The year 1850 was plagued by stormy weather and the turbulent conditions were closely followed by the aptly named George Merryweather, a doctor in Whitby, North Yorkshire, who claimed to forecast storms using leeches. Merryweather had been inspired by distinguished predecessors such as the 18th-century poet William Cowper. “I have a leech in a bottle that foretells all these prodigies and convulsions of Nature,” Cowper wrote. “He is worth all the barometers in the world.” Edward Jenner, inventor of the smallpox vaccine, was another believer in the forecasting abilities of leeches, observing how agitated they became before storms: “The leech...