Various, The Continental Monthly, Vol. 6…
“ The picket line consists of three portions—first, the stations of the main guard; second, some distance in advance of these, the picket stations; and third, some two hundred yards in advance of these, the stations of the sentinels. If the country is open and hilly, the latter need not be posted closely together, but in a wooded country they must be quite numerous. It is their duty not to allow any person to pass their line; and if a force of the enemy, too strong to be resisted, approaches, they fall back on the pickets. ”
