INTRODUCTION.

THE EARTH, DAY. NIGHT, &c.

THIS globe which we inhabit, is one of the feven planets, which, at differ

During the earth's courfe round the fun, which it performs in a year, it turns round on it's axis 365 times; by this means every part of it's furface is alternately turned into funfhine and fhadow, or, in other words, into day and night.

From the rotundity of the earth, the fun darts it's rays direct on the heads of fome, while, on others, it shoots it's beams very obliquely: hencethe polar regions are rendered uninhabitable through extreme cold; while the people of the torrid zone are coloured black through intense heat

The land and water of our Globe are broken into various irregular portions and unequal forms.

LAND AND WATER.

A continent is a large tract of land not feparated by the fea; as Europe, Afia, &c. An ocean is a vaft collection of water not feparated by land; as the Atlantic, Pacific, &c. A fea is a smaller collection of water communicating with the ocean; as the Mediterranean, the Baltic.

An island is a tract of land furrounded by water; as Great Britain, Ireland, &c. A lake is water furrounded by land; as the Lake of Geneva.

A cape, or promontory, is a point of land running far into the fea; as the Bay of Bifcay.

A peninfula is land almoft furrounded with water; as the Morea. A gulf is a part of the fea almost furrounded with land; as the Gulf of Venice.

An isthmus is the narrow part of land which joins the peninfula to any country; as the Ifthmus of Suez. A ftrait is a narrow paffage from one fea to another; as the Straits of Gibraltar.

ATTRACTION.

It seems to be an univerfal law in creation, that bodies have a mutual attraction towards each other; the caufe is inexplicable from any enquiries in natural philofophy, and is only refolvable into the will of the Creator, whofe works we may contemplate with wonder, but the least of which we cannot fully comprehend,

The earth, from it's immenfe fize, being near 25,000 miles in circumference, keeps attached to itself animals, and other loose bodies to it's furface, the waters of the fea, the atmosphere, the light clouds floating therein.

Bodies are faid to fall or defcend, when they approach, or are attracted to the earth; to rife, when they recede from it: this holds with our antipodes, or thofe whofe feet, on the oppofite part of the globe, are directly oppofed to ours: it holds in all the different parts of the world; fo that up and down are only relative terms, the up of one place being the down of another.

CAUSES

CAUSES OF THE SEASONS.

Adopting, however, for illuftration's fake, in defcribing the feafons, the idea of the north pole being the uppermoft part of the earth; it may be faid our globe alternately afcends and defcends in the courfe of it's annual orbit round the fun. At the time of our midwinter, the globe is in this refpect at it's height, we have but a low mid-day fun, and the people at the north pole have none at all-from our winter till midfummer it continually falls to the fouth, gives us an afcending noon-day; and, in midfummer, continual day to the people near the arctic pole; while the fouth pole is in it's turn involved in continual fhade.

To exprefs this technically-the axis of the earth is not perpendicular but oblique to the plane of it's orbit; and, in it's annual courfe, it is conftantly kept nearly parallel to itself.

DEFINITIONS OF CIRCLES, &c.

Aftronomers have confidered the ftarry heavens as a sphere, with our earth in the centre: this is the appearance they make to our fenfes. They have divided the celestial and terreftrial fpheres, by great and lefs circles: great circles are thofe which divide the fphere equally; lefs circles are those which divide it unequally.

To imagine that the earth ftands ftill, and that the fun rifes and falls, is a falfe idea, however confonant to the perception of our fenfes, and as romantic as the notion that houfes, trees, &c. upon land are moving past us, when we fail in a veffel along the shore.

While our earth annually performs an orbit round the fun, the latter appears to defcribe a circle, in the heavens, and we seem to ftand itill; this circle is called the ecliptic. The zodiac is the fame imaginary kind of circle, but extended to a confiderable breadth on each fide of the ecliptic, including the paths of all the planets.

The Ancients divided the Zodiac into 12 Parts, and imagined or contriv. ed certain figns in each divifion. Their names and characters are, as follow:

The equator divides the fphere into the northern and fouthern hemifpheres. The latitude of a place upon earth, and the declination of an heavenly object, as a ftar or planet, are their diftances from the equator. The tropics are parallels of latitude or declination, near 23 degrees from the equator: the tropics bound the ecliptic in the heavens, and on earth, the torrid zone. pelar circles are the fame diftance from the poles, as the tropics are from the

The

equator.

equator. On earth, the temperate zones lie between the polar circles and tropics, the frigid zones lie within the polar circles.

Meridians are indefinite in number; their planes interfect that of the equator at right angles.

The longitude of a place upon earth, and the right afcenfion of an heavenly object are their diftances from a certain meridian. Circles of longitude in the heavens are indefinite in number; their planes interfect that of the ecliptic at right angles. The latitude of any heavenly object is it's distance from the ecliptic; the longitude it's distance from that circle of longitude, which passes through the first point of Aries.

The horizon is that circle which bounds our fight, or it is the termination of what is vifible to us of the fky, when on the fea, or an extenfive level plane. In mathematics, the plane of the horizon is confidered as paffing through the centre of the earth. The point directly over the heads in the zenith, and that directly oppofite to it in the heavens. is the nadir; thefe points are the poles of the horizon. The azimuths, or vertical circles, pafs through the zenith and nadir, and cut the horizon at right angles. The altitude of an heavenly object is it's distance from the horizon; and a circle paffing through it, parallel to the horizon, is an almicanter or parallel of altitude.

SOLAR SYSTEM.

The names and characters by which aftronomers exprefs the planets are as follow, in order from the fun.

The planets are attracted by the fun, and would be drawn into it, and confumed, were it not from an impulfe they have received, which tends to throw them off in a right line; by the combination of thefe two forces, (the centripetal, or centre-feeking, and the centrifugal, or centre-fleeing) they are preferved in their orbits.

A familiar reprefentation of thefe principles and effects is at once obtained, by faftening a ball to the end of a string, and fwinging it round in a circlewhile it is the inclination of the ball to fly off in a line, the ftring, like attraction, holds it in, and makes it defcribe a circle,

The three outer planets have each of them feveral fatellites or moons accompanying them. The comets of our fyftem are fuppofed to be 21 in number, they are found to be under the fame laws with the planets, but their orbis are very eccentric.

STARRY HEAVEN S.

The moon is diftant from the earth

The earth from the fun

The lately discovered planet near

Miles.

240,000

95,000,000

1,710,000,000

And the comets wander fo far beyond the most distant planet of our fyftem, that we quite lofe fight of them till they return nearer to the fun, but go inconceivably far beyond the utmost verge of our magnificent fyftem, where the moon and planets fail to caft their borrowed light, and the fun himself dwindles to a point, fhine the innumerable multitudes of ftars; fo unbounded is creation. The ftars have been fuppofed to be each of them a fun, with it's fyftem of habitable worlds moving round it, and from our little world 30,000 of them have been difcovered.

It is computed, that our folar fyftem is diftant from the fixed fars 20,000,000,000 femidiameters of the earth; that if a bullet fhould come from the nearest fixed ftars, with the fame velocity it hath when discharged from a cannon, it would be 700,000 years in coming to the earth. Well indeed may it be faid, that the human understanding is bewildered in the contemplation of the wonders of the firmament; that the giddy fancy turns round, and is entirely funk in the abyss of creation.

MOONS, CURRENTS, AND WINDS.

The moon accompanies the earth through it's annual courfe, at the fame time moving round it in an orbit, as the earth moves round the fun; this produces thofe various phases or appearances obfervable in the moon.

It is full moon, when, the earth being between the fun and the moon, we fée all the enlightened part of the moon; if it be directly between, the moon is in fhade, and it is a lunar eclipfe. It is change, when, the moon being between us and the fun, it's cnlightened part is turned from us; if directly between, it makes a folar eclipfe. It is half moon, when the moon being in the quadratures, as the aftronomers call it, or half way between the two other pofitions, we fee but half the enlightened part.

The attraction of the moon draws up the water of the ocean underneath it into a fwell, this is the full tide; on the oppofite fide of the earth, there is a fimilar tide thrown up by the centrifugal force; the intervening depreffions are the ebb tides. The fun alfo produces in a fimilar way, but thefe are fo faint, from the immenfe diftance of the fun, that they are only noticed as they affect the lunar ones. At the time of full and change the folar and lunar fwells fall in with each other, and produce fping tides; at the time of half-moon they counteract each other's force, and we have only neap tides.

In general, the tides are much higher in the torrid zone than any where else. The greatest in the world is at the mouth of the river Indus, where the water rifes 30 feet. They are alfo very high on the Malabar coaft, the Straits of Sunda, the Red Sea, the mouth of the river St. Lawrence, along the coafts of China and Japan, Panama, and the gulf of Bengal. At Tonquin, there is only one tide and one ebb in 24 hours, while in every other place there are two. But this appearance, though long confidered as inexplicable, was by Ifaac Newton derived from the concurrence of two tides, one from the South Sea, the other from the Indian Ocean. Of each of thefe there come two every day; two at one time greater, followed by two that are lefs. The time between the arrival of the two, is by him confidered as high tide; that betwixt the two leffer as ebb.

The fluctuation of the fea, by means of the tides, produces another and more conftant rotation of it's waters from east to weft, in which it follows the courfe of the moon, This may be confidered as one great and general current of the waters of the fea; which, though not every where diftinguishable, nevertheless exifts every where, except when oppofed by fome particular eddy or current produced by local caufes. This tendency of the fea towards the weft, is plainly perceptible in all the great ftraits of the ocean: as for inftance, in thofe of Magellan, where the tide, flowing fix hours from the east, rifes 20 feet; but the ebb continues only two hours, and is directed to the weft. This motion to the weftward alfo is very perceptible by navigators failing over large oceans from west to eat, particularly in the ftraits fometimes met with there, fuch as thofe of Magellan; however it is alfo very perceptible, even in the middle of the great Pacific Ocean itfelf; but the most violent motion of this kind, is in the ftraits of the gulf of Paria, which have hence received the appellati n of the Dragon's mouth.

Belides

Befides these two motions, common to the whole collection of waters, there are others belonging only to particular parts, and which are called Currents. Thefe run in all directions, and are formed by various courfes, fuch as the prominence of fhores, the narrowness of traits, inequalities at the bottom of the fea, and the variations of the wind.

The nearer we approach to the equator, the more violent are the motions of the waters, and that of the currents among the reft. So violent are they along the coaft of Guinea, that if a fhip happens to pafs the mouth of any river, to which it is bound, the current prevents it's return, fo that it is obliged to ftand out to fea, and take a very large compafs. Here the currents take a direction contrary to the general motion of the fea, and fet eastward fo ftrongly, that a voyage which, in the direction of the current, may be performed iu two days, is with difficulty accomplished against it in fix weeks; but luckily for navigators, thefe violent ftreams do not extend above 20 leagues from thore. At Sumatra, in the Eaft Indies, there are currents fetting northward with great rapidity, and the fame is found to take place on the western coaft of America ; but here the phenomenon is fuppofed to be occafioned by the fouth wind which blows continually in thofe parts. A current fets conftantly into the western part of the Mediterranean fea, through the Straits of Gibraltar, and another into it's north-eastern extremity from the Euxine fea through the Araits of the Dardenelles.

The great univerfal wind, which blows conftantly from eaft to weft, prevails chiefly in the Pacific Ocean, in the Atlantic between the coafts of Guinea and Brazil, and in the Ethiopic Ocean. When the ships are once got into the proper latitudes on the Pacific Ocean, their courfe is fo much expedited by this conftant wind from the east, that they generally crofs it's immenfe breadth of between 9 and 10,000 miles in fix weeks; fo that, were it not for the danger there is in paffing the fouthern extremity of America, the paffage this way to the Eaft Indies would be much shorter than by the Cape of Good Hope. In their return, the trade wind must be avoided, and the navigators fteer into high northern latitudes, where the winds are variable, and take advantages of every one that can poffibly affilt them. This wind feems to be occafioned by the conftant rarefaction of the air in thofe places on which the rays of the Sun fall perpendicularly, and as his apparent motion is from east to west, there must be a conftant influx of the air, from the eaft to fill up the vacuity. the motion is begun through the day, and in the night the fame continues by reafon of the current continually travelling weftward. All the other tropical winds which blow regularly for any length of time, feem to be fubordinate to this, and many of them only deviations from it's current.

Thus

The univerfal trade wind from east to weft, prevails in thofe places which are near the equator; but as we recede from thence, we meet with another which blows continually from the north on the north fide of the equator, and from the fouth on the fouth fide of it. This may likewife be derived from a fimilar caufe, viz. the influx of air from the colder regions of the north and fouth; in order to fill up the vacuity made by the rays of the Sun in the equatorial parts.

On land, if the country be very flat and fandy, efpecially if any way extenfive, and lying directly under the rays of the fun, a very great rarefaction of the air is produced. In fuch countries, therefore, the wind continually blows in upon the land from the fea, without any regard to the general current. This is the cafe all along the coaft of Guinea; and, for the fame reafon, the ocean to the westward is fubject to almost conftant calms attended with perpetual deluges of rain. For this tract being placed in the middle between the weferly" winds blowing on the coaft of Guinea, and the eafterly trade winds at fone dittance, the air is indifferent to both currents, and therefore remains perpetu

ally

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