Georgius Agricola

Agricola trained in medicine in Italy and then took a post as town physician in Joachimsthal, a silver-mining boom town in the Erzgebirge, where he spent his time underground with the miners rather than only at the bedside. De Re Metallica, finished before his death in 1555 and published the following year, is the result: twelve books covering the search for ore, the law and organisation of mines, surveying, shaft construction, pumping and ventilation machinery, the crushing and washing of ore, smelting, the assay, the separation of silver from gold, and the making of salt, glass and other products of the furnace. It carries several hundred woodcuts commissioned to show the machinery in operation, and the illustrations are as much of the achievement as the text, since a hoist or a pump is far more easily conveyed by a picture.

The book remained the working reference for European mining for something like two hundred years. It was translated into English in 1912 by the mining engineer Herbert Hoover, later president of the United States, and his wife Lou Henry Hoover, a classicist, whose annotated edition is still the one most readers use. He wrote several other works on the same material, including a study of the origin of ore deposits and one of the earliest systematic treatments of minerals arranged by their physical properties.

What makes Agricola valuable to a reference work on esoteric tradition is that he wrote down what the miners believed and then said what he thought of it, keeping the two clearly apart. He records the divining rod, the forked hazel twig cut and held in a particular grip so that it dips over a hidden lode, describes the ritual and the words used with it, and then reports the objection that a rod turns in the hands of a believer and does nothing in the hands of a sceptic, concluding that a prospector should rely on the visible signs of mineralisation instead. He records the underground spirits, the small figures in miners' dress that were said to appear in the workings, some helpful and some malicious, and treats them as part of the life of the mines rather than as demons requiring exorcism or as nonsense requiring suppression. He was also openly sceptical of the transmutation claims circulating in his own century, on the practical ground that he had never met anyone enriched by them. The result is one of the best sixteenth-century records of working folk belief, made by someone who did not share it, and modern histories of dowsing and of mining folklore rely on him heavily for exactly that reason.