# Cambridge Mathematical Bridge

The Mathematical Bridge in Cambridge spans the river Cam, and belongs to the Queens College, one of the many colleges of Cambridge University. This popular and simple wooden bridge is centuries old and has its own story. Most locals would refer to is as the Mathematical Bridge although its official name is the prosaic Wooden Bridge. And the interesting thing is that this bridge can be found in Oxford too.

### Mathematical Bridge Photo

We are sharing the majestic shot of Christopher Chan who managed to capture the bridge in beautiful lights and fine details.

### The Legend of the Mathematical Bridge

According to the legend or anecdote, much favoured by Cambridge tour guides, the Mathematical Bridge was built by **Newton** from nothing else but wood. No nuts, no bolts, just what wood can make and bear. The legend says that Sir Isaac Newton built the bridge to illustrate the principles and properties of force and gravity.

Then, after Newton’s death, the **students** / fellows of Cambridge University, who were curious to learn about the exquisite structure of the clever wooden bridge, disassembled the Mathematical Bridge, but failed to **re-assemble**it properly. As they could not put together the intelligent bridge again, they had to use iron pins, nuts and bolts to make the bridge functioning again.

It is a lovely story, and a wishful credit to the mathematical genius of Newton, but it is nothing more than a **colourful anecdote**. The truth is that such a bridge could not have been built from wood only, taking its size, weight and structure into consideration.

Not to mention the fact that Newton was already dead in 1727, by the time the bridge was actually built in **1749 by James Essex the Younger**.

### The History of the Mathematical Bridge

**1749**: the Mathematical bridge is built

James Essex the Younger, an English builder and architect, built the Mathematical Bridge in 1749 to the design of William Etheridge. James Essex himself was a former grammar student of the King’s College, and worked on many of the colleges of Cambridge University. William Etheridge was an 18th century carpenter working on several bridges, e.g. the first bridge at Westminster, and the one in Walton too. His design for the Walton Bridge was clever and mathematical indeed, as it ” was built so that a single timber could be extracted and repaired without disturbing the rest of the bridge”, according to Colin Bentley in the “History of Walton Bridge”.

**1866**: the bridge is rebuilt and slightly modified

The old Mathematical Bridge, i.e. the Queen’s Bridge of the 18th century had to be rebuilt – to the same design – in 1866, when it became too worn to use. The steps leading up to the bridge were replaced with a ramp / slope, so now the bridge is accessible with wheels too.

**1905**: in 1905 the once oak bridge has been replaced with teak.

**1924**: a copy of the bridge was built in Oxford, England.

**1900**‘s?: the legend of the Mathematical Bridge is born and told many times

### The Mathematical Design of the Bridge

According to the historical tour guide of the Queens College Cambridge, the efficient arrangement of the timbers in the Mathematical Bridge (or Queen’s Bridge) is a series of tangents that describe the arc of the bridge, with radial members to tie the tangents together, and triangulate the structure. This triangulation in turn makes the bridge rigid and self-supporting. The technical term for this type of bridge structure is **tangent and radial trussing**. The technique of tangent & radial trussing is not limited to timber / wood bridges, but was also widespread in the construction of stone bridges. The illustration of the trussing is very helpful (made by Cmglee)

The joints of the present bridge are fastened by nuts and bolts. Earlier versions of the bridge used iron pins or screws at the joints, driven in from the outer elevation. Only a pedant could claim that the bridge was originally built without nails.

Video of the Mathematical Bridge, Cambridge

### President’s Lodge, Cambridge

The red-brick building on the right of the Mathematical Bridge is the so called **President’s Lodge** (ca 1460, the oldest building on the river at Cambridge, almost destroyed in 1756 in order to give space to the Essex Building (1756-60). These two buildings now are connected. On the other side of the President’s Lodge, you can see the Cloister Court. The part of the building that juts out into the river was a garderobe (i.e. a medieval toilet), ideally positioned over the river Cam “for the quick disposal of effluent”, i.e. to pour the waste of the medieval toilet into the river directly (this practice was common until very late, so if you go punting on the river, do not soak or swim in the river Cam).

### The Mathematical Bridge in Oxford

The 18th century Wooden Bridge of the Cambridge Queen’s College, is also one of the footbridges you can walk or ride through in Oxford, England. The Iffley Lock in Oxford is in fact a 20th century scaled-down copy of the Queens’ bridge aka Mathematical Bridge. The Iffley Lock was built in 1924.

### William Etheridge

Who was William Etheridge?

William Etheridge was one of a very long family line of carpenters called variously Edrich, Edriche, Eteridge, or Etheridge from Stradbroke and Fressingfield in Suffolk. His birth is not recorded, but his baptism took place on 3rd January 1708 (possibly old-style, or 1709 in modern counting) at St Margaret’s parish church, South Elmham, about 5 miles north-east of Fressingfield. His career as a master carpenter first comes to light in 1738-1749 when he worked under James King [master carpenter, not King James] in the building of the first bridge to cross the Thames at Westminster, first as King’s foreman, then replacing him after King’s death in 1744. He was credited as the inventor of a battering ram to assist in the striking of the centres, and an underwater saw to cut off piles underwater. From 1747-1750 he worked on the Walton Bridge, and in 1748 produced the design and model for the Queens’ bridge. From 1751-1756 he worked as surveyor for the construction of Ramsgate Harbour in Kent. In 1761 he was consulted on the state of St Olave’s bridge at Herringfleet, Suffolk. He died aged 67 on 3rd October 1776 in Westminster (source: Queens College website)

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What is the span of the bridge?

I would like to build one on my backyard pond. Do you have any plans that could be scaled up or down for use?