Geodetic operations in the Real Gabinetto Fisico

Since the beginning of its observational and data collection activities in 1840, the Royal Physics Cabinet played a leading role in the field of geodesy and topography, giving a well defined contribution to the geodetic survey campaigns in the Kingdom of the Two Sicilies providing both instruments and expertise.
Geodetic operations were carried out in different places in Naples, such as the Shipyard and the Cavallerizze ramps, by using the following instruments: Dollond’s Thedolite, Troughton’s sextant, Giuseppe Spano’s diopter, Schmalcalder’s azimuth compass, and Gambey’s intensity, inclination and variation compass. Geodetic operations relied on the triangulation method, which allowed the calculation of unknown distances through high precision measurements of given angles and distances. It was possible to find how many Neapolitan palms the ground of the second main floor of the Royal Palace (where the Physics Cabinet was located) rose above the sea level, starting from the computation of its latitude and longitude. Furthermore, both the location of the Royal Physics Cabinet and that of the Royal Astronomical Observatory in Capodimonte were determined with respect to the location of the Specola of the Officio Topografico. The final results were compared with the distances quoted on the city plan of Naples. The difference in south latitude as well as west longitude between the Royal Physics Cabinet and the Royal Observatory in Capodimonte was, then, worked out.
Interesting studies on the terrestrial magnetism were also performed, including measurements of both Earth’s magnetic inclination and magnetic declination. Small diurnal fluctuations in the declination of Earth magnetism were detected as well (fig. 1), aimed at investigating the interactions between the solar wind and the Earth’s atmosphere, just when geophysics was emerging as an independent scientific discipline.

___Salvatore Esposito & Adele Naddeo