Arms The Bridge in Winter


The President's Lodge The Mathematical Bridge Essex Building Cripps Court Queens' College Cambridge - Bridge in Winter - JPEG 55K

The Wooden Bridge in winter - view from Silver Street bridge.

The bridge was built in 1749 by James Essex the Younger (1722-1784) to the design of William Etheridge (1709-1776). It has subsequently been rebuilt to the same design in 1866 and 1905.

The red-brick building on the right is the President's Lodge (ca 1460, the oldest building on the river at Cambridge). On the extreme right is the Essex Building (1756-60). Behind the trees on the left is Cripps Court (1974).

For those who have fallen prey to the baseless stories told by unscrupulous guides to gullible tourists, it is necessary to point out that Isaac Newton died in 1727 (biography), and therefore cannot possibly have had anything to do with this bridge. Anyone who believes that students or Fellows could have disassembled the bridge (and then failed to re-assemble it, as the myth runs) cannot have a serious grasp on reality, given the size and weight of the wooden members of the bridge. 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. Other baseless stories are that Etheridge had been a student, and/or had visited China.

History of the Bridge at Queens'

The erection of the bridge occurred at the same time as the building of brick walls along the river banks and alterations in the layout of the Grove. It can therefore be difficult in reading the college records to distinguish one project from another. The following entries in the Magnum Journale appear to be relevant to the Bridge or riverside works:

   

£.

s.

d.

1748 Oct 6  Mr Etheridge for the Design & Model of the Bridge 21. 00. 00
1749 Mar 25  Paid for removeing the Mud from the Bridge 01. 02. 6
1749 Jul 1  Paid for five Men for digging the River Bank 01. 11. 6
1749 Jul 8  Paid for six Men for digging the River Bank 02. 01. 6
1749 Sep 30  Paid for work in levelling the River Bank 0. 07. 6
"  Two Men levelling the Bank at the Bridge 0. 07. 0
"  300 Green Turf for the River Bank 0. 18. 0
"  Paid Wm Christmas for the Use of a Boat 00. 03. 0
"  Mr Groom for the Use of a Boat 03. 00. 0
"  Mr Tucke, the Bricklayer's Bill 114. 16. 8
"  Mr Bottomley, the Mason's Bill 151. 12. 9
"  Mr Essex's Bill for the new Bridge 160. 00. 0
1750 Sep 30  Cook ... a Supper on finishing the Bridge to Mr Essex's Men  0. 17. 9

It was the practice to account for the bills of tradesmen (including the College's own Cook) in a single lump sum on the last day of the academic year, so nothing much can be deduced about the timing of works accounted for on September 30th, other than that they occurred sometime in the previous twelve months. The supper that was accounted for in September 1750 might have occurred as early as October 1749. As Essex was paid in the year ending September 1749, it is reasonable to assume that all the works were executed during the summer of 1749. It is not possible to support the contention of Willis & Clark in The Architectural History of the University of Cambridge that the works took until September 1750.

The college still possesses an old model of the bridge, and we assume that this is Etheridge's model of 1748. It is to be noted that even the model has screws at the joints.

The design of the Queens' bridge resembles Etheridge's much greater Old Walton Bridge, a three-arch bridge over the Thames at Walton, built 1748-50.

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 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 and was buried on 15th October 1776 at Fressingfield.

The Queens' Bridge is the earliest recorded work of James Essex the Younger. He later constructed the Essex Building 1756-60, which was intended to be part of a new building along the complete riverfront, replacing the 1460s part of the President's Lodge, but which was never completed. He is buried in St Botolph's, church of the parish in which Queens' lies. His father James Essex had also been a carpenter, doing work in many colleges, including the panelling of the Hall at Queens'.

Rebuildings of the Queens' bridge

By the 1860s, the original bridge of 1749 was badly decayed. Photographs show many timbers patched, and the sides of the bridge apparently leaning inwards. It was repaired in 1866 at a cost of £348 7s. The entry for 1867 January 10th in the Conclusion Book records:

Agreed that the Bills for repairing the Bridge over the Cam, amounting to £348-7 having been received, that £148-7 be deducted from revenue for this year and £100 from revenue for each of the two next succeeding years.

There was one change of design: the pedestrian decking was sloped instead of stepped on each side, making it possible today for wheeled trolleys to be used over the bridge. The use of the word repairing suggests that this was not a complete rebuilding, however, and maybe parts of the original bridge were retained and continued to decay, explaining why this version lasted less than 40 years.

In 1905 the bridge was completely rebuilt, by the local builder William Sindall, in teak instead of oak. Once again, the cost of the new bridge was partly buried in the costs of a larger project of works to the riverside buildings, overseen by architect Thackeray H. Turner (1853-1937), of Balfour & Turner. The only invoice attributable solely to the new bridge was the final one of £207 6s 6d, but it seems unlikely that a bridge could have been built in 1905 for such a small sum. In this version of the bridge, the joints were fastened by nuts and bolts passing right through the joint, the bolt heads being on the internal elevations of the side arches, and therefore visible to people passing over the bridge. Previous versions of the bridge had the joints fastened by iron pins or screws driven in from the outer elevation, which were therefore not visible to the casual passer-by on the bridge, as the screws did not penetrate as far as the inner elevation. One may speculate that perhaps the sight of bolt heads where none had been seen before might have given rise to the myth of the failed re-assembly.

History of the design

Etheridge had previously been foreman to James King, master carpenter during the building of the first Westminster Bridge 1737-1750. It is to King that the interesting system of trussing may be attributed. The main members of each rib are set at tangents to the circle describing the underside arch of the bridge. An engineering analysis will show that, in the arch itself, each member is in compression with little or no bending moment, an ideal application of wood as a structural material. Where the main members cross, the wood joint is designed to transmit the compressive stress from one member to the next, with a bolt serving to hold the joint together laterally, rather than carrying any stress. There are also radial members which both support the top rail and lock all the overlapping tangents into a rigid structure, by creating triangles out of quadrilaterals. The load bearing deck is attached to the bottom of the radials, close to the junction of two tangents, where the applied load can balance the resultant of the two compressive forces from the tangents.

Westminster Bridge in wood by James King 1737.
James King used this system of tangent-and-radial trussing in his 1737 design for a wooden Westminster Bridge (seen right), but this was abandoned after the structure was damaged when the Thames froze over in the winter of 1739-40. This is the earliest known example of this style of tangent and radial design.

Wooden centre for Westminster Bridge 1741.
In 1741, construction of a Westminster Bridge in stone commenced, and James King was appointed to erect the wooden centres on which the stone arches would be laid. He used the same system of tangent and radial trussing for his wooden arched centres as he had employed in the earlier failed bridge. This design permitted shipping to pass under the arches while they were being erected.

Westminster Bridge, Canaletto 1746, detail.
Pictures by Canaletto show Westminster Bridge under construction with centres of this design under each arch. In the detail of 1746 shown right, wooden centres can be seen still in position under 5 arches, and scaffolding around some of the piers. The balustrade is not yet built, apart from the centre arch on the left.

London seen through an Arch of Westminster Bridge - Canaletto
Another painting by Canaletto purports to show a view of London through an arch of Westminster Bridge while the wooden centre was still in place. St Paul's can be seen on the right. But the artist has fallen into serious error: he has shown the wooden arch to have a semi-circular outline, when we know it was made from intersecting tangents. Also the perspective of the buildings seems to have been taken from roof-level rather than water-level. So I suspect that Canaletto never saw the underside of the wooden centres at all, and that this painting is more of a capriccio than an accurate landscape.

Etheridge took over the work at Westminster after King's death, and went on to use this system of trussing again in his designs for Walton and Queens', both in 1749.

The angle between two adjacent radials in the Queens' bridge (except the ones on the abutments) is one 32nd of a revolution: other examples of this design used different spacings. This is also, of course, the angle between adjacent tangents.

In the 18th century, the generic description for designs of this sort was geometrical construction, from which one might speculate that the phrase Mathematical Bridge could be derived.

Other bridges to this design

Etheridge's Old Walton Bridge has already been mentioned.

There once was a bridge of similar design on the site of the present Garret Hostel Bridge, between Trinity Hall and Trinity College. This was also built by James Essex the Younger in 1769. It was called a Mathematical Bridge in Cooper's Annals of Cambridge.

The footbridge at Iffley Lock, Oxford, is a scaled-down version of the Queens' bridge, built in 1924.

There was a footbridge at Winchester to the same design which lasted until 1976.

Further reading

Arch Bridges and their Builders 1735-1835, by Ted Ruddock, Cambridge University Press, 1979 (out of print).


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