Baliani, Giovanni Battista

(b. Genoa. Italy, 1582; d. Genoa, 1666)

physics.

Baliani, the son of a senator, was trained in the law and spent most of his life in public service. His scientific interests appear to have begun about 1611, when he was perfect of the fortress at Savona. There he noted the equal speed of fall of cannon balls differing greatly in weight. About the same time he devised an apparatus for cooking by frictional heat—an iron pot rotating on a concave iron base.

In 1613 Filippo Salviati met Baliani and wrote of him to Galileo, who began corresponding with Baliani concerning the experimental determination of the weight of air. In 1615 Baliani visited Galileo at Florence and met Benedetto Castelli. The intermittent correspondence that lasted for many years shows Boliani to have been a talented experimentalist and an ingenious speculator. In 1630 he wrote to Galileo of the failure of a siphon that had been expected to carry water over a rise of about sixty feet (eighty piedi) Baliani attributed the action of a lift pump to atmospheric pressure, but doubted that the total weight of a column of air many miles high could be less than that of a thirty-foot column of water, at which height Galileo had already noted the failure of lift pumps.

In astronomy, although Baliani preferred Tycho Brahe’s system to that of Copernicus, he speculated on a terrestrial motion as the possible cause of tides.

In 1638 Baliani published a short treatise on the motions of heavy bodies, which he reprinted in 1646 with many additions. In the first edition he gave correct laws for free fall, motion on inclined planes and pendulums. In the second edition he speculated on the possibility that in immeasurably small successive finite times, the spaces traversed by a falling body might increase in proportion to the natural numbers, assuming that the body received very rapid successive impulses and retained them unimpaired. Baliani’s argument embodied an important step toward the concept of mass and the analysis of acceleration, but it was widely misunderstood as intended to contradict the law that both he and Galileo had explicitly stated: that for successive equal measurable times, the spaces traversed by a falling body are as the odd numbers 1, 3, 5,.... The misunderstanding caused Baliani’s name to become associated with the false hypothesis, specifically rejected by Galileo, that velocity in free fall increases in proportion to space traversed. Although Baliani did not uphold the false law of acceleration, he rejected the parabolic trajectory in such a way as to show that his idea of inertial motion was inexact.

In 1647 Baliani published a treatise on the plague, suggesting a chemical explanation of its nature and its contagious character. In this work he stated the principle that the rate of human population increase as related to arable land and food production would necessarily result in famine were it not for the occurrence of war and pestilence. The quantitative nature of his argument entitles him to be regarded as a predecessor of the Malthusian law.

Baliani returned to Savona in 1647 as governor of its fortress, a post he held unitle 1649. He was then elevated to membership in the principal governing body of Genoa, where he remained until his death.

Baliani’s previously unpublished works were collected and printed in 1666. They include several philosophical dialogues and discussions of light, action at a distance, the existence of a vacuum and of motion therein, and some prismatic experiments. The works were republished in 1792 with an anonymous life of Baliani and a number of letters praising his achievements.

The direct influence of Baliani on other scientists probably was not great; he worked as an amateur with notable ability and success, but his principal fields of interest were those that were simultaneously receiving attention from Galileo and his disciples. He did not arrive at the laws of falling bodies independently of Galileo, and although their explanation in terms of incremental impulse was probably his own, a similar analysis had been published by G. B. Benedetti in 1585. His correct conception of atmospheric pressure remained unpublished, although it may have become known to Torricelli through conversations with Galileo, who rejected it. Baliani’s most important contribution, a discussion of elastic shock, seems to have gone unnoticed until recently, and hence probably did not influence the development of the laws of impact. No final evaluation of Baliani’s place in the history of physics is possible, however, without an exhaustive study of his extant correspondence, for many of his germinal ideas were not published and are known only through his letters.

BIBLIOGRAPHY

I. Origibal Works. Known copies of Baliani’s works in North America not listed in the Union Catalogue are designated as follows: California Institute of Technology, CIT; University of Toronto Library, ULT. His works are De motu naturali gravium solidorum Ioannis Baptistae Baliani patritii genuensis (Genoa, 1638); De motu gravium solidorum et liquidorum Io. Baptistae Baliani patritii genuensis (Genoa, 1646; ULT); Trattato delta pestilenza di Gio. Battista Baliano (Savona, 1647; ULT); Di. Gio. Batista Baliani. Opere diverse (Genoa, 1666); and Opere diverse di Gio. Battista Baliani, patrizio genovese; aggiuntovinell’avviso a chi legge, una compendiosa notiza di lui vita (Genoa, 1792; CIT).

The Baliani-Galieo correspondence is included in Le opere di Galielo Galilei, Ed. Naz. (Folerence. 1934-1937), Vols. XII-XVIII, passim, Baliani’s correspondence with Mersenne has been published to 1640 in Correspondance du P. Maria Mersenne, Cornelis De Waard et al., eds (Paris, 1945-1965). Unpublished Baliani letters at Milan are described in Moscovici’s 1965 article.

II. Secondary Litterature. A general discussion of Baliani and his published works is given in Alpinolo Natucci. “Giovan Battista Baliani letterato e scienzato del secolo XVI1,” in Archives internationales d’histoire des sciences, 12 (1959), 267-283. A critical examination of the misinterpretation by earlier writers of Baliani’s law of acceleration occupies Ottaviano Cametti’s Lettera criticoineccanica (Rome, 1758): its subsequent fate and its implications for the concepts of mass and inertia are discussed in S. Moscovici, L’ expérience de mouvement. Jean-Baptiste Baliani—disciple et critique de Galilée (paris, 1967), which discusses extensively the barometric correspondence with Mersenne and others and which has an appendix with many previously unpublished letters of Baliani. Other aspects of Baliani’s physics are discussed in S. Moscovici, “Les développements historiques de la théorie galiléenne des marées,” in Revue d’histoire des sciences et de leurs applications. 18 , no. 2 (1965). 193-220: and Cornelis De Waard. L’experience barométrique. Ses antécédents et ses explications (Thouars, 1936), p. 95.

Stillman Drake