In this major reevaluation of Isaac Newton's intellectual life, Betty Jo Teeter Dobbs shows how his pioneering work in mathematics, physics, and cosmology was intimately intertwined with his study of alchemy. Directing attention to the religious ambience of the alchemical enterprise of early modern Europe, Dobbs argues that Newton understood alchemy--and the divine activity in micromatter to which it spoke--to be a much needed corrective to the overly mechanized system of Descartes. Yet that religious basis was not limited to alchemy, but suffused the rest of his work. Newton, whose many different studies constituted a unified plan for obtaining Truth, saw value and relevance in all of his pursuits. To him it seemed possible to obtain partial truths from many different approaches to knowledge, be it textual work aimed at the interpretation of prophecy, the study of ancient theology and philosophy, creative mathematics, or experiments with prisms, pendulums, vegetating minerals, light, or electricity. Newton's work was a constant attempt to bring these partial truths together, with the larger goal of restoring true natural philosophy and true religion. Within this broad interpretative strategy, Dobbs traces the evolution of Newton's thought in alchemy, religion, and cosmology, and details his struggles with the interwoven problems of the microcosmic spirit of alchemy and the cause of the cosmic principle of gravitation. A landmark study of the "founder of modern science", The Janus Faces of Genius is an important contribution to the history of science.