We have just seen how the security of the army is expected, from the effect which an advanced guard and flank corps produce on an advancing enemy. Such corps are always to be considered as very weak whenever we imagine them in conflict with the main body of the enemy, and therefore a peculiar mode of using them is required, that they may fulfil the purpose for which they are intended, without incurring the risk of the serious loss which is to be feared from this disproportion in strength.
The object of a corps of this description, is to observe the enemy, and to delay his progress.
For the first of these purposes a smaller body would never be sufficient, partly because it would be more easily driven back, partly because its means of observation that is its eyes could not reach as far.
But the observation must be carried to a high point; the enemy must be made to develop his whole strength before such a corps, and thereby reveal to a certain extent, not only his force, but also his plans.
For this its mere presence would be sufficient, and it would only be necessary to wait and see the measures by which the enemy seeks to drive it back, and then commence its retreat at once.
But further, it must also delay the advance of the enemy, and that implies actual resistance.
Now how can we conceive this waiting until the last moment, as well as this resistance, without such a corps being in constant danger of serious