having been previously determined on, three feet is generally left to be supplied by the puddle-lining. In cutting down the slope, all extraneous matter should be carefully taken away, such as roots of trees and plants; all vermin holes should be well stopped and secured, and indeed every thing which is thought at all likely to disturb the coating about to be added; and when ready it should be worked down quite straight by the excavator's spade, and rendered tight and sound. After so much is done, the lining may be proceeded in, which consists in spreading on a coat of the puddle, varying from seven to twelve inches in thickness, all through the canal line, which is ready to receive it; and when this coat is properly laid, and to the satisfaction of the resident overseer, it should be sprinkled with water, and remain till the following day, when a second coat should be added, and so on, till the coating has assumed the necessary and required thickness; and when done it should be neatly smoothed down, and the water may be let into the canal.

The necessity of particularly attending to the puddle-lining cannot be too much impressed upon all those who may be concerned in canal works. Leakage in a canal is attended with so many embarrassing consequences; among them, loss of water is not the least, dilapidations of the embankments, and perhaps their being wholly carried away; for when percolation takes place, and that through made or artificial ground, its solidity is of very short duration. Nevertheless, it is but too often carelessly done; and this circumstance has led to an enormously extra expense, besides disgust in the contiguous land-owners, who have found their grounds constantly inundated by the leakage.

A canal is said to be performed by level cutting when the natural state of lands through which it has to pass is tolerably level, and approaching to a good summit-level to the next locks, both above and below it; when a line is to be cut through such grounds, nature is said to favor the undertaking, and it is, perhaps, truly said, for in Flanders and Holland the canals require no other consideration than in performing them in this way, and in them few locks are required, as a good summit-level may be accomplished by embankmen's, which are there called dikes. These, in countries like Holland, are of great consequence, and are commonly made wide and handsome, planted with rows of trees on their sides, and sometimes even paved; they are, in fact, the high roads of communication between one part of the country and another, and afford to the public the greatest accommodation, in giving them a dry and commodious road throughout the year, which could not otherwise be easily obtained in such swampy lands, which are more than half the year overflown by the swelling of the Rhine, and the consequent increase of water in the canals.

The Dutch have the credit of having invented the compost or puddling: it is true, their canals are all so lined, and indeed without it, in canals such as theirs, it would be totally impracticable to prevent their leaking. Their embankments, or dikes, are sometimes raised twelve feet, or VOL. VIII.

higher, above the neighbouring land, and the top-water level reaches within two feet of the top of the dike. The difficulty of keeping in the water, in such high embankments, must be great, where nothing but earth is applied for the purpose; but the Dutch puddle appears to make a complete barrier. The writer of this article has examined the principal dikes in Holland and the Low Countries, and he invariably found they were coated with puddle, and in a similar manner to the way described above for weak or infirm embankments, except, perhaps, that they are more neatly done than with us, and they use a kind of marly clay in the compost, which is often rejected by our engineers. Indeed, canal making, in Holland, is a system interwoven with the nature of the country. It would be a complete swamp if it were not for the canals: they perform the double purpose of facilitating inland navigation, and draining the country.

Plate I. fig. 1, ENGINEERING, is the section of a canal, showing it under circumstances of level cutting. AA the line of the contiguous ground; B, B, the artificial embankments; CC the width of the cut at top, and DD at bottom. The external slopes can be so formed as to be used for the towing paths. With respect to the slopes C, D, they are determined upon the principles already stated as prevailing among our best engineers for that purpose, viz. for every foot in depth, giving a horizontal base of one foot and a half; and it follows, from such received data, that a canal six feet deep will require its sides to be sloped three feet, and, if it should be eighteen feet wide at the top water level, it would be fifteen feet at the bottom: hence may be deduced very useful proportions for canals of greater dimensions, in which may be combined the practice found of utility in the smaller ones.

Canals are cut through so many variations in the ground's surface, that it would be impossible to anticipate them all it is intended here, however, to notice two other cuttings, which will, in some measure, allow of great extension of application. When the ground slopes down to the projected canal line it is called side-lying ; and, if a canal be forming through such ground, the work is said to be doing in side-lying ground. Plate I. fig. 2, shows the section of a canal for such cutting. AA the sloping line of the ground; B, B, the embankments to be raised; CC the width of the cut at top, and DD the width at bottom. It is of some importance to so arrange the cutting, that the ground excavated from the canal be equal to make up the embankments on its sides: it is impossible that it should be so in all cases, but a great expense may be saved if a calculation be made of it previously to setting out the summit-level of the work, as then the removal of the soil may be wheeled to the parts where it is most required, which will prevent heaps collecting about the works, which generates slovenliness, and sometimes the greatest inconvenience. Deep cutting arises when the canal approaches a hill, or the side of one, which it is intended to pass by deep or open cutting, rather than by tunneling. Plate I. fig. 3, represents the section of a canal by deep cutting; AA the inclined ground to be passed; CC,

S

width of canal at top, and DD the width at bottom; the sets-off I, I, are generally appropriated in such cuttings for the towing-paths, and are called by the navigators berms. They are also found to be exceedingly useful as a provision to prevent the loose ground which rolls down from the upper banks B and C from falling into the canal. It is in cutting in such situations that the ability of the engineer displays itself; he has often to contend with all the difficulties of a bad stratification, in which, frequently, the percolating waters become so great as to stop the proceedings. In such cases, pumps are had recourse to; but it sometimes happens, nevertheless, that he has no place into which he can convey the superfluous water, or, if he has, he is not sure that it will not increase his difficulties, rather than remove them. To offer expedients for such circumstances is impossible; they must be met by the experience and resources of mind of him to whom the work is confided, and it will be well or ill performed, in proportion as his experience and talent predominate.

Canals of great traffic must be furnished occasionally in their course with passing places. They consist in giving an increase of breadth to the water way of the canal, so as to admit of boats resting by the way, without incommoding the navigation; every canal has them, and the only precautions are, that they be made in as convenient places as can be, to promote the convenience of the traffic; hollow and low places are generally selected as the most eligible, and near to the locks and basins if possible. By such places being formed, the public derive accommodation, as it admits of a ready transit of produce and industry to the inhabitants in its neighbourhood. Reservoirs to canals, in most cases, are indispensable, in order to the keeping up a supply of water in its line; they are artificial collections, getting their water from every source in their neighbourhood; their size must be regulated by the quantity of water they are intended to contain, and that by the line of work which it may be intended to supply. They should be placed in situations so as to contain an equable quantity throughout the year, and so contiguous to the canal, as to admit of an easy communication with it at all times. Wherever the reservoir is to be constructed, all the variations of the ground's surface should be exactly noted down; the nature of the soil proved, in order to ascertain, if bad and porous, where, and in what quantity, lining or puddling may be required for it. The water flowing through all springs, brooks, and rivulets, which it is determined to divert, to supply the reservoir, should be exactly gauged, and also the depth of the rains which usually fall. All such particulars being ascertained, the excavation may be commenced; the same process is to be followed as has been recommended for the same kind of work in canals. The sloping of the banks is made rather more oblique than is practised for canals, commonly to every foot in depth a horizontal base of two feet, and, if the excavation be in a strong clay, the horizontal base is made as much as three feet. The lining is performed in a similar manner to the way pointed

out for such work in canals. Every reservoir should be furnished with a gauge, indicating exactly the quantity of water that it can supply, &c.; if the gauge be a wooden post fixed in the reservoir, it might be accurately divided, so as to show, by its divisions, the water lost by evaporation, or taken for the canal; and this gauge would exhibit at once how the supply kept pace with the consumption. In the event of an excess of water flowing into the reservoir, which cir cumstance should always be anticipated in its construction, many plans have been suggested for disposing of it; the most usual way, however, of providing for a ready exit to such excess, is to form a weir or weirs, sometimes called tumbling bays, frequently at the corners, if the form of the reservoir be square; if round, or a compound figure, at such places as is best adapted to its ready discharge. It will appear quite obvious, that the size and number of the tumbling bays must be regulated by the estimated quantity of water they may be called upon to discharge, or the greatest inconvenience may follow; as in the event of their being too small or too few in number, in great swells of the springs arising from unusual rains, &c., the sides of the reservoirs may be overflown, to the destruction of its banks and perhaps to the effect of blowing up and carrying away the canal works in its neighbourhood. The construction of a tumbling bay consists in forming a vertical syphon in the embankment of the reservoir, composed of well-wrought masonry or brick, properly cemented, to which a horizontal communication is opened by the side of the embankment of the reservoir. The whole workmanship should be done in the most complete and perfect manner; the bottom of the syphon should enter a culvert constructed in a similar way, which culvert or drain should be arched above and below, and be built upon an easy descent, so as to promote an easy discharge of its contents. The culverts are frequently carried under the bottom of the reservoir, in which case it will be essential to keep them sufficiently low to admit of the lining being thick enough to secure its water-tight qualities. In cases in which rivulets or other streams are diverted to the supply of the reservoir, a somewhat different construction will be required than when it is fed by springs; this difference principally consists in an alteration of the approach by which the water is to enter; such water is previously collected into a branch, or, as it is termed, a feeder, which is in fact a canal of smaller dimensions than the principal one. This feeder is constructed so as to promote a current in its waters to the head of the reservoir, which it enters by a weir or gates, the sides or piers of which should be' formed of masonry, built on a piled foundation, in carrying up the work, which should be of large stones well joined, and the walls battering back from the line of their base, and somewhat curved in their whole height. The tops should be coped with broad slabs of granite or free-stone, dovetailed together, or well cramped. The bottom of the weir should be formed by an inverted arch of masonry, well bedded in strong clay or puddle compost. The gates should be made of strong oak, with lower

and upper sills, framed with rails and cross braces, fixed in the stone sides by bars of iron. An iron upper rail should traverse the top side of the whole. The gate or weir should be in height a few inches above the summit level of the reservoir, that the water from the feeder may flow over the bar of iron attached to the upper sill. The reservoir supplies the canal by means of a pipe of cast iron, or other metal, or stone. This pipe is furnished with a cock which works on an endless screw, and is so adjusted as to be easily turned by the overseer of the reservoir. Mr. Longbottom obtained a patent for the construction of reservoirs (see Repertory, vol. 4. p. 145), the only novelty in which was, he depended for a supply of water to the rains falling upon the earth's surface, which he proposes to collect together into one or more reservoirs; the words of the patent run thus: my intention is calculated to supply canals, ponds, sluices, towns, or any other place wanting water, by making reservoirs upon high and moorish ground, or any other suitable place which are to be supplied in manner following.' He adds farther, that 'he found that in twelve months there fall upon a superficial foot of land 3:33 cubical feet of rainwater, exclusive of exhalation, so that upon a statute acre there fall to the amount of 145,054,80 or thereabouts;' again, he says, I can convey water falling upon 3500 acres into reservoirs for instance, I make a reservoir of 100 statute acres in the most eligible situation, from which open drains, or sluices are made in the most proper places for receiving water running from the surface of the grounds in rainy weather, which, according to calculation, will be nearly equal to 5076 cubic feet per acre, or 91,800 cubic feet per annum, brought into the reservoir, except in loss by soakage; this may be done without any prejudice to rivers or mills. The area of a reservoir of 100 statute acres is 4,356,000 superficial feet, and the average depth 975; the parts are not included, so that 4,356,000 the area by 9, gives 39,204,000, as contained in the reservoir of reserved water.' For conducting such water into the canal or sluice, he says, 'I make two aqueducts of stone or brick for conveying the water out of the reservoir, from the bottom when the water falls perpendicular from its surface into the space of a large circle of stone-work, with which the openings of the aqueducts communicate; in each of these I fix a paddle or clough equal to an opening of fifteen inches by twelve inches, which is raised by a screw fixed to it, and moving upright in a piece of iron fixed across at the upper part of it; upon it is a square box including a female screw, in which the other moves, which is turned round by four small hand-levers fixed to the square box, and which rests upon a small iron bar, which raises the screw and also the paddle, to the following heights, viz.: with an opening of three inches by twelve inches may be delivered 317,952 cubic feet of water in twenty-four hours; with one of six inches by twelve inches, 630,730 feet; with one nine inches by twelve inches, 927,936 feet: with one twelve inches by twelve inches 1,222,560 feet; and one twelve inches by fifteen inches, 1,512,000 feet, or a less, or a greater quan

tity, in proportion to the opening and velocity. The quantity of water required to be let out of the reservoir may be regularly ascertained, by fixing at the head of the screw a pointer, and an index above it accurately divided into inches and parts; and, as the paddle is raised by the screw fixed to it, the pointer at the end sliding upon the index will show the quantity of water discharged upon every division of it as set forth; as at three inches in height, 317,952; at six inches, 630,730; at nine inches, 927,936; and so in proportion to all the several proposed elevations.' This specification concludes with directions for forming smaller reservoirs, in which many ingenious suggestions are developed. The reservoirs here treated of have been considered as formed by embankments, which, in porous soils, have been recommended to be lined with puddling; in some, however, such embankments will not answer the purpose, in such cases the whole must be walled with brick or masonry, and if of the former, the greatest care should be taken that they be well laid, and of great substance, with puddle-linings behind them; the cement should be of fresh stone lime (and if ground instead of slaked with water the better,) mixed with sharp sand, and the mortar prepared for use only as wanted. The walls should batter back in their height, with a small curvature outside, diminishing in thickness as they ascend, and finish finally at the top to two bricks and a half. The whole should be coped with granite, with the meetings fastened by dovetails. If it be determined to form the walls in masonry, which, in some situations, may be eligible from the abundance of stone at hand, the same plan in the form of the wall should be had recourse to; and also, in previously lining the embankments, the ashlerings should be in as large pieces as may be conveniently obtained, and all venty or bad stones rejected. The joinings should be as close as possible, with very little cement between them: the whole should be coped, as is directed before, for walls of bricks. Most of our canals are supplied by reservoirs somewhere in their course, so that an engineer can scarcely anticipate a work of canal-making without feeling that he may be called upon to exert his talents to the forming of a reservoir. Reservoirs that have been lately formed to canals are—one at Ripley for the Cromford Canal; another at Milstone for the Grand Junction; also, at Ainsworth for the Nottingham; at Marsden for the Huddersfield; at Littleborough on the Leicestershire Canal. The Rudyerd Vale supplies the branch of the Caldon and Mersey, and occupies upwards of 150 acres, and is more than thirty feet high. The St. Ferriol reservoir to the canal of Languedoc occupies a space of 590 acres ; the walls of which are covered with ashlerings of freestone.

Locks, or pound locks, in the consideration of which many important circumstances develope themselves in the work of a canal, are the barriers by which the water is kept to its summit-level; in the several reaches on its line they also operate as toll bars for collecting the tolls payable on navigating it: they are placed as frequently on the line of the canal as the several levels require