CHAPTER XIV.
FIELD-ENGINEERING.
_Field-Engineering_ includes the making of military reconnaissances, temporary fortifications, and military roads; the planning and construction of military bridges; the attack and defence of military works;--in fine, all the various duties of engineer troops, either in the operations of a campaign, or in the dispositions on the battle-field.
_Military reconnaissance._--By this term is meant an examination of a portion of the theatre of war, to ascertain its military character and resources.

If the examination be made of a large district of country, and for an entire campaign, the reconnaissance is _general_; if made for collecting detailed information respecting a proposed line of march, the passage of a river, the position of an enemy, &c., it is termed _special_.
In making a general reconnaissance, great care should be taken to collect accurate information respecting the general topography of the country; the character of the mountains, forests, and water-courses; the nature of the roads, canals, and railways; the quality of the soil, and the amount of provisions and forage it produces; the population and character of the cities, towns, and villages, the commercial and manufacturing resources of every part of the country, and the means of transportation to be found in each district.

The plan of military operations will be based on the information thus obtained, and any serious error in the reconnaissance may involve the results of the campaign, and even the fate of the war.
In a special reconnaissance, not only accurate but minute information will be required: the character of the roads must be given in detail; the nature of the water-courses, their depth and velocity; the position and character of bridges, and fords;--in fine, a full description of all obstacles to be encountered, and the means that can be made available for overcoming these obstacles.
A reconnoitring officer may usually derive much valuable information from the published maps and descriptions of the country to be examined; additional matters of detail may be obtained from woodsmen, hunters, and fishermen; and also from the innkeepers and local authorities of the district.

But the officer should always verify this information, so far as practical, by personal examination.

In making a reconnaissance in the vicinity of an enemy, he must be supported by a strong escort of mounted troops, and in all his operations the greatest precaution will be requisite to ensure success.
Some simple instrument, such as a pocket sextant, or compass, will be sufficient to enable the reconnoitring officer to measure, with considerable accuracy, the height of mountains, the width of streams, &c., and an ordinary scale and dividers will enable him to make a suitable military sketch.
_Temporary Fortification._--It has been stated in the preceding chapter that temporary fortifications are properly confined to the operations of a single campaign, and are used to strengthen positions which are to be occupied only for a short period; and that they are usually made of earth, thrown up by the troops in a single day.