Canal

CANAL. An artificial cut in the ground, supplied with water from rivers or springs, &c. in order to form a navigable communication between one place and another, and also for supplying towns with water. The advantages to be derived from canals were not unknown to the ancients. Egypt, from the remotest antiquity, contained a number of canals, dug to receive and distribute the waters of the Nile at the time of the inundation ; but the most celebrated canal in that country was that which connected the Nile with the Red Sea, which was completed under the second Ptolemy, and was four days' journey in length. It was subsequently neglected, but was afterwards re-opened by one of the caliphs, in 635, after which it was again neglected, so that it is difficult to trace the remains of it at the present day. The aqueducts of the Romans were a species of canal, and they had many also for draining the water from over flowed grounds ; and attempts were made (although unsuccessfully) by one of the emperors, to cut through the Isthmus which joins the Peloponnessus to Greece. But China, in the number and extent of its canals, far exceeds all other nations, there being scarcely a town or village that is not washed by the sea or by a river, but has a canal. The Great, or Royal Canal, is the most magnificent work of the kind in the world; it is 825 miles in length, 50 feet in width, and 9 feet deep, and extends from Canton to the northern frontiers of the empire. Most of the countries in Europe are provided with one or more works of this kind : those of Holland, from their number and the admirable mode in which they are managed, have long been the theme of travellers; but perhaps the most stupendous work of the kind is the canal of Languedoc, in France, which forms a junction between the Mediterranean and the Atlantic. It was begun in 1666, and finished in fifteen years. The breadth is 144 feet, including the towing paths; the depth is 6 feet, and the length 84 French leagues, and it has 114 locks. Although this country at the present day is superior to any nation in Europe (with perhaps the exception of Holland), in the number and magnitude of its canals, it was one of the last to adopt this important improvement ; for if we except the New River Cut for supplying London with water, England, up to the middle of the last century, had not a canal worthy of notice; and the honour of their introduction is due jointly to the spirit and perseverance of the Duke of Bridgewater, and to the skill and talents of the celebrated Mr. Brindley. The duke had at Worsley, about seven miles from Manchester, a large estate, rich in coal, which had been hitherto useless, on account of the expense of land carriage ; he therefore consulted Mr. Brindley as to the practicability of forming a communication by water, who, having sur veyed the ground, and declared the scheme to be practicable, the duke, in 1758, obtained an act to make a navigable cut or canal from the township of Salford, to or near Worsley Mill, and to a place called Hollens Ferry, in Lancashire ; but extending his views as the work advanced, he subsequently obtained two other acts, the first to carry it over the Irwell to a place called Longford-bridge, and the second to extend it from Longford-bridge to a place on the Mersey River, called the Hempstones. The whole navigation was then proceeded in and completed, being more than 29 miles in length, and having, at its fall into the Mersey, locks which let it down 95 feet. It should be remarked that the locks were formed at Runcorn, instead of the Hempstones. The completion of these works quickly rendering apparent the important advantages of canals to the commercial and manufacturing interests, new undertakings of the kind succeeded each other with such rapidity, that the bare enumeration of those existing at the present day would occupy more space than we could spare for the purpose. Amongst the principal are the Grand Trunk, or Staffordshire forming a communication between the Trent and the Mersey, and, con sequently, between the German Ocean and the Irish Sea ; the Thames and Severn; the Birmingham Canal; Peak Forest and Grand Junction, in England ; and the Caledonian Canal, in Scotland. The total number of canals in Great Britain is 103; the total extent 2688 miles; and the capital sunk in their con struction is computed at upwards of thirty millions sterling. With two or three exceptions, they were all constructed by the combined exertions of private individuals ; and important as these works are now become, none of them were projected prior to 1755. The particular operations necessary for making arti ficial canals depend upon a variety of circumstances. When the ground is naturally level and unconnected with rivers, the execution is easy, and the navigation not liable to be disturbed by floods; but when the ground rises and falls, and cannot be reduced to a level, artificial means of raising and lowering vessels must be employed. The ordinary expedients are either inclined planes or locks. The first of these methods, viz, the inclined planes, is chiefly resorted to in cases where the canal is so very scantily supplied with water that its economy becomes an object of the first importance. For this purpose, an inclined plane of masonry is constructed, extending from one level to the surface of the next above it, and the boats are hauled up the plane upon a kind of cradle or sledge, furnished with rollers, and this, it is said, was the only method employed by the ancients, who appear to have been ignorant of the nature and utility of locks. The engraving on the opposite page represents an improvement upon this method of passing boats from one level to another, by which the boats maintain their parallelism whilst ascending the inclined planes. It is the invention of Mr. J. Underhill, of Parkfield Iron Works, near Wolverhampton. The following is a description of the engraving : a the higher level of the water of the canal ; b the lower level; the bottom of the canal is a little excavated at each of these places, to admit of a kind of cradle carriage to be sunk sufficiently deep for a boat to be floated on to or off it. At c is represented a laden boat, placed upon the upper level in its carriage ff; and at danother, similarly circumstanced upon the lower level, in its carriage gg. Each of them is attached by strong chains to a drum-wheel h, properly mounted in a strong framing, and worked by a steam engine or other adequate power. The carriages are mounted upon two pairs of solid iron wheels, which run upon railways that connect the upper and lower levels. These railways form two inclined planes for the ascent of the carriage, and the same for its descent, whilst the two slopes are connected at top by a horizontal plane. This will be clearly understood by reference to the diagram. The boat e is there represented in its carriage, and ascend ing the double rails or planes r, the hind wheels being on the top rails, and the fore wheels on the bottom rails, but confined in their track by the pa rallel bars o above, which preserve the carriage from shifting out of the hori zontal position. Before arriving at the top, the fore wheels open two latches /, having counter balance weights, and both hind and fore wheels arrive together on the top horizontal the orizontal line of rail. On drawing it for ward for the descent into the lower level of the canal, the latches lbecome closed, and the carriage is sent forward, as shown by the dotted lines before descending, when the fore wheels open the latches for the hind wheels to enter between the parallel bars ; g g skews the boat and carriage delivered on to the lower level of water, where the carriage sinks to a sufficient depth to allow the boat to float away from it. The pa

tentee proposes to employ similar machinery for raising weights on land. But where canals have an abundant supply of water, the usual method of trans mitting boats from one level to another is by locks. A lock is a long narrow passage connecting two contiguous levels, of sufficient width and length to receive a boat, and iu depth extending from the top of the upper lel el to the bottom of the lower level. The sides are usually formed of masonry, and at each end is a pair of strong gates, turning upon centres strongly secured to the walls. The gates next the upper level extend only to the bottom of that level, but those at the lower level extend the whole depth of the lock. These gates are opened and shut by means of long projecting arms or levers, and when closed, the gates meet in an angle pointing up the stream. At the upper end of the lock is a sluice, which the water can be admitted into the lock from the upper level ; and at the lower end is another sluice, by which the water can be discharged from the lock into the lower level. The operation of passing a boat from one level to another is as follows: suppose it be required to pass the boat from the upper level to the lower, and that the water in the lock is at the same height with the water in the lower level, and that the gates at each end of the lock are closed ; the sluice at the upper end is first opened, and the water admitted into the lock from the upper level; and when it attains the same height in the lock as in the upper level, the sluice is shut, the upper gates opened, and the boat hauled into the lock. The upper gates are then closed, the sluice at the lower end of the lock opened to discharge the water into the lower level, and when the water stands at the same height in the lock as in the lower level, the sluice is shut, the lower gates opened, and the boat hauled out of the lock into the lower level. In the reverse operation, or passing a boat from the lower level to the upper, the water in the lock is first reduced to the height of the water in the lower level, when the lower gates are opened to admit the boat into the lock, after which they are closed, and water admitted into the lock from the upper level, until it stands at the same height in each, when the upper gates are opened, and the boat passed into the upper level. The operation just described is extremely simple and easy, but it will be seen that at each transit of a boat in either direction, a lock full of water is drawn from the upper pond and lost. This loss is of such consequence on some canals, that the water is pumped back to the upper level by a steam engine, and numerous plans have been proposed for avoiding or lessening this loss. On the Regent's Canal the locks are double, and placed side by side, with a sluice in the middle pier to admit the water from one lock into the other. In passing a boat from the upper to the lower level by these locks, the water is not discharged from the full lock into the lower level, in the first instance, but it is admitted into the empty lock until it stands at the same height in each ; after which the sluice in the middle pier is shut, and the remainder of the water discharged into the lower level, by which means only about half a lock full is lost at each transit. Mr. Brownill, of Sheffield, has proposed a plan for passing boats from one level to another, with very little loss of water, which we shall endeavour to describe with the assistance of the engraving on the following page, which represents a vertical section of the apparatus. a is the upper level of the canal ; b the lower level; c c section of the end walls of the shaft in which the cradle works ; d one of the side walls of the same ; e the gate of the upper level ; I the gate of the lower level ; g g a number of bearings, supporting the horizontal axis It, on which are placed the large sheaves k k, over which the suspending chains run ; to one end of these chains is attached the cradle o, and to the other end is hung the counterbalance 1 (shown in dotted lines), which rises and falls in a side shaft, there being a similar counterbalance in another shaft on the opposite side of the main shaft d; these two counterbalances are made to act together by means of the large wheel a acting on a similar wheel on the axis of the opposite counterbalance. This arrangement the inventor terms his double union lift. The cradle o has a sluice at each end, fitted with smaller sluices p p; it has also a double bottom q; r is a short lever at the lower end of the cradle, which does not prevent its ascent, but as soon as it arrives above the inclined plane a, its upper end turns over, and rests against the dotted lever t, termed the release lever ; and upon allowing the cradle to descend a little, the lever r, acting upon the inclined plane a, forces the cradle over against the sill of the gate of the upper level. At the opposite corner of the cradle is a similar apparatus (not shown in the drawing,) to act upon the inclined plane x. To pass a boat from the lower level to the upper one, the cradle is forced by the pressure of the lever upon the inclined plane x, close over to the entrance of the lower level ; the small sluices p p are then opened to admit the water into the cradle, until it stands at the same height in it as in the upper level, when the larger sluice in the cradle and the gate f are opened. The boat is now hauled into the cradle, after which the gate and sluices are again closed, and the counterbalances (which consist of large iron tanks filled with water), being at the top of their shafts, as much water is let out from the double bottom q of the cradle o as will cause the counterbalances to preponderate when they descend, and thereby cause the cradle containing the boat to ascend and pass the inclined planes but as there is a small portion of water in the side shafts, the coun terbalances are checked in their descent on reaching this water ; they then rise slightly, and allow the cradle to settle on the inclined plane s, which forces it against the upper level ; the small sluices is next opened, and as soon as the water stands at the same level on each side of the large sluice, the latter and the gate of the canal are opened, and the boat can then pass into the upper level. If now a boat is to be passed from the upper to the lower level, it is hauled into the cradle ; the gate a and the large sluice, and the smaller sluice p are all shut, and as much water is admitted in the double bottom p of the cradle (from a side reservoir, shown dotted,) as will give the cradle a preponderance; and the release lever being let go, the lever r turns over, and the cradle descends, and on reaching the bottom of the shaft it is passed into the lower level in the manner described for passing it into the upper one. The ends of the cradle must be covered with stuffing of some kind, to prevent as much as possible the escape of the water when the sluices are open.