Obviously, however, on canals, as on rivers, the fewer locks or lifts the better. The process of passing through a canal lock is tedious, and while it involves a considerable expenditure of time, it involves also a corresponding amount of cost. For ship canals, it is much better to have no locks or lifts whatever. This aim was kept in view in the laying out of the Suez and Panama Canals, but on the latter canal, the cost of cutting through the Culebra mountain was found to be so very considerable, and the financial position of the company was so unsatisfactory, that M. Eiffel submitted a proposal to make use of locks, which was adopted by M. de Lesseps and his colleagues as a dernier ressort.[272] The Panama Canal has proved that the avoidance of locks can only be purchased in an uneven country at an immense cost, and the canal engineer has therefore to consider whether the resources at his disposal will enable him to pay the price involved. The proposed Nicaraguan Canal is another enterprise that presents some interesting problems of this description. This canal will make use for a great part of the total distance between ocean and ocean—169 miles—of Lake Nicaragua, and as that lake is 600 feet above sea level, it is manifestly necessary to make use of locks. In other words, as the lake cannot be brought to the tide level of the canal, the canal must be carried up to the level of the lake.
A lock chamber, enclosed by a double pair of gates is said to have been employed for the first time in Italy in 1481, the designers and builders having been two clock-makers in Viterbo of the name of Domenico. The State of Venice was the first to adopt the system, but before the end of the fifteenth century, Leonardo da Vinci had united the two chief canals of Milan by six such locks, having a fall of 17 braces.[273]
On one of the canals constructed in Italy, between Padua and Vicenza, about the fifteenth century, there are several sluice-gates, or _pertuis_, which are said by Cresy[274] to have been thus contrived:—
“The lower beam of each gate was framed with the head and heel posts, so as to allow a space of 6 inches between it and the sill. From the middle beam to the top, the gates were planked over in the ordinary way; the lower part was left open, or in skeleton framing, and was closed by paddles or sluices, which were moved up and down by a rack and pinion. When the paddles were let down, they descended 3 or 4 inches lower than the surface of the floor on the lower side, which acted as a rebate, against which they pressed, and effectually shut the lock. They also had a bearing against the lower cross-beam of the gate, and the head and heel posts rested on square stones made fast in the sill.
“To make use of gates upon this construction, it was necessary first to raise the paddle as high as the lower cross-beam, which permitted the water to pass through at the foot of the gate. The paddles were then elevated to the height of the middle beam, which was placed at the ordinary level of the water, usually 4 or 5 feet deep upon the sill.
“These gates were easily opened, as the boarded part was entirely out of the water, and a deposit on the floor of the chamber of the lock could form but little obstruction, as from the scour of the water the greater part would be washed away. The only serious objection to this early contrivance in aid of internal navigation is the injury that vessels might sustain at the time they were passing through, when one half of their length would be out of the water, producing a considerable strain upon them. The water passing through a space, walled in on both sides, would, to a certain extent, allow the barge or vessel to slide down an apparent plane; but, before it could again resume its level position, it would be subjected to another strain. These side walls were, however, made of considerable length, a foot being usually allowed for every inch of fall; a timber floor was laid throughout, to prevent the force of the water from deepening and undermining the foundations.”
The Chinese, who have early distinguished themselves in many inventions that have been worked out and improved upon under our Western civilisation, introduced piers into their rivers and canals, in order to overcome the difficulties incidental to falls or shoal water. These piers have been termed by De la Lande half locks, and it has been remarked by Chapman that the casual position of two pairs of piers near to each other has no doubt suggested the invention of locks, as it would be seen, when the gates of the lower piers were closed, and of sufficient height, that the water would be nearly still between the upper pair of piers, and afford an easy passage, so that, in place of a single pair of piers, two pairs would be erected sufficiently near to each other for the purpose, and capacious enough to hold a fleet of boats. It would soon afterwards be found that in dry seasons the waste of water was greater than could be conveniently afforded, and the operation was tedious for single boats. Thus would progressively arise the invention of locks with walled chambers and sluices through their gates and walls. There are, or were recently, on some rivers, locks of the first construction, composed simply of two pairs of piers, without any connection of walls or pavement between them. The Kennet and the Lea have unwalled locks. Thomas Telford, when projecting the Inverness and Fort William Canal, on account of the great plenty of water, and size of the vessels to be used, proposed not to wall the locks the whole length, but to have earthen banks between the two pair of piers of masonry that support the upper and lower gates of the locks.
It appears from M. De la Lande’s ‘Traité des canaux de Navigation,’ that the first lock was supposed to be erected in the year 1488, upon the Brenta, near Padua; and that shortly after, the two canals of Milan, between which there was a fall of nearly 34 feet were joined by means of six locks, similar in principle to those at present in use. The first lock that James Brindley erected appears to have been at Compton, on the Stafford and Worcester Canal; but they were not at that time uncommon in England, on several of the rivers, and on the Sankey Canal.
Planes.
William Reynolds, of Ketley, in Shropshire was the first who contrived and executed an inclined plane (which was completed in 1788) for the passage of boats and their cargoes. It was found to answer the purpose, and continued in practical use. Thomas Telford has thus described the plane, in ‘Plymley’s Agricultural Report of Shropshire’ (p. 291): “Mr. Reynolds having occasion to improve the mode of conveying iron, stone and coals, from the neighbourhood of the Oaken-gates to the ironworks of Ketley, these materials lying generally at the distance of about a mile and a half from the ironworks, and at 73 feet above their level, he made a navigable canal,” called the Ketley Canal, “and instead of descending in the usual way, by locks, continued to bring the canal forward to an abrupt part of the bank, the skirts of which terminated on a level with the ironworks. At the top of this bank he built a small lock, and from the bottom of the lock, and down the face of the bank, he constructed an inclined plane, with a double iron railway. He then erected an upright frame of timber, in which, across the lock, was fixed a large wooden barrel; round this barrel a rope was passed and was fixed to a movable frame; this last frame was formed of a size sufficient to receive a canal boat. These boats were 20 feet in length, 6 feet 4 inches wide, 3 feet 10 inches deep, and each carrying 8 tons, and the bottom upon which the boat rested was preserved in nearly a horizontal position, by having two large wheels before and two small ones behind, varying as much in the diameters as the inclined plane varied from a horizontal plane. This frame was placed in the lock, the loaded boat was also brought from the upper canal into the lock, the lock gates were shut, and on the water being drawn from the lock into a side pond, the boat settled on a horizontal wooden frame, and as the bottom of the lock was formed with nearly the same declivity as the inclined plane, upon the lower gates being opened, the frame with the boat passed down the iron railway on the inclined plane on to the lower canal, which had been formed on a level with the Ketley iron works, being a fall of 73 feet. Very little water was required to perform this operation, because the lock was formed of no greater depth than the upper canal, except the addition of such a declivity as was sufficient for the loaded boat to move out of the lock; and in dry seasons, by the assistance of a small steam engine, the whole of the water drawn off from the lock was returned into the upper canal by means of a short pump. A double railway having been laid upon the inclined plane, the loaded boat in passing down brought up another boat containing a load nearly equal to one-third of that which passed down. The velocities of the boats were regulated by a brake acting upon a large wheel placed upon the axis, on which the ropes connected with the carriage were coiled. It appears that this plane has an inclination of about 22°, except near the extremities, where it diminishes to about 111°; and that about 400 tons of coals usually descend thereon daily.” In 1789 a copper medal, or halfpenny, having a representation of this plane on one side, and of the cast-iron bridge at Coalbrookdale on the other, was struck and issued by the Coalbrookdale Company. After the practicability of inclined planes had been established, by the success of the Ketley plane, few Acts were passed for a new canal, without a clause authorising the company to erect inclined planes, instead of locks, if they should be found most advisable.