316

HISTORY OF ENGINEERING.

Book I.

high water. The total length, including the abutments, is 250 feet; it is terminated by aT head, 90 feet in length, and of the same width as the main portion of the pier, whichis 30 feet. 'The platform is supported by 22 cast-iron columns, with girders of the samematerial.

There are three columns on each tier, with girders of 22 feet span, and three main spansto where the T head commences; the first two are each 50 feet, the other 51 feet. Thecolumns are 28 feet in length, except in the first tier, which are shorter; their bases

SPRING

MUD

CONCRETE

CHALKFig. 320.

TERRACE PIER.

FLINT

Fig. 321. TERRACE PIER.

are laid level with low water spring tides, and their caps 8 feet above the level of highwater spring tides, which rise 20 feet, so that there is never less than 8 feet headwaythroughout.

By means of a tide guage, employed whilst the works were in progress, it was found thatthe greatest rise of the tide was 22 feet 9 inches, and the lowest ebb was 1 foot 9 inches