and Holland differ, in this respect, one inch. In this country, the yearly average fall of rain at Boston, for a period of 22 years, is 39.23 inches; at Hanover, New Hampshire, 38 inches; in New York State, 36 inches; and in Ohio, 36 inches. A diminution occurring as we advance into the interior, notwithstanding the influence of the great northern lakes, in the last two instances.

RAINS WITHIN THE TROPICS.

173. Upon the ocean, in the region of calms, where the gusts of wind are ever changing their direction, torrents of rain frequently descend. On the land, in all places where the trade wind blows constantly seaward, no rain falls, and the sky is always serene; but, wherever disturbances occur in this current and the monsoons prevail, the rains are periodical, and the year is divided into two seasons, the wet and the dry. These are so marked in their character, that whole months pass away without a cloud obscuring the sky, or mitigating the fierce heat of the sun : then the face of nature entirely changes, the heavens gather blackness, the rain comes down like a deluge, and the parched earth is refreshed, for many successive weeks, by copious showers.

174. RAINY SEASON. The rainy season commences, in all the countries within the tropics, at the shifting of the monsoons; and as this change is dependent upon the position of the sun, it begins earlier in those regions that lie near the equator, than in those more remote.

At Panama, 8° 48′ N. Lat., the rain falls early in the month of March; but it seldom appears at St. Blas, California, before the middle of June. In Africa, near the line, the rainy season begins in April, both upon the sea-coast and in the interior; but in the countries watered by the Senegal, it commences in June, and lasts till November.

How are rains distributed within the tropics?

How is the year divided where the monsoons prevail?

When does the rainy season occur?

In what regions early? In what late? Illustrate.

In India, the rains occur in May, at the southern extremity of the Malabar coast, but do not reach Delhi until nearly the end of June.

175. CAUSE. These stated rains originate in the change of the periodical winds, by which the union of vast volumes of air, differing in temperature, is rapidly effected. The subject cannot be better illustrated, than by recurring to the origin of the monsoons of India. (Art. 106.) Early in the month of June, the soil of the peninsula becomes intensely heated by the vertical rays of the sun, and powerful currents of rarefied air then ascend from the earth. To supply the deficiency thus created, the warm and humid atmosphere of the equatorial seas flows in, constituting the south-west monsoon; this wind now mingles with the cool, dry air, which the northeast monsoon, for the six previous months, has been constantly bringing to the peninsula from the polar and temperate climes, and thus produces a combination favorable to the precipitation of rain, upon a most extensive scale.

176. PERIODICAL RAINS OF INDIA. On the Malabar coast, the south-west monsoon is ushered in by terrific storms of thunder and lightning, the water pours down in torrents, and, when the thunder has ceased, nothing is heard for several days but the rush of the descending rain, and the roar of the swelling streams. In a few days, the storm ceases, and the earth, which before was withered by the glowing atmosphere, is now, as if by magic, suddenly clothed with the richest verdure; the air above floats pure and balmy, and bright tropical clouds sail tranquilly through the sky.

of

After this, the rains fall at intervals for the space a month, when they again return with great violence. In July, they attain their height, and from that time gradually subside until the end of September, when the season closes, as it began, in thunders and tempests.

177. The following table, the result of the observa

How do these rains originate?

Describe those of India.

tions of twelve years, shows the mean monthly average for the rainy season, at Bombay; and serves to elucidate the preceding remarks.

178. The south-west monsoon does not, however, bring rain to the whole of India. Parallel to the western coast runs a chain of high mountains, termed the Ghauts: here the monsoon is arrested in its course, and most of the moisture with which it is charged, is precipitated, ere it arrives at the central table-land of Mysore. On the eastern, or Coromandel coast, its in fluence is not felt, and the seasons are here reversed. From March till June, the winds are hot and moist, blowing mostly from the south, over the Bay of Bengal; from June to October the heat is very great, but about the middle of the latter month, the cool, northeast monsoon commences, bringing the periodical rains, which terminate by the middle of December; the monsoon continuing to blow until the beginning of March.

179. PERIODICAL RAINS OF CONGO. We trace the rainy and dry seasons of Congo, in the southern hemisphere, to the same cause. In general, from about March to September, no rain descends, but gales from the south and south-east temper the burning atmosphere. In October, hot and humid winds blow from the northwest over the Gulf of Guinea, and the country is then flooded by frequent rains, which continue to increase until January. Slight showers then fall at intervals until March, when the rains recommence and continue for a short time.

Illustrate from the table.

What is the influence of the Ghauts upon the south-west monsoon?
What is said of the seasons on the eastern coast?

What wind brings the rains to this region?

Describe the periodical rains of Congo.

RAINS IN THE HIGHER LATITUDES.

180. Beyond the tropics, the rains no longer occur at stated periods, but are distributed throughout the seasons without regard to any law.

Thus, in the west of England, the amount of rain in winter is eight times greater than in summer; but in Germany, it is one-half of what falls in summer, and at St. Petersburg a little more than one-third. In Italy the gre test quantity descends in autumn. There is the same irregularity in the number of rainy days; for in the west of England, there are more rainy days in winter than in summer; but in Siberia, it rains four times as often in summer as in winter.

181. RAINY WINDS. The rains in the higher latitudes, as well as within the tropics, depend upon the changes of the wind; though one wind may be more productive of rain than another, and, in different regions, the rainy winds do not always blow from the same direction.

In Europe, north of the Alps, the north-east wind is dry and cold, since it sweeps over the land from the higher latitudes; but the south-west wind brings the rain, for, coming over the Atlantic from southerly climes, it is warm and humid, and its capacity for moisture is constantly decreasing.

Out of one hundred showers that were noted at Berin, scarcely any occurred when the north-east wind prevailed; while nearly half were brought by the winds from the south-west and west. Moreover, it rained only once for every nine time that the easterly winds blew, but thrice for the same number of times in which the southwesterly breezes predominated.

182. The reverse of this occurs on the eastern coast of the United States, for here the north-east winds give rise to the long storms of the fall and spring. At these seasons, as appears from the observations of Dr. Hale,

Where are the rains irregular? Give cases.
What is the rainy wind of Northern Europe?

Why is it rainy? Give instances.

Whence comes the rainy wind, on the eastern coast of the United States?

of Boston, continued through a period of twenty-two years, the winds are colder than the atmosphere of the land, and as they come from the sea charged with moisture, the cause of the rain is readily discerned.

REGIONS WITHOUT RAIN.

183. EGYPT. In Egypt it scarcely ever rains. At Cairo, there is an average of four or five showers a year; but, as we recede from the coast, it becomes more rare, until in Upper Egypt, under the cloudless sky of Thebes, a man's life may pass away without his ever beholding a single rain.

184. The cause of this scarcity of rain is to be sought in the peculiar conformation of the surface of this country. It is a narrow valley, bounded by two mountain ridges on the east and west; the first prevents the moisture exhaled from the Red sea from reaching the valley, and, as the African deserts extend beyond the western range, no source of rain exists in this quarter.

185. The northerly winds, which blow from May till October, bearing off the vapors of the Mediterranean, pass over the whole length of the valley of the Nile, without meeting any obstruction; and it is only when they are driven up the high range of the Abyssinian mountains, that they become sufficiently cooled to precipitate rain. Here it descends most copiously during the summer months, swelling the tributaries of the Nile, and producing its annual inundation.

186. Much of the humidity brought by these constant winds, can be retained by the atmosphere of Egypt, without being precipitated; since it is far below the point of saturation, in consequence of the prevalence of hot, dry winds from the desert, (Art. 114,) and the extreme aridity of the soil.

So free from moisture is the ground, that myriads of human bodies have rested for centuries within its bosom

Why is it rainy?

What is said of Egypt?

Why is it that rain rarely falls in this country?

What is said of the dryness of the soil?