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Circles of tbesphere.

The horizon.

?oks.

Equator.

Meridian.

Of the Heavens and the Earth ,

We may imagine as many circles described upon the earth as wepleafe; and we may imagine the plane of any circle described uponthe earth to be continued, until it marks a circle in the concave sphereof the heavens.

The horizon is either sensible or rational. The senfible horizon isthat circle, which a man standing upon a large plane, observes toterminate his view ali around, where the heaven and earth seem tomeet. The plane of our sensible horizon continued to the heaven,divides it into tvvo hemispheres; one visible to us, the other hid bythe convexity of the earth.

The plane of the rational horizon, is fupposed parallel to the planeof the sensible ; to pass through the center of the earth, and to becontinued to the heavens. And although the plane of the sensiblehorizon touches the earth in the place of the observer, yet this plane,and that of the rational horizon, will seem to coincide in the heaven,because the whole earth is but a point compared to the sphere of theheaven.

The earth being a spherical body, the horizon, or limit of our view,niust change as we change our place.

The poles of the earth, are thole two points on its surface in whichits axis terminates. The one is called the north pole, and the otherthe fouth pole.

The poles of the heaven, are thole two points in which the earth’saxis produced terminates in the heaven : so that the north pole of theheaven is directly over the north pole of the earth ; and the fouthpole of the heaven is directly over the fouth pole of the earth.

The equator is a great circle upon the earth, every part of which isequally distant from either of the poles. It divides the earth intotwo equal parts, called the northern and fouthern hemispheres. If wesuppose the plane of this circle to be extended to the heaven, itwill mark the equinoSli’al therein, and will divide the heaven intotwo equal parts, called the northern and fouthern hemispheres of theheaven.

The meridian of any place is a great circle passing through thatplace and the poles of the earth. We may imagine as many suchmeridians as we pleafe, because any place that is ever so little to theeast or west of any other place, has a different meridian from thatplace j for no one circle can pals through any two such places andthe poles of the earth.

The meridian of any place is divided by the poles, into two semi-circles; that which paffes through the place is called the geographici,