Chap. VIII.

BRITAIN.

439

width; so that when it was required to ease the centre, wedges were driven along eachother, and slid down the inclined plane into larger spaces than they had previously occu-pied : the whole centre, consequently, could by this means be made to descend very gently,and remain so during any part of the operations.

The inclined piles, which carried the weight of the ribs of the centre, had their bearingon the offsets of the stone piers, which afforded a most effectual and perfect abutment;and it must be acknowledged, that the skill shown in putting together a centre of suchvast weight and dimensions is a strong evidence that improvement in bridge-building hasbeen greater here than on the Continent.

The section through the piers shows their construction, which is of solid granitethroughout; over the spandrills are rows of columns, which carry the roadway, and a pipeconducts the water from the channels of each gutter to an opening immediately above thelast set-off, where the pluvial waters are discharged into the river.

Fig. 412.

SECTION THROUGH PIER OP WATERLOO BRIDGB.

Great attention was paid to have the spandrills of the arches constructed with solidmasonry, laid in regular horizontal courses, and of one uniform thickness throughout, andwhere bedded upon the extrados of the arch, they were very carefully worked, so that thewhole was made solid and secure : before any course was proceeded with, the last executedwas dressed on the surface, and rendered perfectly even, that the layer of fine mortar intro-duced under the beds should have a uniform thickness: over these were constructed in-verted arches, the stones of which increased in dimension with the radius, and these alsowere carefully dressed, so that they should perform their office effectually, contributingadditional strength at the back of the main arches, where these were likely to spring,without adding unnecessarily to the weight on the piers: this feature in the constructionof the arches of a bridge was, perhaps, first introduced at Westminster, but was not thereso admirably executed as in the present example.

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