Until the publication of his Sidereus Nuncius in 1610, Galileo Galilei (1564–1642) was basically a nobody on the European scientific scene. Professor for mathematics, the lowest of the low in the academic hierarchy, at the University of Padua, he was something of a local celebrity due to his flamboyant and provocative character but despite, his obvious capabilities, not a renowned scholar. He had already carried out his studies into the laws of fall and projectile motion but had published nothing so, those studies that would establish his fame as an experimental physicist remained unknown until they were finally published as Discorsi e dimostrazioni matematiche intorno a due nuove scienze in 1638. In 1610 he was an aging mathematicus at a prominent North Italian university with not much to show for himself.
The publication of Sidereus Nuncius radically changed all that almost literally overnight. The book went off like a bomb and catapulted its author to the status of Europe’s astronomer numero uno. He had already used his most spectacular astronomical discovery, the four largest moons of Jupiter, to wrangle himself a new position in Florence as court philosophicus and mathematicus to the Medici, as well as a professorship, without teaching obligation, on the University of Pisa, the institution that had thrown him out eighteen years earlier. His very percipient friend, Paolo Sarpi (1552–1623) advised against the move, arguing that in the Republic of Venice he was safe from the Roman Inquisition but would be exposed to them in Florence. Sarpi defied and attacked Rome from within the borders of Venice for almost two decades.
As well as gracing the court in Florence as a sort of intellectual ornament, Galileo role had a strong similarity to that of court jester. He was expected to entertain the court with his quick wit and debating skills, bringing further lustre to the Medici magnificence. It was one of these public intellectual displays that gave birth to Galileo’s first publication after the Sidereus Nuncius, his Discorso intorno alle cose che stanno in su l’acqua, o che in quella si muovono, (Discourse on Bodies that Stay Atop Water, or Move in It) published in Italian in 1612. This small work tends to get ignored in the general Galileo hagiography but it is another work in the series of the Renaissance battle of the two ‘A’s, Archimedes contra Aristotle, of which we have already seen several in this series, with Galileo, naturally, championing the concepts of Archimedes against those of Aristotle.
In Florence there were a number of Aristotelian philosophers, who launched attacks on Galileo for his astronomical and cosmological views. The most prominent of these was Lodovico delle Colombe (1565–1623), whose name led to the disparaging term used for Colombe and his supporters by Galileo and his friends, Lega del Pippione’ (‘The Pigeon League’); Colombe is the Latin for pigeon. The name also implies that the members of The Pigeon Leage were bird brained.
The affair that led to Galileo’s Discourse on Floating Bodies started during a debate on the nature of cold between Galileo and the Pisan University Aristotelians, Vincenzo di Gracia and Giorgio Coresio (1570–1659?) in the house of Fillipo Salviati (1583–1614), who is today famous as one of the three characters in Galileo Dialogo and Discorsi. When discussing the fact that ice floats on water the Aristotelians argued that although ice was condensed water it floated because of its shape. Galileo, a convinced Archimedean, held that if ice was condensed water it would sink therefore ice was in fact rarified water. To Galileo the fact that ice floated on water proved its was less dense that water.
We of course now know that water is a strange substance that reaches its highest density at 4°C and that ice is in fact less dense than the water on which it floats. This is also the reason why things can live in ponds that are frozen over, as the water under the ice has 4°C.
The affair might have stopped there but for Lodovico delle Colombe, an independent philosopher, who had just returned to Florence and was also already a fierce critic of Galileo’s astronomy and cosmology. Lodovico claimed that he had an experiment or demonstration that proved Galileo wrong. He stated quite correctly that a flat chip of ebony, which is denser than water, floats whereas a sphere of ebony sinks. We now know that the ebony chip floats because of surface tension but the phenomenon was not recognised in the early seventeenth century.
Apparently a public meeting was organised at which Colombe would present his demonstrating and thus refute Galileo. There was a lot of haggling over the conditions for the demonstration. Galileo wanted to be able to wet the ebony chip before it was placed on the water but Colombe blocked this request. Independent judges of good standing were even appointed to adjudicate. Here the accounts differ, according to Galileo’s side Colombe didn’t appear at the appointed time and place. According to Colombe it was Galileo who failed to appear. Colombe now proceeded to make his demonstration in public places throughout Florence, loudly claiming that Galileo was refuted. One should note that there was a strong element of envy in this whole affair, the professional philosophers of Florence objecting to Galileo, a mere mathematicus, having been appointed court philosophicus.
At this point Galileo’s lord and master Cosimo II entered the fray, admonishing Galileo for becoming embroiled is a vulgar public dispute and ordering him to desist. Here we get a clear demonstration that Galileo was Cosimo’s performing monkey on a leash and Cosimo had a firm grip on that leash.
Cosimo now organised a post luncheon entertainment, a debate on the topic at court with the Pisan, university professor Flaminio Papazzoni (1550–1614) presenting the Aristotelean point of view and Galileo that of Archimedes. Galileo enjoyed a small bias during the debate, as Papazzoni had been appointed professor at the Pisan university on his recommendation, as the grand dukes advisor on university appointments, and obviously he was not going to attack his benefactor too hard. Papazzoni was supported in his arguments by Cardinal Ferdinand Gonzaga (1587–1626) and Galileo by Cardinal Maffeo Barberini (1568–1644). It was, of course, Barberini, who later as Pope Urban VII would condemn Galileo to lifelong house arrest but here they were still good friends. The opinions differ as to who won the debate but that was not considered important. The important thing is that it should entertain those present.
Cosimo now suggested that if Galileo should wish to continue the debate that he should present his views in the form of a book and not in undignified debates in the public forum so, Galileo proceeded to set out his views in writing in his Discourse on Floating Bodies, which appeared in the middle of 1612 with an expanded second edition appearing in December of the same year.
The book basically presents a standard Archimedean view on hydrostatics, as it were a textbook on the topic for future reference, rather than a product of the preceding public debate. Galileo did, however, address the arguments of his Aristotelian opponents without actually naming them. Here we see the arrogant, provocative Galileo in action. At one point he argues that given the ridiculous nature of their views he was doing them a favour by not naming them. Instead, his discourse partner in his text was Francesco Buonamici (1533 –1603), a high status, mathematically-literate, Aristotelian philosopher, a worthy opponent, who was conveniently dead. In Book V of his De Motu (1591) Buonamici had proposed a refutation of Archimedes’ theory of buoyancy, which contained a coherent summary of the fragmented arguments of Galileo’s current adversaries.
Having outlined Archimedes’ theory of buoyancy, which was based on the concept of specific weight, i.e. absolute weight divided by volume, Galileo went beyond Archimedes in describing and trying to explain the so-called hydrostatic paradox. As we saw in an earlier post, Simon Stevin (1548–1620) had already discovered the paradox and explained it in his De Beghinselen des Waterwichts (Principles on the weight of water) published in 1586. Stevin’s explanation is better than that of Galileo. Galileo also departed from Archimedes in that he outlined a theory of motion in water this was partially presented mathematically. However, neither the theory nor the mathematics was very convincing.
Of interest is Galileo’s somewhat bizarre attempt to explain away the problem posed by the floating ebony chip. Galileo argued that the chip was not sitting directly in the water but in a trough and it was enclosed in an envelope of air and the specific weight of chip and enclosing air was lower than the specific weight of the water and so it floats. He was naturally totally unable to explain why the air should attach itself to the chip.
There were four attempted refutations of Galileo’s book published by Aristotelians, the most significant being at of Lodovico delle Colombe Discorso Apologetico di Lodovico delle Colombe d’Intorno al Discorso di Galileo Galilei published in 1612.
Galileo simply ignored them and it was Benedetto Castelli (1578–1643) Galileo’s one time student and professor for mathematics at the University of Pisa, who responded in writing in his Risposta alle opposizioni del signor Lodovico delle Colombe e del signor Vincenzio di Grazia, contro al trattato del signor Galileo Galilei, delle cose che stanno su l’acqua, o che in quella si muovono, a book almost certainly largely written by Galileo and published in 1615. Galileo would use the attic of having his views presented by one of his acolytes on more than one occasion. Castelli’s book effectively refuted all of the arguments of Colombe et al and the dispute ground to a halt.
I mentioned earlier that this first publication post Sidereus Nuncius largely gets ignored. The reason for this is quite simple, written and published only in Italian it attracted a comparatively small audience and had almost no impact on the ongoing scientific debates in the early seventeenth century outside of Florence. One might think the same would be true of Simon Stevin’s book on the same topic, written in Dutch, but, unlike Galileo’s tome, it was translated into Latin by Willebrord Snel (1580–1626) and did have a significant impact.
However, this early publication of Galileo’s displays him firmly placed in the in the chain of Early Modern scholars, who were influenced by the mathematical works of Archimedes, in particular his On Floating Bodies–Tartaglia, Benedetti, Commandino, Stevin– and who took up a stance challenging the predominant Aristotelian philosophy. Placing him firmly in this sequence also helps to dismiss the myth that somehow Galileo alone made a quantum leap from the descriptive, philosophical physics of the Aristotelian to the mathematical physics of Archimedes. The renaissance in the works of Archimedes played a significant role in the gradual emergence of modern physics during the sixteenth and seventeenth centuries.