Mathematical Bridge
The Mathematical Bridge is the popular name of a wooden footbridge across the River Cam, between two parts of Queens' College, Cambridge. Its official name is simply the Wooden Bridge. The bridge was designed by William Etheridge, and built by James Essex in 1749. It has been rebuilt on two occasions, in 1866 and in 1905, but has kept the same overall design. The original "mathematical bridge" was another bridge of the same design, also designed by James Essex, crossing the Cam between Trinity and Trinity Hall colleges, where Garret Hostel bridge now stands.

Mathematical explanation
The arrangement of timbers is a series of tangents that describe the arc of the bridge, with radial members to tie the tangents together and triangulate the structure, making it rigid and self supporting. This type of structure, technically tangent and radial trussing, is an efficient structural use of timber, and was also used for the timber supporting arches ( centring) used for building stone bridges.

A popular fable is that the bridge was designed and built by Sir Isaac Newton without the use of nuts or bolts. Various stories relate how at some point in the past either students or fellows of the University attempted to take the bridge apart and put it back together, but were unable to work out how to hold the structure together, and were obliged to resort to adding nuts and bolts. In reality, bolts or the equivalent are an inherent part of the design. When it was first built, iron spikes were driven into the joints from the outer side, where they could not be seen from the inside of the parapets, explaining why bolts were thought to be an addition to the original. Note that Newton died in 1727, 22 years before the bridge was constructed.

Building Activity

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