562 HISTORY OF ENGINEERING. Book I.
length ; it then proceeds to the north-east corner of Loch Oieh, after having passed thelifting lock at Kytra, which is 170 feet in length, and 40 feet in breadth.
Between the western end of Loch Oich, and the east end of Loch Lochy, forty feetdepth of cutting was required, and near the latter place is a regulating as well as a iiftinglock ; the difference between the surface of the water in these two locks is nearly tenfeet.
At the south-west end of Loch Lochy is another regulating lock; the whole length ofthe Loch is not less than 10 miles, and its ordinary level is continued along the canal towithin 1 mile of Loch Eil, where there are eight connected locks, each 180 feet in length,and 40 feet in width, falling altogether 64 feet; this work forms a mass of masonry 1500feet in length ; each of the locks rises 8 feet.
The canal continues on a level, until it arrives at the two connected locks at Corpach,which fall 15 feet, where there is a single sea-lock, which enters the tide-way of LochEil. This is situated at the western extremity of the canal, within 300 feet of high-water-mark. The rock being covered at three-quarters flood, it was necessary to lay thesill in such a position on the rock that a depth of 21 feet water might be obtained upon itat high-water of neap tides. Water-tight mounds, faced with rubble-stone, were formedfor this purpose from the shore, beyond the extremity of the lock-pit, which were con-nected by a wooden cofferdam. A foundation was arrived at after boring to a depth of63 feet below the lower water line of spring tides ; a sufficient space was enclosed with acofferdam, which was framed on the eastern bank, and afterwards put together on the beach,near high-water mark.
The leading frame was made by fixing together, end to end, two pieces of timber,crossed by others 20 feet long, 13 inches broad, and 6 inches thick, laid on oppositesides of the first beams, across the joinings, and fastened by four screw bolts, which passedthrough the whole. When these beams were so fished together, their whole length was95 feet.
To unite the two sides, two others, each 63 feet in length, were laid with mutualinclination, the ends being 63 feet apart; these were secured to the two long beams at theends by halving, or corking down; after which two iron screw bolts were passed througheach. Another beam, 38 feet in length, was laid across each angle, and also screwed to theother beams at the two ends.
When the spring tide was at its height, the first leading beam was floated off, and atlow water was sunk into its proper situation by attaching several large stones to it at itsupper side, three mortises were cut on each side and three in the front, to receive thestandards, which were to be tenoned into them, and which, after being placed upright,were cut off to the level of one foot below high-water neap tides, that they might receivethe middle leading frame, which was made on shore, floated to its place, and sunk by meansof guide piles, driven by a pile engine, placed upon the deck of a sloop, and then securedby screws to the tops of the upright standards already mentioned.
On the top of this second frame upright standards were placed in mortises, which werecut off at high-water spring tide. The upper leading frame was then floated off, andplaced upon the last-mentioned standards, and also bolted to the piles. On this wasformed a temporary scaffold, by laying large timbers across, and driving piles within thespace to support them; when this was done, the whole was loaded with large stones, and apile engine; fixed piles were driven at from 15 to 20 feet apart, entirely around the whole,and these were so securely bolted to the upper frame, that the storms had no effect uponthem.
In March, 1808, the main framing piles were fixed to the rock by iron dcwells, and thiswas performed by means of a cylinder, 8 feet long, and 22 inches internal diameter, formedof 3-inch plank. The joints were closely united and dowelled together, and the wholehooped with iron, and shod at the lower end with a circular iron shoe. On its upper endwere two strong iron eyes, fixed by means of clamps, which were riveted to the sides of thecylinder, and through them passed the iron chain which lifted it up.
At low water the cylinder was placed where the main pile was to lie, there being thenonly 3 feet of water, and 8£ of silt and gravel on the rock; it was then placed upright,close to the inside of the lower leading frame, and on its top was a block of ash timber, 2feet in height, on the under side of which a piecer turned, 6 inches in length, fittingexactly to the top of the cylinder; this prevented the block from shifting, as well as thecrushing of the cylinder whilst being driven. This block and the pile 12 inches square,placed on the top of it, were hooped with iron : the pile was as much above the top of theupper scaffold as it was necessary to sink the cylinder in the mud. When all was perpen-dicularly placed, a pile-engine, 30 feet in height, was applied to drive it, with a ram of 1008pounds weight. When the cylinder had descended some depth into the mud, it wasfound necessary to empty the contents ; this was effected by an auger, which filled at twocomplete turns, when it was lifted out by a purchase at the top of the pile-engine, and thesand cleaned out by means of a shovel.