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 – that is, a new science of motion – and by pioneering the experimental method. In honour of his outstanding contributions to our understanding of the world, he is known as both ‘the father of modern physics’ and ‘the father of science’. Although Galileo is most famous for his achievements in the fields of mathematics and astronomy, his ideas also underpin many advances in horological development. The relevance of his observations to horology, particularly in the context of the international pursuit of a solution to the longitude problem (which would enable accurate determination of longitude at sea), is explored below. Student days, and a new physics Galileo was born in Pisa, Italy, 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 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 and natural philosophy, and he 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 the period between 1581 and 1610 that Galileo essentially invented a new physics and rigorously applied the experimental method to test his hypotheses.[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 Galileo’s discoveries cannot be overstated: at the time, his findings represented the most significant scientific advances in the 2000 years since Greek philosopher and polymath Aristotle (384–322 BC) had laid the groundwork for modern scientific enquiry. It is worth noting that Galileo used a type of clepsydra for his experiments on falling bodies. A clepsydra is a type of ancient Greek water clock that uses the flow of water to track the passage of time. In Galileo’s clepsydra, mercury took the place of water. The law of the pendulum Galileo’s observation of the isochronicity of the pendulum greatly influenced horological innovation during the early modern period in Europe (1500–1800), specifically informing the invention of the domestic pendulum clock in 1656. In this context, the story of Galileo’s so-called eureka moment regarding the isochronicity of the pendulum has gained significant traction. This story, and much of what we know about Galileo, comes to us from Vincenzo Viviani (b. 1622, d. 1703). Viviani was Galileo’s final 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 in favour of 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 affect his writings, we cannot be sure.[3] According to Viviani, in 1581 or 1582, the student Galileo was attending a church service at 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 his initial observation. Viviani then goes on to say that Galileo went on to replicate his observation through experiment, thus discovering an accurate way to measure time. The observation of isochronicity was extraordinary because, during Galileo’s time, mechanical clocks were weight driven and subject to chronic inaccuracy. Indeed, early mechanical clocks were usually out by about 15 minutes at any point during the day, even assuming that that the clock was wound punctually every 8 hours or so. Nowadays, Viviani’s story is widely dismissed as myth because there is no evidence, in his own papers or from other sources, of Galileo 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 complete. 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 his pendulum experiments and concluded that regardless of the mass of the weight he suspended from the string, the period of a pendulum’s swing remained unchanged.[4] He also set up two identical pendulums side by side, with strings of equal length but one with a small arc and the other with a large arc; each pendulum completed its swing in the same period of time. Thus, Galileo demonstrated key laws of pendulum motion. Galileo thus confirmed the isochronous nature of the oscillation period of a pendulum under conditions of differing pendulum weight (mass) or length of swing (arc). This isochronism makes pendulums useful for regulating timekeepers. It should be noted, however, that regardless of the arc of a pendulum, its length must be altered slightly if it is to complete a swing in the same amount of time. Still, Galileo was aware of how other variables 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 he 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 were inaccurate. Galileo’s improved pinwheel escapement design was a leap forward, as in theory it ensured regular oscillations. But Galileo, who was by then in his seventies 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 or movement. However, he did describe his escapement design to his son Vincenzo, who then drew a sketch of his father’s description.[7] Viviani describes the scene in his biography of Galileo: …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] Although Vincenzo 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. In this way, the Dutch mathematician and scientist Christiaan Huygens (b. 1629, d. 1695) was able to obtain a copy, most likely through his father Constantijn, 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. Galileo’s new lenses enabled him 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, Galileo had 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 influenced the international quest to solve the problem of how to determine 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 regarding 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 crosshairs 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’s (then highly controversial) heliocentric theory, in which the sun is at the 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’s 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 formally declared heliocentrism to be 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 1632 publication of his Dialogue Concerning the Two Chief World Systems, in which he specifically defended Copernicus’s 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. Death, and a reputation restored Galileo remained confined to his villa in Arcetri near Florence until his death from natural causes in 1642. The Grand Duke of Tuscany, Ferdinando II, wished for him to be interred in a marble mausoleum in the Basilica of Santa Croce, in Florence, but these plans were opposed by the Church due to Galileo’s conviction as a heretic. Therefore, Galileo 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, his remains were transferred to the main part of the Basilica, and a monumental tomb was constructed in his honour. During the move, three of Galileo’s fingers were removed, one of which (the middle finger of 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 Europe experienced during the 1400s and 1500s). During his period he was considered godless, and by all accounts, he was proud and obstinate in character. However, even in old age and totally blind, he retained his extraordinary mental acuity, and his drive to innovate and discover never waned. Galileo’s scientific contributions would go on to radically reshape the world. If you are interested in learning more about Galileo’s life, work and discoveries, many scholarly studies are available. They include but are not limited to Galileo: Watcher of the skies by David Wooton, and Galileo: And the science deniers by Mario Livio. Furthermore, new and revised translations of Galileo’s writings are now available. These include The Essential Galileo (translated by Maurice A. Finocchiaro) and Dialogue Concerning the Two Chief World Systems: Ptolemaic and Copernican (2nd edition). Additionally, Viviani’s account and biographies of Galileo have been published in monograph form 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] The John C Taylor Collection includes 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 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. De Simone, D. and J. W. Hessler (editors). 2013. The Starry Messenger, Venice 1610: from doubt to astonishment (facsimile). Levenger Press. 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. 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. (Gattei, S., editor) 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: Yale University Press.
