A manuscript collection of drafts and calculations behind Galileo’s groundbreaking work on motion and mechanics
What the Work Is
Galileo Galilei’s Notes on Motion is a digital representation of Codex 72, a manuscript held in the Galilean Collection of the Biblioteca Nazionale Centrale in Florence, Italy. First published in 1998, the work presents the surviving handwritten drafts, drawings, and calculations of Galileo Galilei and his disciples Mario Guiducci and Niccolò Arrighetti. The manuscript consists of 241 folios of varying sizes, with the bulk of the material—from folio 33 recto to folio 194 recto—containing the working notes that would eventually culminate in Galileo’s published theorems on motion.
What the Book Is About
The manuscript preserves the intellectual labor behind Galileo’s landmark contributions to the study of motion and mechanics. These drafts and calculations represent the raw material of scientific discovery—the tentative explorations, corrections, and refinements that preceded the polished theorems later published in Galileo’s Discourses and Mathematical Demonstrations Relating to Two New Sciences (1638). The codex offers an unusually intimate view of how a foundational figure in classical physics developed his ideas about moving bodies, revealing the iterative process of experimentation and mathematical reasoning that underpinned his published results.
Key Ideas and Themes
The notes document Galileo’s investigations into the physics of motion, a subject that occupied him throughout his career and that he ultimately transformed from a qualitative Aristotelian inquiry into a rigorously mathematical science. The manuscript’s contents pertain chiefly to theorems on motion—the kind of work that would establish Galileo’s reputation as a founder of classical mechanics.
The collection reflects Galileo’s characteristic method of combining geometrical demonstration with empirical observation. His approach to motion was revolutionary for its time because it sought to express physical phenomena in precise mathematical terms rather than in the qualitative categories of natural philosophy that had dominated since antiquity. The drafts show him working through problems of speed, acceleration, and the behavior of falling and projectile bodies—questions that would prove central to the later development of physics.
The presence of writings by Guiducci and Arrighetti alongside Galileo’s own hand indicates that this was not solitary work but part of a collaborative intellectual circle. These disciples assisted in the development and recording of ideas that would eventually be formalized in Galileo’s published treatises, suggesting that the manuscript captures a living process of scientific exchange rather than a finished product.
Structure and Approach
The codex is a miscellaneous compilation rather than a unified treatise. Its 241 folios vary in size, and the first 32 folios contain several different writings not included in the electronic representation. The remainder of the manuscript—the portion that constitutes the published work—holds drafts, texts, drawings, and calculations written by Galileo or his disciples. This heterogeneous character is itself significant: it preserves the messiness of actual scientific practice, with false starts, marginal notes, and multiple attempts at formulation coexisting alongside more developed arguments.
The electronic representation focuses on the substantial core of the manuscript, making accessible material that would otherwise require consultation of the physical codex in Florence. By presenting the folios in their original sequence, the work allows readers to trace the development of Galileo’s thinking across the manuscript, observing how individual insights were tested, revised, and ultimately integrated into the coherent theorems that appeared in print.
Significance and Influence
The manuscript’s primary significance lies in what it reveals about the genesis of Galileo’s published work on motion. The Discourses of 1638, written during Galileo’s house arrest following his condemnation by the Inquisition, are widely regarded as a founding text of modern physics, covering kinematics and the strength of materials. The Codex 72 drafts provide the documentary evidence of how those published results were achieved, offering scholars a window into the working methods of one of the most important figures in the history of science.
For historians of science, the codex is invaluable because it preserves the process rather than merely the outcome of Galileo’s investigations. It demonstrates that his celebrated results emerged from sustained practical engagement with problems—through drawing, calculation, and repeated revision—rather than from sudden insight or purely abstract reasoning. The manuscript thus supports a more nuanced understanding of the scientific revolution, showing that the shift toward mathematical physics was accompanied by equally important changes in how scientists worked with their hands, eyes, and instruments.
The collaborative dimension of the manuscript also complicates the traditional image of Galileo as a solitary genius. The presence of Guiducci’s and Arrighetti’s handwriting suggests a working environment in which ideas circulated among trusted associates, with the boundaries between master’s and disciples’ contributions not always clearly drawn. This aspect of the codex has made it a rich source for understanding the social context of early modern science, complementing the purely intellectual history of Galileo’s discoveries.
The codex’s physical characteristics are documented in precise detail within the catalog metadata. It comprises 241 folios of various sizes, carrying folio numbers from 1 to 196. The first 32 folios contain several different writings not included in the electronic representation. The bulk of the manuscript—from folio 33 recto to folio 194 recto—is covered by the electronic representation and holds drafts, texts, drawings, and calculations written by the hand of Galileo or of his disciples Mario Guiducci and Niccolò Arrighetti, mostly pertaining to the theorems on motion published in the Discorsi.
The Author’s Broader Scientific Context
Galileo’s work on motion was part of a larger career that encompassed astronomy, physics, engineering, and applied science. He studied speed and velocity, gravity and free fall, the principle of relativity, inertia, and projectile motion. He also worked in applied science and technology, describing the properties of the pendulum and hydrostatic balances. He was one of the earliest developers of the thermoscope and the inventor of various military compasses.
His astronomical observations, made possible by telescopes he constructed, included the stars of the Milky Way, the phases of Venus, the four largest satellites of Jupiter, Saturn’s rings, lunar craters, and sunspots. He also built an early microscope. These observations were documented in works such as Sidereus Nuncius (Starry Messenger), published in March 1610, which presented his initial telescopic astronomical observations.
The Path to the Discourses
The Discourses and Mathematical Demonstrations Relating to Two New Sciences (1638), which the Codex 72 drafts preceded, was written during Galileo’s house arrest following his trial by the Inquisition. He was found “vehemently suspect of heresy” and forced to recant. The work primarily concerns kinematics and the strength of materials.
Galileo’s earlier work included the Dialogue Concerning the Two Chief World Systems (1632), which appeared to dispute and satirize Pope Urban VIII, alienating both the Pope and the Jesuits. The Dialogue was originally entitled the Dialogue on the Ebb and Flow of the Sea, but the reference to tides was removed from the title by order of the Inquisition. Galileo considered his theory of the tides to provide a “true physical demonstration” that the Earth circles the Sun, a standard that Cardinal Bellarmine had articulated in 1615.
Galileo’s Methods and Instruments
Galileo’s approach to scientific investigation combined empirical observation with mathematical analysis. His study of pendulums began in 1581 while he was studying medicine, when he noticed a swinging chandelier moved by air currents. He observed that the chandelier took the same amount of time to swing back and forth no matter how far it was swinging, and later confirmed this by setting up two pendulums of equal length and swinging one with a large sweep and the other with a small sweep. It was not until the work of Christiaan Huygens, almost one hundred years later, that the tautochrone nature of a swinging pendulum was used to create an accurate timepiece.
Galileo also devised methods for measuring astronomical phenomena. He developed a technique for measuring the apparent size of a star without a telescope by hanging a thin rope in his line of sight to the star and measuring the maximum distance from which it would wholly obscure the star. From measurements of this distance and the width of the rope, he could calculate the angle subtended by the star at his viewing point. In his Dialogue, he reported finding the apparent diameter of a star of first magnitude to be no more than 5 arcseconds, and that of one of sixth magnitude to be about 5/6 arcseconds. His values were much smaller than previous estimates, such as those made by Tycho Brahe, and enabled Galileo to counter anti-Copernican arguments that stars would have to be absurdly large for their annual parallaxes to be undetectable.
The Collaborative Circle
The manuscript’s collaborative dimension is documented in the source material. Galileo’s disciple Mario Guiducci, a Florentine lawyer, was the named author of the Discourse on Comets, although it had been largely written by Galileo himself. The Discourse was part of a controversy with Father Orazio Grassi, professor of mathematics at the Jesuit Collegio Romano, over the nature of comets. The dispute began in 1619 and culminated in Galileo’s Il Saggiatore (The Assayer), published in 1623, which has been referred to as his scientific manifesto. The title page of the book describes Galileo as a philosopher and “Matematico Primario” of the Grand Duke of Tuscany.
Galileo’s Early Life and Education
Galileo was born in Pisa on 15 February 1564, the first of six children of Vincenzo Galilei, a leading lutenist, composer, and music theorist, and Giulia Ammannati. When Galileo was eight, his family moved to Florence, but he was left under the care of Muzio Tedaldi for two years. When he was ten, he left Pisa to join his family in Florence, where he came under the tutelage of Jacopo Borghini. He was educated, particularly in logic, from 1575 to 1578 in the Vallombrosa Abbey, about 30 km southeast of Florence.
Although he seriously considered the priesthood as a young man, at his father’s urging he instead enrolled in 1580 at the University of Pisa for a medical degree. He was influenced by the lectures of Girolamo Borro, Domingo de Soto, and Francesco Buonamici of Florence. Up to this point, Galileo had deliberately been kept away from mathematics, since a physician earned a higher income than a mathematician. However, after accidentally attending a lecture on geometry, he talked his reluctant father into letting him study mathematics and natural philosophy instead of medicine.
In 1589, he was appointed to the chair of mathematics in Pisa. In 1592, he moved to the University of Padua, where he taught geometry, mechanics, and astronomy until 1610. During this period, Galileo made significant discoveries in both pure fundamental science and practical applied science. His multiple interests included the study of astrology, which at the time was a discipline tied to the studies of mathematics, astronomy, and medicine. He also engaged in practical hydraulic engineering, obtaining a patent from the Venetian Republic for a horse-powered water pump in 1594.
Galileo’s Name and Identity
Galileo tended to refer to himself by his first name. At the time, surnames were optional in Italy, and his first name had the same origin as his sometimes-family name, Galilei. Both his given and family name ultimately derived from an ancestor, Galileo Bonaiuti, an important physician, professor, and politician in Florence in the 15th century. When he did refer to himself with more than one name, it was sometimes as Galileo Galilei Linceo, a reference to his being a member of the Accademia dei Lincei, an elite science organization founded in the Papal States. It was common for mid-16th century Tuscan families to name the eldest son after the parents’ surname. The Italian male given name “Galileo” (and thence the surname “Galilei”) derives from the Latin “Galilaeus”, meaning “of Galilee”.
