Nicola Zupo’s vertical pendulum seismoscope

The 1783 disruptive seismic sequence hitting Calabria and north-east Sicily stimulated the physician and naturalist Nicola Zupo to devise a novel pendulum-based seismoscope, able to detect also electrical effects. In fact, as many scientists of his time, Zupo recognized electricism as the primary cause of earthquakes, but in his opinion the source of this electricism had to be found in Calabrian atmosphere rather than underground (fig 1). His device was essentially a three meters long iron rod sharpened at both ends. Two thirds of this rod were inserted into the ground, while the external part bending twice at right angles in such a way to keep a short piece of it parallel to the ground. A small lead ball weighing three pounds was suspended by means of a silk thread to the horizontal piece of the bar, and its lower part was equipped with an iron nail able to eventually draw lines on a layer covered by ashes. In this way the oscillations of the pendulum induced by external perturbations, such as seismic shocks, could be recorded, together with the corresponding direction. A further check of the direction could be provided by a system of four bells arranged according to the four cardinal points and connected to the ball via a horsehair. Finally the whole rod was expected to behave as a lightning rod in such a way to produce a flash of electrical fire during the earthquake, a circumstance claimed by Zupo and acknowledged by Giovanni Vivenzio (fig. 2) in his Istoria e teoria de’ tremuoti: “D. Nicola Zupo di Cosenza, di professione Medico, ed uomo molto versato nella buona Fisica, persuaso, che la causa de’ Tremuoti esser doveva l’Elettricità, profondò nella Terra una Spranga di ferro di dodici palmi lunga, ed osservò nel tempo di molte scosse, dall’estremità puntuta fuori della Terra un pennello di fuoco Elettrico”.

___Salvatore Esposito & Adele Naddeo