quently, their great momentum, arising from this velocity, frequently renders them very destructive, particularly in hot climates. They beat down the crops, strip trees of their leaves, fruits, and branches, and sometimes kill even large beasts and men. A few years ago, a tremendous storm happened in Gloucestershire, accompanied with a most remarkable hailshower. The masses of ice which fell in places where the storm most fiercely raged, bore no resemblance to the usual state of hailstones in magnitude or formation, most of them being of a very irregular shape, broad, flat, and ragged, and many of them measuring nine inches in circumference. They appeared like fragments of a vast plate of ice, broken into small masses, by its descent towards the earth.

6. Dew.-Dew is vapour condensed into visible drops. It begins to be deposited about sunset, and is most abundant in valleys and plains near rivers and other collections of water, and abounds on those parts of the surface which are clothed with vegetation. In this island, the dew is observed, like the drops of drizzling rain, upon the leaves of grass and other vegetables, upon wood, glass, porcelain, etc., or upon the earth, which is thereby rendered sensibly moist. It falls more copiously in spring and summer than at any other times of the year. In countries situated near the equator, the dews are generally observed in the morning throughout the year; and in some places in the east, where rain seldom falls,

they are so copious, as, in a great measure, to supply its deficiency. During the heat of the day, a great quantity of vapour is thrown into the atmosphere from the surface of the earth and waters. When the evening returns, if the vapour has not been carried off by currents, it will happen that more remains diffused in the general atmosphere than the temperature of the night will permit to subsist. A decomposition of the aqueous atmosphere then commences, and is continued till the general temperature and aqueous pressure arrive at an equilibrium, or till the returning sun puts an end to the process.

Hoar-frost, which appears like a powdery crystallization on trees and herbage, is only frozen dew. The conversion of dew into hoarfrost is another wise arrangement of nature by which plants are protected from the severity of a freezing cold atmosphere. Fogs are clouds which float on the surface of the earth, and clouds are fogs in the higher regions of the atmosphere. From many elevated places they may be seen moving in the valleys, and from the valleys they may frequently be seen creeping along the sides of the mountains.

CHAPTER II.

Winds.

1. WINDS in general.-Wind is the motion of a body of air flowing from one place to another. The earth being surrounded by a fine invisible fluid, extending several miles above its surface, is acted upon by heat and cold arising from different causes. This appears to be the general cause of the phenomena of winds; and, according to the force or velocity with which the masses of air move, we use the terms, a breeze, a gale, a storm, a tornado, a whirlwind, a hurricane, etc. When a fire is made in the open air, the rarefied part of that fluid will ascend in a current, and the cooler and denser air will rush in on all sides, in consequence of which a wind is generated, and blows constantly towards the fire. The wind thus produced will be too inconsiderable to be perceived at any great distance, but the rarefaction which arises from natural causes may be such as to agitate our atmosphere sufficiently to produce those torrents of air which have always a powerful effect in nature, and which

sometimes overwhelm and destroy the fairest and most superb productions of human art. Among the causes which produce this rarefaction of the atmosphere, and generate wind, the heat of the sun is not the least powerful. When the solar rays, by their reflection from the earth's surface, have heated or rarefied a portion of the surrounding air, the air so rarefied ascends into the higher regions of the atmosphere, and the colder air, by which it was surrounded, moves forward in a sensible current to fill the vacuity. Likewise, when a condensation of vapour in the atmosphere suddenly takes place, giving rise to clouds which speedily dissolve in rain, the temperature of the surrounding air is sensibly altered, and the colder rushing in upon the warmer, gives rise to a sudden gust of wind. In regard to the particular causes which produce the various winds which prevail in different regions of the globe, different opinions have been entertained by philosophers. And, therefore, instead of examining theories and doubtful opinions on this subject, the writer will confine himself to the statement of a few facts respecting the different species of winds as they are found to operate in different countries.

2. General, or permanent winds. - Winds are commonly divided into three classes, namely, general, periodical, and variable winds. General winds are those which are permanent, and blow always in the same direction, and have received the name of trade-winds. These winds

prevail chiefly within the tropics, and a few degrees beyond. On the north of the equator, their direction is from the north-east, varying at times a point or two of the compass each way. On the south of the equator, they proceed from the south-east. These winds constantly range in one direction, but never extend further than 30° from the equinoctial, either north or south. In the Atlantic and Pacific oceans, under the equator, the wind is almost always easterly; more to the northward, it generally blows between the north and east; and, more to the southward of the equator, it blows between the south and east. The origin of these winds appears to be as follows:-the powerful heat of the torrid zone rarefies the air of that region; in consequence of this rarefaction, the air rises, and, to supply its place, a colder body of air from each of the temperate zones moves towards the equator. But these north and south winds pass from regions where the rotatory motion of the earth's surface is less to those where it is greater. Unable at once to acquire this new velocity, they are left behind; and, instead of being north and south winds, as they would be if the earth's surface did not turn round, they become north-east and south-east winds.

3. Periodical winds, or monsoons.-Those winds, which blow in a certain direction for a time, and at certain stated seasons, change, and blow for an equal space of time from the opposite point of the compass, are called monsoons.