without suffering the least decay; and in a collection of antiquities, now in the British Museum, there is an ancient model of an Egyptian house, the store-rooms of which, when first discovered, were full of grain that had remained uninjured for ages.

187. PERU. Along the coast of Peru is stretched a plain of sand, five hundred and forty leagues in length, and varying from three to twenty in breadth, upon which no rain descends. So rare is the occurrence of a real shower at Lima, that it is a source of terror; and when such an event happens, religious processions parade the streets, imploring the protection of heaven for their endangered city.

The want of rain in this region is thus explained. Parallel to the coast of Peru, and at a short distance from the sea, extends the lofty range of the Andes, the peaks of which rise far above the limit of perpetual frost. The constant east wind, sweeping from the Atlantic to the Pacific, across the extreme breadth of South America, gradually ascends the slope of the Andes; but by the time it has passed their summits most of the vapors with which it is charged, are precipitated, and it comes to the shores of Peru comparatively destitute of moisture.

188. Moreover, as a sandy soil is naturally dry, scarcely any evaporation occurs, and the hot air of the plains possesses but little humidity. For these reasons, the difference in the temperature of two or more combining volumes of air is rarely sufficient to produce rain.

189. A similar destitution of rain exists on the northwest coast of Africa, where the desert of Zahara reaches the Atlantic. In this region, intervals of six or seven years occur between the showers.

190. CONSTANT RAINS. In Guiana, it rains for a

What is said of Peru?

Is a copious shower regarded as a blessing at Lima?
Explain the cause of this scarcity of rain.

What other region is destitute of rain?

great portion of the year; nor is this surprising, when we reflect that this country is a low and marshy region, overspread with immense forests; situated but a few degrees north of the equator, and subjected to the influence of the north-easterly trade.

The fierce heat of the sun fills the atmosphere with vapor, which returns to the earth again in incessant showers, as the cool air from the ocean flows in from the higher latitudes.

In the interior, amid the primeval forests, the sun and stars are seldom visible, and the rains not unfrequently continue for five or six months, with scarcely any intermission.

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191. According to Darwin, rain thus prevails at the Straits of Magellan. "At Port Famine," says the writer, we have rounded mountains, concealed by impervious forests, which are drenched with rain brought by an endless succession of gales: rock, ice, snow, wind and water, all warring with each other, here reign in absolute sovereignty." It is a proverbial saying, in the Isle of Chiloe, 43° S. Lat., that it there rains six days of the week, and is cloudy on the seventh.

192. EXCESSIVE SHOWERS. The quantity of rain that falls during a single shower is sometimes amazing. At Cayenne, Admiral Roussin found, on one occasion, that ten inches and three quarters fell in the course of ten hours. There fell at Genoa, Oct. 25th, 1822, thirty inches in twenty-four hours; and at Geneva, on the 20th of May, 1827, six inches in three hours. In the famous Catskill storm of July 26th, 1819, a tub, very nearly as large at the bottom as at the top, was filled to the depth of fifteen inches and a half in four hours.

193. RAIN WITHOUT CLOUDS. Singular as it may appear, there are yet many well-attested instances of showers occurring when the sky was clear. This phenomenon was several times observed by Humboldt; and,

What is said of the rains of Guiana? What of those at Port Famine? Give instances of excessive showers.

Does rain ever fall from a cloudless sky?

according to Kaemtz, it happens in Germany twice or thrice in a year. On the 9th of August, 1837, a shower fell at Geneva, when the sky was cloudless, that lasted two or three minutes; and at Constantinople, rain was seen to fall by M. de Neveu, for the space of ten minutes, when the heavens were perfectly serene. Accord

ing to Le Gentil, this occurrence is by no means uncommon in the island of Mauritius, during the prevalence of the south-east winds; slight showers falling in the evening, when the stars are shining brilliantly.

194. CAUSE. The following explanation has been given of this phenomenon. When rain is produced by the intermixture of different volumes of air, the precipitated moisture usually assumes, at first, the form of small globules of vapor; an assemblage of which in the higher regions of the atmosphere constitutes clouds. As the process of condensation advances, more moisture is precipitated, and the globules uniting in rain-drops, descend to the earth. Now it is supposed, that, at times, the humidity of the atmosphere is condensed at once into rain, without passing through the intermediate state of cloud; and under these circumstances a shower might fall from a cloudless sky.

CHAPTER II.

OF FOGS.

195. Fogs, or mists, are visible vapors, that float in the atmosphere, near the surface of the earth.

They originate in the same causes as rain; viz., the union of a cool body of air with one that is warm and humid; when the precipitation of moisture is slight, fogs are produced; when it is copious, rains are the result.

Give cases. How is this circumstance explained?

What is the subject of chapter second? Define fogs.
In what do they originate?

196. CONSTITUTION. When a mist is closely examined, it is found to consist of minute globules, and the investigations of Saussure, and Kratzenstein, lead us to suppose, that they are hollow; for the latter philosopher discovered upon them rings of prismatic colors, like those seen upon soap bubbles; (C. 79,) and these could not exist if the globule was a drop of water, with no air or gas within. The size of these globules is greatest when the atmosphere is very humid, and least when it is dry.

DISTRIBUTION IN LATITUDE.

197. TROPICAL REGIONS. Fogs are not generally common in the equatorial clime, its high mean temperature being favorable to the dissolution of vapor. They are however, by no means, unfrequent at certain seasons, and in particular localities.

Thus, in India, just before the commencement and at the close of the rainy season, when the air contains an excess of moisture, but not enough to produce rain, clouds of mist so dense and thick obscure the atmosphere, that they are not dissipated until late in the morning.

During the month of December, the towering summits of the Abyssinian mountains are also shrouded in impenetrable fogs. Peru is remarkable for its misty atmosphere, of which we shall soon speak more particularly.

198. TEMPERATE REGIONS. In the temperate climes, mists frequently occur; but are of comparatively small.

extent.

199. POLAR REGIONS. In the polar regions they spread far and wide, over sea and land, and prevail both in winter and summer.

At the beginning of winter, the whole surface of the northern ocean steams with vapor, denominated frost smoke; but as the season advances, and the cold in

What does a mist consist of?

Where do fogs prevail least? When do they appear in India?
Where do they occur frequently? Where most?

creases, it disappears. Towards the end of June, when the summer commences, the fogs are again seen, mantling the land and sea with their heavy folds. By the middle of summer, these also disappear, to return again at the approach of winter.

So dense are these mists, that they render the naviga tion of the polar seas extremely dangerous, and the nar ratives of the hardy explorers of these inhospitable climes are full of the perils arising from this source. Simpson, who penetrated by land to the Arctic ocean, in 1837, speaks of the dense fog that often involved his party in imminent danger, while coasting along these ice-bound shores.

200. CAUSE. The phenomena of the polar fogs are explained in the following manner. During the short Arctic summer, the earth rises in temperature with much greater rapidity than the sea: the thermometer sometimes standing, according to Simpson, at 71° Fah. in the shade, while ice of immense thickness lines the shore. Flowers also bloom at the surface of the ground, when the soil is firmly frozen four inches below. The air, incumbent upon the land and water, partakes of their respective temperatures; and on account of the ceaseless agitations of the atmosphere, a union of the warm air of the ground with the cool air of the ocean will necessarily occur, giving rise to the summer fogs. But, as the winter approaches, the land becomes colder than the sea; since the heat acquired during the season of summer is lost far more slowly by the latter than by the former; and then, upon the warm surface of the ocean, will float the frost smoke, as the cool air flows down upon it from the adjacent shores.

LOCAL DISTRIBUTION.

It

201. Fogs are found along the course of rivers, upon the sides of mountains, and over shoals and capes. is not difficult to detect the cause of their appearance in these situations.

Describe the polar fogs. Explain the cause of their formation.

In what localities are mists found?