Agustín Udías, born in Santander, Spain, is a Jesuit and Professor Emeritus of Geophysics at Universidad Complutense de Madrid. He has conducted research and held teaching posts at the University of California, Berkeley, at the Wolfgang Goethe Universität, Frankfurt am Main and at the Universidad de Barcelona. Among his books, Principles of Seismology (Cambridge University Press, 1999, 2018), Searching the Heavens and the Earth: The History of Jesuit Observatories (Kluwer, 2003)and Jesuit Contribution to Science. A History (Springer, 2015). He has published scientific articles on the topics of earthquake source mechanism, seismicity and seismotectonics of the Mediterranean region and about the relationship between science and religion and the history of Jesuit scientists.

Preface.- 1. Introduction.- 2. Athanasius Kircher's life and works.- The museum and correspondence.- The books.- 3. The geocosmos and the interior of the Earth.- Short index of the twelve books.- Preface: Earthquakes and volcanoes.- The Earth center of the universe.- The interior of the Earth.- The oceans and seas.- The subterranean fire, water and air.- Fountains, rivers, and lakes.- The terrestrial element.- Nature of the geocosmos.- Fossils, subterranean animals, men, and demons.- Poisons in the subterranean world.- Metals and mines.- Chemical transformations.- "Panspermia", the origin of plants and animals.- Chemical work.- 4. Magnetism and the cosmic magnetic chain.- Early work on magnetism and the Earth's magnetic field.- Kircher and magnetism.- Nature and properties of magnets.- Magnetic declination.- Observations of magnetic declination.- The magnetic map.- Causes of magnetic declination.- Magnetism as a cosmic and spiritual force.- 5. A space journey and the vision of the universe.- Introduction.- Preambles by Schott and Kircher.- Preamble by Schott.- Preamble by Kircher.- Dialog I: Journeys to Moon, Venus, Mercury, Sun, Mars, Jupiter, Saturn and the Firmament.- Dialog II: God's providence in the work of the World.- Ecstatic Journey II.- Dialog I: The water element and the universal principle of things.- Dialog II: The admirable arcane of the Geocosmos or Terrestrial World.- Dialog III: Ecstatic journey to the subterranean world.- 6. Conclusion.- Appendix 1. Books on Athanasius Kircher published from 2000 to 2020.- Appendix 2. Table of Contents of Mundus subterraneus.- Appendix 3. Table of Contents of Magnes sive de arte Magnetica.- Appendix 4. Table of Contents of Iter exstaticum coelestem.- Kircher's Works Mentioned.- Bibliography.- Index by Names