GUN, AND HOWITZER PLATFORM.
For carrying this platform, two men are required for each sleeper; one man for each plank, and ribband. The non-commissioned officer carries the rack-sticks.
A platform may be laid downin an hour by expert men, and may be dismantled in three minutes.
MORTAR PLATFORM.
Detailed as above.One non-commissioned officer, and seventeen men carry the platform.Time required for laying down, and dismantling, similar to the above.
MADRAS PLATFORM.
In an elevated battery, the platform may be laid downby expert men in half an hour,and may be dismantledin three minutes.
The best place for making a breach, in ravelins, bastions, &c., is about thirty yards from their salient angles. The batteries should commence by marking out by their fire the extent of the breach intended to be made, first by striking out a horizontal line as near the bottom of the revetment as possible, and afterwards two others perpendicular to, and at the extremities of this line. Should the breach be required to be extensive, it will be necessary to form intermediate lines. Then, by continuing to deepen these two or more cuts, and occasionally firing salvoes at the part to be brought down, the wall will give way in a mass. The guns must, however, at first fire low, and gradually advance upwards until the breach is effected; and when the wall has given way, the firing should be continued until the slope of the breach is made practicable.
TO BURST OPEN GATES OF FORTRESSES, ETC.
A leathern bag, containing about 50 lb. of powder, should be hooked upon the gate, as near the centre as possible (or be laid on the ground, close to the bottom of the gate, and tamped with sods, &c.), and be fired by means of a piece of portfire, or match, passed through a hole in the bottom of the bag.
Offensive fortificationis the art of conducting a siege.
Defensive fortificationcomprehends military architecture, and is the art of securing, or protecting a place by works, to resist a siege.
Natural fortificationconsists of obstacles, such as marshes, mountain passes, &c., which are found in some countries, and should be taken advantage of to impede the approaches of an enemy.
Artificial fortificationcomprises those works which are constructed to defend a place.
Permanent fortificationis the art of putting towns, &c., into such a state as at all times to be prepared to resist the attack of an enemy.
Field fortificationis the method of fortifying a camp, or position, buildings, &c., and it includes the construction of redoubts, entrenchments, &c. Works of this nature are considered as temporary.
Irregular fortificationis the art of fortifying a place of an irregular figure, situated where the country does not admit of giving to the several works their due proportion according to rule.
A Commandis the vertical elevation of one work above another, or above the country.
A Command in frontis when an eminence is directly facing the work which it commands.
A Command in the rear, or reverse, is when any eminence is directly behind the work which it commands.
A Command by enfiladeis when an eminence is situated in the prolongation of any line of a work, and a considerable part of it may be seen from thence; this line will be subject to enfilade, and such a command is the most dangerous.
The Rampart(A T R) is an elevation of earth, obtained from the excavation of the ditch; and is that part of the fortification which is situated between the ditch, and the town, consisting of an interior slope, terreplein, banquette, parapet, and exterior slope or escarp.—(VidePlate.)
The Interior slope(A) is the inclination of earth nearest to the town.
The Terreplein(T) is the upper part of the rampart, which remains after having constructed the parapet.
The Parapet(R) is a mass of earth elevated on the terreplein of the rampart, on the side towards the country; being from 18 to 22 feet thick, and from 6 to 8 feet high. The top is formed with a slight declivity towards the country, which is called thesuperior slope.
The Banquetteis an elevation of earth, or step, on which the soldiers stand to fire over the parapet.
The Revetmentis the masonry which retains the earth of the rampart on its exterior side. It is about 5 feet thick at the top, and its slope is one-fifth, or one-sixth its height.
The Bermis a space, or path, sometimesleft between theexteriorslope of the rampart, and the ditch. It serves as a communication round the works, and prevents the earth falling into the ditch.
The Tabletteis a flat coping-stone, on the exterior of the top of the escarp of whole revetment.
The Cordonis a semicircular projection of stone, whose diameter is about one foot,placed at the topof the slope of the revetment of the escarp.
The Escarp(a) is the exterior slope, or wall of the rampart.
The Counterscarp(b) is the wall, or slope of the ditch, opposite to the escarp.
The Facesof a work (p q) are those parts which form a salient angle, projecting towards the country.
The Flank(q G) is the part of a work so disposed as to defend another; joining the face of a bastion to the curtain, &c.
The Bastion(M L) is a work composed of two faces, and two flanks. Bastions are joined by curtains, and are constructed salient, and with flanks, in order that the whole escarp may be seen, and that a reciprocal defence may be obtained.
Bastions are of various kinds—viz., full (M), empty (L), also flat, detached, demi, and tower bastions.
A Full bastion(M) is when the terreplein occupies all the interior space of the bastion. From the description of this bastion, that of all the others may be ascertained.
The Curtain(G R H) is that part of the rampart which lies between two bastions, and joins the flanks thereof.
A Front of fortificationconsists of two half bastions, and a curtain.
The Ditch(B) is an excavation from 12 to 24 feet deep, and from 90 to 150 feet broad, surrounding the rampart. The side of the ditch nearest the place forms the escarp (a); and the opposite part, the counterscarp (b) is made circular opposite to the salient angles of the works.
The Covered way(V) is a space of about 30 feet broad, extending round the counterscarp of the ditch, being covered by a parapet from 7 to 9 feet high, with a banquette.
The Glacis(X) is the superior part of the parapet of the covered way, forming a gentle slope towards the country, and terminating at from 120 to 180 feet; it covers the revetment of the body of the place.
The Places of armsof the covered way are spaces contrived in the salient, and re-entering angles of it; those (c) in the re-entering angles flank the branches of it, and contain troops for sallies, and its defence; and those (P) in the salient angles serve for assembling the Troops destined for the defence of the covered way.
The Sally-portsare openings cut in the glacis, at the faces of the re-entering places of arms, and at the branches of the covered way. They are used in making sallies from the covered way.
The Traverses(n) in the covered way, are parapets which cross the breadth of it at the salient, and re-entering places of arms, &c. They cover the troops who are drawn up behind the parapet of thecovered way, from the enfilade fire of the enemy. There are passages cut in the parapet of the covered way, close to the traverses, in order to form a communication from one part of the covered way to another: these passages are about 6 feet wide, and are provided with gates.
A Citadelis a fortress joined to the works of a place, and is fortified both towards the town, and country. It should always be situated on the most commanding ground, serving to keep the inhabitants in awe, and, should the town be taken, it becomes a retreat for the garrison.
The Esplanadeis a space of even ground, clear of buildings, situated between the town, and citadel.
The Body of the place(orEnceinte) consists of the works next to, and surrounding the town, in the form of a polygon, whether regular, or irregular.
Outworksare those works which are constructed beyond the body of the place, such as tenailles, ravelins, &c.
The Tenaille(D) consists of two faces, and a small curtain. It is constructed between the flanks of the bastions in front of the curtain, and has a terreplein, parapet, and banquette.
The Ravelin(P) is constructed opposite the curtain, (in front of the tenaille,) is composed of two faces, which form a salient angle towards the country, and of two demi-gorges formed by the counterscarp.
A Horn-workis composed of two half bastions, and a curtain, with two long sides directed upon the faces of the bastions, or ravelins, so as to be defended from them.
A Crown-workis composed of a bastion between two curtains, which are terminated by half bastions. It is joined to the body of the place by two long sides.
Lunettes, andTenaillonsare works constructed on each side of ravelins, consisting of two faces.
A Flèche, or Arrow, is constructed along the foot of the glacis before the re-entering, and salient places of arms. It consists of a parapet, whose faces form a salient angle, and are about 120 feet long, and it has a communication with the covered way, cut through the glacis.
The Caponiere(Y) is a work intended to cover a passage across the ditch. That from the tenaille to the gorge of the ravelin is a road about 30 feet wide, covered on each side by a parapet 7½ feet high, its superior slope terminating in a glacis about 60 feet wide.
A Cunetteis a small ditch made in the middle of a dry ditch, to drain off the water from the place, &c.
A Batardeau(e) is a solid piece of masonry, 7 or 8 feet thick, crossing the whole breadth of the ditch opposite the flanked angles of the bastions. It retains the water in those parts of the ditch which require to be inundated.
A Ramp(t) is a road cut in the interior slope of the rampart, forming a communication from the town, &c., to the terreplein.
A Cavalieris a work constructed upon the terreplein of a fullbastion, being from 8 to 12 feet above the rampart, with a parapet 6 feet high. Its use is to command some rising ground within cannon-shot, and to serve as a traverse for preventing the neighbouring curtains from being enfiladed.
Parallels, or Places of arms, thrown up at sieges, are trenches formed to connect together the several approaches to a besieged place.
Zig-zags, or Boyeaux of communication, are trenches made for the approaches from the parallels to the besieged place. They are generally 3 feet deep, and have a parapet, and banquette.
A Redanconsists of two faces forming a salient angle (which should not be less than 60°) with parapet, &c.[37]
A Lunettehas two faces, similar to the redan, and also two flanks.[37]
A Redoubtis a square, polygonal, or circular field fort.[37]
A Star fortconsists of a succession of salient, and re-entering angles, formed on the sides of a polygon. These forts are usually constructed on a triangle (when they have six salient points), or a square (having eight salient points).[37]
Têtes de pont, or Bridge heads, consist of redans, &c., which are constructed upon the banks of rivers, to protect the passage across them.[37]
Linesare formed for the entrenchment of armies, and are composed of a succession of redans, &c., joined by curtains, which should not be more than 120 yards distant from each other, to afford mutual protection, and defence.[37]
An Epaulmentis an elevation of earth thrown up to cover troops from a flanking fire.
Loop-holesare oblong holes, from 15 to 18 inches long, 6 inches wide within, and 2 or 3 without. They are cut through timber, or masonry, for the services of small arms.
Palisadesare stakes of strong wood, 8 or 9 feet long, and 6 inches thick, fixed about 3 feet in the ground, and 3 or 4 inches asunder.
Fraisesare a kind of palisades, placed horizontally, or obliquely in the exterior slope of ramparts.
Chevaux de friseconsist of a piece of timber from 9 to 12 feet long, and about six inches in diameter, into which staves are inserted cross-ways, about 9 inches asunder, about 2 inches thick, 6 feet long, and pointed at the end, if not shod with iron. Their use is to stop up a breach, defend a passage, or form an entrenchment against cavalry. Chevaux de frise are sometimes made entirely of iron.
Abattisconsist of trees with their branches shortened, and sharpened at the ends; they are used instead of chevaux de frise on an emergency.
Hurdlesare about 3 feet high, and 2 broad, and are used in sieges to stop up breaches, &c.
Trous de loupare holes dug in the ground in the form of an inverted cone, about 6 feet deep, and 4½ in diameter at the top, having a picket fixed in the centre of the bottom, 6 feet long, and4 or 6 inches square, the point being on a level with the upper surface of the ground. These pits are used to prevent the approach of bodies of cavalry.
PERMANENT FORTIFICATION.
Remarks, and general rules.
The ground plan, and relief of bastioned fortifications are mutually dependent on each other; and, as a variety of causes occur to influence both according to the various sites occupied, it is impossible to give them any fixed arrangement, and dimensions, applicable under all circumstances. However, under the supposition that the site to be fortified is a horizontal plane, a great number, and variety of systems have been proposed at different times; almost every author, who has treated of fortification, having invented one, at least, of his own. Notwithstanding this diversity of opinion, as to the best system, all agree that the following general principles should not be lost sight of in the construction of fortifications.
1. Salient angles should be as large as possible, and never less than 60°. The larger they are the smaller will be the space in front undefended by direct fire. If less than 60°, the salients of earth are too acute to stand firmly for any length of time; and the angles of masonry are easily damaged; besides which the space within the parapets becomes too restricted to admit of a gun being worked near the angle.
2. Angles of defence should be right angles, or slightly obtuse. If less than right angles, the fire from the flanking works might injure the defenders of the works they flank; as troops generally, and more particularly at night, fire in a direction perpendicular to the parapet; and if too obtuse the fire might be directed wide of its object. Besides,embrazures should becut as direct as possible; as the more they are oblique, the more they weaken the parapet.
3. The length of the lines of defence shall be such, that the works defended may be within the effective range of the projectiles used.
4. The works should be so disposed that the assailants may not be able to obtain cover in any part of the exterior, within range of the projectiles of the defenders.
5. The escarps of the body of the place should be of such height, or construction, as to be secure against escalade.
6. The masonry should be sufficiently covered from the view of the enemy, to prevent his making a practicable breach from a distance.
7. The interior of every work should be completely covered from the view of an enemy outside it; so that he may not be able to fire directly into any part of it. Interior works should therefore have a command over those in front of them, at least equal to the height which a besieger can give to the parapets of his lodgments, and which is seldom less than 3 feet.
8. Every opportunity should be seized of so directing the faces ofworks that an enemy may not have it in his power to enfilade them by ricochet fire.
9. In the general construction of fortifications the salients should be few, and sufficiently prominent to force the besieger to take them before he can attack the re-entering parts. The object of this is to reduce the number of points of attack, as, the fewer they are, the less advantage an assailant derives from his numerical superiority.
10. Permanent fortifications must be considered very incomplete without a sufficiency of casemated cover for the sick, and wounded, and for the portion of the garrison off duty. The magazines of ammunition and provisions, should also be secure from the effects of shells; and the supply of water ample, and certain.
11. Small enclosed works, in which the defenders must be crowded, without cover from vertical fire, should never be employed in permanent fortification. The strength they impart can never make up for the loss the garrison must suffer by them.
12. Outworks, and detached works should have easy communications with the main work, to admit of their garrisons receiving reinforcements, or supplies, when necessary; and to enable them to retreat, when the works are no longer tenable.
13. Every enclosed defensive work of importance should, if possible, be provided with a keep, or citadel, or interior retrenchment, to which the garrison may retire when the main enclosure (or enceinte) is forced.
14. Outworks, and detached works near the body of the place, should be so constructed that the enemy, when he has taken them, may not be able to use them as defensive works.
15. Outworks, and detached works, should always be of sufficient strength to force the enemy to makeregularattacks on them. Advanced works of a weak construction are likely to do more harm than good; for the troops of the garrison seeing them taken with comparative facility, would naturally lose confidence in the strength of their remaining defences, while that of the assailants would be increased by early success.
16. All fortifications should be provided with means of egress, and ingress, to enable the garrison to assume the offensive, whenever opportunities offer; and to admit reinforcements into the fortress.
17. There are very few fortified places that agree with any published system, though some resemble one or other of the systems, or consist of combinations, or modifications of them. The systems which have been wholly, or partly carried into execution are, of course, the most interesting, and form valuable subjects of study. A knowledge of their advantages, and defects, and the best methods of attacking, and defending them, will enable the military student properly to appreciate works which have been, or are to be constructed; and the operations by which fortresses have been, or may be captured.
VAUBAN’S FIRST SYSTEM.[38]
To describe three Fronts of fortification, on a hexagon.—VidePlate.
With a radius of 360 yards, the length of the exterior side of the fortification (taken from a scale of equal parts), describe a semicircle, which divide into three equal parts, and draw lines to the points of division; thus formingthree exterior sides. Bisect each of these by perpendiculars drawn to the centre of the polygon, on which set off ⅙th of the exterior side, (if a hexagon,)[39]through which points drawthe Lines of defence; on these set off 2/7ths of the exterior side, from the angles of the circumference, for the length of the faces of the bastions; with radius of the distance between the two faces describe arcs joining the lines of defence, and draw the cord of these arcs forthe flanks of the bastions; a line joining the interior extremities of the flanks will give the length ofthe curtains.
Or, to describe one Front of fortification.For the exterior side, draw a line 360 yards in length, at the ends of which, lines are to be directed to the centre of the polygon, at the angle required; (videPractical Geometry—To find the angles at the centre, and circumference of a regular polygon,) then bisect the exterior side, and draw the perpendicular, &c., &c., as described for the construction on a hexagon.
Or, to describe one Front of fortification.
For the exterior side, draw a line 360 yards in length, at the ends of which, lines are to be directed to the centre of the polygon, at the angle required; (videPractical Geometry—To find the angles at the centre, and circumference of a regular polygon,) then bisect the exterior side, and draw the perpendicular, &c., &c., as described for the construction on a hexagon.
Top viewVauban’s 1stSystem.J. W. Lowry, sc.
Vauban’s 1stSystem.J. W. Lowry, sc.
Vauban’s 1stSystem.
J. W. Lowry, sc.
Main ditch.
From the salient angles of the bastions, with 38 yards as a radius, describe arcs, to which draw tangents, directed to the angles of the shoulders of the bastions.
The Tenaille.
Draw lines parallel to the lines of defence, at the distance of 16 yards, for the faces of the work; its flanks, and curtain are constructed parallel to the flanks of the bastions, and curtain, at the distance of 11 yards.
The Ravelin.
From the re-entering angle of the counterscarp, make the capital of the ravelin 80 yards in length, and from its summit draw lines to points, on the faces of the bastions, 11 yards from the angle of the shoulder; the junction of these lines, and the counterscarp of the main ditch will determine the length of the faces of the ravelin. The gorge is formed by drawing lines 24 yards from the re-entering angle of the counterscarp to the intersection of the perpendicular, and the exterior side. From the salient angle of the ravelin, with a radius of 24 yards, describe an arc, to which draw tangents parallel to the faces, for the breadth of the ditch.
From the outline of the works draw the following parallels inwards:—
Rampart.
1. At the distance of 6 yards, for the thickness of the parapet.2. From which 12 yards, for the breadth of the terreplein.3. From which 6 yards, for the breadth of the interior slope.
Tenaille.
Draw lines parallel to the faces, at the distance of 6 yards, for the parapet.
Ravelin.
To the faces of the work draw the following parallels:—
1. At the distance of 6 yards, for the parapet.2. From which 8 yards, for the terreplein.3. From which 5 yards, for the interior slope.
Covered way.
Draw lines parallel to the counterscarp, at the distance of 11 yards, for the breadth of the covered way.
Salient places of arms.
These are formed by the salients of the branches of the covered way.
Re-entering places of arms.
Set off 40 yards on each side of the re-entering angle of the counterscarp for their demi-gorges, from which points draw their faces at an angle of 100 degrees.
Glacis.
For its breadth, draw parallels to the branches of the covered way, and the re-entering places of arms, at the distance of 50 yards.
Traverses.
Those at the re-entering places of arms are erected perpendicular to the covered way; those at the salient places of arms are formed on the prolongation of the faces of the bastions, and ravelins, across the covered way; all the traverses are 6 yards thick at the top. The passages, cut out of the glacis, to enable the troops to pass round the traverses, are 4 yards wide.
Ramps.
Flank of the empty bastion.—Set off 42 yards, from the angle of the flank of the interior slope, diagonally along the slope, for the length of the ramp, to which draw a parallel line 5 yards distant, for their breadth, which mark by a perpendicular, prolonging it, and setting off 6 yards for the interior slope; to which point, from the end of the ramp, draw a line; and also from the same point draw another line parallel to the side of the ramp, and joining the interior slope of the face of the bastion.
Flanked angle of the empty bastion.—From the angle of the interior slope set off 16 yards on each side, from which points draw lines 42 yards in length diagonally along the interior slope for the length of the ramps; to which draw parallels, 4 yards distant, for their breadth; erect perpendiculars from the points (16 yards from the angle) until they intersect each other, from which point as a centre, with radius of the distance between the ramps, describe an arc joining the head of the ramps of the two faces; concentric to which, with a radius 6 yards less than the former, describe another arc, to which draw tangents from the termination of the ramps, representing their slopes.
Gorge of the full bastion.—From the angle of the interior slope, set off 16 yards on each side, from which points draw lines 42 yards in length diagonally along the interior slope; draw parallels to these at the distance of 5 yards, for the breadth of the ramps; erect perpendiculars at their head, from the intersection of which as a centre, with radius of the distance between them, describe an arc, parallel to which, with radius 6 yards less, describe another arc, to which draw tangents, completing the interior slope of the ramps.
Ravelin.—From the angle of the interior slope, set off 12 yards on each side; from these points draw lines 30 yards in length, diagonally along the interior slope, for the length of the ramps; to which draw parallels 4 yards distant for their breadth; erect perpendiculars at the commencement of the ramps, and from their intersection, as a centre, with radius of the distance from the ramps, describe an arc joining the two ramps; also from the junction of the perpendiculars draw lines to the termination of the ramps, for their slopes.
Caponniere.
Make the passage of this work 30 feet wide, including the banquette on each side; the superior slope of each parapet terminates at 20 yards’ distance.
Bridges, and communications.
These are about 14 feet wide.
Stairs, or Pas de souris.
These steps of masonry are made at the gorges of the several works, and at the salient, and re-entering angles of the counterscarp. Those at the salients are generally 24 feet long, and at the re-entering angles 30 feet; they are 5 feet wide, and their steps 1 foot distant from each other.
Sally-ports.
These passages, cut through the glacis, are about 12 feet wide, and 18 feet long.
Side viewProfile of Vauban’s 1stSystem.J. W. Lowry, sc.
Profile of Vauban’s 1stSystem.J. W. Lowry, sc.
Profile of Vauban’s 1stSystem.
J. W. Lowry, sc.
PROFILE, OR SECTION OF VAUBAN’S FIRST SYSTEM.
Construction.
The interior slope of the rampart has a base of 18 feet, and a perpendicular height of 17 feet 6 inches.
The terreplein has a breadth of 25½ feet, its height being 18 feet sloping to 17 feet 6 inches, the height of the interior slope.
The banquette is 3 feet in height, the tread 4 feet wide, and the slope 5 feet wide.
The parapet is 4 feet 6 inches higher than the banquette, its interior slope is 18 inches, its thickness 18 feet, and its superior slope has a declivity of 3 feet; the revetment is 3 feet thick.
The escarp has a perpendicular height of 36 feet, measuring from the cordon to the bottom of the ditch.
The tablette, or coping-stone, at the top of the revetment, has a projection of 6 inches square.
The cordon is semicircular, its radius being 6 inches.
The slope of the escarp is 6 feet, the thickness of its revetment at the top 5 feet, and at the bottom 11 feet.
The counterfort joins the escarp; it is 1 foot lower than the top of it, 9 feet wide, and it extends to the bottom of the foundation, which is 3 feet below the bottom of the escarp; the retreat, or lessening, has a width of 1 foot.
The ditch is 38 yards wide, from the salient angle of the bastion.
The counterscarp is 17 feet 6 inches in perpendicular height, its slope being 3 feet, and its thickness at top 3 feet, the bottom, therefore, having a thickness of 6 feet; the foundation is 3 feet; and the retreat 1 foot.
The terreplein of the covered way is 20½ feet wide, and its slope is 6 inches. The banquette is 3 feet high, its tread 5 feet, and its slope 6 feet. The parapet is 4 feet 6 inches above the banquette, and its interior slope is 18 inches. The glacis, which forms the superior slope of the parapet of the covered way, is 50 yards in breadth.
The counterfort of the counterscarp is 5 feet in thickness, being 1 foot lower than the top of the counterscarp, and extending as low as the foundation of it.
The counterforts of the escarp, and counterscarp are 15 feet distant from centre to centre of each other, those of the escarp being at the end adjoining it 5 feet 6 inches, and at the termination 3 feet 8 inches thick; those of the counterscarp being in thickness at the larger part 3 feet 6 inches, and at the smaller 2 feet 4 inches.
VidePlate.
Modern System.
Top viewFortification.Modern System.
Fortification.Modern System.
FIELD FORTIFICATION.
REMARKS, AND GENERAL RULES.
1. The size of a work depends in general upon the number of men who are to defend it. If labour is the sole object of attention, the advantage must necessarily be the greater in proportion as the size of the work is less; but if the accommodation of the troops is only to be considered, the advantage depends greatly upon occupying much ground.
2. The form of the work should be such as to contain the greatest surface with the least perimeter. By an adherence to this maxim, we obtain the greatest accommodation for the troops with the least labour. The form of a field work seldom depends upon choice, but generally upon the spot where it is to be raised, the purposes for which it is to be constructed, and the nature of the ground in the vicinity.
3. The interior of the work ought to be so covered by the parapet, that the men within, except when on the banquette, may not be seen from any part without, at the distance of cannon-shot.
4. The circumjacent ground (to as great a distance as possible) ought to be cleared, that the enemy may not conceal, or shelter himself against the fire from behind the parapet. The nearer to the work that the enemy can find cover, the more advantageously he can form his dispositions; and, as his attacks may consequently be made with greater vigour, and be more readily supported, the success will be the more probable.
5. The flanking parts ought to be sufficiently capacious to contain all the men required for the defence of the flanked portions of the work.
6. The flanking parts ought to have nearly a direct view of those flanked; that is, the defence should be nearly at right angles, the most advantageous angle being 100 degrees.
7. The parts flanked ought to be within musket fire of their flanking parts.
8. The fire ought to be equally distributed, that every part of the work may be equally defended.
9. The work ought to be equally strong in all its parts, that it may everywhere equally resist the assaults of the enemy; and the parapet should be thick enough to withstand the shot fired against it.
10. The dimensions of the parapet should not only be sufficient to secure, and cover the troops within the work, but ought also to be ofsuch a form as to afford a full view of the enemy in his approach; and at the same time discover, as little as possible, the men employed for its defence.
Capacity of Field works.
The perimeter of a work, and the number of men to defend it, should bear a just proportion to each other, one yard being allowed for each man, or for each file of men, according to the nature, and object of the work.
In calculating the area of enclosed field works, 10 square feet may generally be estimated for each man, and 324 square feet for each gun, and its stores.
Content of Field works.
In square redoubts, or works having salient angles, if the areas of the sections of the parapet, and ditch, are made nearly equal, there will be too much earth; were the angles of the plan re-entering, instead of salient, the result would be reversed. Bearing this in mind, previous to commencing the excavation of the ditch, a correct calculation must be made to prevent any excess, or deficiency of earth for the parapet, and banquette.
Rules.
1.To find the quantity of earthrequired for the parapet, and banquette of a field work, &c.
Divide the parapet, and banquette into trapezoids, and triangles; compute the contents of each separately (by the rules inMensuration of Planes) and the sum of them will be the superficial content of a section of the parapet, and banquette. Multiply this by the length of the periphery of the redoubt, battery, &c., for the solid content of the parapet, and banquette.
2.To find, rapidly, the quantity of earth required for a parapet, and banquette.
Multiply the height of the crest of the parapet, into the sum of the bases of the superior, and exterior slopes; which will give the superficial content, very nearly.
3.To compute the superficial content of the ditch.
Multiply the depth into the breadth at bottom, to which product add the areas of the escarp, and counterscarp, for the content required.
4.To find the breadth of the ditch, of the usual form.
Divide the area of the section of the parapet by the intended depth of the ditch, and the quotient will be the mean breadth of the ditch; to this add half the sum of the bases of the slopes of the escarp, and counterscarp, for the breadth at top, and deduct the same for the breadth at bottom.
5.To find the breadth of the ditch, having a triangular section.
Divide the area of the section of the parapet by half the given depth of the ditch, and the quotient will be the required breadth at the top.
Construction of Field works.—VidePlate.
Fig. 1. The redan.
Draw a base line, 60 yards, from the centre of which erect a perpendicular, 40 yards; join the terminations of the base, and perpendicular, which will form the crest of the parapet of the work.
Fig. 2. The lunette.
Construct a redan (vide No. 1), base 80 yards, perpendicular 50 yards: make the faces of the lunette 45 yards in length, and draw the flanks to points on the base line, 30 yards, from the perpendicular.
Fig. 3. The square redoubt.
Construct a square, each side 40 yards (videPractical Geometry). To form additional faces when required, bisect the side of the square, draw perpendiculars inwards equal to ⅛th of the side, and join the termination of the perpendiculars, and the sides of the square, thus forming a double number of faces.
Fig. 4. The pentagonal redoubt.
Describe a circle, radius 30 yards, and construct a pentagon in the circle (videPractical Geometry), thus forming the crest of the parapet of the redoubt.
Fig. 5. The hexagonal redoubt.
Describe a circle, radius 30 yards, and construct a hexagon within it (videPractical Geometry); the sides of which form the crest of the parapet of the work.
Fig. 6. The circular redoubt.
Describe a circle, radius 30 yards, which will form the crest of the parapet of the redoubt.
Fig. 7. The star fort, with six points.
Construct an equilateral triangle, and divide each side, 75 yards, into three equal parts, form also an equilateral triangle on the central portion of each side, 25 yards, and the crest of the parapet of the fort will be traced.
Fig. 8. The star fort, with eight points.
Construct a square: divide each side, 60 yards, into three equal parts, and on the central portion, 20 yards, describe an equilateral triangle: the periphery of the fort will thus be obtained.
Fig. 9. The field fort, with bastions, and half bastions.
Construct a square; from the centre of each side, 120 yards, drop a perpendicular equal to one-eighth of the side, through the extremity of which, from the angles of the square, draw the lines of defence; make the faces of the bastions, and half bastions, two-sevenths of the exterior side, and draw the flanks perpendicular to their respective lines of defence.