12. In all places between the polar circles and poles, the fun appears for fome number of days (or rather diurnal revolutions) without fetting, and at the opposite time of the year, without rifing; because some part of the ecliptic never fets in the former cafe, and as much of the oppofite part never rifes in the latter. And the nearer unto, or the more remote from the pole thefe places are, the longer or fhorter is the fun's continuing prefence or abience.

13. If a fhip fets out from any port, and fails round the earth eastward to the fame port again, let her perform her voyage in what time fhe will, the people in that fhip, in reckoning their time, will gain one complete day at their return, or count one day more than those who refide at the fame port; because, by going contrary to the fun's diurnal motion, and being torwarder every evening than they were in the morning, their horizon will get fo much the fooner above the fetting fun, than if they had kept for a whole day at any particular place. And thus, by cutting off from the length of every day a part proportionable to their own motion, they will gain a complete day at their return, without gaining one moment of abfolute time. If they fail weftward, they will reckon one day lets than the people do who refide at the fame port; becaufe, by gradually following the apparent diurnal motion of the fun, they will keep him each particular day fo much longer above the horizon as anfwers to that day's course; and thereby cut off a whole day in reckoning, at their return, without lofing one moment of abfolute time.

Hence, if two fhips should set out at the fame time from any port, and fail round the globe, one eastward and the other weftward, so as to meet at the fame port on any day whatever, they will differ two days in reckoning their time, at their return. If they fail twice round the earth, they will differ four days; if thrice, then fix, &c.

OF THE NATURAL DIVISIONS OF THE EARTH.

THE conftituent parts of the earth are two, the land and water. The parts of the land are continents, iflands, peninfulas, ifthmufes, promontories, capes, coafts, mountains, &c. This land is divided into two great continents (befides the islands), viz. the eastern and western continent. The eaftern is fubdivided into three parts, viz. Europe, on the northweft; Afia, on the north-eaft; and Africa (which is joined to Afia by the fthmus of Suez, 60 miles over), on the fouth. The western continent onfifts of North and South America, joined by the ifthmus of Darien, early 70 miles broad.

A continent is a large portion of land, containing feveral countries or lingdoms, without any entire feparation of its parts by water, as Europe. An island is a fmaller part of land, quite furrounded by water, as Great Britain. A peninfula is a tract of land, every where furrounded by water, except at one narrow neck, by which it joins the neighbouring continent; as the Morea in Greece; and that neck of land which fo joins it, is called an ifthmus; as the ifthmus of Suez, which joins Africa to Afia, and the ifthmus of Darien, which joins North and South America. A promontory is a hill, or point of land, ftretching itself into the fea, the end of which is called a cape; as the Cape of Good Hope. AÀ conft or fhore is that part of a country which borders on the fea fide. Mountains, valleys, woods, deferts, plains, &c. need no defcription. The most remarkable are taken notice of, and described, in the body of this

The parts of the water are oceans, feas, lakes, ftraits, gulfs, bays or creeks, rivers, &c. The waters are divided into three extenfive oceans (befides leffer feas, which are only branches of these), viz. the Atlantic, the Pacific, and the Indian Ocean. The Atlantic, or Western Ocean, divides the eastern and western continents, and is 3000 miles wide. The Pacific divides America from Afia, and is 10,000 miles over. The Indian Ocean lies between the East Indies and Africa, being 3000 miles wide.

An ocean is a vast collection of water, without any entire feparation of its parts by land; as the Atlantic Ocean. A fea is a fmaller collection of water, which communicates with the ocean, confined by the land; as the Mediterranean and the Red Sea. A lake is a large collection of water, entirely furrounded by land; as the lake of Geneva, and the lakes in Canada. A trait is a narrow part of the sea, confined or lying between two fhores, and opening a paffage out of one fea into another; as the ftrait of Gibraltar, or that of Magellan. This is fometimes called a found; as the ftrait into the Baltic. A gulf is a part of the fea running up into the land, and furrounded by it, except at the paffage whereby it communicates with the sea or ocean. If a gulf be very large, it is called an inland fea, as the Mediterranean; if it do not go far into the land, it is called a bay, as the Bay of Bifcay; if it be very small, a creek, haven, ftation, or road for fhips, as Milford Haven. Rivers, canals brooks, &c. need no defcription; for these leffer divifions of water, like thofe of land, are to be met with in moft countries, and every one has clear idea of what is meant by them. But in order to ftrengthen the re membrance of the great parts of the land and water we have defcribed, it may be proper to obferve that there is a strong analogy or resemblance between them. The defcription of a continent refembles that of an ocean; an ifland encompaffed with water refembles a lake encompaffed with land. A peninfula of land is like a gulf or inland fea. A promontory or cape of land is like a bay or creek of the fea; and an ifthmus, whereby two land are joined, resembles a ftrait, which unites one fea to another.

To this defcription of the divifions of the earth, we shall fubjoin a table exhibiting the fuperficial contents of the whole globe in fquare miles, fixty to a degree, and alfo of the feas and unknown parts, the habitable earth the four quarters or continents; likewife of the great empires and prin cipal islands, placed as they are fubordinate to each other in magnitude,

i

To thefe iflands may be added the following, which have lately been difcovered or more fully explored. The exact dimenfions of them are not ascertained: but they may be arranged in the following order, according to their magnitude, beginning at the largeft, which is fuppofed to be nearly equal in fize to the whole continent of Europe:

New Holland,
New Guinea,
New Zealand,

New Caledonia,

Otaheite, or King George's Island,

3,200 Barbadoes

140

2,520 Zante

120

1,935 Antigua

100

1,400 St. Chriftopher's

801

1,400 St. Helena........

1,300 Guernsey

50

1,272 Jersey

431

1,000 Bermudas

40

New Hebrides,

The number of inhabitants com-' puted at present to be in the known world, at a medium, taken from the beft calculations, are about 953 millions.

WINDS AND TIDES.] We cannot finish the doctrine of the earth, without confidering the winds and tides, from which the changes that happen on its furface principally arise.

WINDS.] The earth on which we live is every where furrounded by a fine invifible fluid, which extends to feveral miles above its furface, and is called Air. It is found by experiments, that a fmall quantity of air is capable of being expanded, fo as to fill a very large fpace, or to be compreffed into a much fmaller compafs than it occupied before. The general cause of the expanfion of the air is heat; the general caufe of its compreffion is cold. Hence if any part of the air or atmosphere receive a greater degree of cold or heat than it had before, its parts will be put in motion, and expanded or compreffed. But when air is put in motion we call it wind in general, and a breeze, gale, or ftorm, according to the

monly confidered as things extremely variable and uncertain, depend o a general caufe, and act with more or lefs uniformity in proportion as th action of this caufe is more or lefs conftant. It is found by obfervation made at fea, that, from thirty degrees north latitude, to thirty degrees fouth, there is a conftant eaft wind throughout the year, blowing on the Atlantic and Pacific oceans, and called the Trade Wind. This is occafioned by the action of the fun, which, in moving from east to weft, heats and confequently expands the air immediately under him; by which means a ftream or tide of air always accompanies him in his courfe, and occafions a perpetual eaft wind within thefe limits. This general caufe however is modified by a number of particulars, the explication of which would be too tedious and complicated for our prefent plan, which is to mention facts rather than theories.

The winds called the Tropical Winds, which blow from fome particular point of the compafs without much variation, are of three kinds; 1. The General Trade Winds, which extend to nearly thirty degrees of latitude of each fide of the equator in the Atlantic, Ethiopic, and Pacific feas. 2. The Monfoons, or fhifting trade winds, which blow fix months in one direction, and the other fix months in the oppofite. These are moftly in the Indian or Eastern Ocean, and do not extend above two hundred leagues from the land. Their change is at the vernal and autumnal equinoxes, and is accompanied with terrible forms of thunder, lightning and rain. 3. The Sea and Land Breezes, which are another kind of periodical winds, that blow from the land from midnight to midday, and from the fea from about noon till midnight; thefe, however, do not extend above two or three leagues from fhore. Near the coaft of Guinea in Africa, the wind blows nearly always from the weft, fouth-west, or fouth. On the coaft of Peru in South America, the wind blows conftantly from the fouth-weft. Beyond the latitude of thirty north and fouth, the winds, as we daily perceive in Great Britain, are more variable, though they blow oftener from the weft than any other point. Between the fourth and tenth degrees of north latitude, and between the longitude of Cape Verd and that of the eafternmost of the Cape Verd islands, there tract of fea condemned to perpetual calms, attended with terrible thunder and lightning, and fuch rains, that this fea has acquired the name of the Rains.

is a

It may be alfo useful to ftudents in navigation and geography to obferve farther, that the courfe or latitude our fhips generally keep in their patlage from England to America, and the West Indies, is,

To Boston in New England, and Halifax in Nova Scotia, from 42 to 43 degrees.

To New York by the Azores, or Western Islands, 39 degrees.

To Carolina and Virginia by Madeira, which is called the upper course, 32 degrees; but the usual course, to take advantage of the trade-winds, is from 16 to 23 degrees; and in this courfe they frequently touch at Antigua: it is this courfe our Weft India faips fail in.

The Spanish galleons and the flota from Spain keep from 15 to 18 degrees; and in their return to Spain, about 37 degrees.

TIDES.] By the tides is meant that regular motion of the fea, according to which it ebbs and flows twice in twenty-four hours. The doctrine of the tides remained in obfcurity, till the immortal fir Ifaac Newton explained it by his great principle of gravity or attraction. For, having demonftrated that there is a principle in all bodies within the folar fyftem, by which they mutually draw or attract one another in proportion to their distance, it follows, that thofe parts of the fea which are im

mediately below the moon, muft be drawn towards it; and confequently, wherever the moon is nearly vertical, the fea will be raised, which occafions the flowing of the tide there. A fimilar reafon occafions the flowing of the tide likewife in thofe places where the moon is in the nadir, and which must be diametrically oppofite to the former: for in the hemisphere farthest from the moon, the parts in the nadir being lefs attracted by her than the other parts which are nearer to her, gravitate less towards the earth's centre, and confequently must be higher than the reft. Thofe parts of the earth, on the contrary, where the moon appears on the horizon, or ninety degrees diftant from the zenith and nadir, will have low water; for as the waters in the zenith and nadir rife at the fame time, the waters in their neighbourhood will prefs towards thofe places to maintain the equilibrium; to fupply the places of these, others will move the fame way, and fo on to the places ninety degrees diftant from the zenith and nadir, where the water will be loweft. By combining this doctrine with the diurnal motion of the earth, above explained, we shall be fenfible of the reason why the tides ebb and flow twice in a lunar day, or about twentyfour hours fifty minutes.

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The tides are higher than ordinary, twice every month, that is about the times of new and full moon, and are called Spring-Tides for at thefe times the actions of both the fun and moon are united, and draw in the fame ftraight line; and confequently the fea must be more elevated. At the conjunction, or when the fun and moon are on the fame fide of the earth, they both confpire to raise the waters in the zenith, and confequently in the nadir; and at the oppofition, or when the earth is between the fun and moon, while one occafions high water in the zenith and nadir, the other does the fame. The tides are less than ordinary twice every month, about the first and last quarters of the moon, and are called Neap-Tides: for in thofe quarters, the fun raises the waters where the moon depreffes them, and depreffes where the moon raises them; fo that the tides are only occafioned by the difference by which the action of the moon, which is nearest us, prevails over, that of the fun. These things would happen uniformly, were the whole furface of the earth covered with water; but fince there are a multitude of iflands and continents which interrupt the natural courfe of the water, a variety of appearances are to be met with in different places, which cannot be explained without confidering the fituation of the fhores, ftraits, and other objects that have a fhare in producing them.

CURRENTS.] There are frequently ftreams or currents in the ocean, which fet fhips a great way beyond their intended courfe. There is a current between Florida and the Bahama Iflands, which always runs from fouth to north. A current runs conftantly from the Atlantic, through the ftraits of Gibraltar, into the Mediterranean. A current fets out of the Baltic fea, through the found or ftrait between Sweden and Denmark, into the British channel, fo that there are no tides in the Baltic. About fmall islands and head-lands in the middle of the ocean, the tides rife very little; but in fome bays, and about the mouths of rivers, they rise from 12 to 50 feet.

MAPS.] A map is the reprefentation of the earth, or a part of it, on a plane furface. Maps differ from the globe in the fame manner as a picture does from a ftatue. The globe truly reprefents the earth; whereas a map, being a plane furface, cannot reprefent a spherical body. But though the earth can never be exhibited exactly by one map, yet by