Chap. VIII.

BRITAIN.

423

parallel to the two short sides of each end of the piers, and about 30 feet distance fromthem ; the use of which fenders or guard piles was to secure the works from the approachof barges; the smaller boats were prevented passing between the piles by booms or longpieces of timber, which floated up and down with the tide alongside the piles, to whichthey were fastened by wooden rings, and proper iron work. By means of these boomsthe boats and vessels were secured from damage during the progress of the works.

By the 26th of October, 1738, all the piles necessary for building the two middle pierswere driven, and were found to stand so firmly, that the plates, whale pieces, ties, andbraces, originally intended to

be introduced were omitted. Jj

The number of piles used for * !Tu

building the first large pierwas thirty-four long andtwenty-two short ones; andfor the other large piertwenty-six long ones only.

The engine employed todrive the piles had a ram orweight of 1700 lbs., and theheight of the strokes at amean was 20 feet perpendicular : with two horses, it gave 48 strokes per hour, and withthree horses, 70 strokes per hour. When it had worked sufficiently long for the gudgeons

Fig. 427.

WESTMINSTER BRIDGE.

Fig. 428. WESTMINSTER BRIDGE.

or pivots to be rubbed smooth, and the stiffness of the ropes destroyed, three horses, goingat a common pace, gave 5 strokes in 2 minutes, on the ram being raised from 8 to 10 feet.

At the commencement of October, the grating for the first pier was finished, and thesides of the caissoon were placed upon it; these were made of fir timber, laid horizontallyand close, one over the other, pinned with oaken trunnels, and framed together at all thecorners of the caissoon, except the two points or salient'angles, where they were securedby proper iron work, which being unscrewed permitted two halves to be removed from thecaissoon, which were planked across the timbers, inside and outside, with 3 -inch planks ina vertical position; their thickness being 18 inches at bottom and 15 inches at top, and forfurther strength, every angle but the two points had three oaken knee timbers, properlybolted and secured. The bottom was formed of squared timbers, planked on the undersidewith 3-inch planking, and across the upper was laid timber 9 inches square, making theentire bottom 2 feet thick.

The length of each caissoon from point to point was 80 feet, the breadth 30, the height,including the thickness of the bottom, 18 feet, and the form that of the intended piers;it contained 150 loads of timber, and in capacity was equal to a man-of-war of forty guns.

After the pier was built sufficiently above low water, and the masons could work with-

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