Galileo de Galilei

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Galileo de Galilei

The new astronomers before Galileo had furnished the blue print for the parts of the world machine. They had traced out the curves and shown how the various portions worked, but they did not know by what force they moved. The next problem then was to discover the motive power which made all bodies, great or small, act as they do act (Crombie, 1952). This problem was taken up by Galileo the Italian. Galileo de Galilei, the younger contemporary of Tycho Brahe and the older contemporary of Kepler, was born at Pisa on 15 February 1564.

He came of an ancient family, of which no fewer than fourteen had filled high offices in the government of the Republic of Florence between 1343 and 1528. The original surname of the family was Bonajuti, but for some reason this was exchanged for the name Galilei in 1543. Vincenzio de Bonajuti de Galilei, the father of the great astronomer, belonged to a branch of the family which had suffered from misfortune, and was engaged in trade as a cloth merchant. He appears to have been a man of rare intellectual gifts, a talented musician and a man of wide culture, a mathematician of considerable power, and a good classical scholar (Drake, 2001).

Galileo, who was the eldest of a family of three sons and four daughters, received his early education in Pisa, partly from his father, partly in a private school kept by a friend. At the age of twelve he was sent to the monastery school of Vallombrosa, in order to specialize in classics. When, however, Galileo began to show signs of an inclination towards a monastic life, his father, who had a different career in view for him, removed him from Vallombrosa. This was in 1579, when the future astronomer was fifteen years of age (Drake, 2001).

Vincenzio Galilei, despite his abilities, was in straitened circumstances all his days, and did not feel able to afford a university education for his son. His idea was for Galileo to follow a commercial career and to become a cloth-dealer. But Galileo had other ambitions, and even at this early stage he had been experimenting with mechanics and had constructed several toy machines; he also, as a lad, excelled in music, painting, and drawing. His father accordingly decided at whatever sacrifice to send him to the University of Pisa, where he was enrolled as a student of medicine when seventeen years of age.

Right from the beginning of his university career he came up against the conservatism and traditionalism of the teachers. He was his father’s son-a true ‘chip of the old block’-taking nothing on authority (Drake, 2001). Galileo had no particular desire for the profession of medicine. His interests were in mathematics and experimental science, but his father was not in favour of such a career for his son, owing to the beggarly remuneration attached to scientific posts. The Professor of Mathematics at Pisa, for instance, received a sum equivalent to ? 13 a year.

Nevertheless, Galileo was not to be deterred from entering upon a scientific career, and his father was too wise to forbid him. For a time, after leaving the University, he eked out his living by giving private tuition in mathematics and mechanics. After applying unsuccessfully for professorships at Bologna, Rome, Padua, and Florence, he succeeded in obtaining, at the age of twenty-five, the Professorship of Mathematics in his old University of Pisa (Drake, 2001). The appointment was for a term of three years, and was renewable, but the young professor was not even allowed to complete his term.

For in the course of three years he succeeded in arousing against himself the forces of reaction, prejudice, and superstition. ‘The powers that were’ in Pisa regarded Aristotle as sacrosanct, and would not believe that in any particular the great Greek philosopher could have been mistaken; and during his tenure of the chair Galileo was to commit the unpardonable sin of proving beyond all manner of doubt that Aristotle had been wrong in one of his statements concerning falling bodies.

Aristotle had laid it down as an axiom that if two different weights of the same material were allowed to fall from the same height, the heavier would reach the ground before the lighter, proportionately to the difference in weight (Drake, 2001). It is somewhat remarkable that Aristotle, who was a careful observer of nature, never thought it worth his while to try the experiment; but it is nothing short of extraordinary that during all the centuries which had elapsed since his time, no one else had ever thought of making so simple an experimental test.

Galileo’s own experiments, however, taught him that Aristotle had been wrong. Galileo’s first experiments were in the field of physics and concerned the laws of bodies in motion or at rest. The old physics, like the old astronomy, suffered from the mortmain of the past – the dead hand of authority resting heavily upon it. As already mentioned above, that authority was Aristotle, who declared that the velocity of falling bodies was proportionate to their weight. This would mean that a two-pound weight would fall twice as fast as a onepound, a three-pound weight three times as fast, and so on.

There may have been some excuse for this statement if small bodies are meant. If a coin and a feather be dropped at the same time from a man’s hand the coin reaches the ground first. This is because of the resistance of the air, but Aristotle’s explanation would have involved also the old notion that heavy bodies tend to move rapidly to their “natural” place, the heavy earth, and that light bodies remain in the atmosphere which is “by nature” light. Galileo swept aside this false theory and this lack of observation by a simple experiment.

He took to the top of the leaning tower of Pisa two weights, a shot of one hundred pounds and another of one pound, pushed them over the edge and let them drop together. They struck the ground at the same time. The experiment was a success, but many could not believe the evidence of their senses. The old Aristotelians declared that the young Galileo had done the trick through some unknown cause, probably by the aid of magic. Galileo’s experiments made him unpopular at Pisa. He found a scientific refuge in the Republic of Venice, which was more or less free from the fetters of tradition.

At Padua he carried on further experiments. These dealt with the velocity of falling bodies. According to the old idea, weight determined the speed with which bodies reached the earth. Galileo had shown that the small cannon ball did not lag behind the larger when dropped from the tower. But he did not know what their common speed was. He now rigged up a smooth inclined plane and down it rolled a bronze ball. Then by means of a water clock he found out that a body will be falling at the rate of 32 feet per second at the end of the first second, 64 at the end of the second, 96 at the end of the third, and so on.

In other words a body falls 32 feet faster every second until it reaches the ground. This was exact science. It furnished a fact instead of a fancy. The fact is the law that falling bodies move with evenly increasing speed through their course. The fancy is that a body hastens toward its “natural” place, just as a man hastens more and more eagerly the nearer he gets to his fatherland (Lemon, 1984). Another set of exact results obtained by Galileo concerned projectiles. People at that time did not know exactly what was the line of flight of a ball fired from a cannon.

Galileo showed that a ball begins to fall as soon as it leaves the cannon’s mouth and describes a parabolic curve. This is due to the fact that the force of gravity begins to act at once. So instead of a simple motion due to the powder and a simple motion due to gravity we have a compound motion resulting in a kind of curve familiar to any one who keeps raising the sight of his rifle the farther off the target is (Holden, 2004). These new ideas had to be corrected as time went on. Some details were left out.

For one thing the resistance of the air was not fully allowed for. Galileo of course declared that the air was a hindrance and not a help and that it did not rush in behind and make a body go faster. But the clear proof that a feather and a coin would reach the ground at the same time under proper conditions could not be furnished until the experiment was tried in a vacuum, such as in a vessel exhausted of its air. However, Galileo had laid the foundations of modern mechanics in regard to small bodies.

At the same time he furnished a mass of new materials in regard to great bodies, especially the celestial bodies. This was made possible by means of the discovery of that new instrument the telescope. Who discovered this is not precisely known. Some claim that Roger Bacon in the thirteenth century put certain lenses in a tube and opened up the skies to man’s vision. Some recently discovered writings of the English monk have extraordinary pictures of spiral nebulae or rotating star clusters. If Bacon did discover the telescope he kept it a secret.

He was probably afraid of claiming to have explored the skies beyond the crystalline vault, just as some of Galileo’s friends were actually afraid of peeping through his telescope lest they should “fall into heresy,” as the saying was (Lemon, 1984). By Galileo’s time the telescope was being used. Its invention was claimed by two different firms of Dutch spectacle makers. One story goes that some children were playing with lenses one day and noticed that if two of them were looked through at once, the clock on the distant steeple came out so clearly that the time could be read on it (Holden, 2004).

Whatever the legend, the fact is that Galileo heard of the Holland spyglass and at once set upon improving it. With his knowledge of the laws of optics he was able to construct an instrument that made objects seem thirty times nearer and a thousand times larger than when viewed with the unaided eye. Now followed an astonishing list of discoveries, for a new instrument always brings great results. Take the invention of the gas engine.

From it have followed airplanes, fire pumps, tractors, submarines, motor cars of all kinds; in short, air, fire, earth, and water, all the elements, have one by one been conquered and made subservient to man by this one invention. So with Galileo and the telescope. He directed his little spyglass, not much larger than an opera glass, to the heavens, and here are some of the things he found: spots on the sun, mountains on the moon, phases or different aspects of Venus, four moons around Jupiter, Saturn with curious appendages, and the Milky Way not the path of a comet, but made up of a multitude of stars (Crombie, 1952).

The results of these discoveries were as remarkable as the discoveries themselves. The old system was smashed in all its parts. If the sun had spots, it was no longer the perfect, immaculate body demanded by its place in the heavenly realm. If the moon had mountains and craters, it was no longer the crystal orb of night with its pure smooth face. If Venus had different phases or aspects, like the moon, it was no longer a planet fit to dwell in the unchanging heavens.

The same reasoning applied to Saturn with its appendages, later resolved into rings. Finally, if the Milky Way was made up of a multitude of stars, that would make possible the doctrine of the plurality of worlds (Crombie, 1952). The general result of all this was to destroy the old dualism – the belief that there are two realms – the heavens above, perfect and unchangeable, and below the earth, imperfect and changeable. In brief, the universe now becomes one, heaven is brought to earth and earth is put in the heavens.

There are no longer superior and inferior, but all bodies have equal rights. References Crombie, A. C. (1952). Augustine to Galileo: The History of Science, A. D. 400- 1650. William Heinemann. Drake, S. (2001). Galileo: A Very Short Introduction. Oxford University Press. Holden, T. (2004). The Architecture of Matter: Galileo to Kant. Clarendon Press. Lemon, H. B. (1984). From Galileo to Cosmic Rays: A New Look at Physics. University of Chicago Press.


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  • University/College: University of Arkansas System

  • Type of paper: Thesis/Dissertation Chapter

  • Date: 8 October 2016

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