Sarah Guppy (1770-1852) was an English inventor, wife of a Bristol industrialist and the mother of Thomas Guppy, who worked with Isambard Kingdom Brunel on many projects, including the ss Great Britain.
What did Sarah Guppy patent?
In 1811, Sarah Guppy patented ‘a new mode of constructing and erecting bridges and railroads without arches or sterlings whereby the danger of being washed away by floods is avoided’. She was the first woman ever to patent a bridge.
The patent has no drawings and no detailed information as to how the bridge was actually to be built. However, from her outline description, it is clear that she envisaged a pair of chains over which would be laid timber planks to form the deck. The chains would be anchored to some kind of timber framing protected by piles, though there are no specific details of how she intended to achieve this.
She promoted her design vigorously particularly in the Bristol newspaper, Felix Farley’s Journal, from which it is clear that it was site-specific to the low-level River Avon crossing at Hotwells, upstream of the Avon Gorge. She also made models of her bridge.
Was Sarah Guppy’s patent a new idea?
Bridges made from rope or chain and laid with planks were well known in South America, India and China, and a few had even been erected in Europe. In 1741 the Wynch Bridge across the River Tees in County Durham was completed. Sarah may have visited this bridge or read about it in William Hutchinson’s 1794 book ‘The History and Antiquities of the County Palatine of Durham’. Her bridge was of a very similar type.
How do modern suspension bridges differ from Guppy’s design?
Guppy designed a bridge with an underlying structure of chains slung from bank to bank on which was laid a deck. The deck necessarily followed the curve of the chains beneath and such bridges had a tendency to sway.
The modern suspension bridge consists of a deck hanging from an overhead structure with a stiff flat deck. James Finley in America built the first bridge of this type in 1801, followed by many more. Meanwhile, in Britain, Samuel Brown and Thomas Telford were developing a similar bridge type. By 1820 Captain Samuel Brown completed the Union Bridge over the Tweed, the first suspension bridge designed specifically to carry traffic. It was followed in 1826 by Telford’s bridge taking the Irish mail road over the Menai Straits.
It is impossible to know from Guppy’s patent what form of chain she envisaged but it is likely that they were the type used for ships’ anchors. Finley, Brown and Telford developed long chains made either of round or flat bars.
Did Thomas Telford use Sarah Guppy’s patent?
In 1826 Thomas Telford completed the Menai Bridge. An opinion piece in the Bristol Mercury in 1839 refers back to a letter written by Guppy in 1811 and states that the bridge was completed using Guppy’s patented invention without charge. Since her patent contains no drawings and no construction details of any kind which anyone could use, it is more likely that the Mercury piece was written by her family to rehabilitate her reputation after she married a man more than 20 years younger than she was.
Furthermore, Telford’s bridge was of a completely different type. It has been claimed that Telford used the piles she mentions in her patent. Such piles were certainly necessary when building in the soft ground of riverbanks but they had been used since ancient times for buildings as well as bridges. Telford, as an experienced engineer who had been building bridges since 1790 would have known all about piled foundations for piers on banks and in river beds.
Did Sarah Guppy enter a design into the competition to build a bridge across the River Avon?
When Bristol wine merchant William Vick died in 1754 he left £1,000 in trust to the Society of Merchant Venturers. Once this investment grew to £10,000 it was to be used to pay for a new toll-free stone bridge across the Avon Gorge at Clifton. By 1829 the fund was thought to be sufficiently mature to provide funds for such a bridge and a competition was set up. However, rather than a masonry bridge, a suspension bridge was specified in the advertisement. Guppy was clearly a highly intelligent woman with technical skills and it is impossible to believe that she thought her long-ago patent had any relevance to the competition. Instead, she threw her considerable influence into promoting the Clifton Suspension Bridge.
Should we dismiss Sarah Guppy?
Sarah Guppy was a very unusual woman. At a time when women were expected to dedicate themselves to domestic duties, Sarah’s business acumen, inventions and interest in engineering were certainly breaking the mould. She was exceptionally well-read, talented, creative and charismatic. She took out other patents, though for domestic appliances, to improve the lot of women. Her 1831 patent for a bedstead which included springs and rollers to provide exercise when in it. Although her bridge patent is slight and lacking any engineering information, it was nevertheless an imaginative solution to crossing the Avon and dealing with its high mudbanks. She deserves to be considered in a wider context and the extravagant and incorrect claims made for her bridge have overshadowed her many genuine achievements and the place she managed to win for herself against all the odds in an all-male world.
With thanks to Julia Elton. Read more on the Women Engineers’ History blog.