ABSTRACT
Cast iron resembles a brick to a certain extent in opposing great resistance to being crushed compared to that which it offers to being pulled asunder, while wrought iron far excels the cast metal in tenacity, but is inferior to it in resistance to compression. The Britannia Bridge, which carries the Chester and Holyhead Railway across the Menai Straits, is perhaps the most celebrated example of an iron bridge on the girder principle. The general principle of the suspension bridge is exemplified in a chain hanging between two fixed points on the same level. The use of iron wire instead of wrought bars has enabled engineers to far exceed the spans of the bridges already described. The cables pass downwards through an opening made in each of the middle stones, and are secured at the bottom by stirrup-irons and keys.
