Hour Circle.
4. The Horary or Hour Circle, is divided into twice twelve hours, the two XII’s coinciding with the meridian; the uppermost XII is that at Noon, and the lowermost towards the horizon is XII at Night. The hours on the East side of the meridian are the Morning Hours, and those on the West side the Hours after Noon. The axis of the globe carries round the Hand or Index which points the hour, and passes through the center of the hour circle.
The things above described are common to both globes; but there are some others which are peculiar or proper to one sort of globe. The two Colures, and the Circles of Latitude from the ecliptic, belong only to the Celestial Globes; also the ecliptic itself does properly belong only to this globe, tho’ it is always drawn on the Terrestrial, for the sake of those that might not have the other globe by them. The equinoctial on the celestial globe is always numbered into 360 degrees, beginning at the equinoctial point ♈; but on the terrestrial, it is arbitrary, where these numbers commence, according to the meridian of what place you intend for your first; and the degrees may be counted either quite round to 360, or both ways, ’till they meet in the opposite part of the meridian, at 180.
SECT. III.
The USE of the Globes.
Problem I. To find the Latitude and Longitude of any given Place upon the Globe; and on the contrary, the Latitude and Longitude being given, to find the Place.
1.
Turn the globe round its axis, ’till the given place lies exactly under the (Eastern side of the brass) meridian, then that degree upon the meridian, which is directly over it, is the Latitude; which is accordingly North or South, as it lies in the Northern or Southern hemisphere, the globe remaining in the same position.