By the law of the 12th of December, 1790, on the organization of the public force of France, the Army was defined, "A standing force drawn from the public force, and designed to act against external enemies." [_Une force habituelle extraite de la force publique, et destinee essentiellement a agir contre les ennemis du dehors_.] In time of peace, the whole organized military force of the State is intended when we speak of _the army_; but in time of war this force is broken up into two or more fractions, each of which is called an _army_. These armies are usually named from the particular duty which may be assigned to them--as, _army of invasion, army of occupation, army of observation, army of reserve, &c._; or from the country or direction in which they operate--as, _army of the North, of the South, of Mexico, of Canada, of the Rhine, &c._; or from the general who commands it--as, the _army of Soult, army of Wellington, army of Bluecher, &c._ All modern armies are organized on the same basis. They are made up of a Staff and Administrative departments, and four distinct arms--Infantry, Cavalry, Artillery, and Engineers; each having distinct duties, but all combining to form one and the same military body. In the actual operations of a campaign, these forces are formed into _corps d'armee_, each _corps d'armee_ being composed of two or more _grand-divisions_; each grand-division, of two or more _brigades_; and each brigade, of several _companies, squadrons_, or _batteries_. In speaking of an army in the field, it is sometimes supposed to be divided into two classes of men--the _Staff_ and _the line_. We here include in the first class-- All officers, of whatever arm, above the rank of colonel; All officers of the staff corps of whatever grade, and All officers attached to the staff as aides, &c.; All officers of the administrative departments; All officers of artillery and engineer staffs; The corps of geographical or topographical engineers, and The guards. In the second class are included all troops, of whatever arm, which belong to the active army, in infantry, cavalry, artillery, and engineers. All troops on detached service, such as recruiting, guarding posts and depots, escorting convoys, &c., as well as all sedentary corps, garrisons of fortified places, &c., are not regarded in this classification as composing any part of the _line_ of the army.