Physical and Ethereal Spaces by George Adams (Kaufmann) explores the relationship between physical, Newtonian space and the "counter-space" of the etheric, or living, world. Using 19th-century projective geometry, Adams bridges esoteric Anthroposophical concepts—inspired by Rudolf Steiner—with mathematics to explain how ethereal forces shape living forms, acting as a inverse, inward-turning, or "polar-euclidean" space. Physical and Ethereal Spaces is a foundational text for understanding the mathematical and geometric underpinnings of Anthroposophical, or spiritual-scientific, perspectives on the nature of life and etheric forces, often framing them as a "reciprocating spatiality".