« ... Galileo Galilei was born in Pisa on 15 February 1564. His father Vincenzo was a famous lutenist and music theorist. Giulia Ammannati was his mother. 
From a record dated 1581, we know he studied arts at the Studio pisano. Most probably, he, afterwards, enrolled for a medical degree, but his attention was soon turned towards mathematics. Ostilio Ricci, a pupil of Niccolò Tartaglia became his teacher. 

"Theoremata Circa Centrum Gravitatis Solidorum" (Theorems on the centre of gravity of solids) is dated 1585. La Bilancetta (The Little Balance) is dated 1586. This tract was strongly influenced by the theories of Archimedes. 

He also studied literature. He, even, delivered two lectures (1588) at the Accademia Fiorentina on the arrangement of the world in Dante’s Inferno, supporting Antonio Manetti’s topography of the Inferno; explaining many geometrical problems skilfully and showing a great knowledge of the text. He also lectured on Tasso (1590). 

In 1589, he was appointed to the chair of mathematics in Pisa and, during the following year, he wrote "De motu" (On Motion). In 1592 he moved over to the University of Padua, where he spent eighteen years of his life. 

During this period, he commented Ptolemy’s Almagest and Euclid’s Elements. He also wrote a Brief Introduction on Military Architecture; a Treatise on Fortifications; Meccaniche (Mechanics). In 1597 he published the "Trattato della Sfera o Cosmografia" (Treatise on the Sphere or Cosmography), unfolding Ptolemy’s geometrical system. 

He was often in contact with the Paduan and Venetian cultural circles and found in them a continuous stimulus. He became friendly with many personages of his time such as Giovanni Francesco Sagredo, a Venetian nobleman and an expert optician; the Brothers Paolo Sarpi and Fulgenzio Micanzio and Cesare Cremonini from Padua. He often also visited the house of Vincenzo Spinelli. In Venice he met Marina Gamba (73) who will become the mother of his children. 

In 1606 he printed a manual "Le Operazioni del Compasso Geometrico et Militare" (The Operations of the Geometrical and Military Compass). Some years later, in 1609, he got news of a certain device, that will become crucial for him, the "spyglass". He reproduced this invention and, for sure, he improved it. 

Using the spyglass, he was able to make the discoveries described in his tract Sidereus Nuncius (The Sidereal Messenger - 1610). Galileo became famous overnight. Cosimo II de’ Medici, Grand Duke of Tuscany, appointed him "principal mathematician of the University of Pisa", and "philosopher of his Serene Highness the Duke" without whatsoever obligation to lecture or to reside in Pisa. In this work, Galileo, gave news of the discoveries revealed by the spyglass. 

At first, he was able to discern a great number of new stars. The previous picture of our Universe was changed. The Universe was becoming bigger and bigger. 

Soon after, he announced the existence of sunspots and reported the irregular character of the Moon’s surface, showing mountains, valleys and craters. He concluded the Moon was "rough and uneven, and just like the surface of the Earth itself", a fact that did not conform to the principles of Aristotelian Cosmology. He broke away from the myth of the ethereal existence and perfection of the celestial bodies. 

The ideas of purity, homogeneity and incorruptibility of the cosmic system became old fashioned. 

Finally, he gave a clear description of the Milky Way (or Galaxy): a congeries of innumerable very small stars, far away from Earth, contradicting the belief that the Milky Way was an outermost sphere that carried fixed stars. He also discovered the existence of the phases of Venus and Jupiter’s four stars (satellites). (74). 

The spyglass offered Galileo the possibility to advocate the Copernican theory. It is worth while remembering that many learned people were against this new instrument and that Cesare Cremonini, one of his friends and a convinced Aristotelian, even refused to look through it. 

In 1612 the Dominican Nicolò Lorini, during a sermon held at the Church of San Matteo in Florence on All Souls’ Day, attacked the Copernicans. Problems for Galileo, however, started with the four letters he wrote, advocating Copernicanism (75), and discussing on the relations between science and faith (1613-1615). 

In 1614, again a Dominican, Tommaso Caccini, from the pulpit of the Basilica of Santa Maria Novella, denounced the Copernicans. Soon after Galileo was accused to be close to heresy for his Copernican advocacy, and denounced to the Inquisition by Nicolò Lorini, who used, as an evidence against Galileo, a letter Galileo wrote to Benedetto Castelli. 

In 1616 he was tried (76), and warned to abandon teaching and support to opinions contrary to Scripture. 

Theologians concentrated on two subjects, namely that the Sun lies motionless at the centre of the Universe and that the Earth is not its centre and moves. After just five days, they sentenced that the first opinion was "dangerous and close to heresy", while the second should have to be censured samely as the first. Cardinal Roberto Bellarmino personally handed Galileo an admonition. Galileo "acquievit et parere promisit" (accepted and promised to obey). 

Cardinal Bellarmino himself and the Cardinals Alessandro Orsini and Francesco Maria Del Monte supported Galileo’s high reputation and, in writing, denied such gossip.  

In 1620 all his books championing Copernicanism and non Geostatic systems were banned and their publication was forbidden. (77) 

In 1623 Galileo published "Il Saggiatore" (The Assayer), a treatise on the nature of comets (78). His theories, it is now known, did not prove correct. This work, however, has been referred to as his scientific and philosophical manifesto. 

In this work Galileo explains how science may give a description of what is real, by separating the objective features of the bodies from the subjective ones. Only those aspects that can be quantified and measured are objective. It is not for science to discover the essence of substance. 

Universe is a grand book and its language must be understood. Philosophy is written in this book. The book of nature is re-discovered, it is written in the language of mathematics and its characters are geometric figures. 

Galileo was encouraged by the election of Cardinal Maffeo Barberini, as Pope Urban VIII, who was in friendly terms with him. He, therefore, published "Dialogo sopra i due massimi sistemi del mondo" (Dialogue Concerning the Two Chief World Systems) (79), where he, once again, advocated the Copernican theory. For this work, Galileo was ordered to stand trial in 1633 and requested to abjure. 

Through this work, Galileo, once again, tried to resume his cultural struggle against the system and against the a blind allegiance to the authority of the Church, that through Francesco Ingoli, from Ravenna, secretary of the Congregation of Propaganda Fide, confuted the Copernican system.  

Galileo tried to safe-guard himself declaring, in the introduction to his work, that he considered the theories of Copernicus "mere mathematical hypotheses", trying to show, to who was heretical, how serious the Catholic Church was. (80) This way of acting allowed him to face the question once again. 

The chief characters of his dialogue are Simplicio, Salviati and Sagredo (81). During the first day it is made clear there are no differences between the celestial and the terrestrial world. Differences do not exist. The mountains on the Moon, the spots, the Earth’s motion all vouch for laws of physics that are the same in any system. 

Aristotle based his theory of "perfection" on the perfection of circular motion, but Galileo stressed that such motion is also peculiar to bodies that stand on the Earth. On the second day anti-Copernican issues are countered with the aid of experiments. With the use of one of these experiments, in which a stone is let fall from the top-mast of a boat, he succeeded to put forward the basic principle of relativity, therefore, confuting all anti-Copernican theories and anticipating Einstein’s theory of relativity.  

Galileo wanted to show it is not possible to establish if a system is at rest or in motion, by just performing mechanical observations inside the system itself. Therefore, it is not possible to evaluate the Earth’s motion, while standing onto the Earth. 

For its importance, it must be remembered, Galileo proposed a relative motion, implicitly advocating this motion cannot be attributed to a body itself; therefore, upsetting completely the Aristotelian and Middle Age theories of the "impetus"."Inertia" and "motion" are considered persistent conditions. In absence of an external resistance a force is necessary to stop a body. Such force does not produce motion, but produces acceleration. 

It will be a person well learned in the Aristotelian hypotheses and with a background of studies that will finally contrast such thoughts. 

His personal friendship with the Pope however, did not help him, and his work, once published, was censured by the Inquisition. The same ordered him to stand a new trial on suspicion of heresy. 

The sentence asserted Galileo had deceived Father Riccardi, who had granted the "imprimatur" to his work. He had not been informed of the previous admonition the Church had handed over to Galileo. It also stated Galileo had taught false opinions, contrary to Holy Scripture. Additionally, it was said, he had used vernacular language with the intent to gain the favour of that part of population that was ignorant.  

The Church’s condemnation of Galileo arose great repercussion on the western thought. It conditioned the learned Community, among which Descartes, who decided against the publication of his work "Le Monde" (The World), which will become available to the public posthumously in 1664, thus meaning, fourteen years after his death. 

Galileo’s two trials, divided by nearly twenty years one from the other, are substantially different. The first trial warned Galileo to publicly abandon his support to Copernicanism, but in no way, as previously said, requested him to renounce or withdraw any content of his thoughts and theories. The Church did respect his position and his scientific work and, at the same time, also paid respect to science in general. The second trial, instead, created a great upsetting and a real uproar and strongly influenced liberty of thought and expression. 

Galileo, as a result of the second trial, once again was forced to abjure Copernicanism. At the same time he, symbolically, also recanted all the results of his discoveries, as he was firmly convinced of the methods he had used and of the results he had achieved. He also waived to all the results out-coming from his studies, strictly tied to a Copernican vision of the world. 

Certainly, the Inquisition did not sentence Galileo to the stake: therefore, it is possible to presume the Church was clement with him, or that, at least, Galileo’s person and position were both held in great respect. However, the Inquisition, without doubt, upset Galileo’s life very much. The sentence that was given became an example for all the scientific world that was loyal to the Church.  

Galileo was ordered life imprisonment; the sentence was later commuted to house arrest. After a period with the friendly Ascanio Piccolomini, Archbishop of Siena, Galileo was allowed to return to his home at Arcetri, where he spent the remainder of his life under house arrest. To see people or to write, he was compelled to request a relevant authorization. 

In this situation, he dedicated his time to one of his finest works: "Discorsi e Dimostrazioni Matematiche sopra a due nuove scienze" (Discourses and Mathematical Demonstrations concerning two new sciences), published in 1638 at Leiden (Holland). Meanwhile, his daughter Virginia, who had become a nun, taking the name Maria Celeste, took care of him. (82)  

Characters are same both in "Discourses" and in "Dialogue". Discussions took up the same length of time: four days. During the first two days, discussions regarded how long a material could resist to breakage. Galileo tried to find mathematical ratios between such resistance and " the length and the thickness" of the bodies. In order to find an answer, it was decided to carry out a research on continuity, vacuum and atom: and therefore, on the structure of the substance. 

He opposed the theories of Aristotle that asserted there is no motion in a vacuum. He further refuted the Aristotelian hypotheses on falling bodies, proposing that all weights fall with a uniform acceleration, once resistance is negligible or nil. 

Galileo also took into consideration the pendulum motions and the relevant laws that govern such motion. He understood sound frequency. He attributed resistance to a system of levers and made use of statics, a new science, to emphasize how much geometry helped in the study of physics and biology. 

In the third and fourth day, discussions concerned dynamics, a novel science, and it was asserted that, most important, all laws on motion must be confirmed by experimental data. Physical proof must be carried out: first the experiment must be carefully pondered and, after, brought forward acting with extreme accuracy, to achieve a valid result. Theory implies experiments: both go together and cannot be divided.  

This work was published outside Italy, in Holland, to where it was secretly brought. It emphasized the scientific thought of Galileo and his adherence to experimental results. 

His last years of life were overwhelmed by the death of his beloved daughter. He also went completely blind and suffered from hernia and insomnia. He died on 8 January 1642 and his death was described by Vincenzo Viviani and by Evangelista Torricelli, who both were near to him during the last years of his life. 

We inherited the way Galileo interpreted science. Our modern approach to science, in a certain way, reminds us that of Galileo’s. 

Galileo’s contribution was extremely important from the epistemological point of view. He opposed the static and crystallized context of his times, favouring changes and advocating the new, convinced his ideas were correct.  

Reality, from a mathematical point of view, became legible and understandable to science having an objective value: in particular, it appraises the qualities of the bodies that can be quantified and measured, with the use of mathematics. Moreover, Galileo put a stop to the Aristotelian world based on dogmas, and favoured, instead, a Platonic world. This explains why somebody reads his work "Dialogue", more like a philosophical work, than as a text of astronomy and physics.(83) 

The discovery of the spyglass was extremely helpful. It offered man the possibility to verify and to extend his senses; to record events, that before, could only be imagined and to unveil a number of new ones. 

Galileo is important because he was not afraid to oppose the pre-established theories, the ancient knowledge. Using the spyglass Galileo gave start to a revolution. He demonstrated it was possible to trust human senses, an idea many did not accept. Orthodox philosophy considered mechanics a secondary science, following Aristotle’s theories, while, with Galileo, mechanics became the basis of all research work. Galileo’s revolution also favoured new discoveries in dynamics, physics and standards. 

Galileo asserted the laws of nature are mathematical laws. The Universe is written in the language of mathematics. Arithmetic and geometry are fundamental for all men. 

It is possible to assume that his return from the Venetian region to Tuscany, may imply an estrangement from the Aristotelian circles in favour of an approach towards the theories of Plato, much more congenial to him and, therefore, not only towards a different social position and towards a new appointment. 

Galileo aided the separation of science and knowledge from religion, from any type of religion. Setting a division between science and religion gave both a precise field of action and different purposes: religion regarded spiritual values; science knowledge. 

As so, dogma belonged to religion, not to science. Therefore, it was possible to confute Aristotle and to break away from Scripture, a daring behaviour for the times. 

His fight was titanic. It was not a fight among learned men or philosophers, but between a man and the representation of the Divine on Earth … » 
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