Indeed, he describes how the instrument behaves very strangely and shows different magnifications depending on whether the observed object is a planet or a star. In fact, Galileo could not know the physical explanation of the optical aberration phenomenon which is usually associated with the use of an optical instrument. Therefore, he is hesitant to give the description of a mechanism according to which the instrument is apparently able to enlarge the observed objects in different ways, i.
At this point, Galileo did not have the time to pursue this matter because he urgently needed to make public his numerous observations of all visible objects in the sky of Padua as soon as possible. In the winter of , despite not being an astronomer he was about to totally and definitively revolutionize the image of the sky and also suggest the need to overhaul the model of the Cosmos through his rich innovations. Indeed, the Aristotelian-Ptolemaic model endorsed by the Church encountered a great deal of difficulty in facing up to the whole complex set of new ideas discovered by Galileo.
This depended on the geometric complexity required to take the new, observational data into account and also on the weakness of some of the principles on which the Aristotelian-Ptolemaic system was based. These principles were now being demolished.
The Copernican model was published almost 70 years earlier and was still seen only as an original, mathematical exercise to provide new ephemerides. However, while there were several difficulties with the Copernican system, the situation for its Ptolemaic counterpart was undoubtedly even worse. This observation may indeed appear superfluous when compared with the astonishing announcement of the existence of four new planets.
Moreover, Galileo does not provide many details regarding this problem although he was precise and meticulous in describing these observations. Notwithstanding, these references appear significant. Galileo advances a hypothesis that can explain this apparent variability of the light reflected by satellites after a very long thought process.
Initially, he provides the hypothesis that their orbits can be highly elliptical, being the major axis along the line of sight of the observer. This meant he could explain the weakening of the light by the increased distance of the satellite.
Galileo certainly knew from his previous experience that light intensity decreases with increasing distance from the source. Galileo saw that the brightness of the satellites was at its minimum when they came close to the planet. The only theoretical possibility is thus that the satellite moves away far from Jupiter, its center of motion and therefore that the orbit must be greatly elliptical in relation to the weakening of the light output observed and recorded by Galileo.
The logic that supports this argument may seem compelling. Anyway, this behaviour of the phenomenon is not compatible with the previous hypothesis which seems artificial. However, this hypothesis is a scientific-literal artifice used by Galileo to lead up to a second explanation. In this explanation, he returns strongly to the hypothesis that an atmosphere could surround a celestial body—Jupiter in this case. The presence of a dense shell would weaken the light absorbing a large proportion of the emission from satellites.
It is fascinating to imagine that Galileo had a common purpose for giving an account of two different events which acquires the value of a universal statement— planets have a shell of air around themselves. Nevertheless, this statement is not particularly significant if it is limited to an explanation of observational data but if used as a starting hypothesis which is well supported by observations, it could have deep, cosmological implications.
It would indeed be linked to the disputes concerning the De revolutionibus orbium coelestium of Nicolaus Copernicus. In fact, if the Moon and the planets have an atmosphere in their circular movement around their center-of-motion, then the motion itself is not incompatible with the existence of an atmosphere. Also, if this logical consequence is valid for the Moon and planets as shown by Galileo and if they are similar to the Earth, this obstacle is overcome by imagining an Earth moving around the Sun.
Therefore, the movement of the Earth around its axis and around the Sun does not imply the atmosphere is stripped away. However, if this hypothesis is correct, why was Galileo not more explicit? This is impossible to answer. Again, it should be recalled that the heliocentric system was not accepted by most theologians, astrologers, astronomers and scholars, even if De revolutionibus had not yet been rejected.
All these observations were to be as fundamental as the previous ones. Galileo discovers Saturn to have a strange shape like a small olive.
Venus was watched nightly and every week which showed phases similar to those of the Moon. It therefore became geometrically evident that the Mother of Loves was moving around the Sun as Copernicus had suggested, unheeded, for decades. The next step examined is that in which Galileo describes what he sees pointing his telescope towards the nebulae, or nebulous stars. Immediately he proposes a new radical change in the interpretation of those indistinct spots that had long been considered one of the most mysterious objects in the sky when viewed with the naked eye.
Philosophers, priests, astronomers had provided several proposals to explain their nature which were mostly mythologically based. This is, once again, a real revolution.
In fact, the interpretation of these objects changes dramatically because Galileo reveals that they are composed of myriad stars which are so weak and apparently mutually close that they cannot be distinguished by the human eye.
Thus one has the perception that they are made of a continuous material. Then, in Day Two, he introduces his version of the famous principle of the relativity of observed motion.
This latter holds that observers cannot detect uniform motions they share with objects under observation; only differential motion can be seen. Of course, neither of these principles was entirely original 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.
One key effect of these principles is that the diurnal terrestrial rotation asserted by the Copernican system is unobservable. We only notice departures from shared rotation, such as bodies falling or rising. This blunted standard objections to Copernicanism on the grounds that there is no evidence of terrestrial motion. Having dispelled these arguments against the Copernican system, Galileo then dramatically argues in its favor.
In Day Three of the Dialogue. The resulting diagram neatly corresponds to the Copernican model. In the Dialogue , things are more complicated than we have just sketched. Galileo, as noted, argues for circular natural motion. Yet he also introduces, in places, an intrinsic tendency for rectilinear motion.
For example, Galileo recognizes that a stone whirled circularly in a sling would fly off along the rectilinear tangent if released Galilei , —94; see Hooper Further, in Day Four, when he is giving his mechanical explanation of the tides, he nuances his matter theory by attributing to water an additional power of retaining an impetus for motion such that it can generate a reciprocal movement once it is sloshed against a side of a basin.
We saw it first in the De Motu around , where Galileo discusses submerged and floating bodies, but he learned much more in his dispute over floating bodies which produced the Discourse on Floating Bodies in In fact, a large part of that 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 see Palmieri ; The second science, discussed in the last two Days, deals with the principles of local motion and has been much commented upon in the Galilean literature.
But the first science, discussed in the first two Days, has been misunderstood and infrequently discussed. It has misleadingly 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 science is not about the strength of materials per se. 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.
So it is in Day One that Galileo begins to discuss how to describe mathematically or geometrically the causes of the breaking of beams. But this requires a way to reconcile mathematical description with the physical constitution of material bodies. In this vein, Galileo rejects using finite atoms as a basis for physical discussion, since they are not representable by continuously divisible mathematical magnitudes. Instead, he treats matter as composed of infinitely many indivisible—which is to say, mathematical—points.
This allows him to give mathematical accounts for various properties of matter. Among these are the density of matter, its coherence in material bodies, and the properties of the resisting media in which bodies move. The Second Day lays out the mathematical principles concerning how bodies break. Galileo does all this by reducing the problems of matter to problems of how a lever and a balance function, which renders them mathematically tractable via the law of the lever.
He had begun this back in , though this time he believes he is getting it right, showing mathematically how bits of matter solidify and stick together, and how they break into bits.
On the one hand, if Aristotle is correct, the faster fall of the heavier body will be retarded by the slower motion of the lighter body, so that the conjoined body will fall slower than the original heavy body.
And yet, the conjoined body is heavier than either original body, so it should also fall faster. Hence, there is a contradiction in the Aristotelian position Gendler ; Palmieri ; Brown and Fehige This is now the motion of all matter, not just sublunary stuff, and the treatment takes the categories of time and acceleration as basic. In the projected Fifth Day, Galileo would have treated the power of moving matter to act by impact, which he calls the force of percussion. Ultimately, Galileo was unable to give mathematical principles of this kind of interaction, but this problem subsequently became an important locus of interest.
He offered a new science of matter, a new physical cosmography, and a new science of local motion. It is in this way that Galileo developed the 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 universal, and treated in a way that allowed for coherent discussion of the principles of motion.
It was due to Galileo that a unified matter became accepted and its nature became one of the problems for the new science that followed. After him, matter really mattered. The end of the affair is simply stated. In late , in the aftermath of the publication of the Dialogue Concerning the Two Chief World Systems , Galileo was ordered to appear in Rome to be examined by the Congregation of the Holy Office; i.
In January , a very ill Galileo made an arduous journey to Rome. From April, Galileo was called four times to hearings; the last was on June The next day, June 22, , Galileo was taken to the church of Santa Maria sopra Minerva, and ordered to kneel while his condemnation was read. I have been judged vehemently suspect of heresy, that is, of having held and believed that the sun in the center of the universe and immoveable, and that the Earth is not at the center of same, and that it does move.
Wishing however, to remove from the minds of your Eminences and all faithful Christians this vehement suspicion reasonably conceived against me, I abjure with a sincere heart and unfeigned faith, I curse and detest the said errors and heresies, and generally all and every error, heresy, and sect contrary to the Holy Catholic Church. Quoted in Shea and Artigas , When he later finished his last book, the Two New Sciences which does not mention Copernicanism at all , it had to be printed in Holland, and Galileo professed amazement at how it could have been published.
The details and interpretations of these proceedings have long been debated, and it seems that each year we learn more about what actually happened. One point of controversy is the legitimacy of the charges against Galileo, both in terms of their content and the judicial procedure. Galileo was charged with teaching and defending the Copernican doctrine that holds the sun is at the center of the universe and the Earth moves. The status of this doctrine was cloudy.
In , an internal commission of the Inquisition had determined that it was heretical, but this was not publicly proclaimed. In , at the same time that the Inquisition was evaluating Copernicanism, they were also investigating Galileo personally—a separate proceeding of which Galileo himself was not likely aware.
To confound issues further, the case against Galileo transpired in a fraught political context. Galileo was a creature of the powerful Medici and a personal friend of Pope Urban VIII, connections that significantly modulated developments Biagioli The legitimacy of the underlying condemnation of Copernicus on theological and rational grounds is even more problematic. Galileo had addressed this problem in , when he wrote his Letter to Castelli and then the Letter to the Grand Duchess Christina.
In these texts, Galileo argues that there are two truths: one derived from Scripture, the other from the created natural world. Since both are expressions of the divine will, they cannot contradict one another. However, Scripture and Creation both require interpretation in order to glean the truths they contain—Scripture because it is a historical document written for common people, and thus accommodated to their understanding so as to lead them towards true religion; Creation because the divine act must be distilled from sense experience through scientific enquiry.
While the truths are necessarily compatible, biblical and natural interpretations can go awry, and are subject to correction. 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 are only mathematical hypotheses; since they are just calculating devices, they are not susceptible to physical proof. This is a sort of instrumentalist, anti-realist position Machamer ; Duhem 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 phenomena. Subtler versions of this position, without an Aquinian metaphysical bias, 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, which minimized the kinds of motion ascribed uniformly to all bodies.
He could then employ mathematical calculations to confirm what he would have already suspected regarding the true nature of the cosmos, and by he was synthesizing these evidence-based ideas in the text that would become Starry Messenger. Galileo was certainly aware of the perils of contradicting Church doctrine.
However, by the early 17th century the messages coming from the Church regarding scientific research were mixed. In , the Dominican friar, mathematician, and astronomer Giordano Bruno had been burned at the stake on the orders of the Inquisition for the heretical crime of promoting ideas that ran counter to Ptolemaic geocentrism and thus Church teachings. But, within certain sectors of the Catholicism there had been a gradual acceptance of science and enlightenment.
There was also an alternate cosmology, based on the ideas of Danish nobleman Tycho Brahe, which had gained acceptance, particularly among Jesuit clergy and intellectuals. The Tychonic system was a compromise that blended elements of Copernican heliocentrism with traditional Ptolemaic geocentrism.
This was the milieu into which Galileo fired his first salvo at the hallowed edifices of theologically based science. He was summoned before the Roman Inquisition in and warned against pursuing anything related to heliocentrism.
By most accounts, he initially complied. He received permission to resume his astronomical work and even to publish the findings, so long as he asserted no definitive conclusions that ran counter to Church doctrine. First published in , Dialogue Concerning the Two World Systems is structured as a discussion involving three men.
Sagredo stands in as a neutral and persuadable layman. An unenlightened gentleman named Simplicio stubbornly holds firm on the geocentric, Aristotelian view of the cosmos. Adding insult to injury, he was commanded to recant that which he knew to be absolutely true: that the Earth did in fact revolve around the Sun.
As the temperature of the water changes, it either expands or contracts, thereby changing its density. So, at any given density, some of the bubbles will float and others will sink. The bubble that sinks the most indicates the approximate current temperature. The blue bubble 60 degrees is the heaviest densest bubble, and each bubble thereafter is slightly lighter, with the red bubble being the lightest.
Now, let's say the temperature in the room is 70 degrees. Since the surrounding air is 70 degrees, we know the water inside the thermometer is also about 70 degrees. The blue and yellow bubbles 60 and 65 degrees, respectively are calibrated so that they have higher densities than the water at this temperature, so they sink. The purple and red bubbles each have a density that is lower than the surrounding water, so they float at the very top of the thermometer.
Since the green bubble is calibrated to represent 70 degrees, the same temperature as the water, it sinks slightly so that it is floating just below the purple and red bubbles -- thereby indicating the room's temperature! Sign up for our Newsletter! Mobile Newsletter banner close. Mobile Newsletter chat close. Mobile Newsletter chat dots.
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