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Introducing engineering

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Figure 58 comprises 5 photographs labelled 'a' to 'e' that are increasingly closer views of some components of a bridge. Photograph 'a' shows the complete bridge. The overall external structure of the bridge is evident. It is a very long bridge (over 5,000 metres) but the central span is less than a tenth of that length. The central span is supported by cables connected to very tall slim towers at either side of the span. The rest of the bridge comprises much shorter sections supported by pillars. Photograph 'b' is a close up view of the end of a supporting cable. The cable consists of about 100 smaller cables and each of these is made of multiple strands twisted round a central bar. Photograph 'c' is taken so close to the object that it is not possible to discern the form of the object. The whole photograph is a mosaic of 300 to 400 small irregular shapes. Most of the shapes are a shade of grey or white and the gaps between them are black. About 10% of the shapes are black and it is possible that these are bigger gaps where the lighter shapes do not interlock. Photograph 'd' is just a mottled surface covered in groups of parallel striations inclined about 30 degrees up or down to the horizontal. Photograph 'e' is a pattern of about 600 small circles arranged in about 30 rows slightly inclined to the horizontal.