GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 2.1 GNGTS 2024 Fig. 1 – One of the damped pendulums self-built by Mario Campion in his laboratory. Note the vacuum pump connected to the base of the pendulum where the thermostat system is also located. The glass vacuum cylinder surrounds the pendulum made of invar steel. At the lower end of the rod there is a mass and the precision optical reading system of the instrument, this is connected via an optical fiber to the external rubidium clock. As an element of credibility to validate the ability to record the gravity variations, the gravity trends, reconstructed starting from the measurements of this gravimeter, were compared to the tidal forces. The findings from a comparison carried out between the measurements of the damped pendulum and the tides is reported on the two plots of Fig. 1. Recordings concern the day 10 December 2019, 2 days before the New Moon, which were made simultaneously with two separate gravimeters, operating a few metres from each other with different oscillator periods. The traces in red on the graphs show the coincidence of the two maximums and the two minimums, both with the tide levels in Venice Lido, as well as with each other. Tide levels in Venice Lido were seen to have coincided exactly with the tide forces acting on the same location, most likely due to the complex resonance of the Adriatic Sea. Indeed, the plots do not show tide accelerations, but instead average oscillation times, this is because times are measured by damped oscillator through a focalized laser emitter detected by a Rubidium atomic clock. The period measure is also the motivation for measuring only a relative value of the gravity. In fact, the absolute value requiring the Kater's configuration would need repeated precise measurements of lengths (Lenzen and Multauf, 1964) which inevitably would lengthen measurement repetition times. Standard deviation of hourly averaged periods shown in Fig. 1 are a few units over ten millions. Its correspondent standard deviation on the gravity acceleration can be evaluated by Δ g/g= Δ L/L+2 Δ T/T (1) where L (1 m) is the pendulum length and T (1.53 and 1.57 sec) the measured period. Being the pendulum under vacuum with thermostated (0.01 °C) quartz arm, Δ L/L < 10 -8 , Δ g can be