HORD, (horde, Fr.) a crowd or assemblage of people, who have not any fixed or certain habitation. The term was originally applied to a body of Tartars, who followed a roving life, encamped in different countries, and chiefly lived with their flocks.
HORION, Fr. a term which formerly signified a helmet, and which in the vulgar acceptation of it now, among the French, means a blow upon the head.
HORIZONTAL, parallel to the horizon; on a level.
Horizontal superficies, the plain field lying upon a level, without any rising or falling.
Horizontal plane, that which is parallel to the horizon of the place.
In levelling, the chief object to be considered is, whether two points be in the horizontal plane; or whether they deviate; and in what degree?
Horizontal range, or level range of a piece of ordnance, is the line it describes, when directed parallel to the horizon.
The following useful theorems come from the pen of the ingenious Dr. Halley:
1. A shot being made on an inclined plane, having the horizontal distance of the object it strikes with the elevation of the piece, and the angle at the gun between the object and the perpendicular, to find the greatest horizontal range of that piece loaded with the same charge of powder, that is, half the latus rectum of all the parabolas made with the same impetus.—Take half the angle contained between the object and the nadir, and the difference of the given angle of elevation from that half; subtract the versed sine of that difference from the versed sine of the angle made by the object and zenith. The difference of those versed sines will be to the sine of the angle last mentioned, as the horizontal distance of the object struck to the greatest range at 45 degrees.
2. Having the horizontal range of a gun, the horizontal distance and angle of inclination of an object to the perpendicular, to find the two elevations necessary to strike that object.—Take half the angle contained between the object and nadir; this half is equal to half the sum of the two angles of elevation sought. Then say, as the horizontal range is to the horizontal distance of the object, so is the sine of the angle of inclination to a fourth proportional; which fourth, being subtracted from the versed sine of the angle formed by the object and zenith, leaves the versed sine of half the difference of the angles of elevation, whose half sum was before obtained; therefore, by adding and subtracting half the difference of the angles of elevation to and from the said half sum the elevations themselves will be found.