that each member of the organized body, in his own sphere of action,
should contribute his share to the achievement of the common object.
Further, it is entirely beyond the power of one man, or of a few, to
control every action and provide for every want of a great number of
individuals. The modern system of command, therefore, provides for a
system of grades, in which, theoretically, officers of each grade
control a group of the next lower units. A lieutenant-colonel, for
instance, may be in charge of a group of eight companies, each of which
is under a captain. In practice, all armies are permanently organized on
these lines, up to the colonel's or lieutenant-colonel's command, and
most of them are permanently divided into various higher units under
general officers, the brigade, division and army corps. The almost
invariable practice is to organize _infantry_ into companies, battalions
and regiments. _Cavalry_ is divided into troops, squadrons and
regiments. _Artillery_ is organized in batteries, these being usually
grouped in various ways. The other arms and departments are subdivided
in the same general way. The commands of general officers are the
_brigade_ of infantry, cavalry, and in some cases artillery, the
_division_ of two or more infantry brigades and a force of artillery and
mounted troops, or of cavalry and horse artillery, and the _army corps_
of two or more divisions and "corps troops." _Armies_ of several corps,
and _groups of armies_ are also formed.