568

HISTORY OF ENGINEERING.

Book I.

wherever possible, ties and braces are introduced : the platform which supports the towingpath adJs greatly to the strength of the side to which it is attached, and the water passingunder it prevents in a great measure any injurious consequences from the swell occasionedby the boats in their transit. The span of the arches is 45 feet, and their rise above thespringin : 7 feet 6 inches.

Upon this canal are two short tunnels, one 500, the other 200 yards in length, both inthe rugged ground which lies between the rivers Dee and Ceiriog ; they are each 14 feet7 inches high, 14 feet wide, and the towing-path covers 4 feet 9 inches, leaving 9 feet

3 inches water-way ; this path also stands upon pillars, so that the water is allowed its swellwithout great interruption.

The general summit of the canal is supplied by a navigable feeder 6 miles in length,carried along the bank of Llangollen valley from the river Dee at Llandisilio; a constantsupply of water being ensured by a regulating weir, which dams up the Lake of Bala Pool,

4 miles in length, situated about 20 miles from Llandisilio.

Adjacent to Mantwick, where the Ellesmere canal unites with the Chester, the distanceto the Trent and Mersey, or Grand Trunk canal, at Middlewick, is only 11 miles; in 1826,an act was passed to unite them by a canal, and the works were speedily completed. Thisbranch of 11 miles has a fall of 44 feet; the locks are 82 feet in length, and 7 feet 6 inchesin width. The canal is 16 feet wide at the bottom, 36 feet at the surface, and 5 feet deep,and obtains its chief supply from the Dee.

Erewash Canal , proceeds from the Trent, near the village of Sawley, and terminates atLangley bridge, by uniting with the Cromford canal. From the Trent to where theDerby branch locks down is 3J miles; from thence to Nutbrook 2J miles; from thence toCrotnford canal 6 miles, with a total rise of about 100 feet from the Trent.

Exeter Canal , was probably the first pound-lock canal established in England, for wefind that in 1563 the corporation of the city employed John Trew of Glamorganshire toform a canal, which should restore the navigation already rendered difficult in the river,in consequence of a weir constructed across it in the time of Henry III . The length ofthis canal was 9360 feet, the breadth 16 feet, and depth 3 feet; and several pools orchambers were formed, 300 feet in length, 80 feet in breadth at the top, and 50 feet at thebottom, with the sides walled for the purpose of passing the vessels ; each pair of gateswas 25 feet in height, and each leaf 20 feet in breadth, furnished with iron and brasswork, that they might be moved with facility; specifications of the work remain amongthe papers of the corporation.

The most ancient method of navigating rivers was by flashes of land-waters, so collectedthat boats could be carried over the shoals : in this canal we find the first improvementswere made by’ John Trew, who constructed a number of pools or locks, the vestiges ofwhich may still be seen, consisting of the chamber-walls, partly buried in the ■western partof the canal, which was cut in 1699. In one of the specifications above alluded to is thefollowing entry : —“ for digging a pool between the said two gates, which must be 300 feetin length at least, and about 80 feet in breadth, at the top or surface of the water, and 50feet broad at the bottom, and for walling the same on both sides, for the convenient aminecessary' passing of ships one after the other.” These pools, or pylls, had each a pair ofsluices, and were no other than pound locks, and frequent mention is made of these pairs ofsluices in the several conveyances by the Corporation. There can be no doubt that on thewhole canal there were at least seven sluices ; the pools were fed by the river Ex, whichhad a stake weir constructed across it long before the one of stone.

After the works were executed, we find that the Corporation were by no means satisfiedwith Mr. Trew, for the canal could not be entered at all “tide and tides; ” it was afterwardsconsiderably deepened, and other sluices added.

The two Brothers of Viterbo, as we have already seen, had built a lock chamber, with adouble pair of gates, at the Canal della Martesana, as early as 1481, and it seems extra-ordinary that so novel an invention had not found its way from Italy ' into England untilmore than 80 years afterwards: the canals in France for the purposes of irrigation mayhave suggested the idea of a sluice that could be opened for the passage of boats; Adam deCrapone, employed by Henry II. of France for these works, had, in all probability, seenthe gates which shut the locks in Italy .

Previous to this discovery it was not possible to form an artificial canal, except in a per-fectly level district, and we find attention at once directed to the improvement of inlandnavigation throughout Europe immediately afterwards ; in the Low Countries and in Hol­ land the greatest advantage was taken of the discovery, and a most complete system wasestablished for the passage of vessels of very considerable tonnage.

Forth and Clyde Canal has its course from the river Forth, in Grangemouth harbour,and passes the Loggie water by a stone aqueduct, and the Kelvin by another, when it locksdown in Bowling's Bay r . There is a branch to the Monkland Canal at Glasgow 2^ milesin length. On this canal are thirty-three draw-bridges, ten large and thirty-three smallaqueducts. There is a reservoir at Kelmananmuir, the area of which is 70 acres, which