Chap. XXVII.

CANAL AND RIVER LOCKS.

1547

sufficient play without affecting the ease of the motion; it is also advisable to attachpieces of timber to the hanging-posts, which may be bolted and cramped to the masonry,and by caulking the joints the water is prevented from passing between them and the

Fig. 2860.

2859.

Fig. 2858.

masonry. The strutting-posts also allow a considerable quantity of water to escape,because, if not very exactly fitted, they only touch on one of their edges, and consequentlyit is scarcely possible but that the water should find a passage: to make them touchthroughout their whole length, they should be cut in a circular form, one concave and theother convex, so that if the gates had even a play of some inches, they would always touchvery nicely; the curvature of the posts should form part of a great circle of from 10 to 13feet radius.

The gates of locks of navigable canals are generally made in a right line, but in great sea-locks they are curved: Belidor has demonstrated, that these latter are not more solid thanthe former, but this must only be understood when the curved timbers are made out ofstraight pieces; for it is undoubted that, if naturally curved, they are much stronger, andwill resist more pressure than straight pieces, especially when resting on their two ex-tremities. The collars embrace the whole heel-post, which being generally 12^ inches indiameter produces considerable friction, especially when the balance-beam does not act asa counterpoise: a large bolt may be placed in the axis of the post, and a smaller collar besubstituted to confine it; but this method can only be applied to chamfered posts; roundposts must have a motion in their collar to lean against the hanging-posts, which couldnot be effected by an axis ; the collars must be attached to iron anchors strongly beddedinto massive masonry. The pivotsoften get deranged, the posts, as-generally made, causing consider-able play ; if these were bevelled,the pivots might be fixed andbedded in large stones cramped tothose adjoining, or united withanchors to the surrounding ma-sonry. Formerly the pivots weremade of copper, but cast-iron isequally efficient; they should bethe same siae as the ends of theposts, and terminated at the lowerend in a spherical form. Theother iron work of the gates con-sists of squares laid on at rightangles, which must be very strong;it is also well to lay on the rails ofeach sluice a band or two of ironto bolt them securely together.

Loch Gates measuring 8 feetfrom the centre of one heel-postto that of the other are in somecanals on a segment of a circle,the chord of which is about the