QI The Book of the Dead

safely. They showed him how by driving a herd of thirty wild horses into an eel-infested lake. As the water crackled with electric charge, the terrified horses lunged frantically about with bulging eyes; several succumbed to the shocks and drowned, but gradually the eels ran out of battery. Once the horses were calm (or dead), Humboldt could pick up the exhausted eels (using dry lengths of wood to act as an insulator) and begin his dissections, meticulously noting down all the various shocks he received in the process.
    Humboldt arrived back in Paris to find himself famous. It wasn’t altogether a surprise: he had shrewd marketing instincts. He had sent back many of his most exciting samples well in advance. He had also written letters to friends that began ‘By the time you receive this I will probably be dead …’ – all of which helped to create a sense of anticipation.
    As Bonpland embarked on cataloguing the contents of the teetering stacks of sample cases, Humboldt set out to turn his notes and sketches into a book. His initial estimate of two years’ work proved hopelessly optimistic. The thirty volumes of Personal Narrative: A Voyage to the Equinoctial Regions of a New Continent 1799‒1804 took him almost thirty years (and almost all of his money) to complete. It is one of the great milestones of scientific literature and one of the very few that reads with the mounting excitement of an adventure story.
    One of the reasons the book took so long to finish is that Humboldt had so much else to do. Over the next three decades, he climbed Vesuvius three times, went under the Thames in the diving bell used by Isambard Kingdom Brunel during the construction of the Thames Tunnel, and led a six-month expedition across Russia to the Chinese border. This didn’t quite match the South American journey for new discoveries or excitement but it did lead to the establishment of a network of meteorological stations that stretched first across Russia and then around the world. The data they collected transformed our understanding of the weather and the operation of the earth’s magnetic field. The 1911 edition of Encyclopaedia Britannica described it as ‘the first truly international scientific collaboration’.
    Little is known of Humboldt the private man. The mask of the suave diplomat rarely slipped, although his close friend and fellow scientist François Arago hinted at a more unbuttoned Humboldt behind closed doors: ‘He has the most malicious tongue of any man I know and the best heart.’ He never married. His close friendships with men have led many to suppose he was gay, but he destroyed all his personal papers so the evidence either way is thin. First-hand testimonies of his participation in the lively subculture of nineteenth-century Berlin mostly consist of dark mutterings about him consorting with ‘obscene, dissolute youths’ and tend to come from the more conservative and religious-minded of his younger colleagues. There is also the mystery of why he bequeathed his whole estate to an elderly malevalet, but again that hardly offers conclusive proof of anything, especially as he had no immediate heirs. We’ll never know for sure. It may have been that, like Mary Kingsley, he suppressed whatever sexual urges he had in order to concentrate on his work. This was a man, after all, who survived for eight decades on no more than four hours’ sleep a night.
    Humboldt ended his life in triumph. As he approached seventy, long after most of us have retired, he conceived his crowning achievement: ‘I have the crazy idea to represent in one work the entire material universe.’ The five volumes of Kosmos pulled together his experience of over half a century at the front line of scientific research. The product of what he called his ‘improbable years’, it was a magnificent achievement, rapturously received across Europe and in America. Humboldt lived to see all but the last volume published and died quietly in his sleep just a few months short of his ninetieth birthday.
    After his death, Humboldt’s reputation plummeted rapidly. His works were hardly read at all in the first half of the twentieth century and far more people today recognise the names of Linnaeus and Darwin. Given the pre-eminence he had enjoyed during his lifetime, this is hard to understand. It may be that Humboldt’s work, for all its density and richness of detail, lacks what his greatest disciple, Charles Darwin, could offer: a