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rivers, the Zambesi on the south-east coast, and the Congo on the south-west. No river, except the Nile, flows into the Mediterranean from the north coast of Africa; this arises partly from the Atlas chain lying so near the coast and partly from the rainless character of Northern Africa. The chief fresh-water lakes of Africa are the following:1. Victoria Nyanza, White Nile.

2. Albert Nyanza,
3. Dembea,

4. Tanganika,

5. Nyassa,

Blue Nile.
Qu. Congo.
Zambesi system.

There are two continental basins in Africa connected with Lake Tchad, in Central Africa, and Lake Ngami, in Southern Africa. The waters of these lakes are salt, like that of Utah, because there is no outlet, and the salts washed from the soil by the streams that supply the lakes must continually accumulate.

(d.) River system of Asia and Europe. The great Continent is characterized, as already stated, by a great central plateau, produced by the intersection of the north and south chain with the east and west chain. This elevated plateau forms one-fourth part of the entire continent, and constitutes a great river system in itself, called the Basin of the Continental Streams, because it has no outflow to the ocean. The rivers of this system flow into a number of salt lakes like Tchad and Ngamni, in Africa.

The rivers are :— 1. Volga,

2. Ural,

3. Kur,

4. Amoo (Oxus),

5. Sir Daria (Jaxartes),

6. Helmund.

7. Lob Lake System.

Caspian Sea.

Ural Sea.

The great rivers of Asia flow south, east, and north, from the great central plateau, and may be thus most conveniently grouped:

Rivers South of the Continental Basin,

1. Tigris and Euphrates.

2. Indus.

3. Ganges.

4, Bramapootra,

5. Irawaddy.

6 Menam Kong

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The river system of Europe is on a small scale as compared with that of Asia; its chief feature consists in the Danube, Rhone, and Rhine, rising near each other in the centre, and then flowing south-east, south, and north-west respectively. This arrangement of the rivers has proved of great advantage to trade and communication.

The lakes of Asia and Europe, although not developed on the same scale as those of North America, possess great interest. Among the salt lakes the most interesting are1. Caspian Sea. 3. Lake Balkash. 4. Dead Sea.

2. Sea of Aral.

The Caspian Sea is the largest salt lake in the world, and it lies in a flat depression of the land, for its surface is eightyfour feet below the level of the sea, and its depth in some places is 3,000 feet.

The Sea of Aral stands at a level of forty feet above the Black Sea.

The Dead Sea and Sea of Tiberias belong to the river Jordan, which flows in a narrow deep depression of the land running north and south. They are the lowest lying sheets of water on the globe, the surface of Tiberias being 328 feet below the level of the Mediterranean, and the surface of the Dead Sea being 1,312 feet below the same level. The Sea of Tiberias is fresh and abounds in fish, as everyone knows from the Gospels; its freshness is owing to its having an outlet in the Jordan. The Dead Sea is the saltest water in the world, and has no outlet.

Among the fresh-water lakes of Asia and Europe may be gamed:

1. Lake Baikal.

2. Ladoga and the Finland Lakes.

3. The Swiss Lakes.

4. Sir-i-kcl and Manasarowar.

Lake Baikal, in Siberia, is the largest of lakes placed at a high elevation above the sea, its surface is 1,800 feet above the sea level.

Lake Sir-i-kol, in Turkestan, is the source of the River Amoo (Oxus), and is 15,000 feet above the sea level. This lake and Manasarowar are the highest lakes in the world.

Lake Manasarowar, in Thibet, is the source of one of the branches of the Indus, and is situated 15,000 feet above the

sea.

QUESTIONS FOR EXAMINATION ON CHAP. V.

Pages 69-79.-What are the chief subjects involved in a systematic study of Physical Geography? 2. What is the first law of climate? 3. What is the second law of climate? 4. What is the third law of climate? 5. How does rainfall depend on latitude? 6. How does rainfall depend on the direction of the wind in Europe and the United States of North America? 7. What are the rainless districts of the world? 8. Mountain chains belong to two classes; what are they? Pages 80-86.-What are the meridian deep sea valleys and mountain chains of the southern hemisphere? 2. What are the meridian deep sea valleys and mountain chains of the northern hemisphere? 3. Describe the east and west chains of Asia and Europe. 4. What are the plains and plateaux of Asia and Europe? 5. Describe the plains and plateaux of North and South America, and of Africa.

Pages 87-94.-What are the trade wind zones? 2. What are the anti-trade wind zones? 3. What are the Doldrums and the Horse Latitudes? 4. Where are the greatest and least atmospheric pressures found to exist? 5. Where are the greatest and least number of rainfalls in a given time? 6. Describe the circulation of the North Atlantic Ocean. 7. Describe the circulation of the South Atlantic and North Pacific Oceans. 8. Describe the circulation of the South Pacific and Indian Oceans.

Pages 95-101.-Describe the river systems of South and North America. 2. Describe the lake systems of North America. 3. Describe the river systems of Africa. 4. Describe the lake systems of Africa. 5. Describe the river systems of Asia and Europe.

CHAPTER VI.

ZONES CLIMATES-TEMPERATURE.

WE have seen that, in

consequence of the inclination of

the earth's axis, and its constant direction to the same point the entire annual revolution, the

in the heavens during

* See p. 27.

northern and southern hemispheres are enabled to enjoy in their turn an equal portion of the light and heat of the sun. But though both hemispheres, generally speaking, enjoy an equal portion of light and heat, yet in the hemispheres themselves there is a great diversity of temperature, in consequence of the rays of the sun striking the surface directly in some parts and obliquely in others. In those parts of each hemisphere which lie near the equator, the rays of the sun strike the surface more directly, and these regions are, in consequence, excessively warm; while in the direction of, and about the poles, in both hemispheres, the sun shines more and more obliquely, and the consequence is, that the temperature in these parts of the earth becomes less and less in proportion.

Hence the division of the earth's surface into ZoNEs, and its subdivision into CLIMATES. The word zone means a girdle or belt, and the term climate a gradation. The zones are five in number--namely, one TORRID, two TEMPERATE, and two FRIGID. The Torrid zone encompasses the middle or warmest part of the earth; and hence its name torrid, which implies excessive heat. This division of the earth extends to 23 degrees on each side of the equator, and consequently comprehends a large and equal portion of both hemispheres. Through the northern limit of the Torrid zone the tropic of Cancer is conceived to be drawn, and through the southern the tropic of Capricorn. The Torrid zone, therefore, lies between the tropics, and the sun is, consequently, always vertical or overhead in some part of it.

The North Temperate zone lies between the tropic of Cancer and the Arctic circle, and the South Temperate, between the tropic of Capricorn and the Antarctic circle. Each of these zones, therefore, is 43 degrees broad. Except in those parts which lie near the tropics and polar circles, neither the heat nor cold is in excess; and hence these great divisions of the earth's surface have been denominated the temperate

zones.

The Frigid zones extend from the polar, or Arctic and Antarctic circles to the poles, and are consequently 23 degrees broad each. In these regions of the earth the cold is excessive, particularly about the poles; and hence they have been designated the frigid zones. The extreme cold of the frigid zones is occasioned by the total disappearance of the sun

during the winter; and the great obliquity of his rays during the summer of their

year.

The extent of the zones in degrees will not, it is evident, give us their real magnitudes; but the following estimate will enable us to form an idea of their relative sizes. It has been estimated that if the entire surface of the earth were divided into 100 equal parts, the Torrid zone would contain about 40; each of the Temperate zones about 26, and each of the Frigid zones about 4 of these parts. The inhospitable and frozen regions of the earth, therefore, are almost nothing when compared to the habitable parts of it.

b

The division of the earth's surface into zones was found, though natural and appropriate, to be too general, and hence its subdivision into climates, which may be regarded as small zones or girdles, encompassing the earth from the equator to the poles. The different lengths of the days in different latitudes is the principle upon which this division was founded. At the equator, as we have seen, the days and nights are equal throughout the year--that is, they consist of 12 hours each; but if we recede from the equator, north or south, this equality will cease to exist. When the sun is north of the equator the days are longer than the nights in the northern hemisphere; and when the sun is south of the equator the reverse of this is the case; and in the southern hemisphere, of course, similar changes take place.

At the equator the day is always 12 hours long, but at 8° 34' north or south of it, the length of the day extends to 12 hours. Now, if we conceive parallels of latitude to be drawn through those points of the earth's surface which are 8° 34' distant from the equator north and south, we have inclusive the first climate in each hemisphere. Again, at the distance of 8° 10′ more, or in latitude 16° 44′ north and south, the length of the longest day is found to be half an hour longer-that is, 13 hours; and here, the boundary of the second climate, in each hemisphere, is conceived to be drawn. And, as the longest day increases from 12 hours at the equator to 24 hours at the polar circles, it is evident that there are 24 climates between the equator and each of the polar circles; for in every place where the longest day

⚫ See page 31 for the natural position of the TROPICS and POLAR circles, the boundaries of the zones.

See page 32.

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