following morning.
Here I was suddenly confronted with the responsibility of the command of
the picket forces covering the dividing line between the two hostile
armies. A demonstration of the enemy was to be looked for any moment,
and it was most likely to occur on our front. I had hoped to have a few
days to study up and by observing its practical work get some little
idea of my new duties. But here was the detail, and it must be obeyed.
It should be explained that the picket line consists of a cordon of
sentinels surrounding the army, usually from two to three miles from
its camp. Its purpose is to watch the enemy, and guard against being
surprised by an attack. Except for this picket line, the main body of
troops could never sleep with any degree of safety. To guard against
attacks of the enemy would require it to remain perpetually under arms.
Whereas with its picket lines properly posted it may with safety relax
its vigilance, this duty being transferred to its picket forces. This
picket service being a necessity of all armies is a recognized feature
of civilized warfare. Hence, hostile armies remaining any length of time
in position near each other usually make an agreement that pickets shall
not fire upon each other. Such agreement remains in force until a
movement of one or the other army commences. Notice of such a movement
is, of course, never given. The other party finds out the fact as best
it can. Frequently the withdrawal or concealment of the picket line will
be its first intimation. Ordinarily, picket duty is not only of the very
highest responsibility, but an exceedingly dangerous duty. Until
agreements to cease picket-firing are made, every sentinel is a
legitimate target for the sentinels or pickets of the enemy, hence
extreme vigilance, care, and nerve are required in the performance of
this duty.

The picket line in the presence of the enemy is generally posted in
three lines,--viz., First, the line of sentries; second, the picket
supports, about thirty yards in rear of the sentries, and third, the
guard reserves, about three hundred yards farther in the rear, depending
upon the topography of the country. Each body constitutes one-third of
the entire force, _i.e._, one-third is constantly on duty as sentinels,
one-third as picket supports, and one-third as grand reserves. The
changes are made every two hours, usually, so that each sentry serves
two hours on "post" and four hours off. The latter four