Book II.
1370 THEORY AND PRACTICE OF ENGINEERING,
in their places by transverse ties; the parapets are formed by the introduction of a St.
Fig. 2234.
Andrew’s cross between the pendant binding-pieces,and making a very strong truss, by uniting the wholetogether like an arch, which cannot materially alterits form as long as the stone abutments maintaintheir solidity.
Over the canal at Brussels is a horse bridge, 83 feet span,of very simple construction, and which would havebeen much more solid, if perpendicular posts or blockshad been introduced into the triangular space formedby the inclined timbers which support the platform ofthe bridge.
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Over an arm of the Neckcr, which is 93 feet wide, is a light horse bridge 8 feet span ;two sets of king-post trusses in the parapet strengthen the main longitudinal timbers,
HORSE BRIDGE, NECKER.
but from the disconnection of the middle pieces of framing, thisarrangement of the timbers must be very defective.
Notre jDame at Cahors , built by Sganzin, has a clear widtli ofcarriage-way of 17 feet, and a span of 95 feet, formed of onepolygonal arch, the versed sine of which is between a fourthand a fifth of the span ; its composition is defective, from beingcomposed of too many pieces, which must be subject to aconsiderable shrinking, and seriously derange the whole
Fig. 2237. NECKER.
Fig. 2238. NOTRE DAME AT CAHORS .
framing; when the timbers are thus shortened, the angles of their junction necessarilybecome more obtuse, and in consequence are likely to open, particularly when heavy loadspass over them. This cannot he considered any great improvement in construction overthe bridge of Mulaticre at Lyons.