XI. To find the length of the day and night at any time of the

year.

Double the time of the sun's rising that day, and it gives the length of the night; double the time of its setting, and it gives the length of the day.

XII. To find the length of the longest or shortest day, at any place upon the earth.

Rectify the globe for that place; if its latitude be north, bring the beginning of Cancer to the meridian; set the index to twelve, then bring the same degree of Cancer to the east part of the horizon, and the index will show the time of the sun's rising.

If the same degree be brought to the western side, the index will show the time of his setting, which doubled (as in the last problem) will give the length of the longest day and shortest night.

If we bring the beginning of Capricorn to the meridian, and proceed in all respects as before, we shall have, the length of the longest night and shortest day.

Thus, in the Great Mogul's dominions, the longest day is 14 hours, and the shortest night 10 hours. The shortest day is 10 hours, and the longest night 14 hours.

At Petersburg, the capital of the Russian empire, the longest day is about 19 hours, and the shortest night 4 hours. The shortest day 4 hours, and the longest night 19 hours.

Note. In all places near the equator, the sun rises and sets at six o'clock all the year. From thence to the polar circles, the days increase as the latitude increases; so that at those circles themselves the longest day is 24 hours and the longest night just the same. From the polar circles to the poles, the days continue to lengthen into weeks and nonths; so that at the very poles, the sun shines for six months together in summer, and is absent from it six months in winter-Note, also, that when it is summer with the northern inhabitants, it is winter with the southern, and the contrary; and every part of the world partakes of nearly an equal share of light and darkness.

XIII. To find all those inhabitants to whom the sun is this moment rising or setting, in their meridians, or midnight.

Find the sun's place in the ecliptic, and raise the pole as much above the horizon as the sun that day declines from the equator; then bring the place where the sun is vertical at that hour to the brass meridian; so will it then be in the zenith, or centre of the horizon. Now see what countries lie on the western edge of the horizon, for to them the sun is rising; to those on the eastern side he is setting; to those under the upper part of the meridian, it is noonday; and to those under the lower part of it, it is midnight. Thus, on the 10th of April at four o'clock in the morning, at Charlestown, (Mass.)

It is sunrise at

Sun-setting at
Mid-day or noon, at

Midnight at

MAPS.

Brazil, South America,
S New Guinea, the Japan

Isles and Kamtschatka,
Persia and Nova Zembla,
The Bay of Good Hope,
in the vicinity of King
George's Sound.

A Map is a representation of the earth's surface, or some part of it, delineated on a plane, according to the laws of perspective, and contains such circles, or parts of circles, as the size and situation of the place delineated will admit.

The top of a map represents the north, the bottom, the south; the right hand side, the east, and the left hand, the west. From the top to the bottom, are drawn meridians or lines of longitude; and from side to side, parallels of latitude. The outermost of the meridians and parallels are marked with degrees, by means of which, and a scale of miles usually placed in the corner of a map, the situations and distances of places may be found, as on the artificial globe.

Rivers are described in maps by black lines, and are wider toward the mouth, than toward the head or spring. Mountains are represented as on a picture, by a sort of cloud; forests and woods, by a kind of shrub; bogs and morasses, by shades; sands and shallows, by small dots i

roads, usually by double lines; and towns by an 0 or a small house. Near harbors, the depth of water is sometimes expressed by figures, representing fathoms.

NATURAL DIVISIONS OF THE EARTH'S
SURFACE.

The first grand division of the earth is into Land and Water.

Divisions of Land. A great extent of land, not entirely separated by water, is called a CONTINENT.

There are commonly reckoned two Continents, called the Eastern, comprehending Asia, Europe and Africa: and the Western, including North and South America. New Hol land has sometimes been dignified with the name of Continent; but is usually classed by geographers among the islands of the Pacific ocean.

A tract of land entirely surrounded by water is an IsLAND. Tracts of land, almost encircled by water, as Boston, are PENINSULAS. Necks of land, which join peninsu las to a main land, are ISTHMUSES.

Land projecting far into the sea is a PROMONTORY. The end or point of a promontory is a CAPE.

When land rises to a very great height above the level country, it is a MOUNTAIN. When this high land extends unevenly to a great length, it is called a chain or range of Mountains. When a mountain emits flames and sulphur, &c. it is a VOLCANO. The side of a steep mountain is a PRECIPICE.

When land rises to a small height it is called a HILL. The spaces between hills are called DALES; and very often, and perhaps commonly in America, VALES, or VAL

LEYS.

Divisions of Water. The waters, that cover so great a portion of the surface of the globe, are collectively called the OCEAN and sometimes the SEA.

Different and extensive portions of these great waters have obtained the name of OCEANS. These are the At

lantic, the *Indian, the Pacific, the Southern and the Arctic or Frozen Ocean. The two former are each 3000 miles across; the Pacific 10,000. The extent of the others is not known.

Large collections of water that are nearly enclosed by land are called SEAS; and smaller collections of this kind are called SOUNDS, BAYS, or GULFS; as the Mediterranean Sea, Long Island Sound, Chesapeak Bay, the Gulf of Mexico.

A narrow communication between a sea or bay, and the ocean, or between two seas or lakes, is a STRAIT, MOUTH, ENTRANCE, or INLET.

A great body of fresh water, surrounded by land, or communicating with the ocean only by a long river, is called a LAKE. Smaller collections of fresh water are called PONDS.

The fountains of water at the head of rivers, brooks, or rivulets, and from which wells are supplied, are called SPRINGS. When the fountains are warmer than usual, or are impregnated with fixed air, salts, sulphur, metals, and other mineral substances, they are called MEDICINAL, or MINERAL SPRINGS.

Streams or bodies of running water, according to their magnitude are called RIVERS, BROOKS, or RIVULETS. CREEKS are narrow branches of the ocean, indenting and sometimes insulating the sea coast. Some branches of rivers are sometimes called Creeks. When a large body of water tumbles over a precipice, it is called a CATARACT OF FALLS, as the Falls of Niagara. If the quantity of water be small, it is a CASCADE.

Standing water, in which earth, with grass or shrubs upon it, appears in different parts ;-and low sunken. grounds, full of trees and mire are called MORASSES, BOGS, FENS, but more commonly, among us, SwAMPS.

COMPONENT PARTS OF THE EARTH.

The Earth is composed of land and water, and is therefore called terraqueous. It is ascertained, from recent discoveries, that the waters contained in the concavities of the globe, cover at least two thirds of its surface.

The earth below its surface is composed of various substances, collectively called FOSSILS.

To

All substances dug out of mines, of whatever kind, such as metals, coal, sulphur, ochre, &c. are called MINERALS. Such of the minerals as can be malleated or beaten out with a hammer, are called METALS. These are commonly reckoned seven in number which are reckoned according to their weight in the following order: -1. Platina, a white metal, newly discovered in the gold mines of South-America, in many of its properties resembling gold. 2. Gold. 3. Lead. 4. Silver. 5. Copper. 6. Iron. 7. Tin. these should be added Quicksilver. Three of these, Platina, Gold, and Silver, (of which Platina is much the heaviest) are called perfect metals, because they remain longest unchanged by fire. The other four are called imperfect metals, because they may be destroyed, or changed into earth by fire. By a chymical operation en Iron, Steel is produced. A mixture of Tin and Lead, in certain portions, forms the compound called PEWTER.

The best chymists divide bodies, or the objects of chymistry, into salts, earths, inflammable substances, meta's and wa ters. The effects of heat and mixture on these bodies constitute what is called The Science of Chymistry.

VOLCANOES.

VOLCANOES are burning mountains, which include in their bowels sulphur, bitumen, and other combustible matters, the effect of which when kindled into a flame, is more violent than that of gunpowder, or any thing yet known in nature. As the explosive force of gunpowder arises from the conversion of water into air, that which takes place in volcanoes is undoubtedly from the same cause. Volcanoes may be compared to huge cannon. From their mouths, some of which are a mile and a half wide, are vomited forth dreadful volumes of smoke and flame; torrents of bitumen, sulphur, and melted metals; clouds of cinders and stones; and sometimes rocks of enormous bulk are thrown to a great distance. In the great eruption of Mount Vesuvius, in 1779, a stream of Lava* of an im

• Lava is the melted matter, which issues from Volcanoes.