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Galileo’s career was a major turning point in science. "If science has a beginning date", says Prof. Fred L. Wilson,

"it must be 1632 when the Italian astronomer and physicist Galileo Galilei, published his book, Dialogue on the Two Systems of the World. All the previous work, all the observations, theory, and fighting against dogmatic concepts were brought together by Galileo."

Galileo revolutionised the way scientists approached their work. In this respect he departed from his contemporary scientists or ‘natural philosophers’. He did not confine himself to simply reasoning his ideas through logically as was the practice of his day. He searched for and devised suitable experiments for demonstrating his theories. He measured time and distance. In fact he was the first to conduct time experiments and to use measurements in a more systematic way. He introduced mathematics into physics, reduced things to quantity to examine whether a particular phenomenon could be described with simplicity and generality.

Galileo Galilei is always known by his first name. He owed both his first and his last name to an illustrious ancestor, Galileo Bonaiuti, an eminent physician and magistrate. The family name was changed to Galilei in honor of this illustrious ancestor in the middle of the fifteenth century.

Galileo's two telescopes kept in the museum of history of sciences in florence

Galileo was born on 15th February 1564 in Pisa, in the Tuscany region, of northwest Italy. It happened to be a centre of the Renaissance. His parents were Vincenzio Galilei (1520-91) and Pisan Giulia Ammannati (1538-1620). His father was an accomplished professional musician. Vincenzio was also interested in mathematics and musical theory. He published a book titled Dialogue of ancient and modern music. Galileo’s family moved to Florence in 1572, the heart of Renaissance culture, but Galileo stayed there for another two years. He joined the family in Florence in 1574 when he was 10.

Until he was 11, Galileo was educated privately at home. In 1574 he was sent to the monastery at Vallombroso for more formal education. The monastery was situated in the mountains 30 kilometers east of Florence. Galileo liked the place and the atmosphere in the monastery so much that he joined the order as a novice. However, his father brought him back. Galileo must have been influenced by his father, who did not accept anything unquestioned. To quote his father: "It appears to me those who rely simply on the weight of authority to prove any assertion without searching out the arguments to support it, act absurdly. I wish to question freely and to answer freely without any sort of adulation..."

In 1581 Galileo was enrolled as a medical student at the University of Pisa. While he was in his second year of medical studies, Galileo met Ostilio Ricci (1540-1603), a well-known mathematician of his time. Ricci was the court mathematician of the Grand Duke of Tuscany. Galileo’s encounter with Ricci had a profound effect on his career. He left his medical studies and started studying mathematics. However, Galileo failed to obtain a scholarship he very much needed for his study in Pisa. Finally he left the university in 1586 without a degree and came back to Florence. Though, he left the university, he did not stop studying mathematics. The same year Galileo invented a hydrostatic balance, a device that measured the pressure in fluids. Galileo published a pamphlet about this invention. This first brought him the attention of the scholarly world. However, in those days without a powerful patron it was impossible to secure any academic position. Fortunately Galileo found one in the form of Marquis Guidobaldo del Monte (1545-1607), an influential nobleman. It may be noted that del Monte was very much interested in science. He had written an important book on mechanics. Galileo managed to secure his first academic position, a junior post in mathematics, at the University of Pisa, in the same university he had left without a degree four years earlier. But in those days mathematics was not regarded as an important discipline. The salary associated with the post was low and Galileo had to augment his salary by private tuition.

Galileo took lodgers, the sons of the noblemen, who lived in his home and thus the students had the benefit of constant interaction with the teacher at all hours. This arrangement, a standard practice of his time, not only helped Galielo to increase his income but also spread his reputation as a teacher.

A view of Pisa with it's Leaning Tower

In October 1592 Galileo joined the University of Padua, in the Republic of Venice, where he was offered the chair in Mathematics. Here he taught for 18 years. His salary was trebled. He taught in the Auditorium Maximum (the "Large Auditorium") to packed audiences. People from all over Europe came to listen to his lectures and his audience included Gustavus Adolphus, the crown prince of Sweden, besides representatives of many noble houses. He taught how mathematical principles could be used for practical applications viz. building bridges, planning harbours, fortifying cities and buildings and constructing artillery. He proved to be a very successful teacher. He gave practical demonstrations in his classes. He used to bring bones to his class to prove that strong construction could be made by hollow materials. This resulted in hollow pipe construction and which brought down the construction cost drastically. He urged his students to seek truth in nature by using their own eyes and minds and not to depend solely on ancient revered texts. He showed them how mathematics and experiments could be used to study nature.

In public life Galileo’s fame was enhanced by the publication of his treatise in military fortification. He also published a book on mechanics based on the lectures he was giving in Padua. Though his salary was trebled money was a constant problem for Galielo during his stay at Padua. To solve this problem, Galileo during his stay in Padua was trying hard to make suitable inventions. In this effort he developed an early kind of thermometer. Though the device was quite ingenious, it was not practical enough to commercialise it. Another of his inventions was a system for lifting water for irrigation and Galileo also obtained a patent for the same in 1594. It was technically successful but not commercially.

In 1595-96 Galileo invented a geometrical and military ‘compass’ - a forerunner of the slide rule. It was a kind of all-purpose calculating instrument. Initially it found use as a device for gunners who used it for calculating elevations when ranging their guns. It was a great success after Galileo adapted it to include scales showing the relative densities of various metals, lines for calculating cube roots and square roots and other data useful in geometrical applications. While Galileo sold the instruments cheap, he charged for giving training on how to use it.

Between 1619 and 1624 Galileo started to produce microscopes or "Occhlialini" as he called them. The Galilean microscope was made up of the tube of telescope of reduced size furnished with two lenses.

Towards the end of the 16th century Galileo dedicated himself to research on heat and during this period he invented (1593) the Galilean thermometer, a device which was used to carry out experiments on the relationship between changes of temperature and variations of the level of the liquid. It was a crude device and it took about hundred years or until the time of the French physicist, Guillaume Amontons, to make a reasonable beginning in thermometry. The development of Florentine thermometer had its origins in Galileo’s early research on heat.

Galileo also studied magnetism, inspired by William Gilbert’s De Magnete. He tried to enhance the strength of loadstones by means of special armature.

Galileo produced major insights about motion and mechanics. In 1590 Galileo published his book De motu gravium ("On the motion of heavy bodies") in which he updated Aristotle’s basic thoughts about motion using some ideas of the French philosopher Jean Buridan (c.1295-1358).

It may be noted that though the credit for employing the new scientific methods of observation and experiment for scientific investigations is generally ascribed to Galileo, there were people who had used similar methods before Galileo. One of them was the English physician and physicist William Gilbert (1544-1603). Gilbert made a detailed study of magnetism in a long series of carefully detailed experiments and observations. It is interesting to note what Galileo thought of Gilbert, because it is relevant even in the present context: "I think him worthy of the greatest praise for the many new and true observations which he has made, to the disgrace of so many vein and fabling authors, who write not from their own knowledge only, but repeat everything they hear from the foolish and vulgar, without attempting to satisfy themselves of the same by experiment."

Before Galileo experiment was not popular among scientists or natural philosophers. The Greeks, who dominated the intellectual scene of the West, disliked experiments. They considered experiment not only irrelevant but also a hindrance to the process of beautiful pure deduction. They were content with accepting the ‘obvious’ natural facts as starting points for their reasoning. Moreover in case of a disagreement between an experiment and deduction aiming to arrive at a conclusion, they felt no reason to discard deduction in favour of experiment. In fact the very idea of testing a perfect theory of nature with ‘imperfect’ instruments did not appeal to the Greeks. This became the dominant tradition among the scholars. It is true that philosophers and scholars like Roger Bacon (a.1220-c.1292) and Francis Bacon (1561-1626) made experimentation philosophically respectable and some others, including Achimedes, did use experimentation as a means to arriving at truth. It was Galileo who overthrew the Greek view and ushered in a scientific revolution. He made experimentation attractive. By virtue of his literary ability he could describe his experiments and theories very clearly and beautifully. He made quantitative method famous and fashionable.

Galileo was a true Renaissance man. He liked music and art. He studied literature and poetry. He played the flute for pleasure and he had enough familiarity with painting so that he could illustrate his own astronomical findings. He was an excellent writer.

Galileo is most talked about for three incidents, though their description may be a little far from the truth. They have become legends. These are :

i) Dropping cannon balls of different weights from the leaning tower of Pisa to demonstrate that they reached the ground together.

ii) Inventing the telescope

iii) Being martyred for his beliefs about the Copernicus system.

According to legend Galileo dropped a cannon ball and wooden ball from the top of the Leaning Tower of Pisa to demonstrate that two balls of different weights fall at the same rate. Following Aristotle almost all scholars believed that the rate of fall of any falling body is proportional to its weight. Galileo did not actually conduct the experiment. In fact, his predecessors conducted similar experiments - Benedetti Giambattista published a similar experiment demonstration in 1553 and the Flemish engineer Simon Stevin conducted an experiment in 1586. Whether Galileo conducted the experiment or not but he definitely disproved Aristote’s theory about falling objects. It has been reported that Galileo thought about this, during a hailstrom when he noticed that hailstones of different sizes fell simultaneously with the same speed. However, there is a connection between Galileo, falling bodies and the Leaning Tower. In 1612 one of the Peripatic professors at Pisa dropped objects of different weights from the tower. His purpose was to prove Galileo wrong and he was very happy to note that they did not hit the ground simultaneously. To this Galileo reacted :

"Aristotle says that a hundred-pound ball falling from a height of a hundred cubits hits the ground before a one-pound ball has fallen one cubit. I say they arrive at the same time. You find, on making the test, that the large ball beats the smaller one by two inches. Now, behind those two inches you want to hide Aristotle’s ninety-nine cubits and, speaking only of my tiny error, remain silent about his enormous mistake."

One of the Galileo’s students did perform the demonstration and he found a slight difference in the time the two balls struck the ground. However, this was no surprise to Galileo as he had already explained the effect of the air resistance. The air resistance slows the fall of light objects like leaves, feathers, snow-flakes etc. that offer comparatively large areas to the air. On the other hand, the heavier objects reduce this effect to a quantity small enough to be insignificant value and fall at the same rate.

Galileo’s name is often associated with the inventing of the telescope. However, he was not the original inventor. The telescope was invented by Hans Lippershey in Holland in 1608. Recently it has also been shown that Leonard Digges of England built a telescope before 1550. However, Galielo reintroduced the instrument on his own and used it for the first time for astronomy. He was the best lense maker in Europe at the time and built a number of telescopes.

Figure 1: Evidence of Galileo's interdisciplinary work uniting astronomy and astrology: on the same page a drawing of the Moon oberserved by means of Galileo's new astronomical telescope and the start of a horoscope he cast for Cosimo II di Medici.

He used his 30 power telescope to discover craters on the moon (which he called maria or ‘seas’), sun spots which rotated with the sun, four largest satellites of Jupiter (Io, Europa, Ganymede and Callisto, today known as Jupiter’s "Galilean moons", named in his honour) and phases of Venus, that is he saw that like the Moon, this planet also had phases - from crescent to disc to crescent.

The last two observations demonstrated that the Copernican theory was correct. The discovery of sunspots and craters and mountains on the moon showed that Aristotle was not right in his thesis that the heavenly bodies were perfect and that only on Earth was there irregularity and disorder. Galileo was not alone in discovering sunspots, there were other astronomers who discovered sunspots simultaneously with Galileo. So, there was dispute over priority. But whether Galileo was the first to discover or not, he did something more than mere discovery of sunspots. He used them to demonstrate that the Sun rotated about its axis in twenty-seven days. This he did by following individual spots around the sun.

While Galileo observed that even with the telescope the brightest stars could not be seen bigger than mere dots, the planets became as big as little globes. He also observed that with the aid of telescope many more stars were visible than those could be seen by naked eye. From these observations, Galileo reached the conclusion that the stars were much further away than the planets and the universe might be infinitely large.

In February 1616, the Holy Office of the Church at Rome formally condemned the heliocentric view of the universe propounded by Copernicus. The pope asked Cardinal Robert Bellarmine to convey the ruling to Galileo. Subsequently, Galileo was given an affidavit forbidding him to hold, defend and teach copernicanism.

In 1632, Galileo published his Dialogue on the Two Chief Systems of the World. It went on sale in Florence in March 1632. As the title suggested the presentation took the form of a conversation between two people, one supporting each of the two opposing world views. This form of presentation goes back to the ancient Greeks. Galileo, however, added a third character, who listened to the conversation between the two and raised points for debate. The name of the three characters were Filippo Salviati (who argued the Copernican case or in other words presented Galileo’’s views) Giovanfrancesco Sagredo (the independent observer), and Simplicio (the supporter of Aristotle or the Earth-centred cosmology of Ptolemy). The first two characters were named after Galileo’s friends and the third character after an ancient Greek who had written a commentary of Aristotle’s work. Though Galileo claimed that he meant to show a fair and even battle but by naming the character supporting Aristotle’s view Simplicio he undoubtedly intended to imply that anyone who supported Aristotle was a ‘simpleton.’ Moreover the arguments for Copernicus’ ideas were articulated in a much better way.

Conservatives, those who were after Galileo for quite sometime, persuaded Pope Urban VIII to believe that the character in Galileo’s book supporting Aristotle’s views was nothing but a deliberate and insulting caricature of the pope himself. Further someone dug out of the files the unsigned minute from 1616, forbidding Galileo to ‘hold, defend or teach’ the Copernican view of the universe. Galileo was brought before the Inquisition on charges of heresy. He was summoned to Rome. The infamous trial formally began on 13 April 1633 when Galileo was in his 70th year. Galileo’s opponents refused even to look through Galileo’s telescope or listen to his reasoning. They believed that they knew the truth and if Galileo’s telescope showed something else than there must be something wrong with the telescope itself. So why waste time! He was sentenced to indefinite prison. The sentence was commuted by the pope at the request of Duke of Tuscany. Fearing torture (and he had also the example of Giordano Bruno) Galileo renounced his views in his famous public apology :

"I do not hold and have not held this opinion of Copernicus since the command was intimated to me that I must abandon it."

And he was allowed to live under house arrest in his own house at Arcetri near Florence.According to legend when Galileo rose from his knees having completed his renunciation, Galileo remarked under his breath : "Eppur si muove" [But it (Earth) does move]. There is no evidence whatsoever to prove that Galileo uttered this sentence. However, because of the unparalleled contribution to the growth of science and his unique personality the legend has been kept alive.

During the period Galileo was kept under house arrest he did not stop working. In fact during this period he completed his greatest book, Two New Sciences. The manuscript was smuggled out of Italy and published in Leyden in 1638 by Lonis Elzerir. This book which exerted enormous influence in the following decades summed up all of Galileo’s work, on mechanics, inertia, pendulum, the strength of bodies and the scientific method.

Galileo was aware of the implications of his work. He said that he had

"Opened up to this vast and most excellent science, of which my work is mere the beginning, ways and means by which other minds more acute than mine will explore in remotest corners."

In his later years (1638 onwards) Vicenzio Viviani joined him as his scribe and assistant. It was Viviani who wrote Galileo’s first biography. Galileo died in his sleep on the night of 6/7 January 1642.

The catholic church finally agreed with Galileo. In 1992, a commission under Cardinal Paul Pouperd observed that Galileo had been ‘more perceptive’ in his interpretation of the Bible than his prosecutors. Galileo was formally pardoned on 31 October 1992 that is about 350 years after his death.

Galileo - Dimostrazioni - Disquisition about mechanics and local motion

For further reading

1. Drake, S., Galileo at Work : His Scientific Bigraphy, New York : Dover, 1995.

2. Redondi, P., Galileo Heretic, Princeton, NJ : Princeton Universtiy Press, 1987.

3. Reston, J. Jr., Galileo : A Life, New York : Harper Collins, 1994.

4. Segre. M., In the Wake of Galileo, New Brunswick, NJ : Rutgers University Press, 1992.

5. Sharratt, M., Galileo : Decisive Innovator, Cambridge : Cambridge: University Press, 1994.

6. Sobel, D., Galileo’s Daughter : A Historical Memoir of Science, Faith and Love, New York : Walker, 1999.

7. Shea, W. R., Galileo’s Intellectual Revolution, London: Macmillan, 1972.

8. McMullin, E.(ed.), Galileo: Man of Science, New York and London: Basic Books, 1967.

9. Hall, A. R., The Revolution in Science :1500-1750, London:Longman, 1983.

10. Lloyd, G.E.R, Early Greek Science: Thales to Aristotle, London: Chatto & Windus, 1970.

Source: Subodh Mahanti [ http://www.vigyanprasar.com/dream/]

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