An alchemist in his laboratory searches for the legendary philosopher's stone, 1618. An engraving from 'Tripus Aureus', published in 1618 by Michael Maier, from the original 1599 work 'The Twelve Keys of Basil Valentine'. The lion devouring a serpent represents the process of changing matter into something new. The symbol under the window is the alchemical symbol for mercury. (Photo by Hulton Archive/Getty Images)