Saturday, 2 April 2016

A Mythemagical Bridge

If you've ever visited Cambridge (England, not Massachusetts) it is quite possible you've looked around some of the more picturesque colleges in that fine old university town. There were 27 of them when I lived there, but 4 new ones have sprung up since. Many of the colleges back onto the River Cam (an area known as 'the backs') and several of them straddle it, with land and buildings on both banks of the river.

Queens' College is one such. Queens' was founded in the 15th century and some 300 years later the college authorities took the decision to build a footbridge that would link the two sites to save dons and students the inconvenience of travelling a couple of hundred yards out of college and across the adjacent public road bridge. You may recognise the famous 'Mathematical Bridge', as it has become known, from the photograph below, but it is unlikely you have ever seen it looking so jolly!


Of course, this photograph has been enhanced by coloured overlays to demonstrate the principles of the bridge's construction and strength.

Designed by one William Etheridge, a master carpenter from Suffolk who learned his trade as part of a team that built the first Westminster bridge over the Thames (and is also credited with developing an underwater saw), the 'Mathematical Bridge' was constructed in 1749 as a 'tangent and radial trussing' structure. Yep, what that means is: some of the timbers are arranged in a series of tangents that form the arc of the structure while other timbers are positioned radially to hold the tangents together and make the whole piece self-supporting (in a series of triangulated quadrilaterals). The design places compression stress on the tangential timbers but also transmits that stress evenly through the construct, a most appropriate use of wood as a structural material. If it looks a bit like a segment of the rim of a circle, that's exactly what it is. Thirty-two such bridges conjoined would make a complete wheel!

In fact, such wooden structures were - and are still - used to form the temporary scaffolding over which to fashion permanent stone or brick bridge arches.

The cleverly intricate construction - a beautifully arched span formed entirely out of straight lengths of oak - is what led the Wooden Bridge (to give it its formal title) to acquire its popular nick-name of the 'Mathematical Bridge'. The one which spans the Cam today is not the original version. That first bridge was replaced in 1866 by an exact replica. The second generation Wooden Bridge lasted less than half a century, being superseded in 1905 by the current incarnation, constructed this time in teak rather than oak.

So where, you may be asking yourself, does the myth part come in? Right on cue... It used to be said that the bridge was a work of genius, designed by Sir Isaac Newton and had been so cleverly devised that it was put together and stood strong without the use of a single bolt, nail or screw. Furthermore, that the curious fellows of Queens had, a century later, dismantled the bridge to see if they could figure out how Newton had done it, but then found they couldn't re-assemble it without the use of bolts and screws. All of that is complete - albeit entertaining - cobblers, to use the vernacular; a colourful spiel to spin to gullible tourists. For one thing, although Sir Isaac was Professor of Mathematics at Cambridge, he was a Trinity College man and, more to the point, had been dead for a couple of decades before the bridge was built. For another, Queens' College still retains Etheridge's drawings and original scale model for the Wooden Bridge, showing precisely where the coach-bolts were to be positioned.

That just leaves the magical bit - and for that I offer you this week's poem. Enjoy...

A Mythemagical Bridge
The where, with all beyond recall.
The why, no matter anymore.
The who, well, there's the rub.
We came from out the sea,
We slept in caves, we lived in trees.
We must have loved, perhaps we cried,
Suppose we tried to live good lives.
Please don't attempt to read our thoughts.
You're breaking down an open door...
There's nothing left to free.
Identity parades elusively.
All else denied
But habit, steely instinct,
A segment of that circle which was lost
Rises hopeful still
From out the misty marshland
Of mis-remembered will
To span this chilling ether ridge
Into yon bold, bright electropolis,
There to celebrate at last
The miracle of nostalgia with no past.

Thanks for reading. Have a good week, S ;-)
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1 comments:

Anonymous said...

Have you seen the wonderful Canaletto painting 'A View of Walton Bridge' c 1751? This bridge was also designed by William Etheridge.