that part of grammar which teaches the nature and affections of letters, and the just method of spelling or writing words with all the proper and necessary letters; making one of the four greatest divisions or branches of grammar. See GRAMMAR.

ORTHOGRAPHY, in geometry, the art of drawing or delineating the fore-right plan of any object, and of expressing the heights or elevations of each part. It is called orthography, from its determining things by perpendicular lines falling on the geometrical plane.

ORTHOGRAPHY, in architecture, the elevation of a building.

ORTHOGRAPHY, in perspective, is the fore-right side of any plane, i.e., the side or plane that lies parallel to a straight line, that may be imagined to pass through the outward convex points of the eyes, continued to a convenient length.

ORTHOPNOEA, in medicine, a species or degree of asthma, where there is such a difficulty of respiration, that the patient is obliged to sit or stand upright, to be able to breathe. See MEDICINE.

ORTON, a market town of Westmoreland, situated ten miles south-west of Appleby.

ORVALA, in botany, a genus of the didynamia gymnospermia clas. The superior lip of the corolla is divided into three segments, each being teathed; and the inferior lip is cordated and crenated. There is but one species, a native of Italy.

ORVIETTO, a city of Italy, in the pope's territories, capital of the province of Orvietto, situated at the confluence of the Tiber and the Chiane: E. long. 13°, N. lat. 43°.

ORWELL, a river of Suffolk, which, rising in the middle of that country, runs south-east by Ipswich, and falls into the German sea at Languard-fort.

ORYZA, RICE, in botany, a genus of the hexandria digynia clas. The calyx is a double-valved glume, with one flower; and the corolla consists of two equal valves. There is but one species.

This plant is cultivated in vast abundance in the East, as also in Carolina, for food. It is said to be good in dysenteries, diarrhoeas, &c.