Cross-Section of the Earth's Internal Fire and Hydraulic System

The image is an engraving showing a dark, cross-sectioned view of the Earth's interior, dominated by a large, flame-filled central cavity labeled 'A'. From this central core, branch-like veins stretch upwards and outwards to connect with various subterranean pockets labeled with individual letters of the alphabet, suggesting a complex system of internal circulation. Above and below this subterranean mass are simplified representations of hills and trees on the surface, while specific outlets, labeled 'Thermae' on the right, indicate where internal heat reaches the surface to create hot springs.

This illustration is from Athanasius Kircher's 'Mundus subterraneus' (1665), a seminal work in the history of geology and natural philosophy that attempted to map the Earth's interior according to Hermetic principles and speculative physical theory. It represents an early modern attempt to synthesize observations of volcanoes and geothermal activity into a unified subterranean theory of the globe.