1S18.} across the Mersey, at Runcorn. 10 



if deemed requisite for the more commodious passage of vessels. 

 It is questioned, however, whether one pier in the centre would 

 produce any practical inconvenience, especially if the two side 

 piers were removed 50 or 100 feet towards the shores. 



In this design the central fulcrum, which may be formed of 

 masonry or cast-iron, is 95 feet, and the two others each 85 

 feet in height, above high water-mark • and those on shore are 

 formed rather higher than in Fig. 1, because, in order to pre- 

 serve the requisite height for masted vessels, this plan requires 

 that the upper surface of the road should be about 25 feet 

 higher than in the design, Fig. 1 . 



Over these fulcrums an iron web of chain-work, or any 

 number of lengths of jointed rods (say 30), are to be laid, 

 and stretched so that the catenarian segment may not depend 

 more from the chord line than 25 feet in the two larger openings, 

 iand proportionally in the lesser. This will leave 05 feet clear 

 through the whole extent of the two large openings of 600 feet 

 each, besides from 80 to 90 feet in the angles close under the 

 fulcrums ; thus affording ample room for the passage of vessels. 



The ends of these 30 rods may be inflected over the abutment 

 fulcrum, and fastened to the rock, as in Fig. 1 ; and the strain 

 on these fulcrums may be lessened by rods similar to C, C, in that 

 figure. 



A basis is now secured on which to place the road ; but as 

 it would be extremely incommodious to ascend and descend with 

 the line of segments, in order to avoid this, and have the road 

 on the line of chords, let it be raised so as to form one continued 

 inclined plane from the shore to the summit of the central 

 fulcrum. For this purpose the rods in each segment may be 

 connected crosswise at the distance of (say) 20 feet by a plate 

 and slender columns (say 11), raised from' each plate, of a suffi- 

 cient height to support the road on the chord lines of the arcs, 

 or in any one plane. This road may either be constructed as 

 in Figs. 1 and 8 ; or better, by simply fixing such plates, as 

 Fig. 16, to the plates or beams which connect the tops of the 

 columns. A railing, clay, gravel, &c. as in Fig. 1, may be 

 added, &c. &c. 



The advantages this construction would have over a road ^sus- 

 pended from an arch or arches of rods or chains, are, , 



1. That a greater number of rods may be used, and conse- 

 quently a greater degree of strength acquired.* 



2. That the whole of this strength can be equally brought 



• Since writing the above, I have seen at Mr. Brown's Chain Cable Manufac- 

 tory, Isle of Dogs, a model in which a road is suspended from an inverted cate- 

 narian arch by 16 chains, placed in fours over one another. This is evidently 

 much more secure, and suitable for alteration, renewal, or repair, than trusting 

 to four chaim of equal strength with these 16, and may serve to direct Uie 

 reader's attention to the comparative advantage of my design. 



B 2 



