Alloa, it winds in a most beautiful and picturesque manner: so that, though it is but four miles by land, it is twenty-four by water between those two places. Below Alloa the river expands itself to a great breadth between the counties of Lothian and Fife, till at Queensferry it is contracted by promontories shooting into it from both coasts; so that, from being four to five miles broad, it becomes not above two miles. Here in the middle of the channel lies a small island called Inchgarvy, and, a little below that, those of Inchcolm and Inch-keith. The north and south shores receding, below Queensferry, the body of the water gradually enlarges till it becomes two or three leagues broad, affording several safe harbours on both sides, and excellent roads throughout, unembarrassed with latent rocks, shoals, or sands; and allowing secure anchorage to the largest ships within a league of the coast in almost any part of the Frith, and to vessels of a smaller size within a mile or less. The Forth was known to the ancients by the name of Bodotria, or, as Ptolemy calls it, Boderia, and has been ever famous for the number of its havens. It is navigable for merchantmen as high as Alloa, fifty miles from the sea; and, for coasters, as far as Stirling, twenty-four miles further by water, though only four by land in a direct line, as already observed. The tide flows only a full mile above Stirling. The direct course of this river is scarcely less than 100 miles, and its sinuosities do not occupy a shorter space than 200. Its depth is from three to thirty-seven fathoms, or more; the bottom, in many or perhaps most places, covered with sleach, especially above the ferries. The principal tributary rivers of the Forth are the Goodie, Teith, and Allan, above Stirling bridge; and, below it, the Devon, Carron, Avon, Almond, Leith, Esk, Leven, Tyne, and others these chiefly flow into the river on the south shore. A navigable canal, commencing near Grangemouth, communicates with the Clyde. In the Forth are found great variety and abun dance of fish. Whales have frequented it during several centuries: the porpoise is common. At Stirling salmon are exceedingly plentiful; cod and haddocks are taken in great quantities; and it is frequented by myriads of herrings. At times these are so plentiful that they are sold at the cheap rate of sixpence a hundred. Crabs are caught in many places; lobsters are not rare, but bear a much higher price; and oysters and muscles are in great profusion. Valuable minerals are obtained from almost every part of the environing shores. The beds of coal are inexhaustible, apparently lying under the whole bed of the river between Culross and Borrowstownness. Lime is wrought on both sides, but chiefly at Charleston, in the county of Fife, about thirteen miles north-west of Edinburgh. Along the coast numerous petrifactions occur. Ironstone is plentifully obtained from pits, or collected in scattered nodules; and small portions of fine jasper are frequently seen. The Forth contains several islands, of which the chief are Inchgarvie, Inchcolm, Inchkeith, the Bass, and the isle of May. Light-houses are erected on Inchkeith and on the Isle of May; and the ruins of castles or religious houses appear on all the islands. The towns connected with the river, though they, in general, drive a brisk trade, are principally small; for, excepting Stirling, Alloa, and Leith, few of them contain 3000 inhabitants. Batteries have been erected on different parts of the banks, as also on the island of Inchcolm, for the purpose of protecting the channel. In the year 1774 it was proposed to render the Forth navigable from Stirling bridge to Gartmore, and to cut a canal in a straight line from Stirling to Alloa, whereby the navigation would be shortened from twenty-four miles to six. At a later period, namely, in 1806, a project was entertained of excavating a tunnel under the bed of the river, to obviate the interruption which passengers experience at the two ferries, and elsewhere, from occasional storms; but, after an elaborate survey, the plan was abandoned. FORTIFICATION. FORTIFICATION. The origin of fortification was doubtless that principle of rapacity, which has influenced too many of mankind in all ages and nations to invade the rights and properties of those whom they considered weak or defenceless. In the first ages of the world men were dispersed over the earth in separate families, as appears in the records of the Jews and Scythians, and they wandered from place to place in search of pasture for their cattle. But families soon became numerous, and formed large communities which settled in one place; even before the deluge the earth was filled with violence,' and towns and cities arose. It was now found necessary, for the common security, to surround these towns with walls, and the first, of course, were of the simplest construction; they were single, and perhaps perforated. Then they were built of more solid materials; the best arts of masonry were here called into exercise: they afforded sufficient space for the defenders to use them as stations for attack, and they were crowned by other and smaller works, through which they discharged missiles. Long before Rome was founded, the ancient Grecians used brick, and rubble stone, with which they built a vast wall, joining Mount Hymettus to the city of Athens. The Babylonian walls, built by Semiramis, or, as others state, by Belus, were thirty-two feet thick, and 100 feet high, with towers ten feet higher built upon them, cemented with bitumen or asphaltus. Those of Jerusalem seem to have come but little short of them, since, in the siege by Titus, all the Roman batteringrams, joined with Roman art and courage, could remove but four stones out of the tower of Antonia in the assault of a whole night. The square towers at first used would suffi ciently protect every part of the wall, adjacen to the sides of these towers. But, as there al ways remained one of the faces of the towers which fronted the field that could not be seen from any other part, the circular form was early preferred. This had also the recommendation of presenting a better resistance to battering engines. Still there remained parts of these towers unseen and incapable of being defended; which caused a second change in their figure, i. e. they made them square as before; but, instead of presenting a face to the field as formerly, they presented an angle, the origin of our modern bastion; and thus was effected such a disposition of the works, that no part could be attacked without being seen or defended from some other part. Ditches were added; and thus remained long stationary the art of fortification: indeed until the invention of that terrible assailant gunpowder. This entirely changed the mode of attack, and by consequence that of defence. In the history of fortification we find this obvious division, and we need not take back the modern reader beyond the period of this celebrated invention. When the besiegers began regularly to use artillery, it became requisite that the besieged should also employ it; and, to furnish room for this, a rampart was first raised behind and close to the main wall of fortresses: the towers were enlarged; and the smaller walls were thickened by parapets of earth behind, so as to secure the besieged from the fire of the enemy. For a length of time fortified towns were placed, by these means, in a situation to take their full advantage of the new art of war. Sieges were by no means diminished in their ordinary length: a wall of Magdebourg is recorded to have received 1550 cannon-shot, in the early part of the seventeenth century, without injury to it. If the siege of an important place was not early successful, it generally terminated in the loss of the major part of those who assaulted it. But the great modern proficient in this art, M. Vauban, now appeared, and effected at the end of the seventeenth century a complete revolution in it. He invented a method of attack, against which no mode of defence hitherto adopted has been able finally to stand; and though, during the latter part of his life, he applied his great talents also to a system of defence, upon which Coehorn, Cormontaingne, and others as we shall see have improved, nothing has as yet fully counteracted the mode of ricochet firing introduced by this celebrated commander at the siege of Ath. We shall not fail, in the sketch of this art that follows, to include every principal suggestion that has been made on this subject, and, among others, the plan of M. Carnot, so justly celebrated for his mathematical skill and military talents. But we have completely satisfied ourselves that the vertical fire on which he mainly relies is a chimera. Modern fortification treats of the plan.of defence now used, i. e. turning the walls into ramparts, and square and round towers into bastions, defended by numerous outworks; all which are made so solid that they cannot be beaten down, but by the continual fire of batteries. These bastions at first were small, and at a great dis tance from each other, as are those still to be seen and faces short. at Antwerp, their gorges narrow, and their flanks then, and for some time after the introduction For the invariable practice of them, was to attack the curtains and not the faces of the bastions. But since that time they have been considerably improved and enlarged, and are now arrived to that degree of strength, that it has been a received opinion, that the art of fortification is at its height, and incapable of being carried to greater perfection. This, however, Mr. Glenie, p. 9, Military Construction, disputes, and M. Carnot seemed resolved, a few years since, to confirm his opinions as to all past methods. applied to the besieging and taking fortified Offensive fortification is a term improperly places; it is said further to teach a general how to take all advantages for his troops; the manner a regular or irregular siege, according as circumof encamping, and method of carrying on either propriety be called the war of sieges. See stances may direct. It may with much greater SIEGES. under the terms regular and irregular. Fortification has been sometimes treated of according to the rules of art, and is particularly Regular fortification is that which is erected applied to a construction made from a figure or polygon, which has all its sides and angles equal. The flanked or salient angles in such a fortification are equal to one another, equally distant distance of about that of serious musket shot from one another, and are each of them at the gular fortification having the flanked angles, as from the flanks which defend it. For an irrealso the flanks and lines of defence, unequal, may be constructed from the sides of a regular polygon, as well as from those of an irregular polygon, by drawing the perpendiculars to the regular polygon from points different from those of their bisections. See Glenie's General Rule for Irregular Construction. that where the sides and angles are not uniform, Irregular fortification, on the contrary, is equi-distant, or equal; which is owing to the irregularity of the ground, valleys, rivers, hills, &c. and irregular works. The position of waters, Most fortifications are a mixture of regular hills, and other principal geographical features and various other considerations induce the of a site of ground, previous plans adopted, ablest engineer to be content with arriving only ticle, therefore, we shall pursue the main divisions at the utmost practical regularity. In this arof permanent and field fortification, as embracing all the principal topics we need discuss; and shall present under each a brief sketch of the most approved systems from that of M. Vauban downwards. We shall subjoin a few observations on the mode of attacking fortified places. PART I. OF PERMANENT FORTIFICATIONS. SECT. I.-M. VAUBAN'S FIRST SYSTEM. M. Vauban was clearly indebted to his predecesdefinitions and dispositions, especially in his first sor in this art, the count de Pagan, for his general system. The former has the same divisions of the art into little, mean, and great fortifications, &c. But his line of defence was too long to allow the musquetry fire of the flanks to bear properly, and his ravelins were too small. The large size of his orillons was also objectionable, and the faces of his cavaliers were not flanked. Vauban also materially improved his covert way. His first system adopted, as we said, Pagan's divisions of little, mean, and great fortification; by the first he intended the construction of citadels; by mean fortification, that of all sorts of towns; and by great, that of particular and important places. We shall give the construction of the mean as being most useful; and refer to the table hereafter inserted for those dimensions which are different in other fortifications. Inscribe in a circle a polygon of as many sides as the fortification is designed to have fronts; let AB, fig. 1, FORTIFICATION, plate I. be one of the sides of half an hexagon, which bisect by the perpendicular CD; divide half of it AC into nine equal parts, and one of these into ten others; then these divisions will serve as a scale to construct all parts of the fortification, and each of them is supposed to be a toise or fathom, that is six French feet; and, therefore, the whole side A B is supposed to be 180 toises. As the dividing a line into so many equal parts is very troublesome, it is much easier to have a scale of equal parts by which the works may be constructed. If, therefore, in this case, the radius is taken equal to 180 toises, and the circle described with that radius be divided into six equal parts, or the radius be carried six times round, we shall have an hexagon inscribed; A B being bisected by the perpendicular C D as before, set off thirty toises from C to D, and draw the indefinite lines ADG, BDF; in which take the parts A E, BH, each equal to fifty toises; from the centre E describe an are through the point H, meeting AD in G, and from the centre H describe an are through the point E, meeting BD in F; or, which is the same, make each of the lines EG, HF, equal to the distance E H; then the lines joining the points A, B, F, G, H, B, will be the principal or outline of the front. If the same construction be performed on the other sides of the polygon, we shall have the principal or outline of the whole fortification. If, with a radius of twenty toises, there be described circular arcs, from the angular points, B,A, M, T, and lines drawn from the opposite angles, E, H, &c., so as to touch these arcs, their parts a b, bc, &c., together with these arcs, will represent the outline of the ditch. It will be now necessary to attend to the following Definition of Terms: -1. The part, FEAL N, is called the bastion. 2. A E, AL, the faces of the bastion. 3. E F, LN, the flanks. 4. FG, the curtain. 5. FN, the gorge of the bastion. 6. AG, BF, the lines of defence. 7. AB, the exterior side of the polygon. 8. CD, the perpendicular. 9. Any line, which divides a work into two equal parts, is called the capital of that work. 10. ab C, the counterscarp of the ditch. 11. A, M, the flanked angles. 12. H, E, L, the angles of the shoulder, or the shoulder only. 13. G, F, N, the angles of the flank. 14. Any angle whose point turns from the place is called a saliunt angle, such as AM: and any angle whose point turns towards the place, reentering angle, such as b, F, N. 15. If two lines be drawn parallel to the principal or outline, the one at three toises distance, and the other at eight from it; then the space yr included between the principal one and that farthest distant, is called the rampart. And the space r, contained by the principal line, and that near to it, and which is generally stained black, is called the parapet. 16. There is a fine line drawn within four feet of the parapet, which expresses a step called banquette. N. B. All works have a parapet of three toises thick, and a rampart of eight to ten, besides their slopes. 17. The rampart is elevated more or less above the level of the place, from ten to twenty feet, according to the nature of the ground and the particular constructions of engineers. L 18. The parapet is a part of the rampart elevated from six to seven feet and a half above the rest, in order to cover the troops which are drawn up there from the fire of the enemy in a siege; and the banquette is two or three feet higher than the rampart, or about four feet lower than the parapet; so that when the troops stand upon it, they may just be able to fire over the parapet. 19. The body of the place, is all that which is contained within the first rampart; for which reason it is often said to construct the body of the place; which means, properly, the construction of the bastions and curtains. 20. All the works which are constructed beyond the ditch before the body of the place are called outworks. M. Vauban gives the following Table of Dimensions: Sides of polygons. 80 90 100 110 120 130 140 150 160 170 180 190 200 260 Perpendiculars.. 10 11 12 14 15 16 160 170 20 21 22 23 25 30 31 25 32 |