188 CRITICAL REMARKS

to give the chain a sinking or curve of the one full seventh offthe span. The ends of the chains must descend from the topsof the piers with the same inclination that they take inwards,until each end reaches the bottom of a digging, large enoughto contain stones and other materials sufficient to connterba-lance the weight of the Bridge, and what may chance to bethereon. The chains, if only one to a side, must be madewith four branches, at each end, to be let down through asmany stones, and to be bolted below. These stones are laidflat on the bottom of the digging; other flat stones may beplaced thereon, to.bind and connect the whole, that they mayhave the same effect as a platform of one piece ; four or morejoists will be necessary for the upper tier—to extend fromend to end of the Bridge—each will consist of more than onepiece; the pieces had best pass each other side by side, sothat the ends may rest on different joists on the lower tier.The splice will then extend from one joist to another of thelower tier, and must be bolted together by one bolt at eachend of the splice. The plank flooring is laid on this tier. Itwill be probably found most convenient that the chains bomade with links as long as the space between the joists: eve-ry other suspender must attach to a link of the chain edge up-wards ; perhaps this may best be done by a clevis to go throughthe upper link of the suspender, and embrace the link of thechain and receive a key above—the other suspenders willcome up through the flat links of the chain and receive a keyabove—the lower end of the lower link of the suspender maybe made so wide as to receive the end of the lower tier ofjoists.

The author further observes there are eight of these Bridges,erected since the year one thousand eight hundred and one;the largest is at the falls of Schuylkill, three hundred and six-feet span,* one pier ten feet wide ; supported by two chainsof inch and a half square bar.

One at Cumberland , (Maryland ) one hundred and thirty

* If the ten feet pier is in the centre of the three hundred and six feetlength, the span of each division is one hundred and forty eight feet.