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

Note, The Equator and the Equinoctial are generally synonymous terms; but sometimes the Equator particularly signifies that great circle upon the surface of the Earth, which coincides with the Equinoctial in the Heavens. This circle is also by Mariners commonly called the Line.

Northern and Southern Hemispheres.

The Axis of the World.

Poles of the World, or of the Equator.

The equinoctial divides the globe of the Earth, and also the whole Heavens into two equal parts, North and South, which are called the Northern and Southern Hemispheres. The axis of this circle, is called the Axis of the World, or the Earth’s Axis, because the Earth revolves about it (from West to East) in 24 hours. The extreme of this axis are called the Poles of the World, whereof that which lies in the Northern Hemisphere, is called the North Pole, and the other is called the South Pole. The equinoctial circle is always delineated upon the surface of each globe, with its name at length expressed; the axis of this circle, or the Earth’s axis, is only an imaginary line in the Heavens, but on the globes it is expressed by the wires about which they really turn. The Poles of the world, are the two points upon the surface of the globe through which these wires pass; the North Pole is that which hath the little brass circle, with a moveable index placed round it; and the other opposite to it is the South Pole. The Northern Hemisphere is that wherein the North Pole is placed, and the opposite one is the Southern Hemisphere.

The astronomers divide all circles into 360 equal parts, called Degrees, each degree into 60 equal parts, called Minutes, each minute into 60 Seconds, &c. But besides this division into degrees, the equinoctial is also divided into 24 equal parts, or Hours, each hour into 60 Minutes, each minute into 60 Seconds, &c. so that one hour is equal to 15 degrees, each minute of time is equal to 15 minutes of a degree, &c.

Hour Circles or Circles of Ascension, also called Meridians.

2. All circles conceived to pass through the Poles of the world, intersecting the equinoctial at right angles, are, with respect to any point in the Heavens, called Hour Circles; and the Circles of Ascension, because the ascension of the Heavenly bodies, from a certain point, are by them determined.

These circles are also, with regard to places upon Earth, called Meridians.

The Brass Meridian.