The description and use of the globes and the orrery / To which is prefix'd, by way of introduction, a brief account of the solar system

by Joseph Harris

Hemispheres.

Any circle passing through the center of the sphere, thereby dividing into two equal parts or segments, is called a Great Circle; and the segments of the sphere so divided, are called Hemispheres.

Every great circle has its Poles and Axis.

Poles.

The Poles of a great circle are two points on the surface of the sphere, diametrically opposite to one another, and every where equally distant from the said circle.

Axis.

The Axis of a circle is a right line passing through the center of the sphere, and through the Poles of the said circle, and is therefore perpendicular to the Plane: Therefore

Secundaries.

All circles passing through the Poles of any great circle, intersect it in two places diametrically opposite, and also at right angles; and with respect to the said great circle, they may be called its Secundaries.

Parallel or lesser Circles.