USE OF GLOBES.

A Sphere, or Globe, is a round body, every point of whose surface is equally distant from a point within the body, called the cenue, A Hemisphere is a half globe.

There are two kinds of artificial globes, the terrestrial and the celestial.

The Terrestrial Globe is a representation of the earth, having the seas and different countries delineated on it, as they are situated on the surface of the earth.

The Celestial Globe is an artificial representation of the heavens, having the fixed stars drawn upon it, in their natural situation.

The Axis of a globe is an imaginary line passing through its cen tre from north to south, around which it revolves.

The Poles are the extremities of the axis, terminated by the surface of the globe. One is the north, and the other the south pole; and they are each 90 degrees from the equator.

Great Circles are such as divide the globe into two equal parts. These are the equator or equinoctial, the horizon, the meridians, the ecliptic, and the two colures.

The Less Circles are those that divide the globe into two unequal parts. These are four, the two tropics, and the two polar circles.

The circumference of every circle is supposed to be divided into 360 equal parts, called degrees; each degree into 60 equal parts, called minutes; and each minute into 60 equal parts, called seconds. They are marked thus, 23° 28′ 16′′; i. e. 23 degrees, 28 minutes, and 16 seconds.

The Equator is an imaginary great circle of the earth, equi-distant from the poles, dividing the earth into the northern and southern hemispheres.

The equator is divided by the principal meridian into two equal parts, of 180° each.

Meridians are imaginary great circles passing through the poles and perpendicular to the equator.

The meridian of a place, or the 12 o'clock hour circle, is the meridian that cuts the horizon in the north and south points. The first meridian of any country is the meridian passing through the capital of that country.

The Horizon is either sensible or real. The sensible horizon is a small circle which limits our prospect, where the sky and land or water appear to meet. The real horizon is a great circle which divides the earth into the upper and lower hemispheres.

The horizon is divided into four equal parts of 90° each, by the four cardinal points, East, West, North, and South.

The wooden horizon of the artificial globe is divided into three parts; the innermost is marked with all the points on the mariner's compass; the next has the names, characters, and figures of the twelve signs; and the third is a calendar of months and days. By the last two is instantly seen the sign and degres the sun is in dur ing every day in the year.

The Ecliptic is an imaginary great circle in the heavens, in the plane of which the earth performs her annual revolution roun, be

sun.

The ecliptic is drawn on the artificial globe obliquely to the ea tor, making with it an angle of 23° 28'.

The twelve signs are the twelve equal parts into which the ecup tic is divided, each consisting of 30°.

The Zodiac is a broad belt in the heavens 16° wide, in the inıdIdle of which is the ecliptic.

The names and characters of the 12 signs, and the time of the sun's entering them, are as follows:

The first six are called northern signs, because they are north of the equator; the last six southern, because they are south of the equator.

The Colures are two meridians; one passing through the equinoctial points, Aries and Libra, called the equinoctial colure; the other passing through the solstitial points, Cancer and Capricorn, called the solstitial colure.

The Tropics are two less circles, drawn parallel to the equator, at the distance of 23° 28'; one north of the equator, called the tropic of Cancer; the other south, called the tropic of Capricorn. These circles show the sun's limits north and south of the equator.

The Polar Circles are less circles, described round the poles, at the distance of 23° 28'. The northern is called the arctic circle, and the southern the antarctic.

Zones are divisions of the earth's surface, formed by the tropics and polar circles. They are five, one torrid, two temperate, and two frigid zones.

The torrid zone is included between the tropics; the temperate zones, between the tropics and polar circles; and the frigid, between the polar circles and the poles.

The Latitude of a place is the distance from the equator, north or south, measured on a meridian towards either pole, reckoneu tek grees, minutes, and seconds. It cannot exceed 90°.

The Longitude of a place is its distance from the first meridian, east or west, measured on the equator. It never exceeds 1802.

A Climate, as used by astronomers, is a portion of the earth's surface, included between two parallels of latitude, and of such a breadth that the longest day under the parallel nearest the pole,

half an hour longer than under the other. There are 24 such climates between the equator and each of the polar circles.

PROBLEMS ON THE TERRESTRIAL GLOBE.

PROBLEM 1. To find the Latitude of any Place.

Turn the globe, and bring the place to the engraven edge of the brazen meridian; and the degree on the meridian is the latitude, north or south, as it may be on the north or south side of the equator Thus the latitude of London is 51 degrees north; and of St. Helena nearly 16 degrees south.

What is the latitude of Alexandria in Egypt? Athens? Cape of Good Hope? Cape Horn? Constantinople? Edinburgh? Ispahan? Madras? Moscow? Paris? Boston? Philadelphia? Prague? Stock holm? Teneriffe? Vienna? Botany Bay?

PROBLEM II. To find the Longitude of any Place.

Bring the place to the brazen meridian, and the degree on the equator shows the longitude from London.

Thus the longitude of Madras is 80 degrees east; of Lisbon, 9 degrees west.

What is the longitude of Amsterdam? Archangel? Babelmandel? Dublin? Gibraltar? Jerusalem? Quebec? Syracuse? Tunis? Turin ?

Upsal?

PROBLEM III. The Longitude and Latitude of any Place being given, to find that Place.

Look for the longitude on the equator, and bring it to the brazen meridian, then under the given degree of latitude will be the place required.

Thus the place whose longitude is 30° 17' east, and latitude 31° 11' north, is Alexandria; and the place which has near 6° west longitude, and 16° south latitude, is St. Helena.

What places are those that have the following longitudes and latitudes 36° 17′ east long., and 31° 11' north lat.-113° 2' east long., and 23° 8' north lat. 79° 50′ west long., and 33° 22' north lat. -8° 30' west, and 51° 54' north lat. 4° 5 west and 56° (nearly) north lat. - 76° 50′ west long., and 12° south lat - 8° 35' west long, and 40° 53′ north lat.? What place is that whose longitude is nearly 78° west, but which has no latitude?

PROBLEM IV. To find the Difference of Latitude of any two Places.

If the places are in the same hemisphere, bring each to the meridian, and subtract the latitude of the one from that of the other: if in different hemispheres, add the latitude of the one to that of the other.

Thus the difference of latitude between London and Madras is 38° 28'; between Paris and Cape Horn is 104° 49'. What is the difference of latitude between Copenhagen and Gibraltar?-between London and the Cape of Good Hope?-between Berlin and Bristol-between Bengal and St. Helena? — between Madrid and

Moscow-between Leghorn and Liverpool? - between Pekin and Philadelphia? - How many degrees further north is St. Petersburg than Naples?

PROTILIM V. To find the Difference of Longitude of any two Places.

Bring one of the places to the brazen meridian, and mark its longitude; then bring the other place to the meridian, and the number cf degrees between its longitude and the first mark, is the differer ce of longitude: thus the difference of longitude between Londen and Constantinople is 25° 53'; between Constantinople and Madras, 51° 54'.

What is the difference of longitude between Athens and Batavia? -between Brest and Cape Horn?-between Charleston in South Carolina and Cork in Ireland?-between Rome and Cape Finisterre?-between Canton and the most northerly point of the Orkney Islands?-between Morocco and Thibet?-between Cape Bojador in Africa and Port Jackson New Holland? - between the most northerly point of Madagascar and Otaheite?-between Mecca and Calcutta?

PROBLEM VI. To find the Distance of any two Places on the Globe

Lay the graduated edge of the quadrant of altitude over both places, and the degrees between them, multiplied by 694, will give the distance in English miles. Thus the distance between the Lizard point and the island of Bermuda is 46°, or 3147 miles; between London and Jamaica, 4691 miles.

What is the distance between Samarcand in Tartary and Pekin? -between Warsaw and Ascension Island?-between North Cape and Gibraltar? - between Lisbon and Ispahan?-between Rio Janeiro and the Cape of Good Hope?-between Madrid and Cairo' -between Boston and Cayenne?

PROBLEM VII. The Hour at any Place being given, to find what Hour it is at any other Place.*

Bring the place, where the hour is given, to the brazen meridian,

When the difference of longitude between any two places is known, it is easy to ascertain their difference of time by calculation. It is noon, or twelve o'clock, when any place on the globe is exactly towards the sun, and the succession of day and night, of morning, noon, and evening, may be beautifully shown by turning the Terrestrial Globe in the sunshine, or in the light of a fire or candle. But to ascertain exactly the number of hours and minutes, by which, at the same moment of time, two places differ, it is necessary to divide the difference of longitude by 15, because every 15 degrees is equal to one hour of time; and, consequently, also, every degree is equal to four minutes of time.

For example, when it is noon at London, it will be four o'clock in the afternoon at all places which have 60 degrees of longitude east of Lendon, and 8 in the morning at all places which have 60 degrees west of

London.

At all places which have 180 degrees difference of longitude, it will be 12 o'clock at night, when it is noon at London. And in this manner, the hour in any part of the world may be calculated, by adding to the given hou:, when the place is east, and by subtracting, when it is west

and set the index of the hour circle to that hour, then turn the globe till the proposed place come under the meridian, and the in dex will point to the present hour at that place.

Thus, when it is twelve o'clock at noon in London, it is nearly four in the afternoon at the island of Mauritius; but at Jamaica it is only about seven in the morning.

When it is ten in the forenoon at London, what is the time at Calcutta, Canton, Pelew Islands, Barbadoes, the western side of Lake Superior, Owhyhee, and Easter Island?

What o'clock is it at New York, Moscow, Cape Horn, Genoa, Syracuse, and Leghorn, when it is midnight at Lisbon ?

How much are the clocks of Mexico behind ours?

When it is twelve at noon at Port Jackson, what time is it at Paris and Dublin?

PROBLEM VIII. To rectify the Globe for the Latitude, Zenith, and

Sun's Place.

1. For the latitude: Elevate the pole above the horizon, accord ng to the latitude of the place.

2. For the zenith: Screw the quadrant of altitude on the meridian at the given degree of latitude, counting from the equator towards the elevated pole.

3. For the sun's place: Find the sun's place on the horizon, and then bring the same place found on the ecliptic to the meridian, and set the hour index to twelve at noon.

Thus, to rectify for the latitude of London on the 10th day of May, the globe must be so placed, that the north pole shall be 51 degrees above the north side of the horizon; then 51 will be found on the zenith of the meridian, on which the quadrant must be screwed. On the horizon, the 10th of May answers to the 20th of Taurus, which find on the ecliptic, and bring it to the meridian, and set the index to twelve.

Rectify the globe for London, St. Petersburg, Madras, Pekin, Oporto, Venice, Quebec, Washir gton, Vienna, Dantzic, and Athens, for the 24th of February, the 27th of June, and the 6th of August.

PROBLEM IX. To find at what Hour the Sun rises and sets any Day in the Year, and also upon what Point of the Compass.

Rectify for the latitude and sun's place (Prob. VIII.), and turn the sun's place to the eastern edge of the horizon, and the index will point to the hour of rising; then bring it to the western edge of the horizon, and the index will show the setting.

Thus, on the 16th of March, the sun rises a little after six, and sets a little before six in the evening.

What time does the sun rise and set at St. Petersburg, Naples, Canton, Dublin, Gibraltar, Teneriffe, Boston, and Vienna, on the 15th of April, the 4th of July, and the 20th of November?

NOTE.- On the 1st of March the sun rises due east, and sets due west; between this and the 21st of September, it rises and sets to the northward of these points, and in the winter months to the southward of them. When the sun's place is brough✦ to the east