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. If the armies are very close in comparison to the width of their front, then it will often be impossible to post a vanguard between them, and the armies are obliged to place their dependence on a chain of outposts. A concentrated corps, as it covers the approaches to the army less directly, generally requires more time and space to act efficiently; and therefore, if the army covers a great extent of front, as in cantonments, and a corps standing in mass is to cover all the avenues of approach, it is necessary that we should be at a considerable distance from the enemy; on this account winter quarters, for instance, are generally covered by a cordon of posts. The second circumstance is the nature of the country; where, for example, any formidable obstacle of ground affords the means of forming a strong line of posts with but few troops, we should not neglect to take advantage of it. Lastly, in winter quarters, the rigour of the season may also be a reason for breaking up the advanced guard into a line of posts, because it is easier to find shelter for it in that way. The use of a reinforced line of outposts was brought to great perfection by the Anglo-Dutch army, during the campaign of 1794 and 1795, in the Netherlands, when the line of defence was formed by brigades composed of all arms, in single posts, and supported by a reserve. Scharnhorst, who was with that army, introduced this system into the Prussian army on the Passarge in 1807. Elsewhere in modern times, it has been little adopted, chiefly because the wars have been too rich in movement. But even when there has been occasion for its use it has been neglected, as for instance, by Murat, at Tarutino. A wider extension of his defensive line would have spared him the loss of thirty pieces of artillery in a combat of out-posts. It cannot be disputed that in certain circumstances, great advantages may be derived from this system. We propose to return to the subject on another occasion. CHAPTER VIII. Mode of Action of Advanced Corps