‘Historians of alchemy’, wrote Herbert Butterfield in 1949, ‘seem to become tinctured with the kind of lunacy they set out to describe.’ Seventy years on, readers may believe that this gloriously rude assessment needs no updating. But what, then, are we to make of the fact that the greatest scientific hero of them all, that model of geometric rationality, Isaac Newton, devoted a great proportion of his life to the pursuit of transmutation? This was the problem that faced another titan of his discipline, the economist John Maynard Keynes, when in 1936 he acquired at auction a large number of Newton’s papers dealing with alchemy. Newton, Keynes was forced to declare, ‘was not the first of the age of reason’ but rather ‘the last of the magicians’.