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PLACE YOURSELF AT 52.2022 N, 0.1150E (for armchair travellers, Google Maps will help). Good, you’re now on the River Cam in Cambridge, England, 60 miles north of London. I like to think you are punting.

The building on one side of the bridge is the President’s Lodge of Queen’s College. Built around 1460, the President’s Lodge is the oldest building on the river in Cambridge. Queen’s College was established there in 1448.

The University of Cambridge dates from 1209 and is the second-oldest English-speaking university in the world. Oxford scholars moved there after a town-versus-gown controversy back home. Together, the two institutions of higher learning are often referred to as Oxbridge.

The Mathematical Bridge at Cambridge was designed in 1748 by William Etheridge, c. 1709 – 1776, and erected a year later by James Essex the Younger, 1722 – 1784.

There’s a charming myth that the Mathematical Bridge was designed by Sir Isaac Newton and built without nails. Indeed, the original one used iron pins or coach-screws at the joints, driven in from the external side (and thus not visble to those crossing the bridge.) Subsequent rebuilds used coach-bolts and nuts. As for Newton’s contribution, it would have involved ghostly channeling because he died in 1727.

Other tales are that Etheridge was a student or a Fellow at the University and, having visited China, had copied a Chinese bridge design.

The earliest description in print of the bridge appears in *The History of the University of Cambridge,* by Edmund Carter, 1753: “The Bridge from the Cloister to the Stable, &c. which was wholly rebuilt *A.D. *1746; may without Flattery, be esteemed one of the most curious pieces of *Carpentry *of this kind in *England….”*

My source, queens.cam.ac.uk, observes that “Carter was not renowned for his accuracy: the incorrect date of 1746 was reproduced in many subsequent histories and guides.”

The bridge’s sobriquet appears to date from earlier than 1808, when one guide wrote “Usually known by the name of *Mathematical Bridge*.” Its principal timbers are aligned in a series of tangents to an arc. Its radials tie the tangents together and triangulate the structure.

Technically, such a structure is known as tangent and radial trussing. Its first known use was by James King, for whom Etheridge worked in the construction of London’s Westminster Bridge in 1737.

A tangent and radial trussing design is structurally efficient in several ways: The arches are designed to be in compression, with little or no bending, an ideal application of wood as a building material. Where they meet, the joints are also in compression; their bolts hold them together laterally. The radial elements’ triangulation gives the structure enhanced rigidity and strength. Any one piece can be replaced without affecting the others.

The Mathematical Bridge is 50.8 feet in length. The angles between adjacent radials, except for those at the abutments, are all 1/32nd of a revolution.

You can view the Mathematical Bridge from a punt. It’s just north of Scudmore’s Mill Lane Punting Station. Also, while I’m at it, armchair traveling, I must have a look at Sherlock Court, three blocks east. ds

© Dennis Simanaitis, SimanaitisSays.com, 2016

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