# Catholic Encyclopedia (1913)/Giovanni Battista Guglielmini

From volume 7 of the work.
Scientist, b. at Bologna, 16 August, 1763; d. in the same city, l5 December, 1817. He is known as the first scientific experimenter on the mechanical demonstration of the earth's rotation. He received the tonsure in early youth, with the title of Abate, but does not seem to have received any higher orders, and died single. With the help and protection of Cardinal Ignazio Boncompagni, he pursued higher studies, and graduated in philosophy, in 1787, at the age of 24. Two years later he published his. first treatise in Rome, "Riflessioni sopra un nuovo esperimento in prova del diurno moto della terra" (Rome, 1789). The experiments which followed were made in the city tower of Bologna, called "Asinelli", and famous from former experiments of Riccioli on the laws of falling bodies. A small octavo volume, published in Bologna in 1792, "De diuturno terræ motu experimentis physico-mathematicis confirmato opusculum" gives (in the preface) 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 and mostly after midnight. 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.
The experimental skill and laborious precautions of Guglielmini, however, served his followers, Benzenberg (1802 and 1804) and Reich (1831), as models, and the inner agreement of his results was never surpassed. Guglielmini's theory was right, in considering the absolute path of the falling body (apart from the resistance of the air) as elliptical, or approximately parabolical, and the orbital plane as passing a little north of the vertical, through the centre of attraction, while the errors in his formulæ, afterwards repeated by Olbers, served to incite Gauss and Laplace to develop the correct theory of relative motion. Two years later, Guglielmini was nominated professor of mathematics at the University of Bologna, which office he held for twenty-three years (1794-1817). In 1801, he also filled the chair of astronomy, and during the scholastic year 1814-15, officiated as rector of the University. From about 1802 until 1810, Guglielmini was put in charge of the extensive waterworks of Bologna. 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 previously, he was certainly not his direct descendant. Don Guglielmini bore the title of "Cavaliere", was a member of the "Accademia Benedettina" (founded by Benedict XIV), of the "Regio Istituto Italiano" and "Elettore del Collegio dei Dotti". He was continually in frail health, and died of slow consumption, at the age of 54. In 1837, the city of Bologna ordered a marble bust of him to be erected in the pantheon of the cemetery.
MAZZETTI, Memorie storiche sopra l'Università e l'Istituto delle Scienze di Bologna (Bologna, 1840); Repertorio di tutti i professori... della famosa Università e del celebre Istituto delle scienze di Bologna, etc. (Bologna, 1847); BENZENBERG, Versuche über die Umdrehung der Erde (Dortmund, 1804), 294, 384; POGGENDORFF, Handwörterbuch (Leipzig, 1863); Il Panteon di Bologna (Bologna, 1881).
J. G. Hagen.