by stratagem.
Demonstrations are made at several points at the same time: bodies of
troops are thrown across, after nightfall, in rowboats or by
flying-bridges, to get possession of the opposite bank. The vanguard of
light cavalry may cross by swimming. The pontoniers should have their
bridge equipage in readiness near the intended point of passage, so that
it can be thrown across with the greatest possible rapidity, while the
advanced guards are still able to keep the enemy at a distance. Under
favorable circumstances the pontoniers will have the bridge in readiness
for the passage of the army before the enemy can collect his troops upon
the threatened point.

Cannon-balls and hollow shot are the most effectual means for destroying
an enemy's bridge when our batteries can be planted within reach. When
this cannot be done, we must resort to fire-boats, floating rafts, &c.,
to accomplish our object. Operations of this kind carried on in the
night, are most likely to succeed.

To protect bridges from the action of these floating bodies, stockades,
or floating chevaux-de-frise are constructed across the stream at some
distance above the bridge; strong cables, or chains stretched directly
across the river, or with an angle up stream, may be used in place of
stockades, or in conjunction with them. Guards should be stationed above
the bridge, with boats, ropes, grapnels, &c., for the purpose of
arresting all floating bodies and drawing thorn ashore, or directing
them safely through the _draw_ in the bridge arrangement.

The troops especially charged with the construction and management of
the various kinds of military bridges, are denominated _pontoniers_. The
duties of these troops are arduous and important, and, in a country like
ours, intersected by numerous water-courses, the success of a campaign
will often depend upon their skill and efficiency.

_Sapping_.--This is a general term applied to the operations of forming
trenches, along which troops may approach a work without being exposed
to the fire of the besieged.

In addition to the ordinary sapping-tools, such as shovels, picks,
gabion-forks, &c., used in constructing trenches, there will also be
required a considerable amount of sapping materials, such as gabions,
fascines, sap-fagots, sandbags, &c.

The _gabion_ is a cylindrical basket of twigs, about two feet in
diameter, and some three feet in length, and without a bottom. It is
made by driving into the gr