Gianantonio Tadini and falling bodies: A new documentary source for the reconstruction of the history of experimental proofs on the Earth’s rotation

Gianantonio Tadini (1754–1830) is the little known protagonist in an important experiment carried out in Bergamo between 1794 and 1795. Based on the measurement of the deviation of a falling body, the experiment owes much to the one that was conducted by Giambattista Guglielmini (1760–1817) in Bologna in 1791, which aimed at demonstrating Earth’s rotation. Tadini’s experimental work represents the most successful attempt carried out before the 19th century, and it led to the first correct formulation of deviation’s measurement. In spite of this, it is not well represented in the general literature on the history of experiments intended to show diurnal Earth’s motion. 1 The discovery of Tadini’s diary of experiments as well as some notes and a part of his correspondence – preserved as manuscripts in the Angelo Mai municipal library in Bergamo – allows us now to reconstruct the history of Tadini’s experiment and of his reasoning about Guglielmini’s work. In this paper, I describe the genesis and the development of Tadini’s experiment, clarify the role played by the different personalities involved and set these trials against the background of the widest history of proofs on diurnal Earth’s rotation carried out in Europe in those years.