Niccolò Cirillo, the 1731 Apulia earthquake and the first seismoscope

Born in Grumo Nevano, near Naples, in 1671, Niccolò Cirillo worked at Santa Maria del Popolo degli Incurabili hospital as a physician, later obtaining the chair of Natural Philosophy in 1705 and that of Medicine in 1706, both at the Royal University of Naples. In 1718 he became a fellow of the Royal Society of London and very soon became to collect meteorological data on the climate of Naples. In his correspondence kept at the Royal Society, he also focussed on the volcanic activity of Mount Vesuvius, as well as on seismic events. Very interesting was his report on the disruptive earthquake that in March 1731 hit Apulia, with effects on the whole Kingdom of Naples. Here Cirillo described the whole development of the seismic event according to three different steps: the “Tremor”, the “Succussatio” and, finally, the “Inclination or tottering of the Earth”. The main event was followed by a series of shorter and weaker aftershocks, provoking severe damages to houses and people. By observing that the shocks were centered about the town of Foggia and that their strength diminished with the distance, Cirillo conjectured a progressive motion decreasing in a quadratic proportion to the distance. To test this hypothesis, he carried out observations along with his collaborators based at Ascoli Satriano (near the epicenter) and at Giovinazzo (located at a quadruple distance from the epicenter). They recorded the oscillations of a couple of pendulums, with length equal to a Neapolitan palm (about 26 cm), applied to a semicircle divided into degrees, finding that a weak sesimic activity in Foggia produced small pendulum oscillations in Ascoli Satriano but no oscillations at all in Giovinazzo. Cirillo devised for the first time an experimental device (graphically reconstructed in fig. 1), the vertical pendulum seismoscope, able to detect (in principle) the occurrence of a seismic shock and to provide an estimate of its strength. This device paved the way to the subsequent development of modern seismometers and seismographs.

___Salvatore Esposito & Adele Naddeo