Currents of air, supposed to be occasioned by the unequal rarefaction of the atmosphere, by the operation of heat, are called, winds.

The winds are arranged in three general classes.

First. General or permanent winds; or those` which blow always in nearly the same direction. In the Atlantic and Pacific oceans, under the equator, and on each side of that circle, to the latitude of 28°, the wind blows almost always easterly. More northward of the equator, the wind generally blows between the north and east. More to the south of the equator, its common direction is between the south and east. These general winds have the name of trade-winds.

The periodical winds are those which blow in a certain direction, for a certain time; and at particular seasons, change, and blow, for an equal space of time, from the opposite point of the compass. These are named monsoons.

Variable winds are those which blow without any certain rule.

Hurricanes, or tornados, are tremendous storms of wind, rain and thunder, attended with a furious swelling of the sea, and sometimes accompanied by earthquakes.

Ex

The harmattan is a wind which blows periodically, from the interior parts of Africa, towards the Atlantic ocean. It is accompanied by a thick haze, so as to obscure the sun. treme dryness is another property of this wind. During its continuance, no dew falls. Vegetables are withered, and the grass becomes dry, like

hay. It shrivels up the covers of books, spoils furniture, and scarifies the skin; but it stops epidemic disorders, and relieves from intermitting fevers. The sirocco, or Levant wind, which is frequently felt in Sicily, is extremely hot, and very prejudicial to animal and vegetable health.

The samiel, or simoom, is the most destructive of all winds. It blows in the sandy deserts of Asia and Africa, killing instantly whatever animal is so unfortunate as to inhale it. It ap pears like a purple haze, sailing through the air with great celerity.

Water-spouts are, probably, caused by a sudden vacuum taking place, owing to a local rarefaction of air. This creates a suction which carries up with it whatever happens to be within the vortex ; water, or any other substance. When this is water, it assumes the form of an inverted cone, which, when it bursts and falls, is very dangerous.

Mariners at sea, when they see this phenomenon, frequently fire a great gun, that the concussion of the air may break the approaching water-spout, before it reach their vessel.

Land and sea breezes in the tropical climates, may be regarded as partial interruptions of the general trade-winds.

The earth being heated during the day, the air above it is rarefied, and thus, in the afternoon, a breeze sets in from the sea, which is less heated at that time than the land. On the other hand, during the night, the earth loses its surplus heat, while the sea continues more even in its temperature. Thus, towards morning, a

breeze regularly blows from the land towards the sea, the air in contact with which, is then warmer, and therefore more rarefied, than the air which is in contact with the land.

QUESTIONS.

What is vapour, or steam? What are the causes of rain, of hail, of snow? In what reigons of the globe are meteoric phenomena most frequently seen? What are the meteoric appearances in the torrid zone? Of what kind are the meteors of the polar skies? What are winds? What are trade-winds? What are monsoons? What are variable winds? What are tornados? What is the harmattan? What is the sirocco? What is the simoom? What is a water-spout? What are land and sea breezes?

CHAP. XLIV.

ARCHITECTURE.

CIVIL ARCHITECTURE.

THE origin of architecture must be of very high antiquity; for men must have soon felt the necessity of sheltering themselves from the inclemency of the changing seasons; and when they had begun to build houses for that purpose, they would have proceeded gradually to consult conveniency, and, finally, ornament.

Among the ancient Egyptians, Assyrians, and Persians, architecture was carried to an astonishing length; but its principal character was that of massive solidity, and magnificent gran

deur. Of the former, the pyramids, and of the latter, the ruins of Persepolis, exhibit striking proofs.

The largest of the pyramids is nearly 500 feet high, and contains 313,590 solid fathoms. It is constructed of enormously large stones, some of which are thirty feet long, four feet high, and three feet broad; and this huge pile was coated over with square flags of marble.

The remains of the grand staircase of the palace of the Persian monarchs, at Persepolis, consists of ninety-five steps of white marble, so broad that twelve horses might easily ascend them abreast. Neither the ancient Assyrians, nor Babylonians, knew the method of raising arches; and their buildings were destitute of taste their columns were ill proportioned, and their capitals were badly executed. This was observed by the Greeks, who quickly established a more elegant style of architecture.

The Romans borrowed their architecture from the Greeks; and the ruins of their temples and public edifices show that they nearly, if not quite, equalled their instructors.

The ancient Gothic architecture seems to have been intended rather to astonish by magnitude, than to please by just proportions.

The modern Gothic, or Saracenic style is distinguished for the lightness of its work, the boldness of its elevations, the delicacy, profusion, and 'extravagant fancy of its ornaments. Its pointed arches and columns, consisting of distinct light shafts, are evidently imitations of

clumps of trees growing closely together, and disposed in avenues forming overhanging arches. The art of building houses, bridges, churches, and public edifices, is styled Civil Architecture. The art of erecting castles, forts, and walls, for defence, is called Fortification, or Military Architecture. The art of constructing ships and boats is Naval Architecture.

Proportion, solidity, adaptation to particular purposes, and ornamental beauty, are the chief requisites of good architecture. The principal. ornaments used in architecture are, five orders of columns, pediments, arches, and ballustrades. There are five orders of columns; the Tuscan, the Doric, the Ionic, the Corinthian, the Composite.

Each order is made up of three parts; the pedestal, the column, and the entablature.

The pedestal consists of the base or plinth, the dado or dye, and the cornice. The use of the pedestal is to raise the column to a proper height, and to give it a greater appearance of firmness.

The column consists of a base, a shaft, and a capital.

The entablature consists of an architrave, a frize, and a cornice.

The term plinth is derived from the Greek name of a flat stone, on which columns are supposed to have stood in the infancy of archi

tecture.

The dado, or dye, is so called from its being in a cubical form; and the cornice takes its name from the Latin for a crown or summit.