448 higher, and therefore begins to mask more effectually the revetment of the bastion, In General Noizet s system this demi-caponniere is formed into an elevated mask, which tends to secure the revetment from the breaching effect of the fire from the enemy s battery on the crest of the ravelin glacis. This is shown in fig. C3 ; and the system modified from the former modern system in this respect, as well as in other arrange ments, is now the normal bastioned system of the French schools. In General Noizet s arrangement the flanks are not made perpendicular to the lines of defence, but, as in Vauban s first system, form angles of about 80 with them. In the citadel of Ghent, which is a beautiful example of this system, but with still further modifications, the re trenchment of the bastion is so formed as to take advantage of this construction ; and the flanks, being casemated and pierced in both directions, become on one side the flanks of the retrenchment, whilst on the other they are the ordinary flanks of the bastion, thus giving a much longer curtain to the retrenchment, which occupies the whole gorge of the bastion, than in the form exhibited in fig. 2 of Plate IV. 5. Outworks. Plate IV., fig. 3, shows several kinds of Outworks, as a horn-work g, tenaillons k and k, a bonnette d, lunettes a and d, an entrenched bastion e, a batardeau/, and a caponniere h. These, and other works of a similar description, are con structed for the purpose of occupying ground which might otherwise be of service to the besiegers, or, as in the capon niere, to cover communications ; but their application must of course depend upon localities, and the judgment of the engineer must therefore determine in each particular case, which are the best to adopt. POLYGONAL OR GERMAN SYSTEM. The Systems of Fortification of which mention lias been made were devised to meet the attack of horizontal fire, but henceforward the efforts of the engineer must be di rected to devise methods of protection against curved and indirect fire of greatly increased range and power. It is true that the efforts of the later engineers have been in this direction, but the recent introduction of rifled guns and the still more recent development of indirect fire have rendered a recourse to very different measures absolutely neces sary. ^Before entering upon the consideration of these measures, it may be well to point out that a rigid adherence to the theory of defilade, which is based on the erroneous supposi tion that the path of projectiles is in a straight line, and, as a consequence, that artillery can only strike that which it sees, has contributed more than anything else to detain the art of defence behind the art of attack ; indeed en gineers of great weight were wont to maintain that, if the cordon of the escarp were in the plane passing through the crest of the glacis, the escarp was perfectly covered from artillery fire. Cormontaigne and Montalembert have fallen into this error, and so in more recent times have Choumara and later writers upon the Polygonal System. The increase in the weight, range, and energy of projec tiles, the greater accuracy of fire, not only direct, but indi rect, curved, and vertical, the enormous increase in the numbers of armies, and the wonderful mobility afforded to them by the development of railroads and steam vessels, by the subordination of steam, machinery, telegraphy, and other scientific applications of modern life, to military pur poses, have rendered necessary fortresses of an enlarged and of a more expensive nature, and have led to the adoption of a system of defence more simple, and based upon broader principles. The Bastioned Trace designed to afford from uncovered flanks a complete defence to the escarp of the body of the place can accomplish this end no longer, since these flanks Power of English Siege Artillery. Penetration at 1000 yards with common shell. Xature. e c
Remarks. -g "3
- t 9
~ 3 ~ 3 a o K O B Siege Guns. ft. in. ft. in. ft. in. ft, in. ft. in. The two penetrations marked (*) are with M. L. H. 64 Prs. 17 7 8 0* 4 6* llf battering shell. With brick in cement the penetration i.s about one half that 40 Prs. 1C 6 2 1 G G with brick in mor tar. t This is in sand stone. There is 25 Prs. 10 4 G 1 3 1 3 hardly any pene tration into granite, but the blocks split. J .B. The penetration of the siege howitzers is comparatively small. The low est effective velocities against revetments are considered to be from 460 to 000 feet a second. can now be destroyed by the fire of distant artillery, and the faces of the bastions themselves can be ricochetted from an equal distance. , Moreover, this trace, in which the relations between tho length of the front, the depth of the ditches, and the com mand of the enceinte are obligatory, is difficult of applica tion, and weak in its direct artillery defence, inasmuch as a portion of the rampart which should be available for the defence is withdrawn for the service of the flanks and cur tains. In the Polygonal Trace, which requires no inter-relation between the length of the front, the depth of the ditches, and the command of the body of the place, in which the exterior sides may at pleasure be longer or shorter within the limits of musketry fire, and the line of parapet may be in dependent of the line of ditch, these defects disappear, and its application to every variety of ground is more easy and more economical. As, too, the flanks are entirely protected from distant fire, and the faces are not exposed, or are far less exposed, to ricochet than in the angular traces, the poly gonal trace offers greater facilities for the employment of artillery as the principal arm of defence, while it has yet another advantage, viz., that its communications are far more simple. The main difference between the Polygonal and the Bas tioned Systems lies in the arrangements for the defence of the ditches. In the latter it is provided by the flanks of the bastions, in the former by caponnieres, powerful casemated works, constructed across the ditches. In the flank of the bastion the guns are exposed, and limited in number by the length of the flank ; if the flank be lengthened, the face of the bastion must be shortened, thereby diminishing the direct artillery defence of the bastion, or the flanked angle of the bastion must be diminished, rendering the faces already too liable still more liable to enfilade. Mc/eover, a second or lower tier of casemated guns cannot be added to the flank of the bastion without the suppression of the tenailte and consequent exposure of the curtain ; whereas the caponniere may be increased in length to any reasonable extent, and may be in two tiers. Again, in the bastion the flank is enfiladed by direct fire on the adjoining face, and is taken in reverse by the enfilade of that face, and by the direct fire against the opposite face and flank. Lastly, in the Polygpnal System a direct fire can be given upon the capital of the angle, while in the Bastioned System this capital is undefended. The advantage of this system in direct artillery defence
