RICOCHET, a word expressing the act of rebounding, is applied to the mode of firing ordnance in which (the axis of the piece being parallel, or inclined at a small angle to the horizon) the shot or shell, having described a curve in the air, descends to the ground, and, after striking or grazing it, rises upwards; when, by the force of the impulsion, and the power of gravity, it describes a second curve of small elevation ; the shot, then descending as before, again grazes the ground, from whence it experiences a second reflection. This effect frequently takes place several times before the force of impulse is destroyed.
Ricochet firing is most generally employed in the attack of fortresses in order to enfilade or rake the faces of works, whose fire might be directed upon the ground on which the approaches are to be made : for that purpose a battery of the besiegers is placed with its front perpendicular to the prolonged direction of each rampart or parapet, and three or more guns are laid either horizontally or with alight elevations or depressions, according to the position of the battery, so that their shot may pass a little above the crest of the parapet which covers the line to bo enfiladed. The same mode of firing is also occasionally employed by the besieged against the batteries of the enemy. In either case the intention is to dismount the artillery by causing the shot or shells to strike it obliquely behind the parapet or epaulement, or to destroy the traverses which cover it. It is also used to compel tho troops to abandon the parapets, or to destroy the palisades of the covered-way or ditches, eo as to facilitate the entrance into a work when an assault is to be made by main force.
The practice of firing A-ricochet was first tried by Vauban at the sieges of Philipsburg and Mannheim, in the war of I6S8 ; and in a letter which that engineer wrote to Louvais, lie states that at the former place it had succeeded so far as to dismount six or seven pieces of cannon, and oblige the defenders to abandon a long branch of a hornwork and a face of one of the bastions in front of the ground on which the chief attack took place. The success of ricochet firing appears to have been still greater at the siege of Ath, which was con ducted by Vauban during the same war. ' It is a remarkable circumstance that, soon after the invention of this method of firing, the changes which were made in the trace or plan of fortifications, though attended with many and great advantages, were such as to render the works more liable than those of former times to the destructive action of the ricochet. The great saliency
then given to the ravelins, and the consequent acuteness of the salient angles, allow the prolongation of the faces to be easily observed by the besiegers while at a distance from the work ; and thus the guns in the ricochetting batteries are enabled to enfilade the faces in their whole length with great accuracy. The faces of the bastions were also lengthened about the same time ; and in fortifications constructed on the inferior polygons, or those of few sides, there is a like facility of dismounting the artillery on those faces. The latter evil ceases to exist when the works are formed on the superior polygons, because the prolongations of the faces of the bastions may then fall upon the intermediate myelitis, and thus be invisible to the enemy ; but, for the damage to which the long faces of the ravelins are exposed, no other remedy can be found than in the construction of traverses or blindages on the terrepleins, or in covering the general direction of the faces by en advanced portion of the latter, about twenty yards long, ou each side of the salient angle.
The French engineers divide ricochet firing into two kinds, of which one is designated ricochet moo, and the other richoehct tends (short and long-ricochet); the former comprehending all elevations of the piece, from the greatest which the charge and the gnu-carriage will permit, to that which is but little above the horizon ; and the latter term being applied to all other cases, down to that in which, from the height of the battery, the gun is depressed below the horizontal plane. When the crest of the parapet which covers the rampart or the ground to be ricochetted is above the level of the battery, the coincidence of that crest with the vertex of the trajectory forms the inferior limit to the elevation of the piece ; for if the shot were to pass closely over that crest with a lower elevation, it would at that place be in the ascending branch of the curve, and then the ground behind the coverins parapet not, to a considerable distance from thence, be struck. In pro portion as the elevation of the piece is increased above the same limit, the vertex of the trajectory is nearer to the battery, and thus the shot is in the descending branch when it passes over the crest of the work.