The Mathematical Bridge is the popular name of a wooden footbridge in the southwest of central

Cambridge Cambridge ( ) is a College town, university city and the county town in Cambridgeshire, England. It is located on the River Cam approximately north of London. As of the 2021 United Kingdom census, the population of Cambridge was 145,700. Cam ...

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...

. It bridges the River Cam about one hundred feet northwest of Silver Street Bridge and connects two parts of

Queens' College Queens' College is a constituent college of the University of Cambridge. Queens' is one of the oldest colleges of the university, founded in 1448 by Margaret of Anjou. The college spans the River Cam, colloquially referred to as the "light s ...

. Its official name is simply the Wooden Bridge or Queens' Bridge. It is a Grade II listed building. The

bridge A bridge is a structure built to span a physical obstacle (such as a body of water, valley, road, or rail) without blocking the way underneath. It is constructed for the purpose of providing passage over the obstacle, which is usually somethi ...

was designed by William Etheridge, and built by

James Essex James Essex (1722–1784) was an English builder and architect who mostly worked in Cambridge, where he was born. He designed portions of many colleges of the University of Cambridge, and carried out major restorations of the cathedrals at Ely and ...

in 1749. It has been rebuilt on two occasions, in 1866 and in 1905, but has kept the same overall design. Although it appears to be an arch, it is composed entirely of straight timbers built to an unusually sophisticated engineering design, hence the name. A replica of the bridge was built in 1923 near the

Iffley Lock Iffley Lock is a lock on the River Thames in England near the village of Iffley, Oxfordshire. It is on the southern outskirts of Oxford. The original lock was built by the Oxford-Burcot Commission in 1631 and the Thames Navigation Commissi ...

Oxford Oxford () is a city in England. It is the county town and only city of Oxfordshire. In 2020, its population was estimated at 151,584. It is north-west of London, south-east of Birmingham and north-east of Bristol. The city is home to the ...

. The original "mathematical bridge" was another bridge of the same design, also commissioned by James Essex, crossing the Cam between

Trinity The Christian doctrine of the Trinity (, from 'threefold') is the central dogma concerning the nature of God in most Christian churches, which defines one God existing in three coequal, coeternal, consubstantial divine persons: God th ...

and Trinity Hall colleges, where Garret Hostel Bridge now stands.

Mathematical explanation

The arrangement of timbers is a series of

tangent In geometry, the tangent line (or simply tangent) to a plane curve at a given point is the straight line that "just touches" the curve at that point. Leibniz defined it as the line through a pair of infinitely close points on the curve. Mo ...

s that describe the arc of the bridge, with radial members to tie the tangents together and

triangulate In trigonometry and geometry, triangulation is the process of determining the location of a point by forming triangles to the point from known points. Applications In surveying Specifically in surveying, triangulation involves only angle me ...

the structure, making it rigid and self-supporting. This type of structure, technically tangent and radial

truss A truss is an assembly of ''members'' such as beams, connected by ''nodes'', that creates a rigid structure. In engineering, a truss is a structure that "consists of two-force members only, where the members are organized so that the assembl ...

ing, is an efficient structural use of timber, and was also used for the timber supporting arches (

centring Centring, centre, centering"Centering 2, Centring 2" def. 1. Whitney, William Dwight, and Benjamin E. Smith. ''The Century dictionary and cyclopedia''. vol. 2. New York: Century Co., 1901. p. 885., or center is a type of formwork: the temporary str ...

) used for building stone bridges. Analysis of the design shows that the tangent members are almost entirely under compression, while the radial timbers are almost entirely subject to tension with very little bending stress, or to put it another way, the tangent and radial elements elegantly express the forces involved in arched construction. MathematicalBridge1865.jpg, The Mathematical Bridge (approx. 1865) pictured shortly before it was partially rebuilt in 1866 Mathematical Bridge, Queen's College, Cambridge (South Face).jpg, South face of the Mathematical Bridge Mathematical Bridge tangents.jpg, The tangential members of the tangent and radial trussing are highlighted cmglee_Cambridge_Mathematical_Bridge_from_Riverside_Building.jpg, The bridge from Queens' College's Riverside Building

Myths

A popular fable is that the bridge was designed and built by Sir

Isaac Newton Sir Isaac Newton (25 December 1642 – 20 March 1726/27) was an English mathematician, physicist, astronomer, alchemist, theologian, and author (described in his time as a " natural philosopher"), widely recognised as one of the grea ...

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. Newton could not have been directly involved since he died in 1727, twenty-two years before the bridge was constructed.

References

External links

Photograph
of the original 1748 model of the bridge, made by William Etheridge and still in possession by

Clare College Clare College is a constituent college of the University of Cambridge in Cambridge, England. The college was founded in 1326 as University Hall, making it the second-oldest surviving college of the University after Peterhouse. It was refounded ...

{{Authority control Bridges in Cambridge Bridges completed in 1749 Bridges across the River Cam Pedestrian bridges in England Queens' College, Cambridge Wooden bridges in the United Kingdom Truss bridges Arch bridges in the United Kingdom Buildings and structures of the University of Cambridge Grade II listed bridges Grade II listed buildings in Cambridge

Mathematical explanation

Myths

See also

References

Further reading

External links