Published in 1998, this is a fundamental re-assessment of the world-view of the alchemists, natural philosophers and intelligencers of the mid 17th century. Based almost entirely upon the extensive and hitherto little-researched manuscript archive of Samuel Hartlib, it charts and contextualises the personal and intellectual history of Johann Moriaen (c.1592-1668), a Dutch-German alchemist and natural philosopher. Moriaen was closely acquainted with many of the leading thinkers and experimenters of his time, including René Descartes, J.A. Comenius, J.R. Glauber and J.S. Küffler. His detailed reports of relations with these figures and his response to their work provide a uniquely informed insight into the world of alchemy and natural philosophy. This study also illuminates the nature and mechanisms of intellectual and technological exchanges between Germany, The Netherlands and England.