Benjamin Franklin in London
'Benjamin Franklin in London' was on display at the Royal Society in 2006.
Benjamin Franklin by Joseph Wright 1782
The image is the most familiar in science: Benjamin Franklin flies his kite in a thunderstorm to demonstrate that lightning carries an electrical charge. Joseph Priestley believed that the kite experiment of 1752 was "the greatest, perhaps, in the whole compass of philosophy since the time of Sir Isaac Newton". It had an additional outcome: it made Franklin internationally famous beyond the scientific community as his work was published in the Royal Society's Philosophical Transactions.
This was the high-point of wide-ranging scientific research, much of which was reported to the 18th century Royal Society. Franklin was the first person to develop the hypothesis that whirlwinds and waterspouts have vacuums at their centres, while he revealed a practical, inventive side to his talents. Franklin's Pennsylvania Fireplace', an energy-saving cast-iron stove was the first of many advances for which he refused patent royalties, arguing that ideas should be used for the common good.
The electrical work of this period remains Franklin's best-known achievement. In corresponding with Peter Collinson FRS, a London Quaker merchant, the American learned of the newly invented Leyden jar, an early type of capacitor devised in the Netherlands in 1745. Franklin made his own and wrote back to Collinson with an explanation of how the capacitor stored electricity. His ideas of positive and negative charge and the conservation of charge were vital in building the foundations of modern electrical science, inspiring the next generation of European experimenters, including the Italians Giovanni Battista Beccaria and Alessandro Volta.
These were courageous experiments, cementing the notion that Franklin was a frontiersman in the heroic mould. In 1751, Franklin described to Collinson how he almost electrocuted himself while conducting experiments on turkeys. The kite experiment came one year later, in which Franklin ran a hemp string from the kite to draw down electric charge from a storm cloud, pressing his knuckle to a key on the string to feel an electric spark and charging a Leyden jar at the end of the string. Here was "The Prometheus of modern times", in Immanuel Kant's phrase, echoed in another, fictional scientific archetype in the title of Mary Shelley's Frankenstein: the modern prometheus.
An engraving of the Royal Society's house at Crane Court, 1837
Franklin received the Royal Society's Copley Medal in 1753 and thanked his peers elegantly. "I know not whether any of your learned Body have attain'd the ancient boasted art of multiplying Gold, but you have certainly found the Art of making it infinitely more valuable", he wrote. By 1756, while still resident in Philadelphia, he was elected a Fellow.
The following year, Franklin was sent to London as a colonial agent of the Pennsylvania Assembly. He was greeted in person by his great champion Peter Collinson. It was the first time the two had met, although not Franklin's first visit to the capital. As an itinerant printer's apprentice, the young Franklin had lived in London as early as 1725. Then, he was reduced to selling an asbestos purse to that collector of curiosities, Sir Hans Sloane, President of the Royal Society. Now, Franklin would take a place among his peers at a new President's side, elected to Council of the Society in 1760.
Franklin was popular and at ease in London society. The colonial representative's diplomatic duties were centred on lobbying for the repeal of Stamp Duty but that did not prevent him from both travelling widely and pursuing his philosophical interests. Indeed, Franklin's ability to influence depended partly upon his scientific reputation and in his ability to popularize to non-specialists. In 1761, for example, Franklin perfected his glass armonica, a musical instrument mechanically reproducing the effect of sound generated using a wet finger rubbed around the rim of a wine glass. Both Mozart and Beethoven were later to write pieces for this invention. Franklin demonstrated the machine in morning gatherings at his home which neatly combined science and entertainment.
His scientific circle included John Canton, the first person in England to repeat the experiment of drawing electricity from thunderclouds. They exchanged ideas on mathematical curiosities such as Franklin's Magical Circle of Circles' and on Canton's researches into the compressibility of water. Both would later become patrons of a young Warrington-based non-conformist, just beginning his own electrical work - Joseph Priestley. Franklin aided Priestley's advancement: Fellowship of the Royal Society, and a recommendation for the Copley Medal. The future discoverer of oxygen would eventually follow his mentor to Pennsylvania and into in the new American Republic
Franklin's second London period saw him return to petition King George III for the establishment of central British government for Pennsylvania. The King's physician, Sir John Pringle, was also President of the Royal Society in the years 1772-1778 and a close companion of Franklin. Together, they journeyed to Germany in 1766 and pre-Revolutionary France in 1767, meeting Louis XV at Versailles.
Travel brought out the scientist in Franklin. On transatlantic voyages, he pondered the action of the Gulf Stream and proposed the idea of watertight compartments for ships. Overland, he investigated the way in which oil could be used to calm water surfaces. He first performed this experiment on Clapham Pond in the summer of 1771, and subsequently carried with him a cane containing a small oil holder to repeat his "conjuring trick" on his travels. In the idyllic setting of Derwentwater in the Lake District, the experiment was performed in 1772 by the memorable gathering of Benjamin Franklin, John Pringle and the chemist William Brownrigg. More troubled waters were to follow.
As the inventor of lightning conductors, Franklin was appointed to a Royal Society committee tasked to consider lightning protection for explosives at the naval armoury at Purfleet in 1772. Franklin's preferred pointed iron rods were selected rather than a rival rounded design. In the Americas of the 1750s, there had been religious objections to Franklin's device as circumventing divine wrath the mortality rate of church bell ringers rather made Franklin's case, however. England proved to be no more enlightened. Once Franklin was on the "wrong" side in the War of Independence, the King's loyalists farcically championed rounded conductors and were roundly satirised in contemporary newspapers:
While you, great George, for safety hunt,
And sharp conductors change for blunt,
The nation's out of joint:
Franklin a wiser course pursues,
And all your thunder fearless views
By keeping to the point
Pringle, who backed Franklin's science, lost the Royal Society's Presidency as a result.
Miniature of James Cook
Franklin left London for the last time in March 1775. Shortly afterward he helped to draft the United States Declaration of Independence, severing links with his old homeland before returning to Europe to represent the new Nation in Paris. His carefully cultivated image as a fur cap-wearing frontiersman seeking freedom from an oppressive government endeared him to the French, who featured his portrait on objects as diverse as snuffboxes and chamber pots.
Franklin's primary objective of raising funds for a war against Britain as an enemy nation did not prevent him from promoting the cause of science. In 1778, he drafted a "passport" for Captain James Cook FRS, then on his third voyage of discovery in the Pacific on board the Resolution. Describing Cook and his crew as "common Friends to Mankind", Franklin urged the captains of any armed ships acting for the United States "to treat the said Captain Cook and his People with all Civility and Kindness". Franklin also maintained cordial links with Sir Joseph Banks, Pringle's successor as President of the Royal Society, sending news of the latest in French science.
Franklin perfected bifocal spectacles in Paris, one of his most famous inventions. He was present to witness the first hot air balloon demonstrations in November 1783 by the celebrated Montgolfier brothers. Franklin favoured the hydrogen method and helped to finance balloons tests, sending word of the first manned flight back to Banks shortly after the Montgolfiers' exploits. Technological advances thrilled the philosopher as much as the slaughter of war appalled him and he wrote to Priestley: "The rapid progress of true Science now makes, occasions my regretting that I was born so soon&O that moral Science were in as fair a way, and that Men would cease to be Wolves to one another&"
Franklin would touch England one final time, breaking his journey from France for just a few days to catch a transatlantic packet from London. In 1725, the hearty young printer had swum the Thames from Chelsea to Embankment to entertain onlookers. Now, in 1785, a tired but mentally active gentleman of 79 fell asleep for an hour in Southampton's salt water baths before meeting his English friends and sailing for the New World he had helped to make.