INLAND NAVIGATION.

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jthly. The expence of execution.

Of this little can be said, as it entirely depends on the extent, the se-veral works, &c. which can be accurately known only by an actual sur-vey and estimate; the total of which will of course be considered pre-vious to undertaking works of such magnitude. It may be proper toobserve, generally, that many locks, bridges, or aqueducts, much tun-neling, unfavourable foil, &c. will of necessity incur great expences.

Lastly. The mode os execution.

The foregoing particulars having been attended to, it becomes neces-sary to enumerate the several works, useful and necessary, in the execu-tion of a canal.

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For the passing and repassing of boats, various expedients have beenused; but experience confirms the use of locks, when it becomes neces-sary, by artificial means, to raise or let down boats from one level toanother,

A Lock (technically a pound lock) is a large basin, or, more properly, -a long square cistern, placed lengthways in a river or canal, inclosed byupper and lower gates. The lock should be lined with walls of strongmasonry on each side, and at the bottom ; or if of wood, stout oak pilesshould be used, shod with iron, and lined with two inch and half or threeinch oak plank, with a floor of the same materials, laid on oak sleepers,dove-tailed and spiked into the upright piles.

The use, or locking down iH is thus managed: The lock being full tothe level of the upper water, the gates are then shut, including the boatto be lowered. The water in the^lock is drawn off, in part first, b vmeans of the paddles- in the gates, and completely^ by the gates being

3 A opened;