Book excerpt: By explaining how to sire multicolored horses, produce nuts without shells, and create an egg the size of a human head, Giambattista Della Porta's Natural Magic (1559) conveys a fascination with tricks and illusions that makes it a work difficult for historians of science to take seriously. Yet, according to William Eamon, it is in the "how-to" books written by medieval alchemists, magicians, and artisans that modern science has its roots. These compilations of recipes on everything from parlor tricks through medical remedies to wool-dyeing fascinated medieval intellectuals because they promised access to esoteric "secrets of nature." In closely examining this rich but little-known source of literature, Eamon reveals that printing technology and popular culture had as great, if not stronger, an impact on early modern science as did the traditional academic disciplines.