Galileo di Vincenzo Bonaiuti de' Galilei Galileo Galilei was an Italian astronomer, physicist, engineer and mathematician who drove the scientific revolution of the 1600s by inventing a new physics and crucially advancing the experimental method. He is known as the ‘father of modern physics’ and also the ‘father of science’. Although Galileo’s work was central to the advancement of mathematics and astronomy, it also underpinned many advances in horological development. These observations and the role he played in the international pursuit of the 'longitude problem' (to find a way to accurately determine longitude at sea) are explored below. Student days and a new physics Galileo was born in Pisa in 1564 to Vincenzo Galilei, a famous composer and music theorist, and Giulia Ammannati. Not much information survives about Galileo’s childhood, his intellectual development during his student days or from his early years of scientific experimentation. When Galileo entered university in 1581, he was 17. Initially, he was discouraged from pursuing his interests in mathematics and steered towards the study of medicine. This was probably because the income of a physician was markedly higher than that of a mathematician. However, a career in medicine was not meant to be. After ‘accidentally’ attending a lecture on geometry, Galileo began studying mathematics, natural philosophy and even devoted a term to the study of disegno, a term which encompassed fine art. In 1588, Galileo obtained a position as an instructor at the Accademia delle Arti del Disegno in Florence where he taught perspective and chiaroscuro (the treatment of light and shade in drawing and painting). In 1589 he was appointed to the chair of mathematics in Pisa, and in 1592 he moved to the University of Padua where he taught geometry, mechanics and astronomy until 1610. It is during this period between 1581 and 1610 that Galileo essentially invented a new physics and crucially advanced the experimental method.[1] Historian David Wooton explains that Galileo’s new physics encompassed five innovations: i) the development of the idea of inertia, ii) the formulation of the idea that motion is a relative concept, iii) the discovery of the law of the acceleration of falling bodies, iv) the parabolic path of the projectile, and v) the isochronicity of the pendulum. The importance of his discoveries cannot be overstated; Galileo’s innovations represent the most significant scientific advancement for the previous two thousand years, since the time of Aristotle, the pioneering Greek philosopher who lived from 384 to 322 BC. It is worth noting that Galileo used a mercury clepsydra for his experiments on falling bodies. A clepsydra is a type of ancient Greek water clock that used the flow of water (or, in Galileo’s case, mercury) to track the passage of time. The law of the pendulum Galileo’s observation of the isochronicity of the pendulum greatly impacted horological innovation during the early modern period in Europe (1500 – 1800), specifically informing the invention of the domestic pendulum clock in 1656. As such, the story of Galileo’s so-called ‘Eureka’ moment regarding the isochronicity of the pendulum has gained serious traction. This story, and a lot of what we know about Galileo, comes to us from Vincenzo Viviani (b. 1622, d. 1703). Viviani was Galileo’s last student. He wrote Galileo’s first biography and archived his teacher’s papers.[2] While the history of science owes Viviani a great debt, his accounts of his teacher must be approached with a degree of caution. He was biased towards his teacher; prone to heavily editing Galileo’s writings to make them more palatable for publication and capable of falsifying the record out of concern for preserving Galileo’s legacy. To what extent his biases effect his writings, we cannot be sure.[3] Viviani’s story goes that, in 1581 or 1582, the student Galileo was attending a church service in the cathedral in Pisa when his attention was drawn to the swinging of a lit chandelier above him. He noticed that as the arc of its swing increased and decreased, the period of the swing seemed to remain unchanged. Using his own pulse or the liturgical music as a timekeeper, Galileo measured the period and confirmed this observation. Viviani then goes on to say that Galileo went on to re-confirm the observation through experiment, thus discovering an accurate way to count time. The observation of isochronicity was extraordinary, because, at the time, mechanical clocks were weight driven and subject to chronic inaccuracy. During this time early mechanical clocks were usually out by about 15 minutes at any point during the day, providing one punctually wound the clock every eight hours or so. Nowadays, Viviani’s story is widely dismissed as myth, because there is no evidence of Galileo (in his own papers or from other sources) having any interest in or experimenting with pendulums until twenty or so years later. There is also the fact that the chandelier at Pisa cathedral was installed after Galileo’s tenure as a student was finished. While it is possible that the young Galileo could have observed what a pendulum does in any number of ways, he did not display an understanding of it as a student. It was not until 1604 that Galileo conducted experiments and concluded that, regardless of the weight he suspended from the string, the period of the pendulum’s swing remained unchanged.[4] He even set up two identical pendulums side-by-side; one with a small arc and the other with a large arc. Once again, the pendulums swung back and forth at the same rate. This is known as the law of the pendulum. Through these experiments Galileo confirmed the isochronous property of the pendulum, and it is this property which makes pendulums useful for regulating timekeepers. However, these experiments were problematic because the length of a pendulum must be altered slightly if every swing is to take the same amount of time, regardless of the width of the arc. Still, Galileo was aware of how other variables might affect the swing, so it was not unreasonable for him to conclude that the law of the pendulum would hold in a vacuum.[5] Galileo’s pendulum clock It was not until 1635 that Galileo devised a pendulum that could count seconds and claimed that he was able to build a clock that was accurate to within one minute within a month.[6] What made this possible was a mechanism that would keep a pendulum swinging by pushing it along. He had conceptualised another horological innovation: a refined escapement that could be applied to a clock. The mechanical escapement was probably invented sometime during the late 1200s. By Galileo’s time, most clocks used a verge escapement and foliate balance, which were not true oscillators and inaccurate. Galileo’s improved pinwheel escapement design was a leap forward, as it ensured regular oscillations in theory. But Galileo, who was by then in his 70s and totally blind, never built his pendulum clock with its refined escapement, so he could not speak to its accuracy, especially when said clock had never been exposed to variations in temperature and movement. However, he did describe his escapement design to his son Vincenzio, who then drew a sketch of his father’s description.[7] Viviani describes the scene in his biography: …the idea occurred to him that the pendulum could be adapted to clocks with weights or springs…[he] hoped that the even and natural motions of the pendulum would correct all the defects in the art of clocks. After conversing with his son Vincenzio…[they] finally decided on the scheme shown in the accompanying drawing, to be put in practice to learn the facts of those difficulties in machines which are usually not foreseen in simple theorising.[8] While Vincenzio did begin constructing a prototype of Galileo’s pendulum clock, he sadly never completed it. Vincenzo died in 1649, seven years after the death of his father in 1642.[9] Although Galileo’s pendulum clock never made it to production, the drawings of the prototype played a vital part in horological development. Copies of the drawings were circulated to the courts and scientific communities of Europe. As such, the Dutch mathematician and scientist Christiaan Huygens (b. 1629, d. 1695) was able to obtain a copy, most likely through his father Constantin, who was a curator at the College of Orange in The Netherlands and also a friend of Galileo’s. As a keen astronomer, Christiaan Huygens was aware of the need for accurate time measurement. In 1656, he designed, patented and manufactured the first domestic pendulum clock. While he undoubtedly took inspiration from Galileo’s model, there are marked differences between the two, as it was Huygens who was the first to construct a truly isochronous pendulum. Astronomical observations and solutions While Galileo is occasionally credited with the invention of the telescope, this is incorrect. He did however radically improve the instrument’s magnification abilities. By grinding and polishing his own lenses, Galileo manufactured a telescope with eight times the magnification properties, a significant improvement on the standard spyglasses of the day which only reached three times magnification. These new lenses enabled Galileo to observe what he described as three fixed stars located close to Jupiter and lying on a straight line through it. Further observations showed that the position of these stars changed in such a way that it was impossible for them to be fixed. Within a few days he successfully identified these ‘stars’ as three of Jupiter’s satellite moons orbiting the planet. By 13 January 1610, he had discovered the fourth moon. These moons are now called the Galilean Moons. They are individually known as Io, Europa, Ganymede, and Callisto. Galileo’s discovery of Jupiter’s moons directly impacted the international quest to solve the problem of determining longitude at sea. In her book Longitude, science writer Dava Sobel explains that during the 1600s the accepted theory was that the solution to the problem of longitude would be an astronomical one (rather than a horological one), as many believed that longitude could be calculated by reading the relative positions of celestial bodies, such as Galileo’s moons.[10] However, even Galileo himself was not convinced that the solution lay in the heavens. At the end of his life, he was negotiating with the Dutch government on a proposal for a practical means of determining longitude at sea. This apparently involved the inclusion of his invention for an isochronous marine timekeeper, which was also never built.[11] Vehemently suspect of heresy Galileo’s scientific discoveries brought him into conflict with the Roman Catholic Church, and he spent much of his career in the cross hairs of the Roman Inquisition.[12] In 1610, he published his observations of the Galilean moons of Jupiter as well as other astronomical observations in Sidereus Nuncius (Starry Messenger).[13] This was soon followed by his observations of the phases of Venus, which provided clear evidence that Venus orbited the sun. This demonstrated the validity of Nicolaus Copernicus’ (then) highly controversial heliocentric theory, in which the sun is centre of the solar system.[14] At the time, the geocentric model was taught by the Roman Catholic Church and was the prevailing view of all Christians. This model considers the earth to be the centre of the solar system. Thus, Galileo’s discovery of Venus’ orbiting of the sun and a planet with smaller planets orbiting around it contradicted and undermined the teachings of the Church. In keeping with Church doctrine, many Christian astronomers and philosophers did not believe Galileo's observations to be true. In 1616, the Roman Inquisition declared heliocentrism to be formally heretical. Yet, Galileo continued to be provocative, proposing his theory of tides in 1616 and of comets in 1619. All this was further evidence that the earth orbited the sun and not the other way around. The Roman Inquisition exerted further pressure on Galileo following the publication of his Dialogue Concerning the Two Chief World Systems in 1632, in which he specifically defended Copernicus’ theory of heliocentrism. The fact that his publication was popular must have doubly incensed the Church. In 1633, the Roman Inquisition responded by finding Galileo ‘vehemently suspect of heresy’. They sentenced him to house arrest, forced him to publicly recant his theory and banned his book. He remained confined to his villa in Arcetri near Florence until his death in 1642. Death and a reputation restored Galileo was buried in the Basilica of Santa Croce, in Florence. The Grand Duke of Tuscany, Ferdinando II wished to erect a marble mausoleum in his honour, but these plans were opposed by the Church due to Galileo’s conviction as a heretic. He was initially buried in a small room next to the novices’ chapel. It was not until almost a century later that Galileo’s reputation began to be restored. In 1737 he was moved to the main body of the Basilica, and a monument was erected in his honour. During the move three of Galileo’s fingers were separated from his remains, and one of these (the middle finger from Galileo’s right hand) now resides in the Museo Galileo in Florence. Galileo’s work was central to the Scientific Revolution that took place during the Renaissance (the cultural movement that took place in Europe during the 1400s and 1500s). During his time, he was seen as godless, and, by all accounts he was proud, obstinate and brilliant. Even in old age and totally blind, his mental acuity and drive to innovate and discover never waned. Galileo’s scientific contributions would go on to radically re-shape the world. If you are interested in learning more about Galileo’s life, work and discoveries, many scholarly studies are available including, but not limited to, Galileo: Watcher of the skies by David Wooton, and Galileo: and the science deniers by Mario Livio. There are also new and revised translations of Galileo’s writings available, such as The Essential Galileo (translated by Maurice A Finocchiaro) and Dialogue Concerning the Two Chief World Systems: Ptolemaic and Copernican (2nd ed.). Additionally, Viviani’s account and biographies of Galileo have been published in monograph form and is available under the title, On the Life of Galileo. End Notes [1] De Angelis, A. 2022; Wooten 2010, 18-45. [2] Viviani (ed. Gattei) 2019; Wooton 2010, 19-21. Viviani’s biography of Galileo was not published until 1717. [3] Historian David Wooten lays bare Viviani’s limitations as a biographer in Galileo: Watcher of the Skies (2010), in which he pieces together a provocative account of Galileo’s intellectual development and experimental activity, highlighting the gaps between the surviving historical record, myth and Viviani’s preoccupation with preserving Galileo’s legacy. [4] Wooten 2010, 81-82. [5] Ibid [6] Wooton 2010, 71. [7] de Grijs 2021, 5 fig. 3; Wooton 2010, 237. [8] Viviani (ed. Gattei) 2019. See the sketch of Galileo’s pendulum clock design that was drawn by Viviani in 1659 in de Grijs 2021, 5 fig. 3. [9] There is a 20th century iron model of Galileo’s escapement by Laurits Christian Eichner (b. 1894, d. 1967), a Danish engineer and metal craftsman. Eichner's model is 345mm high and has a pinned frame with central bars terminating in bifurcated feet. It has a three-wheel train, brass winding barrel and wheels of four broadly tapering crossings. The escape wheel has a stepped edge and twelve projecting pins with a pivoted pendulum set to the side. Eichner's model of Galileo's escapement will be exhibited on Clocktime soon. [10] Sobel 2007, especially 31 and 53. For instance, King Charles II and the first Royal Astronomer John Flamsteed shared the ardent belief that the solution to the problem of determining longitude at sea would be achieved by measuring the position of the navigator relative to celestial bodies, such as Galileo’s moons. Charles even issued a warrant in 1675 to initiate construction of the Royal Observatory to pursue the longitude problem and beat the French to a solution. [11] Bedini 1991; de Grijs 2021, 4-5. [12] Livio 2021. [13] De Simone and Hessler 2013. [14] The Polish mathematician and astronomer Nicolaus Copernicus (b. 1473, d. 1543) published his heliocentric theory in De revolutionibus orbium coelestium in 1543. He heavily influenced Galileo’s work. References Bedini, S. A. 1991. The Pulse of Time: Galileo Galilei, the Determination of Longitude, and the Pendulum Clock. Firenze: Bibliotecca di Nuncius. De Angelis, A. 2022. Galileo Galilei’s “Two New Sciences”: for modern readers. New York: Springer International Publishing. de Grijs, 2021. ‘European Longitude Prizes. III. The Unsolved Mystery of an Alleged Venetian Longitude Prize’, in Journal of Astronomical History and Heritage 24/3: 1-39. Galilei, G. (trans. Drake, S.) 1953. Dialogue Concerning the Two Chief World Systems: Ptolemaic and Copernican (2nd ed.). Berkely, CA: University of California Press. Galilei, G. (trans. Finocchiaro, M. A.) 2008. The Essential Galileo. Clearwater, FL: Hackett Publishing Company, Incorporated. De Simone, D. and J. W. Hessler (eds). 2013. The Starry Messenger, Venice 1610: from doubt to astonishment (facsimile). Levenger Press. Livio, M. 2021. Galileo and the Science Deniers. New York, NY: Simon & Schuster. Sobel, D. 2007. Longitude: The story of a lone genius who solved the greatest scientific problem of his time. London: Harper Perrenial. Viviani, V. (ed. Gattei, S.) 2019. On the Life of Galileo: Viviani’s historical account and other early biographies. Princeton, NJ: Princeton University Press. Wooten, D. 2010. Galileo: Watcher of the Skies. New Haven and London: Yale University Press.
