Austria, and of 1806 and 1807 against Prussia and Russia, of 1808 in
Spain, his manoeuvres in 1814, between the battle of Brienne and that
of Paris, and his operations previous to the Battle of Ligny in 1815,
are all brilliant examples under this head.

To change the line of operations, in the middle of a campaign, and
follow _accidental lines_, is always a delicate affair, and can only be
resorted to by a general of great skill, and with disciplined troops. In
such a case it may be attended with important results. It was one of
Napoleon's maxims, that "a line of operations, when once chosen, should
never be abandoned." This maxim, however, must sometimes be disregarded
by an army of undisciplined troops, in order to avoid entire
destruction; but the total abandonment of a line of operations is always
attended with great loss, and should be regarded as a mere choice of
evils. A regular army can always avoid this result, by changing the
direction of its line; thus frequently gaining superior advantages in
the new theatre of action. If the plan of this change be the result of a
good _coup d'oeil_, and it be skilfully executed, the rear of the
operating army will be secure from the enemy; and moreover, he will be
left in doubt respecting its weak points. But such is the uncertainty of
this manoeuvre, that it is very rarely taken by the best troops, unless
actually forced upon them. If the army be of incongruous materials,
generally a change of direction will be less advantageous than to
entirely abandon the line, and save as many as possible of the troops
for some new plan of operations. (Maxim 20.) If, however, the
undisciplined army be sustained by fortifications, it can take up the
_accidental line of operations_ in the same manner, and with the same
probability of success, as is done by a regular force.

We have examples of accidental lines in the operations of the king of