Before arriving at the top, the fore wheels open two latches l, having counterbalance weights, and both hind and fore wheels arrive together on the top of the horizontal line of rail. On drawing it forward for the descent into the lower level of the canal, the latches l become closed, and the carriage is sent forward, as shown by the dotted lines at e, before descending, when the fore wheels open the latches for the hind wheels to enter between the parallel bars; g g shews 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 patentee proposes to employ similar machinery for raising weights on land. Rut where canals have an abundant supply of water, the usual method of transmitting 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 in depth extending from the top of the upper level to the bottom of the lower level. The sides are usually farmed 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, by 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; f the gate of the lower level; g g a number of bearings, supporting the horizontal axis h, 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 l (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 n 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 s, 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 s, 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 s; but as there is a 3mall portion of water in the side shafts, the counterbalances 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 sluice p 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 e 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 mariner 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.

Canal 295Canal 296