In this series we have seen that various scholars over the centuries have questioned, challenged and even rejected Aristotle’s theories of free fall and projectile motion. Just as Tartaglia extended the challenges to his theory of projectile motion with his work on ballistics other scholars took up the challenge to his law of fall in the sixteenth century, decades before Galileo did so.
The standard, unfortunately widespread, myth is that Galileo was the first to challenge the standard Aristotelian theory on fall. As we have already seen John Philoponus (c. 490–c. 570) had challenged both Aristotle’s theories of fall and projectile motion. As did several Islamic scholars. In the sixteenth century we find several scholars continuing those challenges and openly contradicting the central claims of Aristotelian physics.
This anti-Aristotelian tendence is clearly stated in the Questioni sull’Alchimia of the Italian humanist, historian and poet Benedetto Varchi (c. 1502–1564) written before 1544.
Here Varchi discussing the experimental evidence relating to the motion of heavy bodies, mentions the findings of Francesco Beato, a Dominican philosopher at Pisa, and Luca Ghini (1490–1556) an Italian physician and botanist, who created one of the first university botanical gardens and the first ever herbarium at Pisa.
Also, Giovan Battista Bellaso (1505–?) of Brescia, best known as a cryptographer, in his work Il vero modo di scrivere in cifra, published in 1553, asked why it is that a ball of iron and one of wood fall to the ground at the same time.
More interesting is the case of the Spanish theologian Domingo de Soto (1494–1560) like Beato, a Dominican. De Soto was a hardcore Thomist who wrote extensively on international law. Theologically he argued for a strong adherence to Aristotelian philosophy opposing Renaissance Humanism. His Aristotelian philosophy is, however, Aristotle filtered through Albertus Magnus and Thomas Aquinas.
Given his attitude to theology and philosophy, it comes as more than somewhat of a surprise that in his Physicorum Aristotelis quaestiones, published in 1551, he simply contradicts Aristotle’s theory of fall stating that the motion of bodies in free fall is uniformly accelerated, in other words, that their motion is uniformiter difformis with respect to time. This come eighty years before Galileo made the same statement. Even more surprisingly de Soto presents it in a matter-of-fact manner as if it were common knowledge. Having defined motion that is uniformly difform with respect to time, he notes that this motion is:
properly found in object that move naturally and in projectiles. … For when a heavy object falls through a homogeneous medium from a height, it moves with greater velocity at the end than at the beginning. The velocity of projectiles, on the other hand, is less at the end than at the beginning. And what is more, the first increases uniformly difformly, whereas the second decreases uniformly difformly.
Soto goes on to explain that the falling body will cover the same distance during its fall as another body moving at half the velocity with uniform speed, which he calculates out to yield the correct distance of fall.[1]
De Soto’s statements lead almost automatically to two questions. Firstly, were his comment purely theoretical or were they based in some way on experimentation, and if then who’s, his own or somebody else’s. Secondly, did his text have any influence on Galileo.
We simply don’t know the answer to the first question. It is, however, known that apart from Francesco Beato, another Spanish Dominican, Petrus Arches had told Giambattista Benedetti (1530–1590), whom I shall deal with in the next episode, that criticisms of Aristotle’s dynamics were being discussed in Rome in the summer of 1554, so it is possible that de Soto might have acquired knowledge of experimental investigations through a Dominican network.
On the second question, de Soto’s Physicorum Aristotelis quaestiones was quite popular and went through nine editions in the second half of the sixteenth century. The eighth edition was published in Venice in 1582 just as Galileo was beginning his own studies of Aristotle’s physics, at the University of Pisa. Galileo also mentions de Soto’s Physicorum Aristotelis quaestiones in an early notebook. However, there is no real evidence that he took the concept of uniformly accelerated fall directly from de Soto.
However, several Jesuit scholars had studied de Soto’s work and integrated his ideas into their own work. When he began teaching in Pisa, Galileo borrowed Jesuit teaching notes to help develop his own courses and there could well have been an indirect influence there.
A certain source on the subject for Galileo was the very lively dispute between Girolamo Borro (1512–1592) and Francesco Buonamici (1533–1603), who both taught philosophy at Pisa during Galileo’s time there, as a student and then later as a professor.
Girolamo Borro was born in Arezzo and probably studied at the University of Padua.
Around 1537 he entered the service of the diplomate Cardinal Giovanni Salviati (1490–1553) as a theologian, whom he served for sixteen years. Travelling and working all over Europe.
Following Salviati’s death, he began lecturing at the University of Pisa but left again in 1559. Over the next decades he was involved in various accusations of heresy. In 1561, he published a book explaining the motion of the tides based on Aristotelian principles Del flusso e reflusso del mare.
In 1575, he began teaching philosophy at Pisa again, where he remained until 1586, when he was dismissed following pressure on the university authorities by his opponents, including Buonamici. During this period, he published his De motu gravium et levium (1575) and his De peripatetiva docendi atque addtscendi methodo (1584), an exposition of scientific method according to Aristotelian principles.
Borro was a hardcore Aristotelian, who rejected the new Renaissance Humanist developments. He strongly rejected the use of mathematics in philosophy and all forms of Platonism. His basic approach was the Aristotelian interpretations of Ibn Rushd (1126–1198), known in Renaissance Europe as Averroës. Interesting in our context is his emphasis on an experiential approach to the study of natural philosophy in opposition to a mathematical one.
In De motu gravium et levium(pp. 214–217) he described a protoexperiment performed at his home with the aid of students. In order to resolve a dispute over whether a body of heavy material will fall faster than one of light material, he “took refuge in experience [experientia] the teacher of all things.” He described how lead and wood balls were dropped from a “high window” to resolve this question: “The lead descended more slowly, namely [it descended) above the wood, which had fallen first to the ground: however many times we were all there waiting for the result of this occurrence, we saw the latter [the wood) fall downward [before the lead]. Not only once but many times we tried it with the same results.” The conclusiveness and somewhat puzzling nature of his results parallel those described by Galileo in De motu (I, 333–337)[2].
Galileo also owned a copy of Borro’s work on tides which he quotes in his Dialogo.
Francesco Buonamici was probably born in Florence and studied philosophy and medicine at the University of Pisa. In 1565 he was appointed assistant professor (extraordinarius) for philosophy at Pisa and in 1571 he was promoted to full professor (ordinarius) where he remained all of his life. As ordinarius he taught Aristotle’s De caelo, De anima, and Physica in three-year cycles. Buonamici’s most important publication was his more than one thousand pages long De motu libri X, which covers all aspects of Aristotle’s theories of motion but also all aspects of his theories of change. For Aristotle motion, change of place was just one form of change. Buonamici delivers a careful and exhaustive study of the topic with extended discussions of Aristotle’s views as well as that of a long list of commentators both ancient and modern. These include, Lucretius, Proclus, Plutarch, Pseudo-Aristotle, Pappus, John Philoponus, Theon, Archimedes, Nicolaus Copernicus, Pereira, Ludovico Boccadiferro, Christoph Clavius, Zabarella, and Toletus, as well as many others.[3]
Buonamici had an excellent knowledge of Greek and only accepted Aristotelian texts and commentaries translated from the original Greek. Like many Renaissance scholars he rejected texts that had been translated into Latin from Arabic and he also virulently rejected Arabic commentators such Averroës (Ibn Rushd). He attacked the Averroës views on the motion of elements, which was the source of his bitter dispute with Borro.
Galileo had studied under Buonamici and his debate with Borro is traceable in his earliest work on motion, De motu antiquiora.
In particular, there are implicit references to Buonamici’s work in the discussion of the questions of falling bodies and of Archimedean extrusion.
As for the first subject, Galileo, in chapter 22 of his treatise De motu antiquiora, discusses the problem of the fall of bodies of different matters (wood, lead, and iron), in direct reference to the accounts already provided by Buonamici and by his rival, Borro. All of them (Borro, Buonamici, and Galileo) resorted to experimental evidence as a way to corroborate their own theories. From this point of view the famous leaning tower experiment, allegedly performed by Galileo at the time in which he composed his early writings on dynamics, seems to be rooted in a tradition of experimental research shared also by Borro and Buonamici, as well as by other Pisan professors, such as Jacopo Mazzoni and Giorgio Coresio.[4]
As can be clearly seen, there are serious debates on Aristotle’s theories of motion, in particular his theories on falling bodies, that predate Galileo’s own work and also influenced it significantly. Developments that in the popular accounts are attributed to Galileo often preceded him by significant periods of time.
[1] Quoted from William A Wallace, Domingo de Soto and the Iberian Roots of Galileo’s Science, in Domingo de Soto and the Early Galileo: Essays on Intellectual History, Routledge, 2004
[2] Charles B. Schmitt DSB
[3] Michele Camerota DSB
[4] Michele Camerota DSB