In the foregoing observations we have lost sight altogether of outposts, and therefore we must now return to them again.
In saying, at the commencement, that the relations between outposts and stationary troops is similar to that between advanced guards and troops in motion, our object was to refer the conceptions back to their origin, and keep them distinct in future; but it is clear that if we confine ourselves strictly to the words we should get little more than a pedantic distinction.
If an army on the march halts at night to resume the march next morning, the advanced guard must naturally do the same, and always organise the outpost duty, required both for its own security and that of the main body, without on that account being changed from an advanced guard into a line of outposts. To satisfy the notion of that transformation, the advanced guard would have to be completely broken up into a chain of small posts, having either only a very small force, or none at all in a form approaching to a mass. In other words, the idea of a line of outposts must predominate over that of a concentrated corps.
The shorter the time of rest of the army, the less complete does the covering of the army require to be, for the enemy has hardly time to learn from day to day what is covered and what is not. The longer the halt is to be the more complete must be the observation and covering of all points of approach. As a rule, therefore, when the halt is long, the vanguard becomes always more and more extended into a line of posts. Whether the change becomes complete, or whether the idea of a concentrated corps shall continue uppermost, depends chiefly on two circumstances. The first is the proximity of the contending armies, the second is the nature of the country.