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What Were Galileo's Best Debates?

Leonard Kelley holds a bachelor's in physics with a minor in mathematics. He loves the academic world and strives to constantly explore it.

A Bold Questioner

I cannot summarize the conflicts of Galileo’s life as well as Sherwood Taylor. From the Preface, Page vii, of Taylor’s Galileo and the Freedom of Thought,

The essence of his story is the conflict between his view that scientific principles should be established solely by the application of reason to objective observation and the view of the Church and the Scholastic philosophers that the conclusions on natural science must give way to be pronouncements of an authority who alone was content to tell the world what it should think.

According to Viviani, a close friend of Galileo in his later years, recalled that his comrade was, “a bold questioner of established opinions and often found himself opposed to the Aristotelians.”

In this article, I will attempt to cover many of Galileo's best debates, both friendly but often antagonistic. With these, we gain further insights into the mysterious but often too human scientist that continues to fascinate us (Taylor 39).


Hints of the confrontational nature of Galileo can be found as early as his schooling at a monastery of Vallemhosa, where he was training to become a monk. It didn’t last long though before his father Vincenzo pulled him out to personally tutor him.

Vincenzo could certainly help his son in math and music, plus he didn’t trust “argument based on authority,” something surely encountered at the monastery. This trait was certainly passed onto the son and as we shall see led to much intrigue in the life of Galileo (Brodrick 14).

An open example of this was when Galileo turned 23 in 1587. He tried to study math at the University of Bologna but wasn’t accepted, so Vincenzo recommended instead a discipline in medicine. Galileo went to the University of Pisa where he learned under Claudius Galen, considered one of the best in the field with over 117 papers and an expertise on Greek medical history.

But Galileo didn’t care for the class because the lecturing bored him. So to keep it interesting for himself Galileo developed counters to some of Galen’s claims. Probably after much correspondence on the subject, Vincenzo let Galileo drop out of the course. Ironically enough, Marchese Guido Whaldo del Monte got wind of Galileo’s actions and liked that attitude.

So he gets Galileo in as the Chair of Mathematics at the University of Pisa in 1589. It was low pay, but Galileo was doing something he liked (15-6).

During the three years Galileo was at Pisa, he made plenty of enemies, namely Aristotelians. The main reason was the lack of mathematics in physics up to that point. To Galileo, physics without such a tool was all solely imagination without any backing in reality. It should have no place as a science.

But this was a time where Hipparchus and Ptolemaic ideals were bountiful, with epicycles and eccentrics the norm and Copernican ideals not as much. So Galileo decided to confront and see what happened.

He didn’t agree with the nothing of heavier objects falling faster than lighter ones, so (according to legend) he got to the top of the Tower of Pisa and did his famous drop. The Aristotelians were not pleased with the results (17-9).

Later on, Galileo took note of a military invention called the Legham machine. Its primary purpose was to take down enemy defensive walls and Galileo was asked to appraise its value for battle. His estimation wasn’t high when he essentially called the machine useless.

He would have phrased his thoughts better, for the inventor of the machine was the illegitimate son of the Grand Duke. That critique gained Galileo even more enemies, so Galileo left Florence in 1592 and would end up at the University of Padua, where he would be in that position for the next 18 years (19-20).

Galileo was definitely getting a big list of people against him, but he also cultivated allies too. One individual was Cosino II of Tuscany. In 1601, Galileo was needing money for his family and so applied to be the personal tutor of Cosino II’s daughter.

Again and again he tried to get in and finally in 1605 he started summer sessions with her as he continued to teach at the University. It would take a few years, but Cosino II would pay off in other ways for Galileo (24).

Fame and Scrutiny

Not too long after Galileo made a majority of his astronomical discoveries and published Sidereus Nuncius (in English, The Starry Messenger), he was offered the post of “First and Extraordinary” Mathematician of the University of Padua by Cosino II, the Grand Duke, in 1610. Galileo accepted easily, for it is a huge bump in pay.

However, it would also be a part of his undoing by the church later on in his life. Why? For if Galileo had stayed in Venice, he would have been in a place established independent of Rome and not subject to it (Taylor 69).

But moved on he did, and once there he and his work was greeted enthusiastically by most. The elite, however, were not amongst those pleased. They put so little worth into Galileo that initially they didn’t even look into Galileo’s findings to confirm or deny their claims.

That changed when Martin Hoiky made a poor argument against Galileo. He challenges the existence of the Medicean planets by claiming that there have always been 7 planets but now there are 11 because one man says so, and that cannot be enough sure footing to proclaim the matter as fact.

Even Tycho Brahe, with all of his instruments, failed to see the moons of Jupiter because he had no telescope yet denounced their presence. Instead, Brahe felt that they are optical effects stemming from refracted rays of Jupiter. He felt Galileo is just building up hype solely for monetary gain (70-1).

This caused Galileo some disbelief, and he wrote about it to his friend Castelli, a Benedictine monk. Some people, Galileo felt, would never be convinced no matter how much evidence one was presented with. And how true that is, even today. Of course Galileo may have upset people with his confrontational nature, especially with his work. As Galileo stated,

“Perhaps the day has arrived when languishing hope may be revered in those who led by the most profound reflections, once plumbed the fallacies of all my new observations and found them to be incapable of existing.”

This may be why one of Galileo’s friends did disagree with his findings. Cesare Cremonini, the chief professor at the University of Padua and a huge instructor on Aristotelianism, didn’t even look at Galileo’s data before critiquing the findings. His main contention? That the telescope affects one brain and renders anything viewed from it an illusion (Brodrick 41-2).

John Wetherbin and Kepler came to the defense of Galileo (despite not having seen the moons themselves) and pointed out the silly nature of Hoiky’s argument. They simply ask him to look for himself and see if he can spot anything. Once Hoiky does this, he retracts his statements and confirms that the moons exist.

Kepler even wrote Dissertatio cum Nuncio Sidereo as a defense of Galileo’s findings. This in of itself is amazing because Kepler felt resentment towards Galileo for a dropped correspondence between the two, but Kepler was able to push through that and see a fellow collogue needed help (Taylor 71, Pannekock 229, Brodrick 44, Rosen).

Another one of Galileo’s friends presented him with an interesting situation. Christopher Clavius was someone Galileo had befriended during his earlier efforts to get into the University of Bologna and happened to be the Chief Professor of Mathematics at the Jesuit Roman College.

While not a Copernican, he was still open to new ideas and so in December of 1610 wrote to Galileo about how his own telescopic viewings confirming Galileo’s data. The following November would see Clavius visit Galileo with his own supplies and the intent to paint the results Galileo found into a religious context (Brodrick 51, 55).

This was as if Clavius was anticipating some of the arguments against Galileo which were around the corner. Francesco Sizzi, an astronomer at Florence, also felt the moons are optical illusions but then goes on to bring Biblical evidence for just 7 planets.

This included Exodus Chapter 25 Verses 31-37 and Zachariah Chapter 4 Verse 2. He then goes on to bring up the importance of the number 7 in our lives. This included:

  • The 7 months until a fetus was “perfect” aka birthable
  • The 7 days for conception
  • The 7 windows of the head (2 eyes, 2 ears, 2 nose holes, and the mouth)
  • The 7 days of the week (which were based off planets)
  • The 7 metals based off alchemy (Gold – Sun, Silver – Moon, Copper – Venus, Mercury – Mercury, Iron – Mars, Tin – Jupiter, and Lead – Saturn)

And more. But he was not done yet. He goes on to mention that telescopes are producing refractive elements (like Brahe) and that because no one else can see the moons without an instrument, they cannot really exist (Taylor 72-4).

New Status Quo

Despite all of this, the world embraced the new moons and accepted them as science. But the Aristotelians and members of the Catholic Church did not like how it challenged their beliefs and made them feel like victims of an attack.

But Galileo did have some members of the clergy that favored him like the Duke of Tuscany and many cardinals. This meant that any of Galileo’s enemies need to use discretion in their moves against him (74).

One such work was by Ludovico delle Colombe who in 1610/1611 wrote Against the Motion of the Earth. It never mentions Galileo by name but the intent is quite clear, for it attacked Copernicans and many of Galileo’s ideas. In the book, Colombe argues against the use of math in describing the universe, for it is an abstraction that cannot accurately communicate the fine points of nature.

He points out as a case in point a cannon ball fired east versus west. The eastern direction should move faster than a North/South bound ball because of the rotation of the Earth while a westward ball moves slower for it works against the rotation. Colombe claims that no such distinction had been recorded.

In fact, if the Earth really spins then he claimed birds would be flung away, unable to keep up with the planet. Wind should only go in one direction also if the Earth spun because it would move with it. Also, people should be able to jump further west to east rather than east to west for similar reasons (75-6).

And he carries this even further by getting into other sciences. In his worldview, if you dropped a cork and a lead ball at the same time, the cork would fall back further than the lead ball because the Earth spun as both fell. And how, he argued, could the Earth orbit the Sun while the moon orbits us? Seemed to him like a contradiction.

And those mountains on the moon? Merely denser regions, and any voids are filled with transparent material thus ensuring the moon remains a perfect sphere. Finally, Colombe brings scripture into the mix by quoting Psalm 54:5, I Chronicles 16:30, Job 26:7, Proverbs 30:4, Ecclesiastes 1:5, Joshua 10:12, II Kings 20:8-11, and Genesis 1:16 (76-8).

Essentially, Colombe used bad arguments that tried their best to denounce Copernican ideals while supporting Aristotelian concepts. Galileo realized this but was still concerned about addressing this critique.

He sought the advice of his friend Cardinal Conti in regards to how scripture supported the Copernican system. Conti assured him that it does contain references to a changing heaven and thus an Earthly motion would be possible (79).

Public Eye

Feeling confident in his work, Galileo went to Rome in March of 1611 and presented his findings to the archbishops and the Purces of the Church. There, the members of the church voted it into Accademia Dei Lincei (in English, The Academy of the Lynx-Eyed) , the highest honor of the time for a scientist, on April 6, 1611.

This seems amazing considering we know the prosecution of Galileo later on in his life, but perhaps it was the proactive nature he displayed that won people over at the time. Also keep in mind that this was a small portion of the Church that Galileo visited and didn’t represent the viewpoints of everyone.

Also to consider is how they agreed upon the veracity of his findings but not on the theory they supported. Being admitted into the Academy also gave Galileo a greater freedom to use his voice, something that would also come back to haunt him (Taylor 79, Pannekock 230, Brodrick 57).

Not too long after this, a public forum on Galileo’s findings was held at the Jesuit Roman College. Attending the event were several high-profile figures such as Clavius, Father Christopher Greenberger, Father Odo Van Maelcote of Brussels, and Father John Paul Tembo.

Also in attendance were colleagues, scientists, cardinals, and scholars. Much was said that day praising Galileo, but it is worth noting that in attendance that day was Gregory of St. Vincent, a Jesuit. He noted the quiet discontent of the Aristotelians that day, almost like they were gathering fuel for a fire.

And the eight cardinals of the Holy Office in Rome were being cautious of Galileo not because of his findings but for the enthusiasm he had for them (Brodrick 61-2).

However, the remarks of those who did look at the work are revealing. Perpatelics felt that scripture was absolute but had a hard time being reconciled with the evidence against its ideas. The High Church also studied the findings and felt the old ideas of the heavens were out the door, no longer defendable.

With this support, Galileo should have moved on to new work. But instead, he writes an 800 page work attacking Colombe's critique of his work. It is because of this lack of knowing when to quit that gets Galileo into more trouble later in his life (Taylor 79-80).

In his rebuttal, Galileo points out the faults of the Aristotelian system. For example, it states that ice arises from the condensation of water as a result of cold temperatures. Galileo points out how light things float on water making it less dense and therefore a result of refraction and not condensation.

He goes on by stating that floatation is not a result of low gravity but as a difference in densities. Furthermore, shape can affect how an object floats, with a slim object having a greater tendency to sink rather than a broad one. He didn’t quite figure it out but this does hint as surface tension (80).

Later in the year around September, the Grand Duke hosts Cardinal Maffeo Barberini, (the future Pope Urban VIII) and Cardinal Ferdinando Gonzaga. At the meeting, he presents both of them with Galileo’s work on astronomy. Maffeo agreed with Galileo while Gonzaga did not. This would prove to be interesting later on, for they would be players in the indictment of Galileo (Ibid).

Fuel for the Fire

After all that sharing around, Galileo finally publishes his newest astronomical findings in 1612 and it does not take long for the Peripaletics and Colombe to respond. A year later, a new critic enters the scene as well: Vincenzio di Grazia. And over the span of 1611-1613, several university professors who felt their disciplines were being endangered, also critiqued Galileo.

But the stakes entered a new level when on December 16, 1611 Ludovico Cigoli wrote to Galileo warning him of a meeting that Cigoli and others led by Father Niccolo Lorini had with Marzinedici, the Archbishop of Florence, to seek aid in dealing with Galileo by finding some avenue to discredit him.

As it turns out, the Archbishop does nothing, for Galileo is on good terms with so many cardinals and the Grand Duke. But that connection with clergy would be used as a weapon later in Galileo’s life (Taylor 81, Brodrick 83).

Lorini would actively pursue Galileo’s work over the next few years, seeking idea he didn’t like. Near the end of 1612, Signor Pandolfini (another friend of Galileo) overhears Lorini critiquing some of Galileo’s findings. Naturally, Signor told Galileo and with hurt feelings Galileo wrote to Prince Cesi about Lorini’s lack of knowledge in the field.

And on February 5, 1615, Lorini wrote to Cardinal Paolo Sfondrati (the Secretary of the Holy Office) about Galileo’s work supposedly placing scripture below it. Lorini was therefore informing the Holy Office as a duty to his church. The vultures were beginning to get restless (Brodrick 84-6).

Scheimer, a Jesuit, wrote letters to his colleague Mark Welser who forwarded them to Galileo. There, Aristotelian ideals were used to explain the sunspots. In the book that was published by the Lyncean Academy in the spring of 1613, Galileo essentially promotes heliocentrism in his defense of the sunspots and the Catholic Church does…. nothing about it. No cardinal or bishop offered protest at it.

Galileo’s friend Paolo Gualdo points out how lucky Galileo has been lately, for the Inquisition had been running for quite some time and they could turn their eye onto him at any moment. He advises Galileo to use discretion form there on out (Brodrick 67-8).

On December 13, 1613 a big function was held at the Grand Dukes with high ranking people. Eventually, the topic turned to the popular subject of new planets. Peripatetic philosopher Boscaglia, a lecturer of Physics at Pisa, admitted that they were indeed real but that the Earth’s supposed motion is not, for it violates scripture.

This would have been a colleague of Galileo’s who did not agree with him, and at such a high-profile event no one would challenge him. At a different dinner of the Grand Dukes, someone mentioned ice and wondered why it floated.

The Aristotelians said it was because of its shape, but Galileo countered with his work on density and the displacement of fluid. Maffeo agreed with Galileo, another sign of the friendship they had between them (Taylor 81-2, Brodrick 65).

Galileo finds out about the statement Boscaglia gave the next day after his disciple Castelli overhears the remarks people are saying about it. Galileo writes a rebuttal and has Castelli distribute it on December 21. In our modern context it is amazingly insightful, for it discusses the dynamic between science and scripture.

Galileo discussed how religious interpretations are off but that the message behind them is right. He noticed how nature goes on regardless of what scripture says it does, for that pesky interpretation factor must be taken into account. In fact, one could interpret scripture until it matched nature, he argued. Instead of retroactively trying to get details to match, why not find the truth factor? As Galileo put it:

I think it would be prudent if men were forbidden to employ passages of scripture for the purpose of sustaining what our senses or demonst4rated proof may manifest to the contrary. Who can set bounds to the mind of man? Who dare assert that he already knows all that is in this Universe is knowable?

But this view wasn’t right for its time. And to further complicate matters, Galileo was a protestant and not an expert on religion yet tried to have comments on it, such as scripture is right but the reader may be wrong. Another example is how scripture is absolute but that it is not a manual for science but for context (Taylor 82-3, Brodrick 76-8).

Caccini had a problem with this and gave a sermon in Florence where he attacked Copernicanism and expressed scripture connections over Earth motion. A Jesuit church in Florence supported both Copernicus and Galileo and attacked Caccini’s claims as well as his fellow Dominicans. Caccini fires back with an approach against math and its applications.

To put it bluntly, Caccini felt mathematicians should be banished from society. Galileo was not pleased and went to the superior of the Dominican Order Luigi Maraffi who apologized on Caccini’s behalf (Taylor 83-97, Brodrick 87).

More and more similar instances happened over the next few years, with similar outcomes. Clearly, Galileo was stirring the pot, and realizing that it was (intentional or not, depends on who you walk to), he writes to Piero Dini, the Archbishop of Ferne and a friend of his, on February 16, 1615.

Lorini and Caccini put Galileo on edge, and Galileo hopes Ferne will spread the good word about him to the Dominicans, Ferne responds with an assurance that Galileo’s findings are in accordance with Catholic doctrine (Brodrick 88-9).

And things only got better from there.

Works Cited

Brodrick, James. Galileo: The Man, His Work, His Misfortune. Harper & Row Publishers, New York, 1964. Print. 14-20, 24, 41-2, 44, 51, 55, 57, 61-2, 65, 67-8, 76-8, 83-9.

Pannekick, A. A History of Astronomy. Barnes & Noble, New York: 1961. Print. 229-230.

Rosen, Edward. "Galileo and Kepler: Their First Two Contacts." Isis, Vol. 57, No. 2 (Summer, 1966), pp. 262-264.

Taylor, F. Sherwood. Galileo and the Freedom of Thought. Great Britain: Walls & Co., 1938. Print. vii, 39, 69-97.

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© 2017 Leonard Kelley