The duties incident to picketing and outpost stations are so important that several works by distinguished authors have been written concerning them, but most of the rules are of too technical a character for recital in these papers. The friends of soldiers will, however, take interest in some general statements. 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. These should be stationed where they can command the main avenues of approach, and offer resistance to the advanced parties of the enemy. After such resistance becomes useless, the various pickets fall back on the grand guard, which offers a more determined contest. The advance of the enemy should by these means have been delayed for a couple of hours, affording time for the troops to get under arms and take the order of battle. The following diagram exhibits the general arrangement of picketing: [Illustration] Let the line A B represent a chain of sentinels on a mile of picket front, C D a line of picket stations, and E the grand guard. The whole force of men may perhaps be three hundred, of whom two thirds will remain at E, posted advantageously upon some eminence protected in part by a stream and commanding an open country. The remaining one hundred will be distributed among the picket stations and thrown forward as sentinels. The whole arrangement is supervised by an officer of rank--usually a colonel. With a disposition like the above in front of every division in an army, it is obviously impossible for any considerable force of an enemy to approach without detection.