some of which merely present a sparkling appearance, owing to the presence of carbonic acid gas, while others are variously impregnated with mineral substances, the chief of which are iron, sulphur, and salt.

2. Besides these, Iceland presents us a remarkable group of hot springs, called geysers, which burst forth with subterranean noises, and frequently at regular intervals, throwing up water and steam, sometimes to the height of one or two hundred feet. The supposed cause of this peculiar action is the heating of some internal fountain of water

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by volcanic agency, until a sufficient quantity of steam is formed forcibly to expel the wa

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Section of a Geyser.

ter through a

channel which
has its opening
in the spring.
An illustration
of an intermit-
ting spring is
also given, for
the action of
which it is suf-

ficient to refer
to the principle

of the siphon.*

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Intermitting Spring.

3. The excess of water precipitated as rain and snow, over what is evaporated from the surface, runs in streams, called rivers, to lakes, or to the ocean. The position of mountains and elevated ridges determines the course and length of rivFew physical causes have had more influence in the location and fortunes of men, than rivers. Capitals of states and countries are generally on rivers, and large cities either on navigable rivers or bays.

ers.

4. Rivers are associated with the earliest efforts of mankind to emerge from a state of barbarism; but they are no less serviceable to nations which have reached the acme of civilization. In the earliest ages they were regarded with veneration, and became the objects of a grateful adoration, surpassed only by that paid to the sun and the host of heaven.

5. Nor is this suprising; for in countries where the labors of the husbandman and shepherd depended, for a successful issue, on the falling of periodical rains, or the melting of the collected snows in a far-distant country, such rivers as the Nile, the Ganges, and the Indus were the visible agents of nature in bestowing on the inhabitants of their banks all the blessings of a rich and spontaneous fertility; and hence their waters were held sacred, and they received, and to this day retain, the adoration of the countries through which they flow.

The

See p. 347. Intermitting springs sometimes flow only during the dry season. cut above will explain this. Suppose the internal fountain to be empty. When the earth has become fully saturated with water during the wet season, the water begins to penetrate to the fountain, which gets filled as high as the upper bend of the siphon about the time when the dry season commences, and it is just then that the siphon begins to empty it; and it is evident that it will continue to act until the fountain is exhausted. After stopping, the water can not flow again until the fountain has been again filled, which prob. ably will not be until near the end of the wet season.

6. The direction and extent of slopes of land give rise to a classification of rivers called river systems, which can be studied at length in works on physical geography.

LESSON XXII.—CATARACTS.

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THE FALLS OF NIAGARA, as viewed from the Canada side. [On the right of the picture are seen the Horseshoe Falls, on the Canada side of the stream; beyond, and separated from the former by Goat Island, are the Falls on the Amer ican side. The view down the stream has been abridged in order to bring in the Suspension Bridge, which is seen in the distance. The effect of every such picture is greatly increased by looking at it through a tube, which shall shut out the view of surrounding objects. One formed

by partially closing the hand will answer.]

1. SOMETIMES large rivers fall suddenly over perpendicular rocks, forming cataracts, or falls. When a brook or small stream presents a similar phenomenon, it is usually called a cascade.

2. In mountain regions there are cascades hundreds of feet in height so high that, from the resistance of the air, the water reaches the bottom as a fine spray. In southern Asia are several cascades more than eight hundred feet high: the Fall of Staubach, in Switzerland, described in Byron's "Manfred," has a perpendicular descent of eight hundred feet; and the Falls of the Rhine, though not so lofty as many others, are highly celebrated for their beauty.

3. Among American waterfalls, the most noted are those of the Montmorency, 'near Quebec, which descend two hundred and forty feet in an unbroken sheet; the Great and the

Little Falls of the Potomac, in Maryland; the Falls of the Missouri; the Rapids of the St. Lawrence, five hundred miles from its source; and, lastly, the grandest of all, and the mightiest in its mass of waters, the world-renowned Falls of Niagara. From a thousand descriptions of this great natural curiosity, our space limits us to a brief selection.

4. "There is a power and beauty, we may say a divinity, in rushing waters, felt by all who acknowledge any sympathy with nature. The mountain stream, leaping from rock to rock, and winding, foaming, and glancing through its devious and stony channels, arrests the eye of the most careless or business-bound traveler, sings to the heart, and haunts the memory of the man of taste and imagination, and holds, as by some indefinable spell, the affections of those who inhabit its borders. A waterfall of even a few feet in height will enliven the dullest scenery, and lend a charm to the loveliest; while a high and headlong cataract has always been ranked among the sublimest objects to be found in the compass of the globe.

5. "It is no matter of surprise, therefore, that lovers of nature perform journeys of homage to that sovereign of cataracts, that monarch of all pouring floods, the Falls of Niagara. It is no matter of surprise that, although situated in what might have been called a few years ago, but can not be now, the wilds of North America, five hundred miles from the Atlantic coast, travelers from all civilized parts of the world have encountered all the difficulties and fatigues of the path to behold this prince of waterfalls amid its ancient solitudes, and that, more recently, the broad highways to its dominions have been thronged. By universal consent, it has long ago been proclaimed one of the wonders of the world. It is alone in its kind. Though a waterfall, it is not to be compared with other waterfalls. In its majesty, its supremacy, and its influence on the soul of man, its brotherhood is with the living ocean and the eternal hills."-GREENWOOD. n

6. From the vicinity of the famed Table Rock on the Canada side, the whole scene is presented in its highest degree of grandeur and beauty. On the right, and within a few feet, is the edge of the grand crescent, called the British, or Horseshoe Fall, which is more than one third of a mile broad, and one hundred and fifty-three feet in height. Opposite is Goat Island, which divides the falls; and lower down, to the left, is the American Fall, six hundred feet in breadth, and one hundred and sixty-four feet in height. From a writer who first viewed the falls from the vicinity of Table Rock, we take the following description:

I could see

7. "A mingled rushing and thundering filled my ears. nothing, except when the wind made a chasm in the spray, and then tremendous cataracts seemed to encompass me on every side; while below, a raging and foamy gulf of undiscoverable extent lashed the rocks with its hissing waves, and swallowed, under a horrible obscurity, the smoking floods that were precipitated into its bosom.

8. "At first the sky was obscured by clouds, but, after a few minutes, the sun burst forth, and the breeze subsiding at the same time, permitted the spray to ascend perpendicularly. A host of pyramidal clouds rose majes

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