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The keys themselves, against which the ribs abut, are cast with socketson each edge, for the reception of the rounded ends of the main ribs, and withholes through the centre, to admit the wrought-iron bar of the main strut, beforedescribed.

The outside key has its face cast with a sunk panel, the edges of which areneatly rounded; it has also a plate falling beneath the general level of the bottom,in order to hide from view the top part of main street.

A long strip of boiler-plate, 1| inches thick, and 1 foot wide, is to extendthe whole width of the bridge, at the point where the main ties unite, and it mustbe firmly secured to the under edges of the main struts.

The roadway-plates are of two sizes, the one to extend over four ribs, theother over two ; and they must be so arranged that the smaller plates may breakjoint alternately with the larger.

At the points where they rest upon the main ribs they are to have projectingcleats, fitting exactly to the sides of the upper tables of the ribs, to which theymust be bolted down by wrought-iron bolts alternately on each side.

They are also to have diagonal flanges cast on their under sides betweeneach of the ribs, and projecting to the extent shown on the drawings.

The whole of the joints of the roadway plates are to be accurately fitted andcaulked w r ith oakum, so as to be perfectly water-tight; and a layer of concrete,6 inches thick, is to be laid over the w T hole surface.

A string course of cast-iron, in the form of a torus moulding and plinth, is tobe bolted to the top of the exterior ribs, and to the road-plates by lugs occuringat intervals of 2 feet.

It is further steadied by wrought-iron stays attached at one end to these tugs,and at the other to the inner sides of the plinth.

Sockets, as shown, are to be cast on the interior at every 2 feet, for thereception of the standard of the cast-iron railing hereinafter described, and theinside plate is to be cast loose, and afterwards screwed on.

The railing is to be of cast-iron, in lengths of 10 feet, as near as may be.

The standards of the railing are to be fastened into the sockets of the string-course, above described, with wrought-iron wedges, and the middle standard ofeach length is to be steadied by a bracket, or knee, riveted to it and to the top ofthe torus moulding.

The joints of this railway are to be made with half-laps, and neatly andaccurately riveted together.

The form and dimensions of the brickwork and masonry of the bridge areshown on drawing.

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