In all positions of the celestial globe, this broad paper circle represents the plane of the horizon, and distinguishes the visible from the invisible part of the heavens; but in the terrestrial globe, it is applied to three different uses.

1. To distinguish the points of the horizon. In this case, it represents the rational horizon of any place.

2. It is used to represent the circle of illumination,' or that circle which separates day from night.

3. It occasionally represents the ecliptic.

Of the strong brass circle NÆZS. One side of this strong brass circle is graduated into four quadrants, each containing 90 degrees.

The numbers on two of these quadrants increase from the equator towards the poles; the other two increase from the poles towards the equator.

Two of the quadrants are numbered from the equator, to show the distance of any point on the globe from the equator. The other two are numbered from the poles, for the more ready setting the globe to the latitude of any place.

The strong brass circle of the celestial globe is called the meridian, because the centre of the sun comes directly under it at noon.

But as there are other circles on the terrestrial globe, which are called meridians, we chuse to deno→ minate this the strong brass circle, or meridian.

The graduated side of the strong brass circle, that belongs to the terrestrial globe, should face the west.

The graduated side of the strong brazen meridian. of the celestial globe, should face the east.

On the strong brass circle of the terrestrial globe, and at about 23 degrees on each side of the north pole, the days of each month are laid down according to the declination of the sun.

Of the Horary Circles, and their Indices. When the globes are mounted in my father's manner, we use the equator as the hour circle; because it is not only the most natural, but also the largest circle that can be applied for that purpose.

To make this circle answer the purpose, a semicircular wire is placed over it, carrying two indices, one on the east, the other on the west side of the strong brass circle.

As the equator is divided into 360°, or 24 hours, the time of one entire revolution of the earth, or heavens, the indices will shew in what space of time any part of such revolution is made among the hours which are graduated below the degrees of the equator on either globe,

As the motion of the terrestrial globe is from west to east, the horary numbers increase according to the direction of that motion: on the celestial globe they increase from the east to the west.

Of the Quadrant of Altitude, ZA, fig. 1. This is a thin, narrow, flexible slip of brass, that will bend to the surface of the globe; it has a nut, with a fiducial line upon it, which may be readily applied to the divisions on the strong brass meridian of either globe. One edge of the quadrant divided into

90 degrees, and the divisions are continued to 18 degrees below the horizon.

OF SOME OF THE CIRCLES THAT ARE DESCRIBED UPON THE SURFACE OF EACH GLOBE.

We may suppose as many circles to be described on the surface of the earth as we please, and conceive them to be extended to the sphere of the heavens, marking thereon concentric circles: for as we are obliged, in order to distinguish one place from another, to appropriate names to them, so are we obliged to use different circles on the globes, to distinguish the parts, and their several relations to each other.

Of the Equator, or Equinoctial. This circle goes round the globe exactly in the middle, between the two poles, from which it always keeps at the same distance; or, in other words, it is every where 90 degrees distant from each pole, and is, therefore, a boundary, separating the northern from the southern hemisphere; hence, it is frequently called the line by sailors; and when they sail over it, they are said to cross the line.

It is that circle in the heavens in which the sun appears to move on those two days, the one in the spring, the other in the autumn, when the days and nights are of an equal length all over the world; and hence, on the celestial globe, it is generally called the equinoctial.

It is graduated into 360 degrees. Upon the ter

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,