Before Foucault: The proofs of the Earth’s Rotation

we are going to trace the ideas and experiments, since Galileo and until Leon Foucault, aimed at proving the Earth’s rotation. Galileo - incorrectly – tried to explain the phenomenon of tidal forward and backward flow with the Earth’s rotation. After Galileo, the cannon shots towards the zenith and the experiments on falling objects were considered reliable evidences. In Florence Vincenzo Viviani observed and described the rotation of pendulums, but he did not realize its scientific importance. At the end of the XVII century, Newton had the idea of showing the Royal Society, through Hooke, the proof of the eastward deflection of a falling body from considerable height. In the XVIII century, new geophysical proofs of the Earth’s rotation were available. At the end of the century, in Italy, Newton’s direct experiment was taken into consideration again. In Bologna, Guglielmini measured the deviations towards the east and south of small leaden balls falling inside the Asinelli Tower. The experiment was first repeated in other Italian cities and then, in the first years of the XIX century, Benzenberg proposed it again in Germany, exploiting first the height of a bell tower and then the depth of a coal mine. In this period Laplace and Gauss, though with different approaches, came to the correct mathematical interpretation of the phenomenon. Even more accurate experiments in the deviations of falling objects were performed in 1831 by Reich in Freiberg, in Saxony. In 1837 and 1838 Poisson studied the motion of projectiles related to the Earth’s rotation from a mathematical point of view. This study influenced Foucault who may have found inspiration there for his famous experiment on the pendulum, made in the Paris Pantheon in 1851.