tional matters of detail may be obtained from woodsmen, hunters, and
fishermen; and also from the innkeepers and local authorities of the
district. But the officer should always verify this information, so far
as practical, by personal examination. In making a reconnaissance in the
vicinity of an enemy, he must be supported by a strong escort of mounted
troops, and in all his operations the greatest precaution will be
requisite to ensure success.

Some simple instrument, such as a pocket sextant, or compass, will be
sufficient to enable the reconnoitring officer to measure, with
considerable accuracy, the height of mountains, the width of streams,
&c., and an ordinary scale and dividers will enable him to make a
suitable military sketch.

_Temporary Fortification._--It has been stated in the preceding chapter
that temporary fortifications are properly confined to the operations of
a single campaign, and are used to strengthen positions which are to be
occupied only for a short period; and that they are usually made of
earth, thrown up by the troops in a single day. Temporary
fortifications, as a part of field-engineering, may therefore be
regarded rather as an _arm_ than an _art_. The principles of their
construction are derived, of course, from the theory of permanent
fortification, but in applying these principles to practice in the
field, much greater latitude is allowed than in the exact scientific
arrangement of permanent works.

The purpose of field-works (or intrenchments, as they are commonly
called) is to arrest, or at least to impede, the march of the attacking
foe; to shelter the defensive troops from the missive weapons of the
assailants, and to detain them in a position where they will be exposed
to the fire of the defensive force. The numerical and positive strength
of the assailed may be much less than that of the assailant, and yet an
equilibrium exist; the material obstacles compensating for the
difference in numbers. Intrenchments, though inert masses, must
therefore be regarded as most valuable and important accessaries in the
defence of a position.

Intrenchments consist either of _lines_ of works made to cover extended
positions, or of _detached_ works designed simply to defend the ground
they occupy. The former generally present a front against the enemy in
but one direction, while the latter are usually closed on all their
sides.

The following figures have been employed for the plan of simp