Divers of Hermetic Books have such involve'd Obscuritys that they may justly be compar'd to Riddles written in Cyphers. For after a Man has surmounted the difficulty of decyphering the Words & Terms, he finds a new & greater difficulty to discover ye meaning of the seemingly plain Expression.

Fragment in Boyle papers. Cited by Lawrence Principe, 'Boyle's Alchemical Pursuits', in M. Hunter (ed.), Robert Boyle Reconsidered (1994)