Throughout his life, Jesuit polymath Athanasius Kircher (1602-1680) was captivated by the insights that Hermetic and Neo-Platonic thought could bear on a wide variety of topics, from Egyptology and music theory to medicine and science. Kircher's discussion of the earth in Mundus Subterraneus (1664, 1665) represents a philosophical bridge between medieval thought systems and the growing empirical movement of the “scientific revolution.” Inspired by Neo-Platonic philosophy, Kircher used a sophisticated combination of rational and empirical techniques that sustained his holistic view of the cosmos. Facing criticism from Jesuit censors, Kircher used Hermeticism to maneuver through Catholic doctrine to examine the natural world. In Kircher's studies, no event was taken in isolation and his examination of the Earth rested with Plato's philosophy that the world was created by God as a manifestation of his own perfection: “and so he formed it as a single visible living thing which was to include all related creatures …[and] by turning it he shaped it into a sphere … giving it the most perfect form of all.” Within the ideal sphere there is no reference point given greater or lesser importance, and all points on the surface are equally accessible and regarded by the center from which all originate. All points reverberate the spherical pattern of total inclusion and acceptance; therefore, a physical manifestation of the idea of “macrocosm and microcosm.”

Kircher also used hermetic (alchemic) processes as analogs for an interpretation of earth's interior in such a way that his techniques can be seen as antecedent to the modern dictum “the present is the key to Earth's past.” Kircher's maxim that the “modern laboratory is the key to Earth's past” equates the development and workings of the Earth's interior to various alchemic techniques. The inner workings of the Earth are compared to an alchemic project containing the opposing principles of fire and water, and through the conjunction of these two primordial elements the Earth became the perfect spherical eunuch, and hence a neutral stage in all reality for mankind to exist.