The Science of Discworld II

newspapers. Ronald Reagan consulted an astrologer during his time as American President. That stuff certainly hangs around.
    Alchemy is more interesting. It is often said to be an early forerunner of chemistry, although the principles underlying chemistry largely derive from other sources. The alchemists played around with apparatus that led to useful chemists’ gadgets like retorts and flasks, and they discovered that interesting things happen when you heat certain substances or combine them together. The alchemists’ big discoveries were sal ammoniac (ammonium chloride), which can be made to react with metals, and the mineral acids – nitric, sulphuric and hydrochloric.
    The big goal of alchemy would have been much bigger if they’d ever achieved it: the Elixir of Life, the source of immortality. TheChinese alchemists described this long-sought substance as ‘liquid gold’. The narrative thread here is clear: gold is the noble metal, incorruptible, ageless. So anyone who could somehow incorporate gold into his body would also become incorruptible and ageless. The nobility shows up differently: the noble metal is reserved for the ‘noble’ humans: emperors, royalty, the people on top of the heap. Much good did this do them. According to the Chinese scholar Joseph Needham, several Chinese emperors probably died of elixir poisoning. Since arsenic and mercury were common constituents of supposed elixirs, this is hardly a surprise. And it is all too plausible that a mystic quest for immortality would shorten life, not prolong it.
    In Europe, from about 1300 onwards, alchemy had three main objectives. The Elixir of Life was still one, and a second was finding cures for various diseases. The alchemical search for medicines eventually led somewhere useful. The key figure here is Phillipus Aureolus Theophrastus Bombastus 1 von Hohenheim, mercifully known as ‘Paracelsus’, who lived from 1493 to 1541.
    Paracelsus was a Swiss physician whose interest in alchemy led him to invent chemotherapy. He placed great store in the occult. As a student aged 14 he wandered from one European university to another, in search of great teachers, but we can deduce from what he wrote about the experience, somewhat later, that he was disappointed. He wondered why ‘The high colleges managed to produce so many high asses’, and clearly wasn’t the kind of student to endear himself to his teachers. ‘The universities,’ he wrote, ‘do not teach all things. So a doctor must seek out old wives, gypsies, sorcerers, wandering tribes, old robbers, and such outlaws and take lessons from them.’ He would have had a high old time on Discworld, but would have learned a lot.
    After ten years’ wandering, he returned home in 1524 and became lecturer in medicine at the university of Basel. In 1527 he publicly burned the classic books of earlier physicians, the Arab Avicenna and the Greek Galen. Paracelsus cared not a whit for authority. Indeed his assumed name, ‘para-Celsus’, means ‘above Celsus’, and Celsus was a leading Roman doctor of the first century.
    He was arrogant and mystical. His saving grace was that he was also very bright. He placed great importance on using nature’s own powers of healing. For example, letting wounds drain instead of padding them with moss or dried dung. He discovered that mercury was an effective treatment for syphilis, and his clinical description of that sexually transmitted disease was the best available.
    The main objective for most alchemists was far more selfish. Their sights were set on just one thing: transmuting base metals like lead into gold. Again, their belief that this was possible rested on a story. They knew from their experiments that sal ammoniac and other substances could change the colour of metals, so the story ‘Metals can be transmuted’ gained ground. Why, then, should it not be possible to start with lead, add the right substance, and end up with gold? The story seemed compelling; all that they lacked was the right substance. They called it the Philosopher’s Stone.
    The search for the Philosopher’s Stone, or rumours that it had been found, got several alchemists into trouble. Noble gold was the prerogative of the nobility. While the various kings and princes wouldn’t have minded getting their hands on an inexhaustible supply of gold, they didn’t want their rivals to beat them to