L M N the glacis, which, except the abatis near the ditch, is left
free and open, so as to expose the assailants to the fire from the
parapet.
The proportions and angles of all the lines given are fixed
according to mathematical rules.]
The operations of a siege present many incidents of great interest; but
we can do nothing more in this article than illustrate the methods in
which the approaches are made to the works the capture of which is
designed. When reconnoissances have established the conclusion that the
works of an enemy cannot be carried by assault, the lines of the
investing army are advanced as near to them as is compatible with
safety; advantage is then taken of the opportunities afforded by the
ground to cover working parties, which are thrown forward to the place
fixed for the first parallel; sometimes these parties can commence their
work only at night. The parallel is only a deep trench with the dirt
thrown toward the enemy; and after the excavation has progressed, the
trench is occupied by parties of troops to resist any sorties of the
enemy, and to prevent attempts against the batteries established behind
the parallel.
The first parallel being completed, zigzag excavations are made toward
the front to cover the passage of men who proceed to dig the second
parallel. Meanwhile the batteries have commenced to play, and riflemen
have been advanced in trenches at convenient places, whose fire annoys
the gunners of the enemy. The second parallel being made, the batteries
are moved up to it, and the third parallel is proceeded with in a manner
similar to that used for the second.
We give below a rough diagram of these operations:
[Illustration:
A B C D E is the work of the enemy to be besieged. The working parties
advance by the zigzag paths M N and O to the position chosen for the
first parallel, K L. At the proper time they proceed by the zigzag paths
to the second parallel, H I, and then to the third, F G. When this is
reached, the enemy's work can generally be carried by storm, unless
already evacuated, for _ceteris paribus_ the advantages generally lie
with the besieging party. The zigzags are called _boyaux_, and they are
dug in the form represented, so that the bank of earth thrown up may be
always in front of them. Were they in straight lines this could not be.
The above refers exclusively to the siege of a field work. The
principles for besieging a walled fort or a fortified town are the same,
but the operations are much more complicated.]