restrial globe, the numbers increase from the meridian of London westward, and proceed quite round to 360 They are also numbered from the same meridian eastward, by an upper row of figures, to accommodate those who use the English tables of latitude and longitude.

On the celestial globe, the equatorial degrees are numbered from the first point of Aries eastward, to 360 degrees.

Under the degrees on either globe is graduated a circle of hours and minutes. On the celestial globe the hours increase eastward, from Aries to XII at Libra, where they begin again in the same direction, and proceed to XII at Aries. But on the terrestrial globe, the horary numbers increase by twice twelve hours westward from the meridian of London to the same again.

In turning the globe about, the equator keeps always under one point of the strong brass meridian, from which point the degrees on the said circle are numbered both ways.

Of the Ecliptic. The graduated circle which crosses the equator obliquely, forming with it an angle of about 23 degrees, is called the ecliptic.

This circle is divided into twelve equal parts, each of which contains thirty degrees. The beginning of each of these thirty degrees is marked with the characters of the twelve signs of the zodiac.

The sun appears always in this circle; he advances therein every day nearly a degree, and goes through it exactly in a year.

The points where this circle crosses the equator are called the equinoctial points. The one is at the beginning of Aries, the other at the beginning of Libra.

The commencement of Cancer and Capricorn are called the solstitial points.

The twelve signs, and their degrees, are laid down on the terrestrial globe; but upon the celestial globe, the days of each month are graduated just under the ecliptic.

The ecliptic belongs principally to the celestial globe.

The time, or motions in degrees, pointed out on the equator, by means of the semicircular wires ÆO, with two points O, that are to be occasionally slid on these two wires, at the minute of the hour, or the degree given.

ESSAY II.

PART III.

THE USE OF THE

TERRESTRIAL GLOBE,

MOUNTED IN THE BEST MANNER.

OF LONGITUDE AND LATITUDE, OF TERRESTRIAL ME RIDIANS, AND THE PROBLEMS RELATING TO LONGITUDE AND LATITUde.

MERIDIANS are circular lines, going over the

earth's surface, from one pole to the other, and crossing the equator at right angles.

Whatever places these circular lines pass through, in going from pole to pole, they are the meridians of those places.

There are no places upon the surface of the earth, through which meridians may not be conceived to pass. Every place, therefore, is supposed to have a meridian line passing over its zenith from north to south, and going through the poles of the world.

Thus, the meridian of Paris is one meridian; the meridian of London is another. This variety of meridians is satisfactorily represented on the globe, by the moveable meridian, which may be set to every individual point of the equator, and put directly over any particular place.

Whensoever we move towards the east or west, we change our meridian; but we do not change our meridian if we move directly to the north or south.

The moveable meridian shews that the poles of the earth divide every meridian into two semicircles, one of which passes through the place whose meridian it is, the other through a point on the earth, opposite to that place.

Hence it is, that writers in geography and astronomy generally mean by the meridian of any place, the semicircle which passes through that place; these, therefore, may be called the geographical meridians.

All places lying under the same semicircle, are said to have the same meridian; and the semicircle opposite to it, is called the opposite meridian, or sometimes the opposite part of the meridian,

From the foregoing definitions, it is clear that the meridian of any place is immoveably fixed to that place, and is carried round along with it by the rotation of the globe.

When the meridian of any place is by the revolution of the earth brought to point at the sun, it is noon, or mid-day, at that place.

The plane of the meridian of any place may be imagined to be extended to the sphere of the fixed stars.

When, by the motion of the earth, the plane of a meridian comes to any point in the heavens, as the sun, moon, &c. that point, &c. is then said to come to the meridian. It is in this sense that we generally use the expression of the sun or stars coming to, or passing over the meridian.

The time which elapses between the noon of any one day, in a given place, and the noon of the day following in the same place, is called a natural day.

All places which lie under the same meridian, have their noon, and every other hour of the natural day,

at the same time. Thus, when it is one in the afternoon at London, it is also one in the afternoon at every place under the meridian of London.

In order to ascertain the situation of any point, there must first be a settled part of the earth's surface, from which to measure; and as the point to be ascertained may lie in any part of the earth's surface, and as this surface is spherical, the place from whence we measure must be a circle. It would be necessary, however, to establish two such circles; one to know how far any place may be east or west of another, the second to know its distance north or south of the given point, and thus determine its precise situation.

Hence, it has been customary for geographers to fix upon the meridian of some remarkable place, as a first meridian, or standard; and, to reckon the distance of any place to the east or west, or its longitude, by its first distance from the first meridian.

On English globes, this first meridian is made to pass through London. The position of this first meridian is arbitrary, because on a globe, properly speaking, there is neither beginning nor end. The first person, (whose works, at least, are come down to us) who computed the distance of places by longitudes and latitudes, was Ptolemy, about the year after Christ 140.