HORDED'S!, in botany, barley, a genus of the Triandria Digynia class and order. Natural order of Grasses. Essential cha racter: calyx lateral, two-valved, one-flow. erect, by threes, at each toothlet of the rachis. There are nine specks.
in astronomy and geogra phy, that great circle which divides the heavens and the earth into two equal parts, or hemispheres, distinguishing the upper from the lower. The horizon is either sensible or rational : the sensible horizon is that circle, which, being dis covered by our senses, limits our pros pect.
When we are on terra firma, this cir cle commonly seems rugged and irregu lar, occasioned by the unevenness of the ground; but at sea, there are no such irregularities. The semi-diameter of this circle varieth according to the height of the eye of the observer. If a mall, six feet high. stood upon a large plain, or the surface of the sea, lie could not see quite three miles round. To find the distance to which a person can see, at any given height of the eye, or the extent of the vi sible horizon, is a problem of some utili ty, particularly to mariners : the rule is, "multiply the square root of the height of the eye in feet, by 1.225, and the pro= duct is the distance in miles to which we can see from that height ;" thus p.sailor, standing at the top-mast of:a ship 120 feet high, can see a distance in miles = 4/120 j<1.225=13 45= to thirteen miles and a half nearly. • The rational, or true horizon, is a great circle of the apparent celestial sphere, di viding, it into two,equal hemispheres, and serving as the limits of elevation or de pression of celestial objects, This hori zon being parallel to the sensible horizon, is distant from it by the semi-diameter. of the earth, through whose centre it passes: for the astronomers reduce the appear ance of the 'heavens to a spherical sur which is not concentrical to the eye, but to the earth. It divides the heaven and earth into two parts, the one light, and the other dark, which are greater or lesser, according to the condition of the place, &c. It determines the rising and setting of the sun, moon, or stars, itiany particular latitude ; for, when any of these appear just at the eastern part of the ho rizon, we say it rises; and wlien it does so at the western part, we say it sets. And from hence also the altitude of the sun or stars is accounted, which is their height above the horizon. This circle is
divided by astronomers into four quad rants, or cardinal points The poles of this horizon are the zenith and the nadir : and the innumerable circlesdiawn through these poles to the horizon are called the vertical circles, or azimuths. These two horizons produced to the fixed stars will appear to coincide into one, since the earth compared to the sphere in which, the fixed stars appear is but a point ; therefore the two circles, which are but a point distant from each other, may well considered as coinciding into one.
Ifonrzoly of a globe, - See GLOBE.
HOltIZONTAL,something relating to the horizon : or that is taken in, or on a level with the horizon :. thus we say, an horizontal, plane, Eto: It frequently happens at sea, that the atmosphere is so hazy as to prevent a distinct view of the horizon, which is a great hindrance to accurate ohservationst This inconvenience is remedied by an Haat zoNTAT, consists in a well polishedmetal speculum, about three, or four inches in diameter, inclosed within a rim of brass; so fitted, that the centre of gravity of the whole shall fall near the point on which it turns. This is of a steel' axis running through the centre of the speculum, above Which it finishes in a square, for the convenience of fitting a roller on it, by which it is set in motion by means of a piece of tape wound round-the roller. The cup in which it turns is made of agate, flint; or other hard substance, and a cover to the whole may be made of glass; by this means an observation may be taken it as well -covered as open, which will prevent injury from the spray of the sea. These specula are as useful by night as by day ; for as the images of the stars may be seen in the speculum, conse quently any object that can be seen re flected upon the glasses of, the quadrants may be observed by the specuftirn, , and these are all the stars of the first- magni, tude, the planets Ventis, Mars, Jupiter, Saturn; and the Moon; so that by having the declinations .uf these bodies in the Nautical Almanack,;. or indeed in any ephemeris, they may be used in observa tions`aS well as the sun.
IIoarznsrax, dial, that drawn on a plane parallel to the horizon, haying its style elevated accordingto.the altitude of the poll, in the place it is designed for.
See DIAL. •