G E O G R A P H Y.
ward from us, have noon, and every other hour, an hour ſooner than we have. They whoſe meridian is fifteen degrees weſtward from us, have noon, and every other hour, an hour later than we have: and ſo on in proportion, reckoning one hour for every fifteen degrees.
For the ecliptic circle, ſigns, and degrees, ſee Astronomy, p. 435.
The tropics are leſſer circles in the heaven, parallel to the equinoctial; one on each ſide of it, touching the ecliptic in the points of its greateſt declination; ſo that each tropic is 23 degrees from the equinoctial, one on the north ſide of it, and the other on the ſouth. The northern tropic touches the ecliptic at the beginning of Cancer, the ſouthern at the beginning of Capricorn; for which reaſon the former is called the tropic of Cancer, and the latter the tropic of Capricorn.
The polar circles in the heaven, are each 23 degrees from the poles, all around. That which goes round the north pole, is called the arctic circle. The ſouth polar circle, is called the antarctic circle, from its being oppoſite to the arctic.
The ecliptic, tropics, and polar-circles, are drawn upon the terreſtrial globe, as well as upon the celeſtial. But the ecliptic, being a great fixed circle in the heavens, cannot properly be ſaid to belong to the terreſtrial globe; and is laid down upon it only for the conveniency of ſolving ſome problems. So that, if this circle on the terreſtrial globe was properly divided into the months and days of the year, it would not only ſuit the globe better, but would alſo make the problems thereon much eaſier.
For the earth’s motion round its axis every 24 hours; its motion in the ecliptic round the ſun every year; and the viciſſitude of ſeaſons; ſee Astronomy, p. 452.
[See Plate XLIV. fig. 2.]
The equator, ecliptic, and tropics, polar circles, and meridians, are laid down upon the globe in the manner already deſcribed. The ecliptic is divided into 12 ſigns, and each ſign into 30 degrees. Each tropic is 23 degrees from the equator, and each polar circle 23 degrees from its reſpective pole. Circles are drawn parallel to the equator, at every ten degrees diſtance from it on each ſide to the poles: theſe circles are called parallels of latitude. On large globes there are circles drawn perpendicularly through every tenth degree of the equator, interſecting each other at the poles: but on globes of or under a foot diameter, they are only drawn through every fifteenth degree of the equator; theſe circles are generally culled meridians, ſometimes circles of longitude, and at other times hour-circles.
The globe is hung in a braſs-ring, called the brazen meridian, and turns upon a wire in eace pole ſunk half its thickneſs into one ſide of the meridian ring; by which means, that ſide of the ring divides the globe into two equal parts, called the eaſtern and weſtern hemiſpheres; as the equator divides it into two equal parts, called the northern and ſouthern hemiſpheres. The ring is divided into 360 equal parts or degrees, on the ſide wherein the axis of the globe turns. One half of theſe degrees are numbered, and reckoned, from the equator to the poles, where they end at 90: their uſe is to ſhew the latitudes of places. The degrees on the other half of the meridian ring are numbered from the poles to the equator, where they end at 90: their uſe is to ſhew how to elevate either the north or ſouth pole above the horizon, according to the latitude of any given place, as it is north or ſouth of the equator.
The brazen meridian is let into two notches made in a broad flat ring, called the wooden horizon; the upper ſurface of which divides the globe into two equal parts, called the upper and lower hemiſpheres. One notch is in the north point of the horizon, and the other in the ſouth. On this horizon are ſeveral concentric circles, which contain the months and days of the year, the ſigns and degrees anſwering to the ſun's place for each month and day, and the 32 points of the compaſs.—The graduated ſide of the braſs meridian lies towards the eaſt ſide of the horizon, and ſhould be generally kept towards the perſon who works problems by the globes.
There is a ſmall horary circle, ſo fixed to the north part of the brazen meridian, that the wire in the north pole of the globe is in the centre of that circle; and on the wire is an index, which goes over all the 24 hours of the circle, as the globe is turned round its axis. Sometimes there are two horary circles, one between each pole of the globe and the brazen meridian.
There is a thin ſlip of braſs, called the quadrant of altitude, which is divided into 90 equal parts or degrees, anſwering exactly to ſo many degrees of the equator. It is occaſionally fixed to the uppermoſt point of the brazen meridian by a nut and ſcrew. The divisions end at the nut, and the quadrant is turned round upon it.
The exterior parts of this machine are, a compages of braſs rings, which repreſent the principal circles of the heaven, viz. 1. The equinoctial A A, which is divided into 360 degrees (beginning at its interſection with the ecliptic in Aries) for ſhewing the ſun's right aſcenſion in degrees; and alſo into 24 hours, for ſhewing his right aſcenſion in time. 2. The ecliptic B B, which is divided into 12 ſigns, and each ſign into 30 degrees, and alſo into the months and days of the year; in ſuch a manner, that the degree or point of the ecliptic in which the ſun is, on any given day, ſtands over that day in the circle of months. 3. The tropic of Cancer C C, touching the ecliptic at the beginning of Cancer in e, and the tropic of Capricorn D D, touching the ecliptic at the beginning of Capricorn in f; each 23 degrees from the equinoctial circle. 4. The arctic circle E, and the antarctic circle F, each 23 degrees from its reſpective pole at N and S. 5. The equinoctial colure G G, paſſing through the north and ſouth poles of the heaven at N and S, and through the equinoctial points Aries and Libra, in the ecliptic. 6. The ſolſtitial colure H H, paſſing through the poles of the
