Therefore, he had to devise or shall we say, discover principles of local motion that will fit a central sun, planets moving around that sun, and a daily whirling earth. This he did by introducing two new principles. Then, in Day Two, he introduced his version of the famous principle of the relativity of observed motion. This latter held that motions in common among bodies could not be observed.

Only those motions differing from a shared common motion could be seen as moving. The joint effect of these two principles was to say that all matter shares a common motion, circular, and so only motions different from the common, say up and down motion, could be directly observed.

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Of course, neither of the principles originated with Galileo. They had predecessors. But no one needed them for the reasons that he did, namely that they were necessitated by a unified cosmological matter. In Day Three, Galileo dramatically argues for the Copernican system. Salviati, the persona of Galileo, has Simplicio, the ever astounded Aristotelian, make use of astronomical observations, especially the facts that Venus has phases and that Venus and Mercury are never far from the Sun, to construct a diagram of the planetary positions. The resulting diagram neatly corresponds to the Copernican model.

Earlier in Day One, he had repeated his claims from The Starry Messenger , noting that the earth must be like the moon in being spherical, dense and solid, and having rugged mountains. Clearly the moon could not be a crystalline sphere as held by some Aristotelians. In the Dialogues , things are more complicated than we have just sketched. Galileo, as noted, argues for a circular natural motion, so that all things on the earth and in the atmosphere revolve in a common motion with the earth so that the principle of the relativity of observed motion will apply to phenomena such as balls dropped from the masts of moving ships.

Yet he also introduces at places a straight-line natural motion. For example, in Day Three, he gives a quasi account for a Coriolis-type effect for the winds circulating about the earth by means of this straight-line motion Hooper Further, in Day Four, when he is giving his proof of the Copernican theory by sketching out how the three-way moving earth mechanically moves the tides, he nuances his matter theory by attributing to the element water the power of retaining an impetus for motion such that it can provide a reciprocal movement once it is sloshed against a side of a basin. We saw it in De Motu in , with submerged bodies, but more importantly he learned much more while working through his dispute over floating bodies Discourse on Floating Bodies , In fact a large part of this debate turned on the exact nature of water as matter, and what kind of mathematical proportionality could be used to correctly describe it and bodies moving in it cf.

Palmieri, , a. The second science, discussed so to speak in the last two days, dealt with the principles of local motion. These have been much commented upon in the Galilean literature. But the first two days, the first science, has been much misunderstood and little discussed. This first science, misleadingly, has been called the science of the strength of materials, and so seems to have found a place in history of engineering, since such a course is still taught today.

However, this first science is not about the strength of materials per se. See Machamer , Machamer and Hepburn , and the detailed work spelling this out by Biener Galileo realizes that before he can work out a science of the motion of matter, he must have some way of showing that the nature of matter may be mathematically characterized.

Both the mathematical nature of matter and the mathematical principles of motion he believes belong to the science of mechanics, which is the name he gives for this new way of philosophizing. Remember that specific gravities did not work. So it is in Day One that he begins to discuss how to describe, mathematically or geometrically , the causes of how beams break. He is searching for the mathematical description of the essential nature of matter. He rules out certain questions that might use infinite atoms as basis for this discussion, and continues on giving reasons for various properties that matter has.

The most famous of these discussions is his account of acceleration of falling bodies, that whatever their weight would fall equally fast in a vacuum. The Second Day lays out the mathematical principles concerning how bodies break. He does this all by reducing the problems of matter to problems of how a lever and a balance function. Something he had begun back in , though this time he believes he is getting it right, showing mathematically how bits of matter solidify and stick together, and do so by showing how they break into bits.

The second science, Days Three and Four of Discorsi , dealt with proper principles of local motion, but this was now motion for all matter not just sublunary stuff and it took the categories of time and acceleration as basic. Interestingly Galileo, here again, revisited or felt the need to include some anti-Aristotelian points about motion as he had done back in Then, he says, join the bodies together.

In this case the lightness of the small one ought to slow down the faster larger one, and so they together fall as a speed less than the heavy fell in the first instance. Then his punch line: but one might also conceive of the two bodies joined as being one larger body, in which case it would fall even more quickly. So there is a contradiction in the Aristotelian position Palmieri His projected Fifth Day would have treated the grand principle of the power of matter in motion due to impact.

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## Galileo backed Copernicus despite data | Nature

He calls it the force of percussion, which deals with two bodies interacting. He has a new science of matter, a new physical cosmography, and a new science of local motion.

In all these he is using a mathematical mode of description based upon, though somewhat changed from, the proportional geometry of Euclid, Book VI and Archimedes for details on the change see Palmieri It is in this way that Galileo developed the new categories of the mechanical new science, the science of matter and motion. His new categories utilized some of the basic principles of traditional mechanics, to which he added the category of time and so emphasized acceleration.

But throughout, he was working out the details about the nature of matter so that it could be understood as uniform and treated in a way that allowed for coherent discussion of the principles of motion. Thereafter, matter really mattered. The end of the episode is simply stated. In January , a very ill Galileo made an arduous journey to Rome.

Finally, in April Galileo was called before the Holy Office. This was tantamount to a charge of heresy, and he was urged to repent Shea and Artigas, f. Specifically, he had been charged with teaching and defending the Copernican doctrine that holds that the Sun is at the center of the universe and that the earth moves.

Galileo was called four times for a hearing; the last was on June 21, The next day, 22 June, Galileo was taken to the church of Santa Maria sopra Minerva, and ordered to kneel while his sentence was read. Galileo was made to recite and sign a formal abjuration:. Galileo was not imprisoned but had his sentence commuted to house arrest. In December he was allowed to retire to his villa in Arcetri, outside of Florence.

During this time he finished his last book, Discourses on the Two New Sciences , which was published in , in Holland, by Louis Elzivier. The book does not mention Copernicanism at all, and Galileo professed amazement at how it could have been published. He died on January 8, There is also controversy over the legitimacy of the charges against Galileo, both in terms of their content and judicial procedure.

It has even been argued Redondi that the charge of Copernicanism was a compromise plea bargain to avoid the truly heretical charge of atomism. Though this latter hypothesis has not found many willing supporters. Legitimacy of the content, that is, of the condemnation of Copernicus, is much more problematic. Galileo had addressed this problem in , when he wrote his Letter to Castelli which was transformed into the Letter to the Grand Duchess Christina.

In this letter he had argued that, of course, the Bible was an inspired text, yet two truths could not contradict one another.

## Galileo Galilei - When the World Stood Still (eBook, PDF)

So in cases where it was known that science had achieved a true result, the Bible ought to be interpreted in such a way that makes it compatible with this truth. The Bible, he argued, was an historical document written for common people at an historical time, and it had to be written in language that would make sense to them and lead them towards the true religion.

Cardinal Bellarmine was willing to countenance scientific truth if it could be proven or demonstrated McMullin But Bellarmine held that the planetary theories of Ptolemy and Copernicus and presumably Tycho Brahe were only hypotheses and due to their mathematical, purely calculatory character were not susceptible to physical proof. This is a sort of instrumentalist, anti-realist position Duhem , Machamer There are any number of ways to argue for some sort of instrumentalism. Duhem himself argued that science is not metaphysics, and so only deals with useful conjectures that enable us to systematize the phenomena.

Subtler versions, without an Aquinian metaphysical bias, of this position have been argued subsequently and more fully by van Fraassen and others. Galileo would be led to such a view by his concern with matter theory. Of course, put this way we are faced with the question of what constitutes identity conditions for a theory, or being the same theory.

The other aspect of all this which has been hotly debated is: what constitutes proof or demonstration of a scientific claim? This argument, about the tides, Galileo believed provided proof of the truth of the Copernican theory.

Galileo argues that the motion of the earth diurnal and axial is the only conceivable or maybe plausible physical cause for the reciprocal regular motion of the tides. How could the moon without any connection to the seas cause the tides to ebb and flow? Such an explanation would be the invocation of magic or occult powers. Differences in tidal flows are due to the differences in the physical conformations of the basins in which they flow for background and more detail, see Palmieri One can see why Galileo thinks he has some sort of proof for the motion of the earth, and therefore for Copernicanism.

Yet one can also see why Bellarmine and the instrumentalists would not be impressed. Second, the tidal argument does not directly deal with the annual motion of the earth about the sun. And third, the argument does not touch anything about the central position of the sun or about the periods of the planets as calculated by Copernicus. It is a resounding success.

## Galileo Galilei: When the World Stood Still

The story of his life and times The translation into english is excellent. This book brought home to me the full extent Anyone with an interest in the life and times of Galileo will adore this new account It is beautifully printed, attractively bound Highly recommended. Much of the argument The background of the build up to the trial with all the necessary detail is handled in a masterly manner There are 13 pages of index and references which will allow the assiduous reader to delve further into the scientific life of seventeenth century Italy — a journey well worth making Perkins, The Mathematical Gazette, Vol.

This biography deals with both these aspects, making full use of recent historical research. Altogether is presents a rounded picture of his life in a highly readable account. Altogether it presents a rounded picture of his life in a highly readable account.

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