March or April, and is over in August; when the spring, or rather the summer, begins. The nights are very cold; and the nights in summer are colder than in winter.

In Jamaica the rain commonly begins in May. July is always very wet; and toward the end of that month, and the beginning of August, the weather is very close. In September and October hurricanes are frequent.

In Nicaragua it rains six months, from the first of May to the first of November; in the other six months it is hot and dry.

88. That part of the frigid zone which is inhabited, viz. Greenland, Lapland, &c. has only two seasons, winter and summer. Their night of winter, the sun never appearing above the horizon, is extremely se

vere.

The most rapid rivers are sometimes frozen five or six feet deep or more; the largest lakes and bays are frozen to bear any weight, and rocks often burst by the intensity of the frost. The brilliancy of the stars, the Aurora Borealis, and the full moon, which never sets, make some atonement for the absence of the sun. The long twilight also, which they enjoy before the sun rises and after he sets, considerably diminishes the time of their total darkness.

The transition from winter's frost to summer's heat is very rapid in the frigid zone. The short summer is very warm, but foggy. The continual sunshine now enables the inhabitants to lay up a store of provisions for winter.

89. The hottest part of the earth is in the middle and western parts of Africa. The trade winds, in passing over the extensive sandy deserts of this continent, become heated to an extreme degree before they arrive at the western coast.

The climate, on the western continent, is much colder than it is in similar parallels on the eastern continent.

Canada, in North America, which is nearly in the same parallel with France, has the winters almost as severe as at

Petersburg: the river St. Laurence, notwithstanding its breadth, is frequently frozen the whole of the winter, strong enough to bear even carriages upon it. Philadelphia and New York, nearly in the same parallel with Madrid, have often severe winters, but the heat of the summer is excessive. The cold in the southern hemisphere is much greater than in the northern. The climate of Terra del Fuego is an instance of this: situated as far south as Newcastle is north of the equator; and, therefore, were the degrees of heat and cold proportionable to the latitude, we might expect the summers of Terra del Fuego as warm as those on the banks of the Tyne; yet Captain Cook, who was there at Midsummer, found the cold so excessive, that a party botanizing on the hills, was in danger of perishing by cold.

The mountains and vast fields of ice, around the South Pole, extend to a much greater distance than those around the North Pole. Navigators have penetrated to within 9 degrees of the North Pole; yet Captain Cook could not get nearer the South Pole than within 18 degrees.

90. In great Continents the weather is more settled than it is in islands: the summer's heat is greater, and the winter's cold is more intense.

In islands the heat is tempered by clouds and vapours from the surrounding sea; but the weather is inconstant. The cold of winter is also mitigated from the same cause, and the frost is generally of short duration. This is particularly the case with respect to Great Britain.

SECTION V.

GEOGRAPHICAL PHENOMENA.

Of Winds.

91. THE wind is nothing else but the air put violently in motion; and this is occasioned chiefly by means of heat. For, when any part of the air is heated by the sun, or otherwise it will swell, and thereby affect the adjacent air; and so, by various degrees of heat in different places, there will arise various motions of the air.

When the air is much heated, it will ascend towards the upper part of the atmosphere, and the adjacent air will rush in to supply its place; and therefore there will be a stream or current of air from all parts, towards the place where the heat is. And hence we see the reason, why the air rushes with such force into a glass-house, a tile kiln, or towards any place where a great fire is made; and also why smoke is carried up a chimney, and why the air rushes in at the keyhole of a door, or any small chink, where there is fire in the room. In general, we may take it for granted, that the air will press towards that part of the world where it is most heated.

92. The winds are divided into four principal ones, the north, south, east, and west, which receive their names from the four quarters of the world.

From the Frigid Zone comes the north wind, which is consequently the coldest.

The south wind is the warmest, and particularly in the summer, because it comes from the Torrid Zone, over countries where the sun is most vertical.

The east wind is the dryest, because it comes across the vast continent of Asia, which is but little watered by rivers or

seas.

The west wind often blows us rain; because, as it crosses the great Atlantic ocean, it attracts a great quantity of

vapours.

When these impetuous winds happen to meet, the greatest inconveniences follow. The sulphureous exhalations from the south, torrents of nitre from the north, and watery vapours from every side, become indiscriminately blended together in one confused mass. From hence proceed tempests, thunder, rain, hail, and whirlwind.

93. The velocity of wind is at the rate of 50 or 60 miles an hour, in a great storm; that of a common brisk wind is about 15 miles an hour; and some winds move not even one mile in that space of time.

A person, therefore, où horseback, and even sometimes on foot, may be said to outstrip the wind; for, if he moves faster than the wind, which is very possible, he will have a wind in his face, though he move in the same direction with the wind.

The velocity of sound is thirteen times as great as that of the strongest wind.

Of the Tropical Winds.

94. There are certain winds, called tropical winds, which blow almost always from the same point of the compass. They are of three kinds.

The general trade winds, which extend to nearly thirty degrees of latitude on each side of the equator, in the Atlantic, Ethiopic, and Pacific oceans. On the north side of the equator, they blow from north-east, on the south side, from the south east, and near the equator from almost due

east.

The monsoons, or shifting trade winds, which blow six months in one direction, and the other six months in the opposite direction. These are mostly in the Indian, or Eastern ocean, and do not reach above two hundred leagues from the land. Their change is at the vernal and autumnal equinoxes, and it is accompanied with terrible storms of thunder, lightning and rain. The monsoons are occasioned by the cold air moving towards those places, in which the air is rarefied by the heat of the sun, in order to restore its equilibrium.

The land and sea breezes, which are periodical winds, and blow from the land, from night to about mid-day, and from the sea, from about noon to midnight. These winds do not extend above two or three leagues from the shore.

Beyond the latitude of thirty degrees, north and south, the winds, as we daily perceive in Great Britain, are more variable, though it may be observed, in general, that the tendency of the wind is from a colder region to that which is hotter.

Of the Aurora Borealis.

95. In illustrating the two seasons of the year in the frigid zone, (north); we had occasion to mention the benefit derived from the Aurora Borealis.

That shining light which is often seen by night in the heavens, and which is vulgarly called the northern lights, or streamers, is the Aurora Borealis, which, till the month of March, 1716, was not much observed in England.

This phenomenon is supposed to be the result of electrica fluid passing from one region to another; though some have strangely enough supposed it to be produced by nitrous and sulphureous vapours thinly spread through the atmos

phere and above the clouds, where they ferment, and taking fire, the explosion of one portion kindles the next, and the flashes succeed one another till all the vapour is set on fire. But we know sufficient of the electric fluid's powers and operations not to believe it the cause of those streams of light, which under the name of the Aurora Borealis, seem to converge towards the zenith of the spectator, or to that point of the heavens which is immediately over his head.

Now black, and deep, the night begins to fall,
Drear is the state of the benighted wretch,

Who then, bewilder'd, wanders through the dark,
Perhaps, impatient as he stumbles on,

Struck from the root of slimy rushes, blue,
The wild fire scatters round, or gather'd, trails
A length of flame deceitful o'er the moss:
Whither decoy'd, by the fantastic blaze,
Now lost, and now renew'd, he sinks absorpt,
Rider and horse, amid the miry gulf:

At other times, gleaming on the horse's mane,
The meteor sits; and shows the narrow path,
That winding, leads through pits of death; or else,
Instructs him how to take the dangerous ford.

Of Refraction.

THOMSON.

96. The earth is surrounded by a body of air called the atmosphere, through which the rays of light come to the eye from all the heavenly bodies; and since these rays are emitted through a very rare medium, and fall obliquely upon the atmosphere, which is a dense medium, they will, by the laws of optics, be refracted in lines approaching nearer to a perpendicular from the place of the observer (or nearer to the zenith,), than they would be were the medium to be removed.

Hence all the heavenly bodies appear higher than they really are, and the nearer they are to the horizon the greater the refraction, or difference between their apparent and true altitudes will be; at noon the refraction is the least. The sun and the moon appear sometimes of an oval figure near the horizon, by reason of the refraction: for the under side being more refracted than the upper, the perpendicular diameter will be less than the horizontal one, which is not affected by refraction.