them, and make a kind of step in the line throughout its course. They have been the great desideratum in canal-making among the moderns, as by the making of which, waters have been pent up in the reaches between them, supplying the means of navigation through high and low lands, from one part of the kingdom to another. In setting out a lock care ought to be taken to get their falls as equal as possible, and this can only be done by the previous care taken in adjusting the summit-level of the canal. The lock comprises of itself a chamber and two pairs of gates; the former is made of length and width adequate to admit one or more boats at a time either in ascending or descending the canal; this is effected by letting the water out of the chamber; if it be ascending, by opening the lower gates: but it is not usual to keep the lower gates of a lock shut, so that a boat or boats coming up the canal can be immediately towed into the lock, which, when in this state, is said to be empty, although it contains as much water at least as is in the lower reach of the canal; when boats have thus entered the lock, the lower gates are loosened, and the paddles of the upper gates are gradually raised, which admit the water to rush into the chamber of the lock: the velocity of the stream soon closes completely the lower doors: and when they are shut, the upper gates are regularly opened till the water has completely filled the lock, which it does in a very short time, and becomes at rest between the lower gates and the upper reach of the canal. The tolls being paid to the overseer of the locks, the boats are towed out, and if no others are waiting to descend the canal, the lower gates are opened and the upper ones are again closed, when the lock empties itself and regains its former state It will be perceived, that the upper line of the canal will lose its waters in proportion to the working of the locks, hence it becomes desirable to make them as small as possible; and it is also of importance that they should be of the same size throughout the line of the canal, that the loss at each lock may be equal, in which case the supply to be anticipated may be correctly ascertained. In the approaches to all locks, both above and below them, there should be made resting places, provided with oaken piles driven down close to the embankments, which they may be made to support, with their upper ends crossed by strong whaling boards of oak, bolted with iron bolts to the heads of the piles. If the whaling boards have large iron rings fixed in them, the bargemen will have the advantage of fastening their barge to them during the time they may have to wait for passing the lock. Twenty-five-ton boats, according to Mr. Fulton, consume, in ascending a lock of eight feet rise, 163 tons of water, and in descending the same, 103 tons; now, if such a datum be correct, it would enable an engineer to make very accurate calculations of the loss in water in all his several locks upon the proposed line of the canal; that more water should be lost by ascending a lock than in descending, appears probable, although the same space requires filling in both cases; but it does not appear so obvious, how so great a difference as sixty tons can take place; but this

could be settled by a reference to the draft of the boat employed, knowing that it displaces as much water as its cubical contents, if it be laden adequately: these are all investigations pressing on the consideration of the engineer. Plate I. fig. 4, is the ground plan of a lock; A, A, A, A, strong piers of masonry or brickwork bonded into the wing walls, F, F, F, F; B the chamber of the lock; C, C, the gates; D, D, the side walls of the chamber; E, E, the vertical syphons to take off the superfluous water from the head of the lock. The building of a lock requires the utmost attention in all its constructive parts; when the form is traced out, and the top soil removed, the ground should be proved to ascertain its nature. and if soft and porous the foundations should be piled all through, the tops of the piling should be regularly sawn down and planked with oak of not less than three inches in thickness; which planking will form the platform on which the walls are to stand; in forming the foundation wall, some attention must be had to the inverted arch, which composes the flooring of the chamber of the lock. See section, plate I. fig. 5. The inverted arch, K, should be formed of hewn stone of small curvature; its thickness in the centre about two-thirds of that of its spring; the joints of the voissoirs are also all traced from the centre of curvature of the arch, and also the springing line; the bottom of the arch should lie upon a good lining of puddle, and the joints of the stones should be well cemented so as to be watertight; the abutments, or bottom of the side-walls of the chamber, should be of twice the thickness to what they are above, and should rack-back in ascending; linings of puddle will be judiciously employed in covering the earth of the embankment behind the chamber walls. Lock walls are usually parallel to each other, and the lock varying in width from fourteen to eighteen feet, and in length from seventy to ninety feet. The plan, (plate I. fig. 4) is conformable to this proportion: the side walls of the chamber batter back as they approach the coping at their tops, about six inches from their perpendicular; and if they were made to have a slight curvature in their height, they would be much stronger for it. In building the piers, as shown in the plan at A, it is necessary to observe, that they should be out of large blocks neatly worked and hollowed out to admit of the gates working in them. The wing walls should be raised in a similar way to the walls of the lock, except that no provision is required in them to receive an inverted arch, as the approach or breast of the lock requires no such protection. Apertures should be made through the side walls of the wings to admit of the superfluous water entering the culvert through the syphon, as seen in the plan at E, and in the section by the dotted lines; and if the culvert be bent in its course, this water, if it be required, may be made to enter the chamber of the lock, a circumstance of some importance when there is a scarcity of water. When the lock is so far formed, and its syphons and culverts made, the lock sills should be put down; they consist in forcing into the ground, at the two ends of the bottom of the chamber of the lock, a row of narrow piles extending from one side to the other:

they should be driven as close together as possible, and, when so driven, they will form a chain across the two ends of the lock; in this state their tops should be sawn off quite ievel and smooth, and a sheeting, as it is called, of good oak or cast iron should be bolted on them with iron bolts, to form the lock sill for the gates to move upon, and also to protect the approaches to the lock. In the wing walls there should be inserted in their progress some large blocks of stone, projecting somewhat from the face of the ashlering of the wall, and called bumping stones, for the boats to strike against as they enter the approaches to the lock. The lock wails and those of the wings should be coped with granite, firmly fixed and cramped. The gates C, C, are made in two parts, aud form at their meeting an obtuse angle; they move in the hollow quoin stones, and by means of iron joggles fitted into sockets, which should be let into the hollow quoin stones of the piers A. Plate I. fig. 5, is the section of the lock; GG the granite coping; HH the top of the sloping side walls; II the base of the sloping wall; K the inverted arch at the bottom of the lock; L, L, the syphons of masonry or cast iron, worked up in the wing walls at the head of the lock to carry off the overflowing water; M M the culvert or drain; Na cesspool to receive any matter carried by the water through the culvert, to prevent its overflowing or stopping up; 0,0, the horizontal apertures in the wing walls communicating with the syphons L, L. These apertures should be made a few inches below the top-water level, and if formed in stone composed of a large block perforated quite through, and the size of the opening regulated by the quantity of water to be discharged, but they might be formed of cast iron with the best success. It will be unnecessary to add, that all the work of a lock requires the materials and workmanship of the very best quality, and the engineer will more develope his constructive talent in adjusting its form and the mode of putting the materials of which it is to be formed together, than he can in any other of the arrangements arising out of the works connected with canal construction. Plate I. fig. 6, is a pair of lock gates: they are shown to a larger scale than the plan or section of the lock which accompanies them, in order to exhibit the mode of their framing more obviously. They should be made of good seasoned oak, free from vents or sap, and are composed of several pieces known by the following designations: P, P, the balance beams; Q,Q,Q,Q, the rails; R,R,R,R, the vertical stiles; S,S,S,S, the braces; T, T, the paddle holes; and they are finally covered by oak planking, grooved into the bottom rail and the balance beam at top, the joints of which are also rebated, or grooved and tongued. In some lock gates the boarding is fitted in diagonally, in which case the braces may be dispensed with; but greater strength can be accomplished by framing them as shown in fig. 6, and there will be also a saving of wood. The scantling of the timber in the lock gates may be varied to meet the pressure they may have to sustain, but it will be indiscreet to attempt making them too light. The rails Q,Q,Q,Q, should not be less for ordinary purposes

than ten inches in depth and six inches and a half in thickness, and this would be a very good scantling for the stiles R,R,R,R; and, supposing the planking to be two inches and a half, the cross braces S,S,S,S, woubl be properly proportioned to be left seven inches on the face by four inches in thickness. The balance beam, which also forms the top rail of the gates may be made somewhat larger in scantling than the lower framing, and the stiles might be framed into it. If this beam was made at its smallest end eight inches square, and at its opposite end ten inches and a half, it would act as a good balance to the gates, and give them great strength. The boarding should be flush on the upper side, and well spiked to the middle rail and also the braces. The projecting edges on the inside of the gates of the rails and braces should be splayed downwards in order to the water running quickly off them, and the balance beam should be weathered on its top edge. The iron work to the gates consists merely of its hinges, the sockets of which are previously inserted in the stone quoins of the wing walls. In fixing the iron work it should be made to lap quite over the outside stiles and be bolted with iron bolts, with nuts, and screws. Sometimes the bottom of the gates is shod by plates of cast iron, and these plates are also continued up the centre stiles, and it must add great additional strength to the framing. Some have recommended the giving to the external form of loca gates a small degree of curvature, supposing, no doubt, that by such curvature they would give additional strength to the gates; but the momentum of form would be more than surpassed by the loss of strength in the materials, as cutting wood purposely circular so crosses its grain as to leave it with very little strength at its joining, besides a double expense in the actual cost of the gates themselves. It has been deemed proper to notice this circumstance to prevent theoretical engineers from disappointing themselves in the application of curvatures to wooden framings in which strength is sought; for it will lose strength by such curvature in a ratio of greater proportion than it can possibly gain it, which will be easily discovered by an inspection of the state of the fibre in circular wood framing.

The paddle holes T,T, are small openings left in each gate, generally about twenty inches square, and to which a small door is fitted; they are found of the greatest utility in preventing a too sudden swell in filling the chamber of the lock, and also in removing a portion of the pressure of the water from the gates when they are required to be opened in letting a boat descend the canal. They are so adjusted to the boarding of the gates that they can be easily raised or lowered by the overseer of the locks. This is done by supplying a guard bar to the top of the gate, which is operated upon by a rack and pinion, that has the effect of lowering or raising the paddle-doors at pleasure. Amidst the considerations arising out of the detail of a lock, it will be proper to notice that in long lines, and on which there is great traffic, sometimes there arises too great a scarcity of water to supply the upper reaches, in consequence of which many expedients have been recommended, and some have been ha i

recourse to, to avoid the inconvenience. On the Grand Junction Canal reservoirs have been made, to collect the waste water of the lockage, to which a steam engine has been erected, which pumps the water, after having emptied itself into the reservoir, back again into that part of the canal from which it has been lost. And there has been also another expedient recommended to remove the same inconvenience, under the designation of side ponds. A side pond or ponds consist in forming, on the right and left of the chamber of the lock, a number of projecting cisterns, varied gradually in their elevation, beginning a small distance from the bottom, at the lower end of the lock, and stepping up to the upper end or head of the lock, provided with paddle doors. These cisterns, in capacity, are made so as to contain all the water, or nearly so, that passes the upper gates on a boat or boats, ascending or descending the lock. When the chamber of the lock is full, the highest paddledoors are opened, and the water empties itself into the cisterns right and left, and so on till all the cisterns are full, observing to shut the doors of the cisterns as the water retires in the lock; and this is done till the chamber of the lock is so emptied as to allow of its lower gates being opened. When the boat ascends or descends the canal, it will be seen by this plan that very little waste or consumption of water by lockage can accrue, except that which must necessarily be so by allowing a sufficient quantity in the bottom of the lock to keep the boat afloat and level with the lower level of the water of the canal. Mr. Playfair, an architect who gave rise to this invention, obtained a patent for it in July 1791; the specification of which may be seen in the Repertory, vol. iii. p. 303. In the patent the application is supposed to be employed under the following circumstances, for example: a lock is supposed to be constructed twelve feet deep, sixty feet long, and six feet wide,' and it is calculated that the quantity of water required to fill such a lock, to enable it to pass a boat is 4320 cubic feet, and in ascertaining what water may be necessary for supplying the canal, allowing for waste by evaporation and soakage, it is found (according to the number of boats that may be expected to pass), that there will not be above 800 cubic feet for each; and hence, it is added, it will be necessary to save five-sixths of the whole; to do which ten cisterns are directed to be made, each of which must be one foot deep, and each have a surface of 360 feet superficial. The aperture or entrance to the lowest cistern must be one foot above the level of the water in the lower part of the canal, and eleven feet under the level of the high water; the second cistern two feet above the level of low water, and the third three feet, and so on. It has been deemed desirable to quote so much of Mr. Playfair's specification to illustrate the application of side ponds, and it cannot fail of producing a conviction of their great utility to canal locks, whenever there is reason to anticipate a want of water, as generally the greatest source of its loss is by the lockage. By the application of side ponds, this inconvenience may be, in a

great measure, superseded, and at no great additional expense to the works.

BASINS. These are formed in all towns to which the canal has a communication, in order to make a commodious place for the boats to unload their cargoes and to take in fresh ones. Their size varies according to the importance of the town, or to the trade carried on at it. Surrounding the basins, a spacious area of ground should be gotten to admit of warehouses, cranes, toll-houses, and other stowage for goods, being built with adequate space for all the vehicles employed in the trade to receive a ready transit and exit in their business about the basin. Convenient approaches should be formed to the wharfs for carts, and also roads with the shortest and readiest way of their departing when laden or unladen. The toll-house should be placed near the principal entrance to the basin, and should consist of two or more rooms for the keeper, with an office and weighing bridge. In the office should be written, in legible characters, the different tonnage and other charges to be collected, by the keeper, of the persons who trade on or about the basin of the canal. The construction of a basin consists in forming a chamber or head, sufficiently capacious to admit of boats resting in it, with room to unload and retire. The size, as before observed, must be commensurate to the number of boats expected at the basin. The embankments should be quite level with the wharfs, on contiguous ground, and about one foot higher than top-water level. The termination of the basin is generally made to form a bow or semi-circle on the plan. All the enbankments are faced by walls of masonry or brick, and the tops should be coped with large blocks of granite. In raising the facings to a basin, the same precautions should be had recourse to which have been previously recommended in the construction of the chamber of a lock; for instar.ce, if a soft and porous soil, piling must be employed in the foundations, with a covering of oaken plank, and the earth enbankment must be covered with a puddle-lining previously to raising the walls of the facing. The walls should be of great thickness at the bottom, racking back on their outsides and battering over on their insides; and their slope will require to be in proportion and parallel to the canal embankment, in order to the general surface of the lines approximating together. In carrying up the facing walls, nevertheless, a few niches of curvature to produce a swell internally in their height, would add greatly to their strength in resisting pressure. A basin must also be provided with a weir, syphon, or waste gate, in order to discharge the water constantly flowing into it from the upper reaches of the canal by waste of lockage, &c. If it be determined to discharge this water by a weir or syphon (perhaps more than one may be necessary), culverts should be made to receive the water and discharge it at the most convenient places; these culverts require executing in the most substantial manner to prevent their blowing up by the weight of water they may be called on to discharge. They should have also some cesspools in their course to receive any solid or other