Caught in a thunderstorm in Batavia (Jakarta), the Endeavour was struck by lightning—Franklin’s chain worked and the ship was unharmed. A Dutch ship nearby had its mainmast shattered.
Cook’s faith in Franklin’s ingenuity was made obvious again on the second voyage to New Zealand, aboard the Resolution. On May 18, 1773, Cook was sailing in a burgeoning storm towards Stephen’s Island when he encountered six waterspouts. As the sky darkened with cloud, threatening strong winds, he ordered all sails “clewed up” to lessen the risk of damage. Four waterspouts rose and spent themselves between the ship and the land, a fifth was further to sea and posed less risk, but the sixth passed about 50 m away from the stern of the Resolution.
Cook was familiar with Franklin’s theories about waterspouts, particularly his speculation that a large gun fired into one would disrupt it. Years earlier Franklin had chased a whirlwind down a country road in Virginia on horseback armed with two pistols, but it got away over a fence before he could shoot it. Cook endeavoured to try the experiment in the stormy strait. He ordered a cannon loaded, but by the time the gun was ready the waterspout had moved out of range. This moment was immortalised by the ship’s artist, William Hodges, and remains one of the definitive works of New Zealand’s early European history.
Franklin’s printing business was so successful he was able to retire at 42, which gave him time to enter politics and indulge in scientific speculation.
But it was Franklin’s work on electricity that won him international renown. The experiments he proposed, in a paper published by the Royal Society, set out to prove that lightning was a form of electricity, which had long been the subject of speculation. Franklin proposed building a sentry box on a tall tower with a 10 m iron rod connected to an electrical stand. A person holding a grounded wire with insulated handles could draw sparks from the iron rod to the wire when an approaching thunderstorm charged the rod. But as Franklin was waiting for a tall tower to be built in Philadelphia, he hit upon the idea of flying a kite into a storm and drawing sparks from a key attached to the kite string. By the time he successfully carried this out in June 1752, his original experiment had twice been successfully conducted in France, although news of this had not yet reached America.
Franklin was the first to use the terms positive and negative to describe electric charge. He also came up with the concepts of batteries and capacitors, and the distinction between insulators and conductors.
Aside from explaining the nature of lightning, Franklin made other contributions to meteorology. He explained the paradox that an easterly storm could affect Philadelphia before it reached Boston, even though Boston lay further east. (The reason was that the storm is a large anti-cyclonic vortex of wind that moved eastwards across the land.) He correctly deduced from summertime hail that there must be a high layer in the atmosphere where temperatures were always as cold as winter. And he astutely attributed the “dry fog” experienced throughout the Northern hemisphere in 1784, which had resulted in an extremely cold winter, to volcanic eruptions in Iceland.
But if his meteorological science was prescient, his long-range weather forecasts—a year in advance—were tongue in cheek. “Ignorant men wonder how we astrologers foretell the weather so exactly…Alas! ‘tis easy as pissing abed,” he said. “For instance: the stargazer peeps at the heavens through a long glass; he sees perhaps Taurus, or the great bull, in a mighty chase, stamping on the floor of his house, swinging his tail about…Distance being considered, and time allowed for all this to come down, there you have wind and thunder.”
Franklin’s scientific work made him the most famous American in Britain and Europe. He was the first person outside Britain to receive the Royal Society’s Copley medal. Hailed by the German philosopher Immanuel Kant as the “modern Prometheus”, Franklin was elected a foreign associate of the French Academy of Sciences and received honorary degrees from numerous universities.
In politics he played a vital role in the decades before the American Revolution. Once war broke out, he helped write the Declaration of Independence, after which he was given the crucial task of handling the French Alliance. He was hailed as the “electrical ambassador” in France, where the French statesman, Turgot, said: “He snatched lightning from heaven and the sceptre from tyrants.” One portrait showed Franklin enthroned in the sky surrounded by winged deities with a lightning bolt behind him. Louis XVI, although helping the American cause, became jealous and had a Sèvres chamber pot made with Franklin’s portrait inside as a gift for one of Franklin’s admirers.
By the time Britain was defeated and a treaty negotiated, Franklin was 80 years old. Sailing home, he found time to measure the depth of the Gulf Stream using a corked bottle on a 35 fathom line. The pressure at that depth forced the cork into the bottle, which was followed by water. Pulled back to the surface, the water in the bottle was 12ºF colder than the surface water, proving that the Gulf Stream was a relatively shallow layer of warm water.
Back on land, Franklin returned to politics and helped revise the Constitution. He died aged 83, and was one of the most remarkable statesmen-scientists the world has seen.