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DESCRIPTION OF THE PLATES.

operating in an opposite direction, to tear it asunder. To resistthese opposing forces, it will be observed, that the flexiblenature of the material required a greater number of cells on thetop than what appears to be necessary in the bottom. In fact,from the nature of the strain, cells are not required in the bot-tom ; and it will be noticed, that in order to effect the greatestpower of resistance, the plates are not only double the lengthof those on the top, but they are differently constructed, anddifferently jointed to those intended to resist compression. Inthe width of the D and E platforms, the plates are six in num-ber ; they are each 12 feet long, and are composed of twoseparate layers, one over the other, with alternate joints meetingon the middle of each plate ; and by the use of long and strongcovering plates “ chain-riveted,” as shown on Plate V., a power-ful and continuous series of horizontal and vertical platforms arethus presented to the tensile strain of the tube. These plat-forms are composed of plates which vary in thickness from -^thsin the middle to -^-ths at the ends, and are tongued or dove-tailed into each other, as shown at A, A, A, &c., fig. 4. Thebreaks or jointings of the different thickness of the plates arerepresented in the same manner in all the other figures, each ofwhich must be viewed as a separate and detached part of thetube.

The letters G, H, K, fig. 1, represent sections of those partsof the piers of the Britannia Bridge wheron the tubes rest.In that view K is the land abutment, H one of the piers at themargin of low water-mark, and G the Britannia tower, built onthe rock of that name, in the middle of the straits.

Pig. 6 is a section of the tube, and to which the letters A, B,D and E, on figs. 2, 3, 4 and 5, refer.