Chap. XXVII.
1555
engineers are deemed preferable to locks : in the neighbourhood of Taunton are examplesof both systems, which, by the aid of machinery, enable the boats to pass from one canalto the other, from a height of above 80 feet. At the summit of the inclined planes is asteam-engine, of sufficient power to pull up a sledge, which receives the loaded boat; thechains pass over a cylinder of large diameter, but are frequently out of order, and some-times break, to the destruction of the vessel to be hauled up.
The Lifts are more easily worked, as a single attendant can raise or lower a boat fromone level to the other. There are two lock chambers, at the summit level of which,working in a lofty frame, are three or more large wheels; the outer circumference, orrather their radii, are exactly over the middle of each lock-chamber; around their peri-phery chains are suspended, and at the end of each is a fork or iron attached to the twosides of a sledge or boat, large enough to receive the one freighted, passing either up ordown the canal. When a boat is to be raised, the sledge which receives it is at the bottom,and the other on a level with the upper water of the canal, which the attendant allows torun into it, and when the weight is sufficient, it descends in the lock-chamber, and infalling raises the other which contains the freight; the end of the sledge opens, and it isthen admitted through a pair of gates into the upper channel: when it is required todescend, the sledge receives the boat, after that at the bottom has been filled with water;and when it has acquired nearly its balance by letting off a portion, it mounts and theloaded boat descends.
Means of making the Water enter and leave the Locks. —One of the greatest inconveniences,and causing great injury to locks, arises from the velocity with which the water from theupper interval rushes into the chamber, or from the chamber into the lower interval;the great difference in the level of the water and the space requisite for the opening, in orderto avoid loss of time in filling or emptying a lock, causes a considerable rush of water,which, falling from the upper interval on to the platform nearly perpendicularly, seriouslyinjures it, as does also another volume of water issuing from the lower gates, although itseffort is nearly horizontal, and consequently less injurious: the weight is, however, morethan double that of the upper part, the rapidity of the water and its consequent effectgreater; false platforms are therefore constructed some distance below the locks, to protectthe edges of the canal in this part, but, notwithstanding every precaution, frequent repara-tions are required. The gates being inclined towards each other cause the currentthrough the sluices not to be parallel to the sides of the canal, and to strike the edgesat a certain distance, whence they rebound from side to side, producing considerabledamage. If the two sluices were opened at once with equal velocity, the two currents meetingwith equal force, a mean current would be the result, taking the direction of the lock, butthere is frequently only one lock-keeper to open the sluices, and if there are two, they donot act together; the current is therefore almost always directed to one side, especiallywhen the sluices are first opened, at which time the rapidity is the greatest.
A great inconvenience arising from the rapidity of the water is modified by making itflow from the bottom of the platform in several smaller streams, which prevent its force frombeing more directed to one side than to the other. For this purpose, on the upper sideunder the lower pointing sill, and in the thickness of the wall which constitutes the fall ofthe lock, an arch is turned, having the top perforated by two holes 2 feet 2 inches indiameter; in the upper shoulder walls, behind the gates, are also two conical recesses, 3 feet2 inches square, forming an entrance for the water, the bottoms being paved with a largestone pierced by a hole 2 feet^ 2 inches in diameter; these openings communicate bymeans of bent tubes worked into the masonry, either of cast-iron or stone; if of thelatter material, semicircular gargoulles are cut,cramped together, and the joints united withmoss and mastic; or they may be made of severalflat stones properly cramped, forming a squaretrough, the joints being stuffed carefully, and thewhole confined within a mass of well-executedmasonry. The openings are closed with conicalplugs of the shape of the holes in the stone,furnished with a handle acted upon by a leveron the platform of the lock, and by the action ofwhich the water passes from the upper intervalinto the chamber: to close the pipe the plug islet fall, and a blow is given to the handle with amallet; this method is more expeditious thanracks or screws, and the most efficacious forclosing an opening.
The water passes from the chamber of the lockinto the lower interval by a nearly similar ar-ra ngement in the platform behind the gates, and
5(1 2
Fig. 2895. LOCK CHAMBER.