Part 10

The different slopes for the works must depend upon the nature of the soil, and the materials of which the work is composed. The interior slope of the parapet, though it be fascined, should be ⅙ of its height; exterior about ⅔ its height. The slope of the banquette equal to its height. The slope of the scarpe or counterscarpe of the ditch, should be from half its height to its full height, according to the soil. The superior slope of the parapet must entirely depend upon the situation of the work, and that of the surrounding country. The interior slope of the parapet is generally lined with fascines, to keep up the earth; but it is not absolutely necessary to fascine the exterior slope, if the soil be pretty stiff. The embrazures are generally made 20 inches wide on the inside, and 9 feet on the outside; they must always be lined with something to retain the earth; turf is generally preferred, as fascines are so apt to take fire.

The manner of making the materials for field works, may be seen under the heads _Fascines_, _Gabions_, _Hurdles_, &c. and the manner of estimating the quantity of materials for works of this kind, may be seen under the word _Battery_.

_Fortification—Permanent._

A _parapet_, to resist cannon, should never be less than 18 feet thick in earth, and 8 or 9 in masonry. A wall need only be two feet thick in masonry, to resist musquetry. The parapet should always be 4½ feet above the banquette, and 7½ or 8 feet above the rampart, or terre plein.

The _Rampart_ should always be sufficiently wide to allow for the platform, and for two carriages passing each other; about 9 fathoms at top. A parapet of earth, though it takes more room, is always preferable to one of masonry, when it can be raised; though the only objection to the masonry is the number of splinters it produces.

Entire _Revetements_ of masonry are not advantageous for the same reason. The masonry of revetements should not be so high as to be seen or battered from a distance: earth parapets are battered in vain, as the earth forms a natural slope.

The best _Escarpe_ is made of masonry, either in wet or dry ditches, be the earthen one ever so well fraized or palissaded. The earthen one may be stormed without making a breach. The escarpe should be 30 or 35 feet high.

The _Counterscarpe_ should also be of masonry, and not less than 12 feet high. The inconveniences of an earth or low counterscarpe, are the impossibility of defending to the last the covert way; as the enemy may descend into the ditch, and again mount the covert way, and so get in the rear of the traverses. The enemy may find his way along the natural slope of an earth counterscarpe, and is not delayed by a tedious operation of getting into the ditch. Besides, the natural slope of the end of an earth traverse prevents its effectually covering the covert way.

_Ditches_ are generally 15 or 18 toises wide. Dry ditches are always preferable to wet ones, on account of the shelter they afford the troops, and the ready communication with the outworks, without the constant trouble and danger of bridges.

The _Covert way_ should be 5 toises wide; less would crowd the troops, and more would allow room for the enemy to erect batteries in it.

The whole of the glacis should be seen, not only from the crest of the parapet, but from the embrazures in the parapet.

The _Tenaile_, must not be so high as to prevent the flank guns in one bastion seeing the breach that may be made in the collateral one.

_Ravelins_ are best without flanks; their faces directed to 10 toises from the shoulders of the bastions.

The crest of the parapet of the body of the place should be 8 feet above the crest of the glacis, to command it across a ditch of 15 or 20 toises.

The crest of the parapet of the ravelin is 3 feet lower than that of the body of the place, in order that it may be more effectually commanded from the place; and therefore to enable the parapet of the ravelin to command its own glacis, the ditch is only made 10 toises, and this glacis is a foot lower than that of the body of the place.

There must be an equilibrium of defence established through every front of a fortified place; for it will be needless to strengthen any particular front, if the others from their weakness be left exposed. The following remarks may enable an observer to appreciate the value of particular works, in the proper application and arrangement of which that equilibrium consists.

_Intrenchments_ within the works add much to their defence. In large bastions with obtuse flanked angles, the best intrenchment is formed of the front of a fortification, or of two demi bastions and a curtain, connecting the angles formed by the flank and curtain. If this intrenchment be advanced to the shoulders of the bastion, so as to include its flanks, as is often the case, it will be subject to be taken in the rear, by the fire from the counter batteries opposed to the flanks. But in bastions with acute flanked angles, which do not afford sufficient space for this kind of intrenchment, Cormontaigne proposes one in the form of a cavalier, whose faces and flanks are parallel to those of the bastion. The first kind of intrenchment does not operate in the defence of the place, till after the passage of the ditch; till which time it remains entire, and then capable of a very great defence. The second kind becomes a support to the bastion from the first commencement of the siege; but it is therefore subject to have its defences destroyed at a distance. Nor is its defence equal to that of the other form.

_Counterguards_ should possess the three following properties: 1st. They must cover effectually the principal work before which they are placed; at least that part of it, which can be battered in breach. 2d. They must be lower than the work which they cover; but not so low as to permit its revetement to be seen. 3d. They must be so narrow as not to afford room for the besiegers to erect batteries in them, against the work which they cover, and therefore not leave the besiegers a choice of positions. The counterguards in Coehorn’s system are only of earth, through which it is necessary to make an opening, before the capital work can be battered.

_Horn_ or _Crown Works_, unless to occupy some important point, to strengthen some weak side, or to afford more room for a confined garrison, are rather a weak than a strong arm to a place. This is particularly the case when they are constructed with smaller, and consequently weaker fronts, than that part of the body of the place which they cover; as they facilitate, when taken, the approaches to the body of the place. This is remedied by constructing their fronts of the same strength as the front or fronts which they cover. They also facilitate the taking of the place, by exposing the revetement of the work on which their branches are directed, to be battered in breach, along the ditches of those branches. This is a great evil, even to an outwork, but is of serious consequence if they rest upon the body of the place. This defect has been remedied by placing these works altogether outside of the covert way, and allowing their ditch no communication with those in the rear. In this case their gorge must be made very secure to prevent its being turned.

An _Advanced Covert_ way, is esteemed amongst the best means of adding to the defence of places. Besides the advantages common to the usual covert way, it has many peculiar to itself. It however seems necessary to ensure to it the many advantages of which it is susceptible, (beside being properly palissaded,) that it should be secured in the rear by a wet ditch, as the only means of giving it an inaccessible counterscarpe, and at the same time keeping it under the fire of the musquetry of the place. This kind of covert way is generally supported by redoubts upon the capitals of the bastions and ravelins; which from their position cannot mask the fire of the place; and being mounted with artillery, oblige the besiegers to commence their attack at a great distance, and very much to extend their operations; and as their establishment upon this covert way must effectually mask the fire of their first batteries, it must greatly increase their labour. The retreat from these redoubts must be secured by an underground passage.

_Countermines_ are undoubtedly one of the first means of strengthening places. For this article we refer to the word _Mines_.

_Detached Redoubts_, when circumstances of situation favour them, are employed with great success. They are usually detached and totally unconnected with any of the works of the place, by any covert way or other aboveground work; and have for objects, either the opposing an additional obstacle to the besiegers at the point they occupy, or the rendering the adjoining fronts inaccessible, by an enfilade or reverse fire upon the approaches. They also afford at their gorge, a most excellent rendezvous and retreat for sorties; upon the level of the country, and without the difficulty of filing troops through the barrier of a covert way.

But in order to insure to the detached work or works, all these advantages, it is necessary that they should be either totally inaccessible to the besiegers, by reason of the natural difficulties of their situation, as in an inundation, morass, &c. or be made secure by art, from being taken by storm, and only attackable by regular approaches. They should be under cover of the fire of the place; but if their distance be too great for that, an intermediate work must be established to give them support. Their best form is that of a bastion with retired flanks; and a strong system of countermines the most effectual way of prolonging their resistance.

_General Remarks._—The larger the flanked angles of works, the more direct will be their fire, and that of their covert way, upon the approaches; the greater extent will they oblige the besiegers to occupy in their parallels and batteries; and the more will they oblige the besiegers to expose themselves to the fire of the fronts collateral to the one attacked. Faces of works directed to inaccessible situations, such as rivers, lakes, &c. from whence they cannot be enfiladed by ricochet batteries, add greatly to the strength of a front.

If the flanked angle of a ravelin be so advanced as to see in reverse any battery erected upon the crest of the glacis, or in the covert way of the bastions, it will increase the strength of that front; because it will oblige the besiegers to gain possession of the ravelin, before they can make any lodgement, from which they can batter the bastions. This is the case in Cormontaigne’s system: and a place thus fortified, obliges the besiegers to attack and gain two ravelins, to get at the bastion between them. Beside, if this system be applied to a right line, or to a polygon of many sides, the prolongations of the faces of the bastions, will be intercepted by the flanked angle of the ravelins, and consequently make the establishment of enfilading batteries against them very difficult. A work which admits of a breach being made in it (particularly the body of the place) at a distance, very much facilitates its being taken. The ditch of the ravelin affords an opening through which the besiegers may make a breach in the face of the bastion, from the glacis, opposite the flanked angle of the ravelin, and is therefore subject to this defect. A counterguard before the bastion, lessens this evil, by transferring the breach from the body of the place to the ravelin; but it requires a counterguard also before the ravelin, effectually to cure it. A crown or horn work also produces this evil; its remedy was given, in speaking of those works.

The direction of the flanks or faces of a work is not so material as relating to the fire of artillery, as to that of musquetry; for artillery is never fired without being pointed, but musquetry is fired mechanically, and perpendicular to the parapet, without much attention to the object to be struck.

A work in the neighbourhood of a height must be defiladed[7] from that height, that is, instead of being built upon a horizontal plane, it must be erected upon an imaginary inclined plane, passing from somewhere in the interior of that work, over the most commanding points of the height: and every part of the works must bear the same relation to this inclined plane, that they would do, to a horizontal plane in a level country.

A work is not therefore always to be condemned, because it is in the neighbourhood of a height; for if it be properly defiladed from that height, it will receive a great advantage over the approaches of the besiegers, carried on down an inclined plane towards it. But a work to be properly constructed in the neighbourhood of heights, must not uniformly preserve the same distance from those heights, unless their summits be all upon the same level; but must approach them at their lowest parts, and recede from them as they rise; thus will the necessary plane of defilement preserve nearly the same degree of obliquity throughout.

_The Dimensions in the following Table of Vauban, are thus applied_:

The _Fort_ is mostly for squares.

The _Little_ for citadels, commonly pentagons.

The _Mean_ for all fortifications from the hexagon and upwards.

The _Great_ is seldom used but in irregular fortifications, and particularly on rivers.

[7] The compiler must here apologize for coining the word _defiladed_, which he is obliged to do, never having seen this subject treated of in English. But the French use the word _defile_ in a contrary sense to _enfile_; and as we admit the words enfilade and enfiladed from the latter, we cannot refuse the terms defilade and defiladed from the former.

_Principal Dimensions of Fortifications, according to_ VAUBAN.

+-----------------+-------+-------------+--------+----------+ | |Side of| Length of |Faces of|Capital of| | |Polygon|Perpendicular|Bastions|Ravelins | +-----------------+-------+-------------+--------+----------+ | Forts. | 80 | 10 | 22 | 25 | | | 90 | 12 | 25 | 28 | | | 100 | 12½ | 28 | 30 | | | 110 | 14 | 30 | 35 | | | 120 | 15 | 33 | 38 | | | 130 | 16 | 35 | 40 | | | | | | | | Little | 140 | 20 | 40 | 45 | | Fortification. | 150 | 21 | 42 | 50 | | | 160 | 23 | 45 | 50 | | | 170 | 25 | 47 | 52 | | | | | | | | Mean. | 180 | 30 | 50 | 55 | | | 190 | 31 | 53 | 55 | | | | | | | | Great. | 200 | 25 | 55 | 60 | | | 260 | 22 | 60 | 50 | +-----------------+-------+-------------+--------+----------+

_Dimensions of Walls and their Counterforts, from 10 to 50 Feet high, having a Slope of ⅕ their Height._

+--------------------------------++-----------------------------+ | Wall. || Counterforts. | +--------+-----------+-----------++--------+---------+----------+ | | | ||Distance| | | | | Thickness |Thickness ||between | | | |Height. | at Top. |at Bottom. || them. | Breadth.| Length. | +--------+-----------+-----------++--------+---------+----------+ |Feet. |Feet. Inch.|Feet. Inch.|| Feet. |Feet. In.| Feet. In.| |10 | 4 0 | 6 0 || 8 | 2 8 | 4 — | |15 | 4 3 | 7 3 || 10 | 3 4 | 5 — | |20 | 4 6 | 8 6 || 12 | 4 0 | 6 — | |25 | 4 9 | 9 9 || 14 | 4 8 | 7 — | |30 | 5 0 | 11 0 || 16 | 5 4 | 8 — | |35 | 5 3 | 12 3 || 18 | 6 0 | 9 — | |40 | 5 6 | 13 6 || 20 | 6 8 | 10 — | |45 | 5 9 | 14 9 || 22 | 7 4 | 11 — | |50 | 6 0 | 16 0 || 24 | 8 0 | 12 — | +--------+-----------+-----------++--------+---------+----------+

The heights in the above table are taken only from the bottom of the ditch, and do not include the foundations.

When the rampart is partly walled and partly turfed; then ⅕ of the height of the turfed part must be added to the breadth of the wall at the top given in the table.

The bases of all inward slopes of earth should be equal to their height, if not more.

The bases of all outward slopes of earth ⅔ of their height.

The superior slopes of all parapets ⅙ of their breadth.

The slope of all walls, or revetement ⅕ of their height.

Though the above principles given for the erection of field works may assist an officer’s recollection who may be employed on that duty, the memorandums given respecting _permanent_ fortification pretend to no such object: but may serve to remind an officer, if he should visit a fortification, of its essential requisites; and may assist his observations in passing round the works.

_FUZES.—Composition._

Saltpetre 3 lbs. 4 oz. Sulphur 1 — Mealed powder 2 12

+--------+------------------------+-------------------------+------+ |Nature. | Fuze Diameter. | Composition. |Drove | | +--------+-------+-------+---------+-------+-------+by one| | | below |at the | at the|Diameter.|Length.|Time it|man in| | |the cup.|bottom.| cup. | | |burns. |1 day.| +--------+--------+-------+-------+---------+-------+-------+------+ |Inches. | Inch. |Inches.|Inches.| Inch. | Inch. | ″ | Nᵒ. | | 13 | 2.1 | 1.575 | 2.49 | .5 | 8.4 | 35 | 25 | | 10 | 1.8 | 1.35 | 2.13 | .438 | 7.2 | 33 | 25 | | 8 | 1.3 | 1.25 | 1.78 | .375 | 6.37 | 29 | 30 | | 5½ | 1.1 | .825 | 1.3 | .275 | 4.4 | 18 | 50 | | 4⅖ | 1.0 | .75 | 1.18 | .25 | 3.5 | 15 | 700 | |Grenades| 0.8 | .6 | .9 | .2 | 2.25 | | 1000 | +--------+--------+-------+-------+---------+-------+-------+------+

Diameter inside the cup is 3 diameters of the bore.

Depth of the cup 1½ do.

Thickness of wood at bottom of the bore, 2 diameters.

_To find the Length of Fuzes for any Range._

The 13 and 10 inch fuzes of the same length burn so nearly equal, that one common length answers both, as do the 8 inch, 5½ and 4⅖. Therefore, to find the length of fuze for any range, multiply the time of flight by .22 for the 13 and 10 inch, and by .24 for the 8, 5½, and 4⅖; which is the decimal part of an inch a fuze burns in a second. Fuzes are thought to keep better by being painted; and for field service, are often marked off by black lines into seconds and ½ seconds.

_GABIONS._—Small gabions of 3 feet high, and 2 feet diameter, are made with least trouble, and are easiest carried. The pickets for them must be 1½ or 2 inches thick, and 4 feet long. Large gabions are 6 feet high, and 3 feet in diameter; and require two men to carry them. The smallest gabions or baskets are formed of pickets, 1 inch in thickness, and 1 foot long: they are 12 inches in diameter at top, and 10 at bottom. The small gabions have 7 or 8 pickets, the large ones 9 or 10.

_To make them._—The pickets are first to be fixed in the ground in a circle, the size of the bottom of the intended gabion; then a few twigs are to be wove through the upper ends, to keep them from flying out; afterwards the work must be begun at the bottom and continued upwards; and the whole being well driven down with a mallet, the edges must be secured by twigs, wattled up and down. The twigs of willow, birch, hazle, alder, poplar, and beech are proper for this purpose. The top of the gabion must be made very even, because that becomes the bottom when finished. Four men are usually employed on each gabion, with a billhook, a mallet, a spade, and two axes. Two collect the wood, while the other two form the gabion. A 3 foot gabion ought to be made in half an hour.

_GIN Triangle._—Length of arms of the gin 16 feet 4½ inches. Roller, 6 feet long. Tackle fall, 78 feet of 3 inch white rope. Sling, 6 inch white rope.

For the different exercises of the gin, see the word _Exercise_.

_GRAVITY.—Table of the Specific Gravity of several Solid and Fluid Bodies._

Platina 23400 Nitre 1900 Fine gold 19640 Ivory 1825 Standard gold 18888 Brimstone 1810 Quicksilver 11325 Solid gunpowder 1745 Fine silver 11091 Sand 1520 Standard silver 10535 Coal 1250 Copper 9000 Boxwood 1030 Copper halfpence 8915 Sea water 1030 Gun metal 8784 Common water 1000 Cast brass 8000 Oak 925 Steel 7850 Gunpowder, close stacken 937 Iron 7645 ” in loose heap 836 Cast iron 7425 Ash 800 Tin 7320 Maple 755 Crystal glass 3150 Elm 600 Marble 2700 Fir 550 Common green glass 2600 Charcoal Flint 2570 Cork 240 Common stone 2520 Air 1.232 Clay 2160 Brick 2000 Common earth 1984

The several sorts of wood are supposed dry.

This table also contains the weight of a cubic foot of each body in avoirdupois ounces; from whence results the following rules:

1. _To find the Magnitude of any Body from its Weight._

As the tabular specific gravity of the body Is to its weight in avoirdupois ounces, So is one cubic foot, or 1728 cubic inches, To its content in feet or inches respectively.

2. _To find the Weight of a Body from its Magnitude._

As one cubic foot, or 1728 cubic inches, Is to the content of the body, So is the tabular specific gravity To the weight of the body.

_GRAPE SHOT._—See the word _Shot_.

_GRANADES._—Hand granades may be thrown to the distance of 13 fathoms. For their dimensions, see the word _Shell_.

_GUNNERY._—By the assistance of good tables of practice, and the tables of amplitudes, sines, tangents, and secants, all the cases in gunnery in a nonresisting medium may be easily solved; and perhaps the solution may be sufficiently correct for practice, if the initial velocity of the projectile be not so great as to make the air’s resistance considerable.

For the tables of ranges with ordnance, see the different natures, as _Gun_, _Mortar_, &c. and for the tables of amplitudes, sines, tangents, and secants, see pages 151 and 152.

_Upon Horizontal Planes._

1. The greatest range is at 45° nearly.

2. The ranges with different elevations with the same charge, are as the double sines of the angles of elevation.

3. Any angle and its complement give the same range nearly.

4. The times of flight, are as the sines of the angles of elevation.