1818.] across the Mersey, at Runcorn. 25 



view so well as the second, which is that attempted in the design 

 submitted. 



The first part of the construction calculated to resist resiliency 

 is the entire suspension of the road from one shore to the other. 

 Did it rest on a solid body of cast-iron or masonry at the ful- 

 crums, instead of being suspended from them, that part of the 

 road being fixed would become a point of resistance to reflect 

 back the impulse propagated horizontally by a heavy body 

 moving from the fulcrums along the road in either direction, and 

 would thus (in a lightly constructed and highly loaded road at 

 least) occasion, first a springing or undulatory motion, and then, 

 not having exhausted itself, a degree of lateral resiliency. But 

 by the road in this design being every where suspended, it no- 

 where affords points of resistance ; whatever motion is generated 

 never can increase, because it meets with no interruption ; it 

 will, therefore, expend itself in gentle pulsations lengthwise. 



Lateral resiliency is occasioned by an interrupted longitudinal 

 motion. As above hinted, it can hardly take place in this road ; 

 but if it should, the divergency of the suspending rods will 

 oppose a salutary counteraction. 



IV. As to the Mode of Execution. 



A few hints shall be submitted under this head, lest some 

 should imagine this design more difficult of carrying into effect 

 than an inverted arch. 



The fulcrums, being previously fitted together where cast, may 

 be erected with scarcely any other scaffolding than what they 

 themselves afford. Triangles may be screwed to the columns, and 

 the separate pieces hoisted up, and dropped in their places, &c. 

 Sec. The rods forming the basis of the road are to be elevated, 

 and fixed in their situation, by the following arrangement : 



Form a catenarian arch of six or eight common chains, and 

 let it be stretched from shore to shore over the tops of the ful- 

 crums, but having pulleys, with ends of ropes over them, fixed 

 eveiy 40 feet asunder. Raise this arch so as to be a few yards 

 higher than the situation of the road. This being done, and the 

 basis chains all attached, and in order, place that length of 

 basis belonging to the centre opening of the bridge on a platform 

 of boats directly under the suspended arch : then let 26 or 52 

 men seize the ropes dependent from the chains, and hoist up 

 the basis rods to their situation. One or two men may then 

 mount by the fulcrums, and belay or fasten the ropes. The 

 hiisis rods of the two sides are to be raised in like manner ; and, 

 wlicn elevated, joined under the fulcrums. 



The permanent suspending rods are now to be laid over the 

 fulcrums, and to be attached (beginning at the fulcrums) to the 

 basement rods, fixing with them the outside plates of the 

 wrought-iron frames, as shown at Fig. 9. This must of course 

 be done 8,0 as what is on one side of a fulcrum may always be 



