Giovanni Battista Guglielmini

Giovanni Battista Guglielmini (Italian pronunciation: [dʒoˈvanni batˈtista ɡuʎʎelˈmiːni]; 16 August 1763 – 15 December 1817) was an Italian physicist. Guglielmini's experiments take place in the list of experiments by scientists (Hooke, Guglielmini, Benzenberg, Reich, Foucault) to demonstrate the Earth's rotation experimentally.

Guglielmini was born at Bologna, received the tonsure in early youth and was a secular priest ("abate"). His career in the Church is unknown; he died single. A protégé of Cardinal Ignazio Boncompagni, he pursued higher studies, and graduated in philosophy, in 1787, at the age of 24. If he was a relative of the famous engineer and physician, Domenico Guglielmini, who had been general superintendent of the Bologna waterworks a hundred years before, he was certainly not his direct descendant.

In 1789 Guglielmini published his first treatise, Riflessioni sopra un nuovo esperimento in prova del diurno moto della terra (Reflections on a new experiment to prove the daily motion of the Earth). The experiments were made in the Asinelli tower of Bologna, famous from former experiments of Riccioli on the laws of falling bodies. The preface of a small octavo volume, published in Bologna in 1792, De diuturno terræ motu experimentis physico-mathematicis confirmato, gives the history and description of Guglielmini's experiments, then resumes in the first article the contents of the Riflessioni, defends the same in the second article against opponents, and in the third presents the results. The book bears the imprimatur of the Holy Office at Bologna.

Sixteen balls were dropped from a height of 241 feet, between June and September, 1791, and the plumb-line fixed in February, 1792, all during the night, to minimize the effects of road traffic. The mean deviations towards east and south proved to be 8.4''' and 5.3''' respectively, while the computation gave 7.6''' and 6.2''' (1'''= 1-12 inch). In spite of their agreement both observation and calculation were defective, the plumb-line having been determined half a year later, and the theory of motion relative to the moving earth being as yet undeveloped. However, the tangential force that was applied to the body was known since Newton due to the rotation motion of the earth. Guglielmini therefore contributed to the understanding of the Earth's rotation.

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