inches, while on the sea-coast it is not half that amount. On the Great St. Bernard it is 63 inches, and at Paris only 21. "The description of Judea by the sacred writer, contrasting it with the flat lands of Egypt, though not intended to be philosophic, is in harmony with the teachings of science respecting the important part performed by mountains in the general economy of the earth: For the land whither thou goest in to possess it, is not as the land of Egypt, from whence ye came out; but the land whither ye go to possess it, is a land of hills and valleys, and drinketh water of the rain of heaven.' By arresting the course of the clouds, and producing a condensation of aqueous vapor when a warm current of air lights upon their cold summits, the elevations contribute to precipitate the moisture of the atmosphere, often amid a terrible display of electric phenomena a blaze of fiery horrors, and the echo of heart-thrilling sounds."'*

476. In some portions of the world rain is entirely unknown, or occurs so seldom as to be quite a phenomenon. The rainless or nearly rainless regions of the New World comprise portions of California and Arizona, of the Mexican table-land, and of Guatemala, also the coast region of Peru and Bolivia, and much of Patagonia east of the Andes. Those of the Old World comprehend an immense territory, stretching from Morocco, through the Sahara, a part of Egypt, Arabia, and Persia, into Beloochistan, with another great zone, commencing north of the Hindoo-Koosh and Himalayas, including the table-land of Tibet, the desert of Gobi, and a portion of Mongolia.

477. The rains of most tropical countries are periodical,— seasons of extreme humidity regularly alternating with those of excessive drought. The length of time of the rainy season differs in different districts, but lasts generally from three to five months. The periodical rains commence in Panama, on the west coast of America, in the early part of March; in Africa, near the equator, and on the banks of the Orinoco, they begin in April; in the countries watered by the Senegal, and at San Blas, in California, they begin in June. The violence of these tropical showers may be inferred from the large annual amount of rain, and from its fall being limited to a few months, and to a few hours during the day. The drops are enormous, very close together, and fall with such rapidity as to occasion a sensation of pain if they strike against the skin.

478. In both continents the districts which have their periodical rains are subject to an occasional intermission, and become rainless for considerable intervals, the drought inflicting terrible suffering on man and beast. Such a period happened between the years 1827 and 1830 in the state of Buenos Ayres, and is known by the name of the gran seco, or the great drought. This interval was very destructive to animals. The loss of cattle in the province of Buenos Ayres alone was estimated at one million head. Cattle in herds of thousands rushed into the Parana, and being exhausted by hunger, they were unable to crawl up the muddy banks, and thus were drowned.

LESSON X.

SNOW AND HAIL.

479. SNOW is vapor somewhat condensed, and congealed before it collects in drain-drops. Snow-flakes exhibit forms

Questions.-476. What do the rainless or nearly rainless regions of the New World comprise? What, those of the Old World? 477. What is said of the rains of most tropical f countries? Length of the rainy seasons? When do they commence at Panama, etc.? Violence of these tropical showers? 478. To what are the rainless districts of both continents subject? Example? Destruction of cattle? 479. What is snow?

• Rev. Thomas Milner.

of exquisite beauty, regularity, and endless variety. These varied shapes are assumed while the body passes from the vapor form to the solid state. The tendency of vapor to crystallize, while in the process of congelation, may be observed in frost as it collects on the window-panes in winter.

480. A microscope applied to a flake of snow which has fallen in a still atmosphere will unfold its wonderful mode of structure. It is only in the polar regions that snow assumes its most beautiful and varied forms. Captain Scoresby has figured ninety-six different varieties, which he discovered during his arctic voyages, and which he distributed into classes of la mellar,* spicular, and pyramidal crystals, as shown in the

above representation. It will be seen that the annexed forms are mostly hexagonalt stars, and consequently snow-flakes belong to the hexagonal system of crystals. Kaemtz observes that flakes which fall at the same time have generally the same form; but if there is an interval between two consecutive falls of snow, the forms of the second are observed to differ from those of the first, although always alike among themselves.

481. The limits of the fall of snow at the level of the sea, in the northern hemisphere, are about the parallel of 30° in Amer

ica, which cuts the southern part of the United States; 43° in the center of the North Atlantic; and 36° in the Old World, the latitude of Algiers. But for several degrees above these limits its appearance is rare and brief.

482. Snow performs an important part in the general economy of nature. In winter it serves as a mantle to keep the ground warm, and thus protect vegetation from being destroyed by the frost, or by cold biting winds. Accumulated on elevated mountain chains, it affords, by its thawing, a regular supply to rivers and to the interior reservoirs of the earth, while in low latitudes it tempers the heat of warm regions.

483. Hail appears to be partly the result of intense cold rapidly produced in the atmosphere; it is supposed to be also somewhat dependent upon electricity, which is almost always powerfully developed during hail-storms. In very high latitudes it is unknown, and it is also rare at the level of the sea within the tropics. The icy particles which fall vary in shape and size. True hail is an opaque mass, and has generally the form of a pear, or of a mushroom; large hailstones are surrounded by a thick coat of ice, and are composed of alternate layers of snow and ice. No one has ever seen hailstones formed entirely of transparent ice.

484. Many instances are well authenticated of hailstones having a circumference of from 6 to 9 inches, and a weight of from 12 to 14 ounces; but much larger masses are recorded. June 15, 1829, the hail beat in the roofs of the houses at Cazorta, in Spain,-some of the hailstones weighing upward of 4 lbs. avoirdupois. In Hungary, May 8, 1832, a block of ice fell, about 39 inches in breadth and length, and 27 inches in depth. Mr. Dar

win mentions a fall of hail in the state of Buenos Ayres which killed a large number of wild animals, ostriches, and smaller birds. These enormous

SNOW STORM.

masses are either the fragments of a thick sheet of ice suddenly formed, and broken in the atmosphere in falling, or are due to the union of a great number of hailstones in their descent.

NOTE.-The map-questions on pages 63 and 64 should receive attention before proceeding with the following lesson.

Questions.-482. What are some of the uses of snow? 488. Of what does hail appear to be the result? Upon what is it supposed to be also somewhat dependent? Where is it unknown and where rare? Appearance of true hail? 484. Size of some hailstones observed? Examples of destructive effects of hail? What is remarked of these enormous masses? 485. What is said of climate? What does the term climate commonly denote ? Taken in its more general sense, what does it signify?

LESSON XI.

CLIMATE.

485. CLIMATE, in its relation to animal and vegetable existence, constitutes one of the most interesting and important subjects belonging to physical geography. The term, as it is commonly understood, denotes the temperature of the air in the various regions of the globe; but taken in its more general sense, it signifies all those states and changes of the atmosphere which sensibly affect our organs,-temperature, humidity, variation of atmospheric pressure, the purity of the atmosphere, or its admixture with more or less deleterious exhalations, and lastly, the degree of habitual transparency of the air and serenity of the sky, which has an important influence on the feelings and the whole mental disposition of man.

486. Climate is determined by a variety of causes, the chief of which are: 1. The latitude of a country; that is, its geographical position with reference to the equator.. 2. Elevation of the land above the sea-level. 3. The proximity to, or remoteness of a country from, the sea. 4. The slope of a country, or the aspect it presents to the sun's course. 5. The position and direction of mountain chains. 6. The nature of the soil. 7. The degree of cultivation and improvement at which the country has arrived. 8. The prevalent winds. 9. The annual quantity of rain that falls in a country.

487. (1) The latitude of a country, and the consequent direction in which the solar rays fall upon its surface, are the. principal causes of the temperature to which it is subject. At the equator, and within the tropics, the greatest heat is experienced; because the sun is always vertical to some place within those limits, and the solar action is more intense in proportion as the rays are perpendicular to the earth. As we recede from the equator, they fall more obliquely; and because fewer of them are spread over a larger space, they are less powerful, or, in other words, less heating. It has been calculated that, out of 10,000 rays falling upon the earth's atmosphere, 8,123 arrive at a given point if they come perpendicularly; 7,024, if the angle of direction is 50°; 2,821, if it is 7; and only 5 if the direction is horizontal.

488. The latitude of a place is therefore of the first importance in determining its temperature, since a decrease of heat takes place with an increase of latitude as we travel, at the same level above the sea, from the equator toward the poles. This is true of countries lying between the tropics and the poles, but it is not true of places situated between the tropics and the equator.

489. "If the ecliptic, as shown on a terrestrial globe, be examined, it will be seen that toward the northern and southern limits, for a considerable distance, it neither approaches nor recedes from the equator or the pole, but has a direction due east and west. This ecliptic is, in point of fact, the path or the point of direct heat and sunlight over the earth's

[CONTINUED ON PAGE 64.]

Questions,-486. What are the principal causes which determine climate? 487. What principally determine the temperature of a country? Why is the greatest heat experienced within the tropics? What happens as we recede from the equator? 488. Why is the latitude of a place of the first importance in determining its temperature? Is this true of countries lying between the tropics? 489. Expiain why a greater degree of heat prevails at the tropics than at the equator.

heat." band. ister to the polar regions, in their due proportion, light and serves its parallelism. The object of it is obviously to minround an axis which has an inclined position, and which premade to revolve round the sun, rotating at the same time of that simple and admirable provision by which the earth is light at its nearest approach to the poles, is a necessary result 490. "This lingering of the point of direct heat and sunof the two outer bands 3 times as long as in the middle the point of direct sunlight would be found to linger in each be imagined to be divided into three equal bands of the earth,It has been calculated, that if the space between the tropics distance for a considerable time; or, as it were, lingers there.. turn back toward the other pole, but remains at that nearest reached its nearest approach to either pole, it does not at once surface. Thus, then, it appears that when this point has

the equator-an evidence of a higher temperathe Andes, in 17° south latitude, is higher than at cer; and it has been found that the snow-line of in Beloochistan-coincide with the Tropic of Canof the Senegal, the Tehama of Arabia, and Mekran where the greatest heat is experienced-the banks 491. In the northern hemisphere, the countries

ture.

earth. level of the sea. ature is experienced, until we arrive at a point where to increase our elevation, a rapid change of temperdiminished temperature; but the moment we begin face of the earth, before we become sensible of a the equator toward the poles, along the level surWe may travel several hundred miles from ther from the heat reflected from the surface of the of the air, and to the circumstance of being farthe cold increases,-an effect due to the rarefaction As we ascend in the atmosphere affected by the extent of their elevation above the 492. (2) The temperature of countries is largely

constant frost prevails.

part, from the region on the southeast? Is the breadth of the
Mediterranean such that the northerly winds which occasionally
blow over it would be likely to bear much moisture thence to
the Sahara east of the Atlas region? Is there any great chain
of mountains traversing this part of the Sahara which would
check these winds, and condense their scanty supply of vapor?
Would the increasing heat, as they blow toward the region
south of the Tropic of Cancer, expand their vapor and pre-
vent its precipitation until they encountered lofty barriers or
were met and condensed by the pressure of opposing winds?

As the tendency of the prevailing winds both in the northern
and southern half of the torrid zone is toward the region of great-
est heat, would the above-mentioned winds from the north, if un-
disturbed by local causes, be most likely to meet with opposing
winds in the region of the "Equator of Temperature or line of
maximum heat?" Does the Equator of Temperature pass
through Soudan? [See map, page 54.] Would the vapors from
the Mediterranean, therefore, be more likely to be precipitated
in Soudan than in the Sahara? Would the fact of the meeting
of the winds and condensation of their vapors in the region of
the Equator of Temperature prevent the passing over of vapor-
laden breezes from the south into the Sahara? Is the Sahara a
rainless region? Does this render it a desert? How, then, does
it happen that it is interspersed with fertile spots or oases?
Ans. Because these spots lie considerably below the general level of the
desert, and therefore are watered by subterranean springs.

Remark. We have observed that the general tendency of the
prevailing winds in both the northern and southern half of the
torrid zone is toward the region of greatest heat, and that as
they advance toward this region their vapors are expanded by
the increasing warmth, and therefore fail to yield rain (unless
the winds are obstructed) until they arrive near the "line
of maximum temperature," or, in other words, till they reach

the region where the pressure of the opposing winds etc.
causes their condensation. Accordingly, in the Atlantic and Pa-
cific (where the northeast and southeast trade-winds prevail
with much regularity, meeting each other in the Equatorial
"Zone of Calms'), the principal rains uniformly occur within
the Calms; while the regions between the latter and the vicinity
of the tropics are nearly rainless. But the region of greatest heat
or of the Equatorial Calms and the trade-wind regions are not
fixed; they move somewhat to the north and south, with the
apparent course of the sun. Hence the rainy belt of Calms,
passing over different sections in its northerly and southerly
course, gives them a wet season (the season of periodical rains);
while the trade-wind belt following, gives them a dry season.
This order of the seasons between the tropics occurs not only in
the Atlantic and Pacific, but in all the land regions open to the
trade-winds from thence. It is important, therefore, in consid-
ering the amount of rain which falls in the latter, and its
effect upon their condition as compared with that of the land in
most parts of the temperate zones, to bear in mind that it is
precipitated almost wholly during a few months, and the change
it produces is therefore exceedingly marked; while the change
which follows from prolonged drought is no less striking.-

Nearly the whole of the torrid region of South America is open
to the trade-winds from the Atlantic; should we infer, there-
fore, that it would be well supplied with periodical rains? Does
the map show that this supply is very abundant? What mount-
ain chain on the western side of South America, owing to its great
altitude, arrests and condenses whatever rain-clouds are borne
thither from the Atlantic? Is there a copious supply of rain
along the eastern side of this chain in the warmer latitudes ?
Supposing the existence, in the neighborhood of the equator, of
a great central valley reaching from the vicinity of the Andes
to the Atlantic, with numerous

lateral

valleys

opening

into it,

would this valley, owing to the abundance of the rains, neces-
sarily be traversed by a vast stream of water? Would the period-
icity of the rain cause this stream to be greatly swollen at some
seasons, and comparatively low at others? What immense river
of such a character, exists here?

Does the mountainous chain of islands belonging to the Lesser
Antilles (north of South America), receive a great amount of
rain? What island in this chain has over twenty-four feet
(292 inches) of rain a year, or more than has been observed
elsewhere in the New World? Are the borders of Central Amer-
ica and southern Mexico, east of the high plateaus or mountain
ranges which traverse them, well supplied with rain?

We have observed that the Andes of South America arrest
and condense the clouds borne to them from the Atlantic;
would easterly winds ever bring rain to the region between the
Andes and the Pacific? Would the northeast or southeast
trades of the Pacific supply rain to this region? Does much of
the western side of South America appear to be rainless, owing
to the above causes? What of this portion, in respect to pro-
ductiveness? Ans. It is mostly desert, except along the margins of the
streams descending from among the Andes. On the northeast coast of
South America and the western coast of Central America pe-
riodical winds, at intervals, blow toward the land; are these
coasts well supplied with rain?

Westerly winds prevail chiefly in the south temperate zone,
from a little below the "Tropic of Capricorn;" is the western
side of the Andes in this region supplied with abundant rain?
Is the supply extremely scanty on the eastern side, except near
the Atlantic? What is the result of this? Ans. By far the greater
part of the Republic of La Plata (or Argentine Republic) is a mere
pastoral region; while much of its western border and of Patagonia is a
forbidding desert.
NOTE.-The student may now attend to Lesson XI., on page 61.

the surface of the earth, from the equator toward the poles, and incronswhy? State the difference, as affecting climate, between traveling on largely affected? What occurs as we ascend in the atmosphere, and heat is experienced? 492. By what else is the temperature of countries is said of the countries in the northern hemisphere where the greatest light and heat at the tropics? What is obviously its object? 491. What Questions.-490. What is said of the lingering of the point of direct POTOSI IN THE ANDES (ELEVATION 13,350 FEET). †

ing our elevation.

† See paragraphs 69 and 70. * Professor Moseley's " Astro-Theology."