other circles, is divided into 360 degrees; but as these divisions are too minute for common use, it is also divided into 32 equal parts, called rhumbs or points of the compass. Winds are denominated east, west, north, south, &c. according to the points of the compass from which they blow; and with respect to their direction, are distributed into three classes, viz. general, periodical, and variable.

General winds are such as blow always nearly in the same direction. They are found to prevail in the Atlantic and Pacific oceans between the latitudes of about 28 degrees north and south; blowing generally at the equator from the east, on the north side of it between the north and east, and more northerly the nearer the northern limit; and on the south side, between the south and east, and more southerly the nearer the southern limit, and are also called tropical or general trade winds.

Periodical winds are such as blow nearly in certain directions during certain periods of time. The monsoons or shifting trade winds, and the land and sea breezes, are of this kind. The monsoons blow six months in one direction, and then six months in the opposite, the changes happening about the times of the equinoxes. These winds chiefly prevail in some parts of the Indian Ocean. The land and sea breezes are winds, which blow from the land in the night, and from the sea in the day time, changing their direclion every 12 hours. They obtain in some degree on the coast of every country, but are most remarkable between the tropics. At the islands between the tropics, the sea breeze begins about nine o'clock in the morning and continues till about nine in the evening; a land breeze then succeeds and continues till about nine the next morning.

The periodical winds arise from the difference in the temperature of the air over land, and of that over water, occasioned by their not acquiring or losing equal degrees of heat in a given time. The Indian ocean is bounded on the east and north by part of Africa, Arabia, Persia, and India, the shores of which are situated within the limits of the trade winds; and the sun, after the vernal equinox, renders the air above these extensive tracts of land hotter than that above the adjacent sea, and thus produces a wind, which soon begins to blow toward the land. This direction of the wind

continues from April to October, when the sun having passed to the south side of the equator, the air over the land toward the north becomes colder than that over the water, the direction of the wind is inverted, and it blows on the opposite point the remaining six months of the year. And with respect to the land and sea breezes, thereffect of the sun in heating the air over the land in the day time being greater than the heat it produces in the air over the adjacent seas, sea breezes arise; and in the night, the air, which before was hottest, becomes and continues coldest, and a land breeze is the consequence.

Variable winds are those, which are subject to no regularity of duration or change. All the winds in latitudes higher than 40° are of this kind.

Variable, as well as periodical, winds are principally owing, without doubt, to the different temperatures of air incumbent on land and water.

Between the fourth and tenth degrees of north latitude, and between the longitudes of Cape Verd and the easternmost of the Cape de Verd Islands, is a tract of sea, which seems to be condemned to perpetual calms, attended with dreadful thunder and lightning, and such frequent rains, that it has acquired the name of the Rains. This phenomenon seems to be caused by the great rarefaction of the air on the neighboring coast, which causes a perpetual current of air to set in from the westward, and this current meeting here with the general trade wind, the two currents balance each other, and cause a general calm; while the vapors carried thither by each wind, meeting and condensing, occasion these frequent deluges of rain,

Dr. Derham, from repeated observations upon the motion of light, downy feathers, found that the greatest velocity of the wind was not above 60 miles in an hour. But Mr. Bruce justly observes, that such experiments must be subject to great inaccuracy, as the feathers cannot proceed in a straight line; he therefore estimates the velocity of winds by means of the shadow of a cloud over the earth, by which he found, that, in a great storm, the wind moves 63 miles an hour; in a fresh gale, 21 miles an hour; and in a small breeze, 10 miles an hour. Mr. Rouse makes the velocity of a hurricane 100 miles an hour,

TIDES.

By the term tide is meant the regular alternate rising and falling of the water in the sea and rivers. The phenomena of the tides occasioned a variety of opinions among the ancient philosophers, and the cause was considered as one of the greatest mysteries in nature. It remained in obscurity till the latter end of the 16th century, when Sir Isaac Newton clearly pointed it out, and showed the agreement of its effects with the observed phenomena.

A heavy body, being thrown up in the air, falls again to the earth in a direction perpendicular to its surface, or in a line tending to its centre. The cause of the body's falling is a species of attraction, called gravity or gravitation. This principle operates not only between the earth and all bodies near its surface, but also between all the bodies which compose the solar system, and probably between all the bodies and systems of the universe. And it is abundantly proved by experiment and observation, that the force of gravity is inversely as the squares of the distances of the bodies from one another, that is, the force decreases in the same ratio as the squares of the distances increase, and vice versa.

The flowing and ebbing of the sea are to be attributed to the attraction of the sun and moon; but principally to that of the moon on account of its less distance from the earth.

The attractive force of the moon varies at different distances,

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being greater at a small distance and smaller at a great distance. Its power is found to diminish as the squares of the distances increase. Thus, if at the distance of 10,000 miles, the attractive force be considered as 4, at the distance of 20,000 it will be only 1. Hence the waters on the side of the earth directly under the moon are more attracted by the moon than the central parts of the earth, because they are nearer to the moon, and the central parts of the earth are more attracted than the waters on the opposite side of the earth. Consequently the waters directly under the moon will be as it were attracted from the centre of the earth and be made to rise towards the moon; and the centre of the earth will be as it were attracted from the waters on the side of the earth opposite to the moon, so that those waters will be less near the earth's centre than if the moon did not operate, i. e. they will rise. On the meridian directly under the moon, therefore, there will be a high tide and a similar one on the opposite side of the earth, at the distance of 180°. On each side, however, at 90° distance from that meridian, in consequence of the moon's very oblique attraction, the waters will be depressed.

The tides are higher than ordinary twice a month, viz. about the times of the new and full moon; and these are called spring tides. Because at these times the attraction of the sun conspires with that of the moon, or their agency is in the same right line; and consequently the tides must be more elevated. When the two luminaries are in conjunction, or on the same side of the earth, they both conspire to raise the water on the nearest and remotest part; and when they are in opposition, that is, when the earth is between them, the part nearest to the one is remotest from the other, and vice versa, consequently the effects of their agency are united.

The tides are less than ordinary twice a month; that is, about the times of the first and last quarters of the moon; and these are called neap tides. For in the quarters of the moon, the sun raises the water where the moon depresses it; and depresses it where the moon raises it; the tides are made therefore by the difference of their actions.

LENGTH OF MILES IN DIFFERENT COUNTRIES.

There is scarcely a greater variety in any thing than in this sort of measure; not only those of separate countries differ, as the French from the English, but those of the same country vary in the different provinces, and all commonly from the standard. Thus the common English mile differs from the statute mile, and the French have three sorts of leagues.

We shall here give the miles of several countries, compared with the English, by Dr. Hally.

The English statute mile consists of 5280 feet; 1760 yards, or 8 furlongs.

Eleven Irish miles are equal to fourteen English.

The Russian verst or werst is little more then English.

The Turkish, Italian, and old Roman less, mile is nearly 1 En

glish.

The Arabian, ancient and modern, is about 14 English.

The Scotch mile is about 14 English.

The Indian is almost 3 English.

The Dutch, Spanish, and Polish, is about 3 English.

The German is more than 4 English.

The Swedish, Danish, and Hungarian is from 5 to 6 English. The French common marine league is nearly 3, and

The English marine league is 3 nautical miles.

96000 240 48 24 8 A Day's Journey 33 288 0

The East used another span equal to one third of a cubit. The above are sacred measures, in the lengths of which there must necessarily be some degree of uncertainty. Arbuthnot makes

The ancient Egyptians and Romans supposed the day to begin at midnight; and it is also now considered by the United States of America, Great-Britian, France, and most European countries, as beginning at that time. In Astronomy, however, it is supposed to begin at noon, or the time when the sun is on the meridian. The beginning has been fixed at sunrise by some nations, as the ancient Babylonians, Persians, &c. and at sunset by others, as the ancient Jews, Grecians, &c.

In the Julian calendar or old style, a method of reckoning time, adopted by Julius Cæsar, about 45 years before the birth of Christ, which was much preferable to any that preceded it, a year was supposed to consist 365 days and 6 hours; each of 3 years in succession was considered as a common year of 365 days, and on account of the annual excess of 6 hours, another was added to every fourth, which consequently consisted of 366 days, and was called leap year. As the solar year, or the time of the apparent annual revolution of the sun, is not exactly 365 days and 6 hours, but nearly 365 days, 5 hours, 48 minutes and 48 seconds, it follows, that the Julian year exceeded the solar by about 11 minutes and 12 seconds. This annual excess amounts to 1 day in 129 years. Notwithstanding this inaccuracy, the Julian style was generally used in Europe till the year 1582, when it was reformed by Pope Gregory the thirteenth, who introduced what is called the Gregorian or new style.

It having been found that the vernal equinox, which had been fixed to the 21st of March by the council of Nice, held in the year 325, happened the 11th of March in 1582, the difference of 10 days between the civil and real time was taken from the October of that year, and the 21st of the next March reduced to the true time of the equinox. But the Protestant states refused, at that time, to accede to the new style, which the Pope had enjoined on all the ecclesiastics within his jurisdiction, and exhorted the Christian princes to adopt in their respective dominions; and it did not commence in the British empire, of which the present United States of America then made a part, till the year 1752, when the error having increased to 11 days, they were, by an act of parliament, struck out of the calendar from the month of September, the third day, according to the old style, being called the fourteenth.

The reformation of the calendar consisted not only in expunging the excess of the civil above the real time, but also in the introduction of a principle which should prevent a like accumulation of error in future. According to the old style the last year