This dissertation is the first full-length scholarly analysis of Johannes Kelpius (1667-1707), a transatlantic radical Protestant theologian from Transylvania who settled in Philadelphia in 1694. This dissertation reads the life and legacy of Kelpius to understand the Protestant reception of Hermetic literature in the seventeenth century and how this reception shaped the Protestant response to climate change during the same period. The dissertation goes on to explore Hermetic Protestantism in the Americas during the period, focusing on the areas of southeastern Pennsylvania where Kelpius and his colleagues settled at the turn of the eighteenth century. The final chapters turn to Kelpius’s contested and misunderstood legacy in American literature and history since his death in 1707, ultimately concluding that the transformation of environmental knowledge that Kelpius lived through rendered him incomprehensible to many of his later Enlightenment readers.