Kant wrote three papers on the catastrophe. The first, On the Causes of the Terrestrial Convulsions (1756), was an essay on the physical dynamics of earthquakes; Kant speculated that there are giant caves underneath mountain ridges (1:419–20). Sometimes gases in the caves form combustible mixtures. When the gases release, the caves collapse, shaking the earth (1:422). Although Kant’s conjecture is false (quakes are usually due to plate tectonics), it is methodologically beyond reproach, employing known data (mining explosions) to formulate a testable hypothesis. The second tract, History and Natural Description of the Most Curious Occurrences associated with the Quake (1756), is a report on what happened in Lisbon. The third, Further Observation on the Terrestrial Convulsions (1756), is a refutation of superstitious causes such as invidious astrological conjunctions.