4th. When, by dispatching a _detachment_, you may be able to intercept a
convoy, or reinforcement, coming to the aid of your enemy.

These are apparent rather than real exceptions to the rule of
concentration. This rule does not require that _all the army should
occupy the same position_. Far from it. Concentration requires the main
body to be in immediate and supporting reach: small detachments, for
temporary and important objects, like those mentioned, are perfectly
legitimate, and in accordance with correct principles. Napoleon's
position in Spain will serve as an illustration. A hand, placed on the
map of that country, will represent the position of the invading forces.
When opened, the fingers will represent the several detachments, thrown
out on important strategic lines, and which could readily be drawn in,
as in closing the hand, upon the principal and central mass, preparatory
to striking some important blow.

"If, as we have seen, it be the first great rule for an army acting on
the offensive principle, to keep its forces _concentrated_, it is, no
doubt, the second, _to keep them fully employed._ Is it your intention
to seize a particular province of your enemy? to penetrate to his
capital? or to cut him off from his supplies? Whatever measure be
necessary to open your route to these objects must be _promptly_ taken;
and if you mean to subsist yourself at his expense, your movements must
be more rapid than his. Give him time to _breathe_,--and above all, give
him time to _rest_, and your project is blasted; his forages will be
completed, and his magazines filled and secured. The roads of approach
will be obstructed, bridges destroyed, and strong points everywhere
taken and defended. You will, in fact, like Burgoyne, in 1777, reduce
yourself to the necessity of bleeding at every step, without equivalent