Great lives speak to us across the centuries, and what the life of the ­sixteenth-century John Dee, as curated via a new exhibition at the Royal College of Physicians (until 29 July), says is: “So you thought you were busy, did you?”Dee was a polymath: indeed, the word could have been invented for him. He was a scientist; a geographer; an astronomer. An astrologer; a mathematician; an explorer. A courtier; an alchemist; a scholar; and even, for good measure, a secret agent. It might be quicker to list what he wasn’t, including – odd, given that he was known as Dr Dee, and that his life is being unravelled by physicians – being a doctor. But – naturally, given his status as perhaps Britain’s most comprehensive Renaissance man – he was ext