4>2G Mr. Seaward on Suspensio?i Chain Bridges. 



were the principle of the design clearly understood, it would 

 Bieet with a favourable reception. 



The number of chain bridges and piers which are now 

 building or projected, render these structures objects of great 

 importance : the principles of their construction therefore 

 cannot bp too fully investigated. 



In the accompanying design and description which I have 

 the pleasure of handing you, in the hope that it may be 

 found worthy of a place in your widely circulated publica- 

 tion, I have endeavoured to set the merits of the two plans 

 fairly at issue, so that their respective advantages may be 

 fully appreciated. 



It is right you should be informed that I find I cannot 

 claim the originality of the idea, as I have learned (but not 

 till long after I had written the accompanying description) 

 that a bridge on nearly the same principles was projected 

 some years back by a gentleman of the name of Anderson, and 

 a similar one by another gentleman of the name of Loudon. 

 The plan of the latter is accompanied by some geometrical 

 references, but which I do not think are quite explicit, or 

 calculated to place the merits of the question in the clearest 

 point of view. I am yours, &c. 



12 Walcot Place, Lambeth, JoHN Seaavaud. 



Dec. 11, 1823. 



The first suspension bridges that were ever formed, were 

 probably nothing more than two or three ropes or flexible 

 chains stretched across a river from two eminences, upon 

 which boards were placed, and thus formed a tolerably easy 

 communication between the opposite shores : something of 

 {his kind we are informed were the bridges of the Peruvians 

 and other primitive nations. 



But when suspension bridges became objects of attention 

 to more polished nations, the plan of forming the roadway 

 upon the chains themselves was soon perceived to be attended 

 with many inconveniences ; a much more eligible plan was 

 therefore early adopted, namely, the forming the roadway in 

 a perfectly horizontal straight line, and suspending it by 

 means of chains attached to high towers placed at the ends of 

 the bridge. On this plan a suspension bridge has lately been 

 built over the river Tweed : and the noble structure intended 

 to form a communication between the opposite shores of the 

 Menai is proposed to be executed in a similar way. Fig. 1 

 is an elevation of a suspension bridge of this description: — 

 ACB represents the chain in the form of the catenary curve ; 

 the horizontal roadway EF being supported by vertical rods 

 attached to the suspending chain. 



Notwitli- 



