Page:Encyclopædia Britannica, Ninth Edition, v. 9.djvu/474

 450 FORTIFICATION have been disposed with a view of keeping an enemy at not less than that distance from the dockyards. Upon the sea fronts the works consist generally of iso lated forts, placed, according to the width of the channels, at intervals of 1500 to 2500 yards ; these forts, being ex posed to the very heavy rifled guns which form the arma ment of the largest iron-clads of the present time, are protected with shields or walls of iron upon their sea fronts, and when they stand alone in advance of the channel are constructed with a continuous iron wall. The various modes in which the iron composing their armour is disposed will be discussed in a future paragraph. The power of heavy rifled guns is shown in accompanying table. Upon the land fronts the forts are ordinarily placed at Table showing the power of the present English Armour-piercing Guns, and of a few of the corresponding Foreign Guns. loTii-&amp;gt;iniiir* of inrift Ppnptrntirm Nature. Battery Projectile. Ibs. Charge. Ibs. Muzzle. Remaining at 1000 yard?. Penetration in indies in to unbacked wrought iron plates ut 1000 yards. Remarks. Velocity. Feet per second. Energy in Foot-tons. Velocity. Feet per second. Energy in Foot -tons. Heavy English M. L. K. &quot;Wrought iron.

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Heavy French B. L. R. Heavy German B. L. R. Medium French B. L. R. Medium German B. L. R. 17 in., 100 tons. 2000 375 1545 33000 1407 27484 22 The muzzle energy lias since reached 41,000 foot-tons. It is proposed to increase the length of this from 14 55 to 21 calibres. The 7-inch of 6 5 tons may be taken as the same. Steel. A bronze gun. Steel. 16 in., 80 tons. 1700 425 1600 30177 1500 26523 22 12 -5 in., 38 tons. 810 130 1420 11183 1302 9400 16 11 in., 25 tons. 535 85 1315 6415 1199 5335 12 10 in., 18 tons. 400 70 1364 5160 1228 4185 11-25 9 in., 12 tons. 250 50 1420 3496 1236 2648 9-5 7 in., 7 tons. 115 30 1525 1835 1261 1265 7 5 12 6 in. (32 cent), or 34-28 ton. 771-6 138-89 1371 10054 1257 8451 13 14 in. (35-56 cent), 56 5 ton. 1143 279-6 1631 21077 1515 18186 18-0 6-5 in., (16 cent), 5 tons. 99-3 16-5 1312 1185 1112 760 5-5 5 87 in. (15 cent), 3 tons. 61-1 13-67 1608 1096 1440 813 6-0 intervals of about 2000 yards, though these intervals vary according to the nature of the ground. Where the ground is uneven they are smaller, but where the ground. is level 2000 yards should be the least interval, and the forts should be of considerable size ; beyond this distance the movement of troops becomes indistinct, and the support afforded by o 1 1 th F 1G. 64. plan of Sea Fort, with continuous Iron Wall. The piers marked (*) are filled with concrete. one fort to another is lessened, especially at night and in thick weather. A strong reason for constructing large rather than small forts is that at night or in thick weather offensive measures may often be resorted to with the happiest results. But the garrison of a small fort can never be in a position to undertake such measures ; it must always re strict itself to a passive defence, whereas the garrison of a large fort will be able to act offensively, will be in better heart, and better commanded. Brialmont, speaking of small detached forts, says that one of the inconveniences of works of mutual defence is to require a great number of com mandants, while in the best armies the men fit to command a fortified place are few. The trace of these forts is very simple. It ordinarily consists of five sides, the longest of which fronts the enemy ; FIG. 65. Section through AB of fig. 64. the flank defence of the ditches is provided by three ca- ponnieres, one in the middle and one at each extremity of the front face. The ditches are deep with good scarps, and the defensive power is increased by a keep, which is separated