Should a sufficient number of roads for the different columns not exist, the officer is to ascertain whether or not others may be made by cutting through hedges, walls, or woods, by forming causeways over marshes, or by constructing or repairing bridges over rivers or streams; and also whether the country affords the materials necessary for these purposes. The rates at which it is possible for troops to march in the several roads, defiles, &c., must be estimated according to 'the breadth of the latter or the degree of their practicability ; for on a right esti mate of such rate, together with the known length of the road, depend the number of battalions and the class of troops which ought to be appointed to follow each particular route, when it is required that the different columns should arrive at the same time in some given position. The plan should show the situations of farms, mills, houses, &c., which may be capable of being defended or of affording quarters for the troops; and on it should be indicated, by some scale of numbers or otherwise, the relative heights of the ground, that it may be ascer tained what positions can be occupied with advantage for offensive or defensive operations. The representation of a simple line of march should also indicate the places where roads diverge from or cross the route, with the distances of the nearest towns or villages from thence ; and any particular survey of the ground for an encampment should extend to at least a mile every way beyond the supposed chain of out posts. [MILITARY POSITIONS ; PIQUET.) The report must state what are the resources of the country in corn, cattle, and forage ; and the number of carriages, horses, and other draught animals that it may furnish for the conveyance of artillery and stores. if the line of march is in the directisn of a navigable river which may be available for the last-mentioned purpose, it will be necessary to ascertain its breadth and rapidity, and also the obstructions which may be met with from shallows, weirs, &e. Marshal Suchet caused his artillery to be con veyed by the Ebro from Mequinenza to Xerta, in 1810, preparatory to forming the siege of Tortoea.
An open country presents the greatest facilities for reconnoitring, since the positions of its towns or villages, and the directions of its roads and rivers, can then be easily distinguished and represented on paper. A tract covered with wood ie not only surveyed with difficulty, hut it imposes on the officer, In addition, the necessity of ascertaining all the directions in which it is capable of being penetrated by the enemy, and in what manner the passes may be blocked up or defended. Open plains intermingled with wood, fields surrounded by hedges, ground intersected by streams of water, ravines, and hollow ways, demand great exactness in the survey, since such tracts afford the most Important advantages, both in the higher and in the secondary opera tions of warfare, to the army which is beat acquainted with their details. They allow troops to pass unseen from one point to another when a surprise is attempted or a rapid retreat is to be made ' • they also afford cover from whence the enemy may be annoyed with little loss. In mountainous districts it is important to ascertain the forms and directions of the chains of heights, with their acclivities on both sides ; and, if the line of march is between them, the collateral ravines should be examined to a considerable distance : the commencements and directions of the ravines should also be shown, and all the defiles by which the valleys communicate with each other. Through these defiles troops detached from the army are enabled to fall suddenly on the enemy during his march, to sepa rate his columns, and intercept his supplies or cut off his retreat; and, on the other hand, since the enemy may attempt the like measures, it becomes necessary that the employed to recon noitre should ascertain by what means the passes may be barricaded, either to impede the enemy or enable the troops to defend themselves.
In reconuoitring a country, when it is intended to act on the defen sive, it should be well known by what roads the enemy can penetrate, and where are the best situations for forming intrenched camps or establishing posts in order to be enabled to keep the field and cover the magazines. Again, if it be intended to carry the war into an enemy's country, it is necessary to discover the position occupied by. his army ; to find the tract of country most proper for the march, and the spots where the localities permit encampments to be formed with due support on the flanks and security in the rear. If it be intended to besiege a fortress or to attack the enemy's position, the reconnois sance may be made quite up to alb glacis of the place, or to the works which protect the position. In the .former case it is necessary to ascertain the nature of the fortifications, aud the fitness of the ground about them for the operations of the siege; and in the latter, to find out the strength and dispositions of the enemy's troops. An armed force is generally required on these occasions, as, in order to approach near enough for the purpose, it may be necessary to drive in some of the outposts. During the war which ended in 1814, the English and French out-sentries appear to have entertained a mutual understand not to molest each other, and to retire to their supports before they commenced firing when either army was about to make a move ment. Colonel Napier relates that Lord Wellington, being once desirous of reconnoitring the enemy's position at Bayonne, ordered his escort to fire upon some of the enemy who occupied the top of a hill which he wished to ascend ; but one of the men going up to the French soldiers and tapping his musket in a particular way, the latter, who understood the signal, quietly withdrew.
In a maritime reconnoissance the circumstances which it is of most importance to ascertain are : whether the coast is rocky, or bordered by downs, and what is the state of the bays or roads with respect to shelter from the prevailing winds; the seasons in which winds blow off and on the shore, and whether the anchorage is secure or otherwise ; the nature of the tides, the hours of high and low water, and the depth at either of those times. Precise information should also be obtained of the places at which troops might land, and where there exist rising grounds on which artillery may be disposed to protect them. Rivers should be ascended to a considerable distance if possible, in order to ascertain their depths and the nature of the vessels employed on them by the people of the country. On the other hand, if it were required to examine the coast preparatory to putting it in a state of defence, it would be necessary to find out what points of land are convenient for the situations of forts or batteries by which the enemy may be prevented from landing, and where beacons may be established for the purpose of giving timely alarm. If there are islands on the coast, it would be proper to include them in the survey, since they might be fortified and made to serve as advanced works ; and all places should be indicated which are capable of being converted into military posts to prevent the enemy from penetrating into the interior of the country.