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XIII. — On the Security and Limit of Strength of Tubula 

 (xirder Bridges constructed of Wrouffht Iron. By WlL- 

 LiAM Fairbairn, Esq., V.P. 



Read April 2, ISSO. 



Bridges have been in use from remote antiquity, and 

 have received in all ages that consideration which the im- 

 portance of the structure, and their great public utility, so 

 justly entitle them to. They form the connecting link 

 between one part of the earth's surface and another ; allow 

 of a continuous coijimunication, by connecting the opposite 

 banks of rivers and deep ravines, and overcome various 

 obstacles which might otherwise be considered impassable. 

 They, in fact, form a very important element in that system 

 of communication by which the civilized nations of the world 

 hold intercourse with each other, and which constitutes the 

 jnedium of commercial interchange between the different 

 districts of a country. They add facilities for the enjoy- 

 ment of social life — for the easy direction of the necessary 

 political supervision — and for that invaluable interchange 

 of intellectual and physical relations, which contributes so 

 largely to the wealth and intelligence of a nation. They, 

 moreover, in modern times (associated with that wonderful 

 development of iron " highways," which now traverse in 

 every direction the surface of the country) constitute a 

 medium of concentration in that union of distant objects, 

 which is productive of so much benefit, and by which — 

 through the aid of the locomotive engine — the remotest 

 districts of the empire are now united. 



