Chemistry as an earnest and respectable science is often said to date from 1661, when Robert Boyle of Oxford published "The Sceptical Chymist" — the first work to distinguish between chemists and alchemists — but it was a slow and often erratic transition. Into the eighteenth century scholars could feel oddly comfortable in both camps — like the German Johann Becher, who produced sober and unexceptionable work on mineralogy called "Physica Subterranea", but who also was certain that, given the right materials, he could make himself invisible.