broad oak-rail on their tops, splayed away to receive the two end-rails of the platform of the bridge. B, B, the embankments to the bridge. G the platform of the bridge. E the vertical posts, fixed on the bank of the canal, a little behind the hinges of the bridge; on the top of these posts are two long tapering pieces F, called the balance-beams, which turn up by means of hinges near their middle, the small ends being connected with the platform of the bridge by means of chains at their further end, and which the heavy ends of the balance-beams are made to counterpoise. When such a bridge is required to be raised for a boat to pass it, it is necessary to take hold of the chains appended to the large ends of the balance-beams, which, being only just counterpoised, are easily pulled up, and when raised, the chains are hooked to the upright posts, to prevent accidents, and the bridge remains suspended. Bridges, called swivel-bridges, are sometimes made use of on canals; they are much more expensive, and may be easily put out of order by the want of attention in using them; they consist of a platform of wood covered with planks, which is made about half as long again as is required for the bridge: one end of the platform is made light and the other heavy, for the purpose of counterpoise, and the additional weight to the heavy end is produced by means of stowing large stones or pigs of iron at it, so that the bridge, when in its place, or at rest, may attain an equilibrium. At a point of about onefth of its length from the heavy end, a round plate is fixed, with an iron axis or pin standing up to enter a hole in the platform, which is prepared to receive it; and on this pin the bridge is suspended, and which is also its centre of motion; and, in order to prevent impediments in turning the bridge round, a number of iron balls, two inches and a half or three inches in diameter, are let into the round plate, both above and below, to act as rollers to lessen the friction on the plates. The banks are formed with a kind of recess to receive the bridge when moved from across the canal. The two ends of the platform, in order to allow of this horizontal motion, are struck into two arcs, the centres of which are the axis or pin in the centre of the friction-plates. At Brussels, and in other parts of Flanders, they have a kind of drawing-bridges composed wholly of iron: they are made somewhat similar to our drawing-bridges, except that they are raised by a cast-iron wheel with cogs; this wheel is about three feet in diameter, and is firmly fixed in the bank, and, by being turned by a handle, raises the platform. It takes up much less room than our drawing or swivelbridges, and answers every purpose. There are nine or ten to be seen at Brussels, constantly in motion, as ships or craft are passing up the canal. Some of these iron bridges are cut in two in the centre, with wheels in each bank, so that by working the wheels a few degrees a ship may pass the canal, by its masts entering through the space left by raising the two platforms. This kind of bridges are made necessary from the great width of the canals in comparison of ours. The occupation bridge, at Rotterdam, is of this last description, and consists of two separate segments, each supported independently; and, when up for the craft to pass, a void is made between the meetings of the segments by which the masts enter. The convenience of such bridges is obvious, as the towing can go on without removing the line; foot passengers also can pass by the bridge while in motion, as the opening between the meetings is never so wide but a person may step over it. The canals in Flanders, Holland, and every part of France abound in ingenious light bridges: their drawing-bridges are on a scale the engineers of this country have not an idea: there are some over streams 120 feet wide, moved by wheels with more ease than our little ones of twenty feet are by balance-beams. The bridges of masonry on canals consist of one arch generally, with the difference only, of making its span as much more than the canal as to admit a towing-path under it. The towingpaths are made commonly on the lower side of the canal. The bridges over the canal at Paddington have towing-paths on both sides, and this, when there is room to do it, is a great convenience; besides adding additional strength to the abutments of the bridge. Guard-rails should be fixed to the wings and approaches of the bridge, and also to the embankments under the bridge, to keep the boats from damaging the works. Docks, from at first being only a simple contrivance at arsenals for the purpose of building or repairing a single ship, have extended themselves to a magnitude in capacity competent to contain whole fleets. In splendor the docks created in London, and at many of the out-ports, are a monument which excel the famous port Pireus in Greece, or Alexandria in Egypt, as much, or more, than we have excelled the Greeks and Romans in all the facilities to navigation, and the grandeur of our naval architecture. The Greeks and Romans no doubt have far surpassed us in all the elegancies of taste and invention in the fine arts: in these arts they have combined and given form to matter, which could have resulted only from a higher degree of feeling, united to juster notions of nature, than the coldness of our climate and habits can perceive, or hardly give power to copy. But if we are behind in the fine arts, which, as mere copyists, we must be contented to be: in supplying all manner of facilities to commerce (in which we excel all nations, ancient and modern), in erecting the immense docks and warehouses inland, which we have done to receive and house safely the produce of the world, and to an extent adequate for that purpose, we have formed a monument at once of our genius, wealth, and skill, which will be as famous in the page of science as the monuments of Athens and Rome are now in the volume of the arts. A dock consists in the first place of a basin commensurate to its intended purpose. A canal communicates therewith, supplied with an entrance-lock and gates. The building of a dock embraces all the skill applied to buildings in water. The embankments are to be traced out in the same manner as is done for canal lines, by setting up bench marks to indicate the plan upon the ground. The whole of the embankments of a dock are supported by walls of masonry or brick-work; and, as the docks for ships require a great draught of water, they must be made in depth adequate to allow of ships of burden riding in them in safety in consequence of which the depth of the docks must be great in comparison of canals. The London docks are upwards of twenty feet deep. In raising the walls on the sides of such reservoirs (as they may be called), it will be obvious that the greatest care must be taken. The foundations of walls for works of this nature should be formed of double or even treble rows of piles; and the inside row, which runs parallel to the embankment, should be grooved on their opposite sides, and be forced into the ground as close together as possible; and, after being so driven, stiles of yellow fir wrought should be driven down into the groove made in each pile, so that the whole inside piling may form a continued chain throughout its whole extent. The planking to form the platform for the wall, should be all scorched previously to being laid upon the heads of the piling, and the joints or meetings of the planking should be crossed or dove-tailed together. If the walls be to be built of bricks, care should be taken to have them of the best quality, and as square and even as can be; and, in order to strengthen their bond in the wall, tiers of Dundee granite should occasionally be incorporated. The walls themselves should be for a height of twenty feet, of fifteen bricks in thickness at the bottom, on planking rackingback on the side next the earth embankment, and battering on the inside of the dock, with tiers of bond of Dundee granite at every twentieth course throughout the height. The slope of the wall should be in proportion to a scale before recited for lock-walls of canals; and a curvature or swell should be formed in the inside section of the wall in the proportion of two inches to every six feet: the walls should, finally, finish at their tops to four bricks in thickness, and the whole be crowned by blocks of Dundee or other granite, as a coping. The mortar used for these kinds of works ought to be particularly looked after, in order to its being of good quality, or very little solidity will result to the work. The ground stone lime with washed siliceous earth, the former as fresh as possible, is the most likely to prove a good cement. The Roman cement, or Parker's, is of great utility in some parts of dock-works. The docks, as Helvoetsluys, are formed with clinkers cemented by Dutch tarras : it has tiers of bond traversing at every four feet, vertically, composed of black marble neatly wrought, which in every other stone goes quite through the wall, and the top of the wall is coped with large slabs of the same marble. The work of these docks from the smallness of the bricks (about six inches long, three in width, and one and a half inch in thickness), and the joint having very little cement in it, makes the whole appear uncommonly neat, and which is not less solid. These docks are about eighteen feet perpendicular in depth, the side slopes from their base five feet eight inches. The opposite end to the canal of communication is formed into a bow or crescent. The walls all round this dock have a slight swell or curvature in their height. The canal leading to a dock generally branches out of its side, and is walled in a similar manner to the dock itself, and at its upper end or head is contracted by the walls being bent into a circular shape till they meet or intersect the wing walls of the lower end of the chamber of the lock. The lock is the pound or chamber through which the ship or ships enter from the sea or river to which the dock is contiguous: to docks of consequence the locks are made from thirty to forty feet wide, about eighteen feet deep, and 150 feet long. They have gates at both ends, which require the utmost skill in contriving them for tidal-rivers. The bottom of the lock is formed by an inverted arch of masonry in a similar manner to that of canal-locks, except on a larger scale, and of course of a more ponderous nature. The walls are raised battering similar to those of the docks, and, finally, coped at their tops, weirs, syphons, waste-gates, and culverts, are all of use to dock-work, and must be called in as the nature of the situation requires them. Wherever it is intended to form docks a large site of ground should be selected, in order to admit of abundance of room for all kinds of stowage and warehouses being built thereon; for without abundance of room very little accommodation can be expected by creating docks on such sites. The necessity of room in such concerns will more obviously appear by considering the space occupied by the docks themselves in the three great concerns now effected in London. See Docks. After docks, there is another appendage equally flowing from our great maritime power, and which consists in creating artificial piers or break-waters, projecting into the sea for the purpose of giving security to vessels at anchor against the violence of winds and currents, at such places where it has been deemed eligibl to form ports or places for ships to anchor at. The late Mr. Smeaton was the first engineer amongst us who embraced, in the boldness of his genius, the requisite science for such undertakings, which has had the effect of establishing his reputation beyond the chance of a failure. Every part of the country exhibits something of his contrivance, either in canals, bridges, harbours, or machinery; and, of course, every thing from such authority is of importance, inasmuch as it may teach those who have now to follow him how true fame may be acquired and become imperishable. It is extremely difficult to give precise ideas for buildings connected with sea-ports and their harbours; for in such places the natural vicissitudes are what offer the impediments, and they must be met, in the various ways in which they present themselves, by the skill and enterprise of him to whom such buildings may be confided. There have been piers or break-waters erected at many of our ports extending an immense distance out into the sea; for instance, at Sheerness, Ramsgate, &c.: and there have been also several on the opposite coast; the one at Cherbourg is pre-eminent for boldness and genius. See CHERBOURG. Some account of Mr. Bentham's plan, adopted at Sheerness Pier, will be seen under the head of Buildings in Water, in our article MASONRY. The great national work in Plymouth Sound is perhaps on a scale far beyond any thing of the kind ever set about in the world before. We have happily to record its completion. See our article PLYMOUTH. The erection of beacons and light-houses is a branch of the royal prerogative. The king has the exclusive power, by commission under his great seal. He can order them to be erected, not only upon the royal demesnes, but upon the lands of the subject; which power of the crown is usually vested, by letters patent, in the office of the lord high admiral. And if the owners of the land, or any other person, shall destroy them or take them down, he shall forfeit and pay £100, and in case of inability to pay it, be ipso facto outlawed. By statute, 8 Eliz. c. 13, the corporation of the Trinity House were empowered to set up any beacons or sea-marks wherever they might think them necessary, and in them now almost the whole business, respecting the management of beacons, light-houses, &c., is vested. The beacon is a simple contrivance, of very early origin, as we find frequent mention made of such objects, not only in the Scriptures, but in ancient history, and particularly in the early part of our own. Beacons consisted chiefly in erecting on high places marks whereon were fixed barrels containing pitch or other combustible matter, which, by night operated as a warning, by being lighted, and by day they gave notice of the approach of an enemy, by the volumes of smoke emitted. By the discovery of gunpowder, such expedients have been discontinued; as rockets and other contrivances are found to answer the purpose infinitely better. A light-house is a different kind of building to a beacon, inasmuch as it requires greater constructive excellence in the erection. Its use is chiefly to warn mariners, when navigating in the night, from approaching too near certain parts of the coast known as dangerous, either by rocks, shoals, or currents; and it is also a land-mark by day. These structures are of great national importance, and, as such, cannot receive too much attention, either in forming them in the most substantial manner, or supplying them with the best lights. A lighthouse, as now erected, consists of an upright shaft of masonry or brick-work, built hollow in the inside, in which are winding stairs leading to its summit. The top is generally surmounted by a cornice of stone, with a space left suffic'ently large to admit a single person safely to walk round upon it. On the top of the whole fabric is erected a lantern, often from twelve to fourteen feet high, and six or seven feet in diameter, in the inside of which is a frame, to which are suspended, in various angles, and in as many elevations, a number of lamps and reflectors; the lamps vary from ten to as many as fifteen in some light-houses. Such a body of light and that reflected with the greatest power on an immense height, as they most frequently are, creates a surprising effect, which is discovered at sea by mariners when many leagues off, and which enables them to shape their course accordingly. The Eddystone light-house was erected by the late Mr. Smeaton, and in this is employed, perhaps, more ability than in any similar structure in existence, arising out of the difficulty of erecting any thing in such a perilous situation. Mr. Winstanley began a light-house on the Eddystone rock in 1696, which he was four years in finishing, which was formed wholly of wood. The following notices respecting his operations may not be unacceptable. The first summer was spent by Mr. Winstanley and his people in making twelve large holes in the rock, and fastening as many irons, to hold the future work. In the course of the next summer, a solid body or round pillar, twelve feet high, and fourteen feet in diameter was completed. In the third year it was increased to sixteen feet in diameter from the foundation, and the whole building was raised, which was eighty feet to the vane. In the fourth year, the diameter of the pillar was encompassed in a new work, four feet in thickness, and the building raised forty feet higher when the light was exhibited. This building was formed almost wholly of timber, and it did not meet with any accident till 1703, when standing in need of repair, Mr. Winstanley came to see it; and having been among his friends previously to going off with his workmen, to view the repairs, the danger was intimated to him, and that one day or other the light-house would certainly be overset: he replied, He was so well assured of the strength of his building, he should only wish to be there in the greatest storm that ever blew under the face of the heavens, that he might see what effect it would have on the structure.' Mr. Winstanley was but too amply gratified in his wish; for while he was there with his workmen, that dreadful storm began, which raged the most violently upon the 26th of November, 1703, in the night; and of all the accounts of the kind with which history furnishes us, we have none that exceeded this in Great Britain, or was more injurious or extensive in its devastion. The next morning, November 27, when the violence of the storm had in some measure subsided, so that it could be seen whether the light-house had suffered by it, nothing appeared standing, but, upon a nearer inspection, some of the large irons whereby the works were fixed upon the rock; nor were any of the people, or any of the materials, ever heard of afterwards. The next light-house, built on the Eddystone, was by Mr. Rudyerd: it was finished in 1709, and destroyed by fire in 1755. It was now deemed eligible to erect a superior building, if possible, and one not so likely to meet its destruction, either by the violence of the sea, or the effect of fire, as both the former had been destroyed by one or the other. Mr. Smeaton was employed, and, contrary to the received and popular opinion, that no building could be made to stand except one formed of wood, he showed a contrary design, and boldly projected a lighthouse of stone. He himself says, 'he shall endeavour so to form it and put it together, that, by a similarity of construction, no man shall be able to tell him at what joint it should overset; for if at any given height the uppermost course was then completed safe, it became more safe by another course being laid upon it; and though that upper course were somewhat less in weight, and in the total cohesion of its parts, than the former, yet every course, from the first foundation, was less and less subject to the heavy stroke of the sea."' This building was formed to resist the effect of both wind and water, and these acting on it occasionally in a most tremendous way. The light-house is wholly of cut-masonry, about sixteen feet in diameter at bottom, and diminishing upwards conically; it is seventy-three feet six inches in height, measuring from the rock on which it stands to the top of the cornice. Mr. Smeaton chose a curve for this structure with its concavity turned outwards, and the judiciousness of such a choice is now fully established. From the top of the cornice to the base of the lantern is seven feet six inches, and from thence to the summit of the ball seventeen feet six inches, which, together, make a total height for this structure of ninety-eight feet six inches. See also BELL ROCK LIGHT-House. The form of such buildings has involved considerable intricacy of mathematical investigation. M. La Grange has calculated that a cylinder is the strongest form for resisting flexure, which is contrary to the known fact, and could be only deduced from the intricacy of the investigation. If it were calculated what would be the best form for a wooden column, which to a certain depth was always to remain exposed to the water, it would be found that a cone or pyramid would possess the greatest possible strength for supporting the pressure of the water; and for resisting the wind also, the figure must be made more acute than it would otherwise be necessary for resisting the water only. For withstanding a force which tends to overset the building, the form in which the weight gives the greatest portion of resistance is that of a conoid, or a solid, of which the outline is a parabola concave towards the axis. And for procuring, by means of the weight, the greatest quantity of adhesion of the parts, the form should be cylindrical. To effect with success any works exposed to all the multiplied events arising out of the effects of nature, will require a tedious investigation, which will involve all the skill and foresight of the engineer to whom such works may be confided. The forming of roads is of considerable importance to every well regulated country; and although it has been, perhaps, too much neglected in our own, it is now receiving that attention which its importance requires. We shall devote to the important subject of high roads, a separate article, embracing the latest improveSee ROADS. ments. The origin of iron or rail-roads may be traced back to the year 1680. About that period coal came to be substituted for wood as fuel in London and other places: the consequence was, that at the mines the greatest inconvenience accrued in conveying the coal from them to the ships, as well as immense expense in horses and machinery for the purpose; to remove which, waggon roads were made, consisting of wooden rails or ledges, which the waggons were formed to move upon, from which improvement it was found that a single horse could easily draw a waggon on these rails, which previously required three or more horses to be employed to effect by the common roads; and it was also drawn more quickly, arising fromlaying down the frames upon an easy descent, which was always done. In 1738 this invention was farther improved by substituting cast-iron rails instead of the old wooden ones; but owing to the old fashioned waggons continuing to be employed, which were of too much weight for the cast-iron, they did not completely succeed in this first attempt. However, about the year 1768, a simple contrivance was attempted, which was to make a number of smaller waggons and link them together; and, by thus diffusing the weight of one large waggon into many, the principal cause of the failure in the first instance was removed, because the weight was more divided upon the iron. In 1797 these roads having impressed the minds of intelligent men as of great importance, numerous essays appeared, setting forth their utility, and as many plans for rendering them of permanent construction. See Dr. Anderson's Recreations, Nicholson's Journal, Repertory, &c. &c. Hence cast-iron rail-roads became a second desideratum to canals, excepting only' that the invention is due to Englishmen. After this time the cast-iron rail-ways began to be constructed as branches to canals, and in some places as roads of traffic from one place to another, established upon permanent principles, so as to produce a permanent revenue to the undertakers. In surveying a line to set out a rail-' way upon, it will be necessary, as a preliminary step, to ascertain, as accurately as the nature of the thing admits, the quantity of lading expected to traverse each way upon its line; because in forming the slope or descent, this will be the datum on which to ground a medium for effecting the required purpose most easily. If it should turn out that as much lading is expected one way as the other, with a preponderance at periods only, the railing must in such a case be set out in levels or in lines nearly level, and the ascents and descents made by planes inclined accordingly. Previously to beginning any part of the work, that is of laying the sleepers, &c., for the iron-rails, a rough sketch or section of all the different routes intended to be passed by the rail-way should be made; from which, and a view of the ground, the engineer will be enabled to determine the place, and also the extent of the inclined planes which will be required in passing the steeper parts or the rising ground to which these planes are to be employed: it will always be desirable to get them as short as the site of the place will admit. In tracing out the line of a rail-road, the following method is pursued by our best engineers: they begin at the highest point, using a chain (of 100 links), and also berms, or bench-marks, and targets, as they are called. The chain is stretched out upon the ground, one end being held at the point of the deepest turn, and the other turned round upon the face of the descent, until a point marked by this end is found, which is one link lower than the upper end, or nearly so. The chain is still carried forwards till its hinder end reaches the point last determined. The other end is then moved, and another point is ascertained one link lower than the last, and the operation is so continued, by which a line having the regular descent of one link to each chain will be traced out on the site of the intended railroad. The bench-marks are to be put in at each successive observation to mark the place found, and if it turn out irregular and crooked, the operation must be again repeated till the line appear more regular and without any sudden bends or crooks which must be always removed and made undulating and easy, as it will prevent unnecessary friction in the wheels of the carriages against the ribs of the rails. The railroad when first marked out has a stake or mark set up at every chain in length, and these marks are the guides by which the workmen begin the operation of putting down the roads. When sudden valleys present themselves, approaching to higher ground, it will be necessary so to conduct the line as to cut into the hill at each side, and the cutting from the latter will be useful in raising the road-way of the former. On approaching rivers or brooks which it is determined to pass, it will be necessary to keep up the rail-road to a higher level by embankments, and on passing the water to raise a platform on purpose for it, composed of piers of masonry or columns of iron, with a covering of iron also to receive the rails; or a bridge, similar to an aqueduct bridge, will answer the purpose. Rail-ways may be divided into single and double by the former it is understood that a single road only is to be formed; by the latter, that two or more are to be made for the ready passage of waggons up and down the road. Single roads are generally made, including horse and attendant paths, four yards wide; and double ones vary from six to eight yards wide, exclusive of all the common appendages to such roads of drains, fences, &c. &c. In forming permanent rail-ways stone-sleepers are necessary. These consist of pieces of good sound free-stone, with their upper faces wrought fair, and should weigh from 150 to 200lbs. each, with their ends, which come together wrought smooth, so that the joints may be firm and close. The work of setting the sleepers must commence as soon as the road has received a tolerable surface in point of regularity. In cases in which there has been much making up or embanking the ground, short piles (as shown plate 2, fig 7, B, B,) should be driven down to receive the stone sleepers, taking care to let the head of the pile come exactly under each meeting or joint of the stone-sleeper. In commencing the work of laying down the stones, great exactness will be necessary in order to the iron-rails lying firmly on them; when one of the stone-sleepers is laid in the proper place for one side of the rail-way, and nicely bedded and rammed down, another is to be laid at four feet distance from it, and bedded in a similar way. When these two stones are laid, they will operate as guides for proceeding in laying more stones, right and left, which should be carried forward together. A,A, plate II. fig. 7, represent the stone-sleepers: B, B, the piles or blocks for supporting the sleepers in infirm ground; C, C, the sections for the cast-iron rails. Every tram or rail-road must be provided with passing places; a passing place consists in forming large plates of cast-iron, in such a manner as to admit of common rails being joined to them, and which will allow the waggons traversing the road to pass off into another or adjoin.ag tract. Plate II. fig. 8, shows a passing place for a double rail-road drawn to a quick sweep: buc the turning or passing place need not be of such acuteness in general, but may follow a more obtuse shape, as best suits the nature of the place to be passed. Plate II. fig. 8, represents the plan of the two meeting cast-iron plates, D, D; these plates should be accurately modelled in wood for the founder; and they should be so adjusted as that one model may serve for as many passing places as possible on the line of the proposed road; F, F, shows the joints where the common rails meet the passing ones; E, E, are moveable iron tongues placed in the centre of the passing plate, DD; which allow, by turning them round on a centre, of being removed to either side of the plate to keep the wheels of the waggons in the tract required; so that a waggon may go on either side of the road by putting the tongue in the opposite direction. The side rails are shown at G,G; these consist of common side rails, except only that they must be modelled and founded to the intended shape of the passing place. HH shows the horse-path of the rail-road at the passing place. Plate II. fig. 9, exhibits a single length of a common rail for a road, with its projecting margin, K, to keep the waggon wheels in the tract; as also the grooves, I, I, through the ends or meetings to allow of their being fastened to the stone sleepers. The common method of fastening the cast-iron rails to the stone-sleepers, consists in previously making in the stone an octangular perforation opposite to every joint intended in the cast-iron rails, into which a trunnion of good sound oak is fitted, with the grain of the wood presenting its section uppermost. The perforations to receive the oaken trunnions should be made quite through the stone, in order to prevent the effects of the frost, which, if not through, the water lying in the hole will become frozen, expand, and shiver the stone into pieces. When the iron rails are nicely arranged upon the bearers or sleepers, they are to be fixed down by driving an iron key pointed at its lower end, so as to allow of its being driven into the oaken trunnion; the iron key has a head projecting similar to the letter T: and its lower shaft is made exactly in size to fill the void or groove left in the ends of the iron rails, as shown at I, I, fig. 9. The common cast-iron rails for roads are formed in lengths of about three feet each they are made about four inches wide upon the flat, or that part intended for the wheel of the waggon to move upon, and which is about one inch in thickness, sloped off a little to the horsetract: the projecting rim rises two inches and a half from the flat or bottom of the rail; in its centre forming the segment of a circle projecting |