456 Proceedings of the 



Proceeding's of the Royal Institution of Great Britain, 



On the evening o^ Friday^ the 16th of March, Mr. Ainger gave an 

 historical view of the principle and construction of Suspension 

 Bridges. The following is an abstract of his discourse : 



Suspension bridges appear to be among the earliest inventions 

 of mankind. They are known to have existed over mountain- 

 clefts and torrents at very remote periods in all parts of the world, 

 especially in Asia; and they are now found, of great magnitude, in 

 countries so little advanced in civilization and science as to prove 

 that they require no considerable exertion either of skill or saga- 

 city. These early bridges consist mostly of ropes manufactured 

 from vegetable fibres, sometimes of wooden bars linked together* 

 and, very seldom, of iron chains. It is said also that, in the East, 

 they use for this purpose the rattan, or common cane, which, when 

 young, is so flexible as to allow of being tied in knots, like a 

 string. 



In all these cases the roadway of the bridge has been laid im- 

 mediately upon the ropes or chains, and has thus partaken of their 

 curvature ; differing, in this respect, from the bridges of the last 

 twenty years, in which the roadway, being suspended below the 

 chains, may be made perfectly level. This improvement, combined 

 with the increased and economical manufacture of iron, has given 

 an impulse to constructions of this sort, from which the greatest 

 commercial benefits may be anticipated. 



The credit of this application is due to America, whose example 

 has been rapidly followed in this kingdom, and has since extended 

 to the continent of Europe. The most magnificent work of this 

 kind which has yet been executed, is the stupendous bridge over 

 the Menai Strait, erected by Mr. Telford. 



The most striking circumstance in these bridges is their great 

 economy as compared with ordinary, or what are called insistent 

 bridges. That economy arises from the power of a suspension 

 bridge to vary its curve so as to adapt it to any variation or partial 

 excess in its load, in consequence of which the strength of the 

 chains may be with great precision adjusted to any required strain, 

 and no more : while in insistent bridges the liability of the arch 

 to a fatal derangement of its form by partial or excessive pressure, 

 requires an enormous increase of weight and of strength beyond 

 what is requisite for the mere support of its load, supposing it to 

 be uniformly distributed. 



