578

HISTORY OF ENGINEERING.

Book 1.

Fig. 557.

SALTER.SFORD WEIR.

Mr. Telford had the old paving broken into small masses, and laid in water lime mortar,well grouted, upon the banks after they had been shaped with the proper declivity.

Fig. 558.

ELEVATION OF SALTERSFORD WEIR,

Upon this bed of broken stone in mortar was set a pavement of scabled or roughlydressed stones, about 18 inches in depth; these were laid in mortar, and all the joints groutedwell in, which no storms have penetrated or deranged. The whole cost was 17,000/.

Grand Western Canal has a contrivance which to a certain extent supersedes the use of thelock; this is by means of a lift, which has some advantages in the saving both of time and water.These lifts are 46 feet in height, and consist of two chambers, with a pier of masonrybetween them ; they are of sufficient dimensions for each to contain a timber cradle, inwhich the boat required io ascend or descend is placed. The cradle, when on a ieve'l withthe canal, allows the boat to swim into it, by simply raising up a water-tight gate at theend. The two cradles which work in the chambers, when full of water, or when either orboth of them contain a boat, balance each other on very strong chains, which pass over threecast-iron wheels, and are so arranged that the water in the upper cradle is kept about 2inches below that in the pond, which gives it a slight preponderance, sufficient to set themachinery in motion. It is necessary to pay particular attention to the strength of thematerials. The boats in this instance weigh about 8 tons, and pass up and down the46 feet in about 3 minutes, consuming 2 tons of water only, whereas in the ordinary way3 tons would be required.

Wisbech Canal runs from the Nene river to the old river at Outwell.

Worcester and Birmingham unites Birmingham with the river Severn at Deglis, a littlebelow Worcester . The tunnel at Westheath is 2700 yards long, 18 feet high, and 18 feet6 inches clear width, with a depth of water of 7 feet 6 inches. The tunnel at Tardebig is500 yards long; that at Shortwood 400; that at Oddingley 120, and that at Edgbaston110 yards long.

Wyrley and Essington Canal, from Wvrley Bank to Birch Hill in the parish of Walsall :there are several branches from this canal; one connects the Coventry' Canal,near Hudders-field, another Hayhead lime-works, another Lord’s Hay', and another Essington Woodcolliery