510

HISTORY OF ENGINEERING.

Book 1.

The two arches, through which the road passes, are 9 feet in width, and 15 feet to thespringing of the arches.

The width of the piers, taken on the transverse section at the base, is 66 feet 3 inches ;at the set-off, above the High water line, 58 feet 2 inches, diminishing at the top to a widthof 33 feet 8 inches, as measured at the bottom of the hollow which forms the cornice orcapping. Their depth, as measured in front, immediately above the set-off, above the highwater line, is 40 feet 1} inches. The construction of the pier is exhibited in the sections.

The resident engineer was Mr. W. A. Provis, the prover of the iron-work Mr. J. Provis,the contractor for the masonry Mr. J. Wilson, the iron-founder Mr. Iiazeldine, and thesuperintendent engineer of the iron and timber work Mr. T. Rhodes.

The masonry of the piers above the level of the roadway was strengthened by drillingholes through the stones of each course, and, after the insertion of iron bolts, fixing themwith Parker’s cement; wherever arches spring over the roadways, iron horizontal ties wereintroduced to prevent any spreading. In May and June, 1824, the two pyramidal pierswere constructed, and the cast-iron saddle plates fixed on their summits.

The Abutments, Piers, and Arches were commenced in the year 1820, and by March, 1822,all the piers were carried up to the level of the springing course, and the centres for thearches fixed ; by the end of the year, the whole of the arches were turned, and the spandrillsbuilt to the level of the cornice.

Fig. 513.

SECTION AND ELEVATION OF MAIN PIER.

The span of the side arches is 52 feet 6 inches, and their versed sine 26 feet 3 inches,forming semi-circles; the height of the small piers above the level of high water, to wherethe arches spring, is 65 feet.

There are four of these arches on the island side, and on that towards Caernarvonshire three; the distance from the centre of one pier to that of the other is 579 feet 10} inches.

The span of the catenary is 570 feet, and its versed sine 43 feet.

Materials employed. — For the masonry the grey marble was employed, which wasobtained on the shores of Penmon, at the north-east extremity of the island of Anglesea,7 miles from Beaumaris, and the price paid by the government to Lord Bulkley was 6d.per ton.

This fine stone bears a beautiful polish, and the natural layers or shelves afforded blocksof any required dimensions, which could be drawn from the quarry without blasting; it