1546
THEORY AND PRACTICE OF ENGINEERING.
Book II.
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I
i.
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from the side of the hang-ing-post, and crossing themsolidly, especially that of thediagonal above the hanging-post, and at the extremityof the lower cross-piece; orinstead of a plank, a piecemay be let in in an oppositedirection to the cross-pieces,which must not be mortisedinto, or very little, thatit may not be in any wayweakened; this piece unitedcarefully to the lower cross-piece would tie it to thepost, and give more solidityto the framework; the dia-gonal position of the planksgives them more strengthto resist the pressure: thereis a little loss of material,but, on the other hand,plank of different kinds maybe used after cutting outthe knotty or defectiveportions.
Gates areopened bymeans of largetimbers fixedabove the posts,forming a coun-terpoise to thegate, and pre-venting it from
grinding the collars and rackingthe framework; for this purposethe tail of the balance-beam mustbe very large: trees are some-times used with their butt endsnot cut off, to which it is easy toadd any additional weight j thisbalance-beam should be unitedto the upper tail by a St. An-drew’s cross, which serves alsoto maintain the entire frame-work. The hanging-posts oftenallow much water to be lost, inconsequence of being obliged togive them sufficient play, andthis could scarcely be preventedif the pivot had not a littlemotion, and the collar fittedexactly; but the weight of wateroccasions the gate to unite bypressing it considerably againstthe hanging-post; still as thisis cut circularly, it only leansagainst a small portion of itssurface, and the water easily
passes, notwithstanding the great -■
pressure. To remedy these de-fects, the posts should be partlycut in a circular form, and partly Fig. 2855.
bevelled; the latter leaning along
its whole length upon the rebate made to receive it, which having a correspondingbevel interrupts any filtration; the circular part should not touch the masonry, but have
Fig. 2854.
Fig. 2853
-E n n _s
TIDE GATE WITH ITS APPARATUS.