However, materials could be misapplied in bridge structures, and disaster could follow very quickly. During the expansion of the railways in the 1830s and 40s, many bridges were needed to cross rivers and estuaries to create a viable network. Growth of the rail network was vital for industrial growth by opening up local markets to a wider audience, and for transport of energy resources, especially coal, and materials such as natural fibres and iron itself.

One such bridge across the Dee at Chester, was made using cast iron beams. It cracked in the middle while a train was passing over, and the carriages fell into the tidal river below killing seven (Figure 4). Robert Stephenson claimed that the train hit the bridge and caused the collapse, but the local inquest jury found the design to be faulty, and condemned it in very forthright terms. The tragedy happened just four years before the Great Exhibition, and led to changes in the way cast iron was used, and greater use of wrought iron, which is much tougher and can be used in beams (such as those in the Crystal Palace).

Figure 4: The collapse of the Dee Bridge, Chester 1847

The rail network helped industry transport its products, and grew yet further in the century, further stimulating industrial growth (a process known as positive feedback). Workers were more mobile as well, so that special skills could be traded over a much bigger area than before. However, the larger estuaries provoked problems, especially by their size or the height of the surrounding country. The Forth and Tay estuaries in particular, proved to be substantial obstacles to the network, especially if lines from Edinburgh to the North were to be shortened. The story of the bridging of the two estuaries is both tragic and heroic. The first attempt was made by bridging the Tay with a 2 mile long bridge, then the longest in the world. It survived for just over two years before falling in a severe gale on December 28th, 1879, taking with it a whole train. There were no survivors from the 75 passengers and crew (Figure 5). During its short life however, it stimulated the growth of the textile industry in Dundee by providing coal for the steam engines which powered the looms and other textile machinery. So why did it collapse?

Figure 5: The fallen Tay Bridge, as shown in the popular press

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