Before Foucault. The Proofs of the Earth’s Rotation

We are going to trace the ideas and experiments, since Galileo and until Léon 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 evidence. 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 a considerable height. In the XVIII century, new geophysical proofs of the Earth’s rotation were available. At the end of the century, in Italy, 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 decades of the XIX century, it was proposed again in Germany. Theoretically Laplace and Gauss, though with different approaches, came to the correct mathematical interpretation of the phenomenon. In the following years new mechanical proofs were sought but the effects due to earth rotation were too small to provide any certainty. Only Foucault managed to solve the problem.