through the ditch of the ravelin. The covered-way is made
en crémaillère, and at each bend there is a sort of redoubt,
or casemated traverse, not a simple hollow traverse loop-
holed, such as those in the detached works of Corfu. It
has been objected to Bousmard's system that his advanced
works would be speedily taken by turning the gorges both
of the ravelin and its redoubt, but it should be remembered
that the interior slope of both is replaced by a loopholed
wall, being the front of an arched gallery running all round,
so that the enemy could not remain within these works ex-
posed to the fire from the galleries, as well as from the body
of the place. Without advocating the precise form and
disposition of the works recommended by Bousmard, it may
be reasonably asserted that in every case of a powerful and
well-appointed garrison, the defence will gain by assuming
an active character beyond the precincts of the glacis.
As already observed, an unmerited indifference has been
manifested by many engineers to the merits of Carnot,
principally, it may be believed, from his exaggerated esti-
mate of the effects of a vertical fire of small projectiles.
Although he appealed to imagination rather than to calcu-
lation, when he assumed that by substituting 600 wrought
iron balls, weighing each Ib, for the one shell of 150 tb,
with 6 mortars projecting 3600 balls, he might expect to
put hors de combat 20 men at each discharge, or 2000 in 100
discharges, he was right in urging the importance of vertical
fire. Carnot constructed his escarp without a revetment,
but placed a detached loopholed wall in front of it with a
chemin des rondes between, which is one essential feature
of his system, the wall being constructed with arched niches
in rear so as to shelter the men defending it; the loopholes
are in two rows. He provided arched casemates for mortars
on the gorge of his bastion in order to fire upon the capital,
and the loopholed wall of an inner curtain, being continued
along the retired flanks and in front of these mortar case-
mates, formed a complete inner retrenchment. Between the
tenaille and the ravelin was an earthen cavalier, occupying
the position of a redoubt in the ravelin, before the bastion's
counterguard, so that the whole of the interior works were
masked by these earthen envelopes. There is much inge-
nuity in these arrangements, and at least as full an appre-
ciation of the value of earthen works as can be found in the
writings of any modern writer. Carnot's leading principle,
however, was, that a successful defence must depend on the
active operations of the garrison, and that sorties therefore
should be frequent and determined as soon as the enemy
had approached close to the fortress. For this purpose he
removed the revetment from the counterscarp, and formed
it into an easy or countersloping glacis, to admit of the
ready advance of the troops from the ditch upon the head
of the besiegers' sap. He supposed that the overwhelming
vertical fire of the 10 mortars in the mortar batteries in the
gorges of his bastions would prevent the enemy from accu-
mulating large covering parties in the trenches, and that he
should therefore be able to fall upon the working parties
and successfully delay the progress of the works. It has
been shown that Carnot entertained an exaggerated view of
the effects of vertical fire, but the idea of securing his mor-
tars in casemated buildings is good, and has been adopted
in the citadel of Ghent, and in several English works at
Portsmouth and Plymouth; and it is impossible to study
his works without profit.

adopted so defective an arrangement." But notwithstanding this strong condemnation, it is at least doubtful whether such works are not the most suitable for a vigorous defence by a strong garrison, as they would enable the besieged to fall upon the assailants at the most critical moment of their attack with a powerful force; and it may be added that a skilful engineer would know how to throw many difficulties in the way of turning these advanced works, whilst the continance of the besiegers in them might be rendered both difficult and dangerous in the extreme.

The most remarkable feature in Dufour's modification of the modern system is, that one face of the redoubt in the re-entering place of arms is carried across the ditch, and connected with the coupure of the ravelin, so as completely to close the ditch and cover the face of the bastion from the fire of a battery on the glacis of the salient of the ravelin. Dufour also raised the salient of the ravelin into a high cavalier, so as to secure the faces from ricochet; and he proposed that the cavalier should be formed of gravel or small stones, so that the fire from the body of the place might, by scattering about these natural missiles, cause great damage to the enemy, when attempting to form a lodgment.

General Noizet has been already mentioned in connection with the Modern System, his modification of which is now the normal system adopted at the French military schools. Rejecting Dufour's mode of closing the ditch of the ravelin by carrying across it one face of the redoubt of the re-entering place of arms, he effected the same object by placing a massive mask between the coupure of the ravelin and the re-entering place of arms, from the inner escarp of which it is separated by a passage. The counterscarp of the bastion is carried continuously along the inner edge of the mask, whilst in front of it is a ditch which separates it from a demi-caponnière forming its counterscarp and covered-way, and a glacis sloping down the ravelin, of the ditch. The mask, the lunette redoubt in the ravelin, and the redoubt in the re-entering place of arms form a combined series of works of great efficiency for defence, which completely cover all but the salient portion of the face of the bastion. The flank of the bastion, as before observed, forms an angle of 80° with the line of defence, and the advantage taken of this in the citadel of Ghent in forming a most powerful intrenchment in the bastion, with a curtain as long as that of the main front, has also been pointed out.

General Haxo,' one of the ablest engineers of modern times, did not publish his scheme of defence, nor did he reproduce it as a whole in the works he constructed, doubtless considering, as has been so frequently urged, that systems, so called, can only be looked upon as the exhibition of great principles, not as rigid rules for their application. His ravelin is made very prominent, and the salient is formed into a traverse, or mask, casemated and armed with artillery. Within the ravelin there is a redoubt, and within that a casemated caponnière or bastionette. The ditch of the ravelin is closed by continuing the counterscarp across it with a glacis slope into the ravelin ditch, and by this arrangement the ditch of the redoubt in the ravelin is also closed. The counterguards, the higher and the lower bastions, form almost three lines of defence, of which two, the outer and inner, are powerfully armed with artillery. The peculiar characteristic of the system is, that Chassel up (1754-1835), like Bousmard, placed his rave- the parapet is thrown back, and made in its trace independlin in advance of the glacis, and provided it with a small ent of the escarp, so that, whilst the latter retains the usual casemated keep, the flanks of which are pierced for two straight line, the parapet is broken into several portions not guns each. The tenaille is also provided with casemated in the same line, and thus secured from the effects of ricoHanks, and in front of it is a casemated redoubt or bastion- chet-an arrangement of very great merit, and largely ette to supply the place of the ordinary ravelin, and to adopted in the Polygonal system. Haxo is probably better flank the salient portion of the face of the bastion, the known to English engineers as the inventor of casemated general face being by him bent into two, so as to place the batteries à l'Haxo than from his merits as an engineer, salient portion in line with the exterior side of the polygon, great as they were. These batteries are formed in the parand thereby secure it from the ricochet fire. Casemated re- apet, and though arched over with masonry, are covered doubts in the re-entering and salient places of arms, a de- with earth. They are open in the rear to the terreplein, fensive barrack, and a permanent entrenchment on the bas- and the openings in front for the guns are continued into tion are also included in his arrangements. De Sellon embrasures formed in an extension of the parapet at these (Mémorial de L'Ingénieur Militaire) observes, "It would points beyond its ordinary retired position in Haxo's sysindeed be well to force the besieger to pass through two tem. These batteries are thus secured from the effects of Bieges, if the outworks pushed so far forward had higher the enemy's fire, and when the embrasures are masked are scarps, and were not so easily turned at the gorge, but as equally hidden from his view, so that they may at any the scarp is only 13 feet high, this possibility of attacking moment suddenly open a powerful and unexpected fire the works by the gorge without a previous descent into the upon the besiegers. Being open in the rear, and connected ditch presents such serious inconveniences that it is surpris- together by arched openings between every pair, the circuing to observe that Bousmard and Chasseloup should have lation of air is sufficient to do away with the inconvenience 1 [François Benoît Haxo (1774-1838), a French engineer, fortified Belfort, Grenoble, and Sedan.-AM. ED.]

from smoke, so generally complained of in casemated batteries. The batteries à l'Haxo have been used at Grenoble and Lyons, in the forts of Loyasse and Sainte-Foy, and in many English works. Their value has been much diminished by the range, penetration, and accuracy of modern rifled artillery.

|

=

10

Rs.

Now

let S side of cubical box to contain the charge (55 lb of powᎡ

der thrown loosely in, filling one cubic foot), and S = 10 X 55

=

0.122 R, or nearly R in feet. The pits for fougasses vary generally from 8 to 12 feet in depth, and from 3 to 4 feet in width, being made square, and are revetted with planks when the earth is not firm enough to stand without support; and for this latter purpose gabions may be used of different diameters, so that the smaller may be slipped, through the larger, which have been previously fixed. The box for the powder is well tarred, and when intended to be left in the ground for some time, it should be covered with tarred canvas and put into another box, also tarred both inside and outside. The charge about an inch in diameter, filled with powder, and enclosed in is ignited by Bickford's fuze, or by a saucisson or linen tube a wooden case well tarred. The saucisson and its covering should be laid in a trench, sunk some feet in the earth, from the charge and pit to the place of ignition, in order to secure it from accidents as well as from the enemy's observation (see fig. 26, page 378, in which is also represented the mode whereby the fire is applied by what may be called the fire-box, the end of the trough and powder-hose being introduced into it). As for the thorough fulfilment of the object of a military mine the explosion should be "immediate," it is requisite to employ a contrivance for producing instantaneous ignition. This can be most is now as a rule employed in regular mining operations. readily and perfectly effected by employing electricity, and this

mated. When the line of least resistance, or shortest line drawn from the centre of the charge to the surface of the earth, which in this case is the depth of the pit, is 10 feet, a charge of 100 tb will produce an entonnoir or excavation, the radius of which is equal to the line of least resistance; and it has been ascertained that the volume of the excavation varies with the The work of the commandant of engineers, M. Chou- the same, and that the volume varies also as the cubes of the charge, the line of resistance and the resisting medium being mara, entitled Mémoires sur la Fortification, was published lines of least resistance; hence, therefore, if W represent the in 1847. In this treatise he maintains the principle that weight of the charge, B the bulk of the entonnoir corresponding the direction of the parapet should be independent of that to 100 th of powder and a line of resistance equal to 10 feet, and of the escarp, the latter being formed in straight lines, and that of the entonnoir corresponding to the charge W and the considered permanent during the siege, whilst the former line of least resistance R, we have 100: W:: B:b; but as B: may be broken into several lines, and may be modified dur-b:: 103: R3, we have 100: W:: 103: R3, and W = ing the siege so as to facilitate the defence in any direction. Haxo had in his lessons or studies pointed out the importance of this principle, but Choumara was the first to advocate it in print. The castle of Naples exhibits an early example of the reverse operation, a new escarp having been built in front of the ancient round tower forts, so as to change them at the base only into bastions, whilst the upper portion of the towers became retired and independent parapets. Choumara, not relying on the bent trace of his retired parapet as a security from ricochet, proposed a traverse on the capital of his bastion, placed outside of the retired parapet, and 33 yards in length. This traverse, made 26 feet high and 78 feet wide at its base, would occupy less than two-thirds of the space of the twelve ordinary traverses required to secure from enfilade the faces of Choumara's bastions 164 yards in length, whilst it would cover not only the bastions but the flanks also. In addition to the traverse or mask on the capital, Choumara proposed high traverses, parallel to the flanks, at about 22 yards from the salients, which would not only secure the faces from enfilade, but would form secure or interior flanks, as cavalier flanks, commanding and firing over those in front. By making the cavalier flanks 98 yards long, and casemating them à l'Haxo, 15 guns might be placed in each, and the covered-way of the bastion attacked would be commanded by 30 guns in addition to those of the ordinary flanks, whilst the traverse of the capital would secure the flank cavaliers from ricochet. The last and most remarkable suggestion of Choumara is the proposal to widen his ditch to about 50 yards, and leaving a passage of communication of 16 yards round the base of the escarp, to form an interior glacis, sloping up from the base of the counterscarp towards the summit of the escarp, and having a base of 34 yards wide, thus constituting a continuous mask round the escarp. In respect to countermines, Choumara proposed to replace the great galleries, which are usually made 6 feet high and 3 feet wide, and which are the great arteries of a system of mines, by large vaulted galleries from 16 to 20 feet wide, pierced through the counterscarp, and continued as far as the third parallel. Six of these galleries were to be formed in each front, being placed about 55 yards apart, and connected together by minor transverse galleries or branches. Galleries of this magnitude would, in time of peace, be useful as stores, and in time of war would greatly facilitate the operations of the miner.

Experience has shown how little real injury the explosion of fougasses does to an assailant; but, as the moral effect of them is a degree of hesitation or irresolution often greater than that produced by musketry fire, and as they are easily extemporized, the fougasse may still be considered an ob stacle of some value to the defence. Loaded shells packed in a case may be substituted for the ordinary charge, the case being formed with a horizontal partition, and the fuzes of the shells placed on the lower portion of the case, passing through holes in the partition, so as to be brought into connection with the firing-hose in the upper portion of the case. Another form is the stone fougasse, which is probably the most effectual of all. It is constructed thus. A conical pit is made in the earth about 5 or 6 feet deep, the axis being directed towards the enemy at an angle of 45° with the plane of construction, and at the bottom a charge of 50 tb of powder is placed in a well-tarred box. Over the box, and perpendicular to the axis of the cone, is fixed a lid on which as a platform are packed either stones or The details of military mining cannot be discussed here; broken bricks, which, on explosion, are scattered over a but it may be stated that this subterranean warfare re-space of about 60 by 70 yards. It should be laid down as quires great skill on the part of both besieged and besieger. The besieged has the advantage of having had the main galleries of his countermines formed beforehand, but in spite of this a war of mines must generally be in favor of a besieger, since every explosion of the mines of the besieged, however destructive it may prove to the assailants, must destroy some portion of the works of defence, whilst every explosion of the besieger's mines must operate upon his enemy only. Starting, however, upon the assumption that a fortress, except in situations which render regular attack impossible, must ultimately fall, the real object of defence is to occupy the enemy for at least the time for which the fortress was designed to resist; and the destruction of the lodgment or of the battery of a besieger may materially protract the resistance of the intrenchment formed in a bastion, and thus enable the besieger to maintain his ground the longer.

The most simple form of mine, and that which may be most readily applied as an obstacle in the way of the assailant, is the fougasse. It consists of a chamber placed at the bottom of a pit about 12 feet deep. The charge is placed in a wooden box, and both the charge and size of the box may be thus esti

a rule that facilities for discharging mines ought to be in every fortress, whether electric apparatus be used for the purpose, or openings be prepared in the works through which the powder-hose may be carried.

The last great modification proposed by Choumara is the extension of the exterior side, and the value of this can no longer be matter of doubt, now that the effective range of musketry has so much increased. The length of the line of defence may now be safely and advantageously fixed at between 400 and 600 yards, so that musketry and artillery can co-operate together efficiently. Chasseloup had, indeed, proposed to make his exterior side about 700 yards long, and he was no mere speculative engineer, for he had fortified with great skill Alessandria in Piedmont; but it must be borne in mind that no greater distance should be allowed for musketry than is compatible with distinct vision and a correct appreciation of distance; and further that the men intended to use the rifle in a fortress ought to be well trained for that object. The Gatling gun may in fitting positions be used with effect instead of musketry; it de livers a continuous stream of bullets at the rate of 400 per minute. The value of one Gatling is equal to 22 rifles, and

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