' The meridian on the globe or sphere is represented by the brazen circle, in which the globe hangs and turns. It is divided into four times 90, or 360°, be ginning at the equinoctial. See °Loss.
On it, each way from the equinoctial, on the celestial globes, is counted the south and north.declination of the sun or stars; and on the terrestrial globes, the latitude of places north or south. There are two points of this circle, which are called the poles of the world ; and a diameter con tinued from thence through the centre of either globe is called the axis of the earth or heavens, on which they are supposed to turn round. On the terrestrial globes there are usually thirty-six meridians drawn, one through every tenth degree of the equator, or through every tenth degree of longitude. The uses of this circle are, 1. To set the globes to any par ticular latitude. 2. To shew the sun's or a star's declination, right ascension, or greaten altitude, &c.
" To find the sun's meridian altitude or depression at night by the globes." Bring the sun's place to the meridian above the horizon for his altitude at noon, which will shew the degrees of it, count ed from the horizon. For his midnight depression below the north point of the horizon, you must bring the opposite point to the sun's present place, as be fore to the meridian ; and the degrees there intercepted between that point and the horizon are his midnight depression.
Meridian line is an arch, or part of the meridian of a place, terminated each way by the horizon. Or it is the intersection of the plane of the meridian of the place with the plane of the horizon, vulgarly called a north and south line, because its direction is from one pole towards the other. It is of peat use in astronomy,
geography, dialhng, &c. and on its exact. ness all depends ; whence divers astrono mers have taken infinite pains to have it to the last precision.
Magmas line, on a dial, is a right line, arising from the intersection of the me ridian of the place with the plane of the dial: this is the line of twelve o'clock, and from hence the division of the hour. lines begin. See Mar..
Mascaras, magus:Meal, is a great circle passing through the magnetical poles, to which the magnetic needle, or needle of the mariner's compass, conforms itself. MERIDIAN altitude of the sun and stars, is their altitude when in the meridian of the place where they are observed. Or it may be defined an arch of a great cir cle perpendicular to the horizon, and comprehended between the horizon and the sun or star then in the meridian of the place.
" To take the meridian altitude with a quadrant." If the position of the meridian be known, and the plane of an astronomi cal quadrant be placed in the meridian line, by means of the plumb-line suspend ed at the centre, the meridian altitudes of the stars, which are the principal obser vations whereon the whole art of astro nomy is founded, may easily be deter mined. The meridian altitude of a star may likewise be had by means of a pen dulum-clock, if the exact time of the star's passage over the meridian be known. Now it must be observed, that stars have the same altitude for a minute before and after their passage by their meridian, if they be not in or near the zenith ; but if they be, their altitudes must be taken every minute when they are near the me ridian, and their g•reatest altitudes will be the meridian altitudes sought.