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 Rene Descartes, J.A. Comenius, J.R. Glauber and J.S. KA1/4ffler. 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.