Galileo Galilei

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Galileo Galilei


Born Feb. 15, 1564, in Pisa; died Jan. 8, 1642, in Arcetri, near Florence. Italian physicist, specialist in mechanics, and astronomer. One of the founders of natural science; poet, philologist, and critic.

Galileo belonged to a noble but impoverished Florentine family. His father, Vincenzio, a well-known musician, had a great influence on the development and shaping of Galileo’s abilities. Until the age of 11, Galileo lived in Pisa and attended school there; then the family moved to Florence. Galileo received further education at the monastery of Vallombrosa, where he was admitted as a novice into the monastic order. There he became acquainted with the works of Latin and Greek writers. Under the pretext of a serious eye ailment, his father withdrew him from the monastery. In 1581, at his father’s insistence, Galileo entered the University of Pisa, where he studied medicine. There he became acquainted for the first time with Aristotelian physics, which from the very beginning seemed unconvincing to him. Galileo turned to reading the ancient mathematicians—Euclid and Archimedes. The latter became his real teacher. Fascinated by geometry and mechanics, Galileo abandoned medicine and returned to Florence, where he spent four years studying mathematics. This period of his life produced the short essay “The Little Balance” (1586; published 1655), which describes a hydrostatic balance constructed by Galileo to quickly determine the composition of metal alloys, and a geometric treatise on the center of gravity of bodies. These works for the first time brought him fame among Italian mathematicians. In 1589 he received the chair of mathematics in Pisa and continued his scientific work. His “Dialogue On Motion,” which was written in Pisa and directed against Aristotle, has been preserved in manuscript. Some of the conclusions and arguments in this work were erroneous, and Galileo later repudiated them. But already here, without naming Copernicus, Galileo presents arguments refuting Aristotle’s rejection of the diurnal rotation of the earth.

In 1592, Galileo was awarded the chair of mathematics in Padua. The Paduan period of Galileo’s life (1592-1610) was the most productive. During this period he originated his statical studies of machines, where he proceeded from the general principle of equilibrium, which coincided with the virtual work principle. His main works in dynamics—works on the laws of free falling bodies, on motion along an inclined plane, on projectile motion, and on the isochronism of the pendulum—came to maturity. Also from this period are studies on the strength of materials and the mechanics of animal bodies. Finally, it was in Padua that Galileo became a confirmed follower of Copernicus. However, Galileo’s scientific work remained secret from everyone except his friends. His lectures, which were read according to the traditional program, expounded Ptolemy’s theory. In Padua, Galileo published only a description of proportional dividers, the use of which made it possible to make various calculations and constructions quickly.

In 1609, on the basis of information about a telescope invented in Holland, Galileo built his first telescope of approximately threefold magnifying power. The operation of the telescope was demonstrated from the basilica of St. Mark in Venice and made an overwhelming impression. He soon built a telescope with a power of 32. Observations made with it put an end to Aristotle’s “ideal spheres” and the dogma on the perfection of celestial bodies. The surface of the moon proved to be covered with mountains and pitted with craters, stars lost their apparent magnitudes, and for the first time their enormous remoteness was perceived. Jupiter was found to have four satellites, and a great number of new stars became visible in the sky. The Milky Way broke down into separate stars. Galileo described his observations in the work Sidereus nuncius (Starry Messenger, 1610-11), which had a shattering impact. At the same time bitter polemical controversy arose. It was charged that everything Galileo had seen was an optical illusion; it was also argued simply that his observations contradicted Aristotle and were therefore wrong.

The astronomical discoveries were a turning point in Galileo’s life. He left teaching and moved to Florence at the invitation of Duke Cosimo II de’ Medici. There he became the court “philosopher” and “first mathematician” of the university, without having to lecture.

Continuing his telescopic observations, Galileo discovered the phases of Venus, sunspots, and the rotation of the sun, studied the motion of Jupiter’s satellites, and observed Saturn. In 1611, Galileo traveled to Rome, where he was given an enthusiastic reception at the papal court and where he became friends with Prince Cesi, founder of the Accademia dei Lincei (Academy of the Lynx-eyed), of which Galileo became a member. At the duke’s insistence, Galileo published his first anti-Aristotelian work— Discourse on Things That Float (1612), where he applied the principle of equal moments in deducing the conditions of equilibrium in liquids.

However, in 1613 a letter from Galileo to the monk Castelli in which he defended Copernicanism became known. The letter provoked the direct denunciation of Galileo to the Inquisition. In 1616 the Jesuits declared Copernicanism to be heretical, and Copernicus’ book was placed on the Index of Forbidden Books. Galileo was not named in the decree, but he was privately ordered to cease advocating the theory. Officially Galileo obeyed the decree. For several years he was compelled to remain silent about the Copernican system and not even to allude to it. His only major essay during this period was “The Assayer” (1623), a polemical treatise concerning three comets that had appeared in 1618. In terms of literary form, wit, and stylistic refinement, this is one of Galileo’s most remarkable works.

In 1623, Cardinal Maffeo Barberini, a friend of Galileo, acceded to the papal throne under the name Urban VIII. For Galileo, this event seemed tantamount to being released from the bonds of the interdict (decree). In 1630 he came to Rome with an already finished manuscript, Dialogue on the Ebb and Flow of Tides (original title of Dialogue Concerning the the Two Chief World Systems), in which the systems of Copernicus and Ptolemy were presented in discussions between three interlocutors: Sagredo, Salviati, and Simplicio.

Pope Urban VIII agreed to the publication of the book, in which the Copernican theory was to be set forth as one of the possible hypotheses. After a long censorship ordeal, Galileo received the long-awaited permission to print the Dialogue with certain changes; the book appeared in Florence in Italian in January 1632. Several months after publication, Galileo was ordered by Rome to stop further sales of the book. Galileo was compelled to come to Rome in February 1633 at the command of the Inquisition and stand trial. In four interrogations —from April 12 to June 21, 1633—Galileo renounced the Copernican theory, and on June 22 he publicly repented on his knees in the Church of Maria Sopra Minerva. The Dialogue was banned, and for nine years Galileo was considered a “prisoner of the Inquisition.” First he lived in Rome, in a ducal palace, then in his Arcetri villa, outside Florence. He was forbidden to speak with anyone about the motion of the earth or to publish any works. Despite the papal interdict, a Latin translation of the Dialogue appeared in Protestant countries, and Galileo’s discourse on the relationship between the Bible and natural science was published in Holland. Finally, in 1638 one of Galileo’s most important works, Discourses and Mathematical Demonstrations Concerning Two New Sciences, was published in Holland; this work summed up the results of his physical research and laid the basis for dynamics.

In 1637, Galileo went blind. He died on Jan. 8, 1642. In 1737, Galileo’s last wish was carried out—his remains were transferred to the Church of Santa Croce in Florence, where he was interred next to Michelangelo.

Galileo’s influence on the development of mechanics, optics, and astronomy in the 17th century was invaluable. His scientific work, his discoveries of enormous importance, and his scientific courage were of decisive significance in the triumph of the heliocentric system of the world. Galileo’s work in creating the basic principles of mechanics was especially significant. While Galileo did not express the basic laws of motion with the clarity that I. Newton did, the law of inertia and the law of the composition of motions were, in essence, fully recognized and applied by him to the solution of practical problems. The history of statics begins with Archimedes; the history of dynamics begins with Galileo. He was the first to advance the idea of the relativity of motion (the Galilean principle of relativity) and solved a number of basic mechanical problems. His work in mechanics included, above all, the study of the laws of falling bodies and their motion along an inclined plane, the laws of projectiles, and the establishment of the conservation of mechanical energy during the swinging of a pendulum. Galileo dealt a blow to the dogmatic Aristotelian notions of absolutely light bodies (fire, air); in a number of witty experiments he demonstrated that air is a heavy body and even determined its specific weight with respect to water.

The basis of Galileo’s world view was recognition of the objective existence of the world, that is, its existence outside and independently of human consciousness. The world is infinite, he maintained, matter is eternal. In all processes occurring in nature, nothing is destroyed and nothing is born—only a change in the mutual disposition of bodies or their parts occurs. Matter consists of absolutely indivisible atoms, and its motion is a unique, universal mechanical movement. Celestial bodies are similar to the earth and are subject to the same laws of mechanics. Everything in nature is subject to rigorous mechanical causality. Galileo considered the search for the causes of phenomena to be the real purpose of science and understanding the internal necessity of phenomena as the highest level of knowledge. He regarded observation as the point of departure for understanding nature, and the experiment as the basis of science. Rejecting the attempts of the scholastics to derive the truth by comparing the texts of the recognized authorities and by means of abstract reasoning, Galileo contended that the scientist’s task “is to study the great book of nature, which is the real subject matter of philosophy” (Dialog o dvukh glavneishikh sistemakh mira ptolomeevoi i kopernikovoi, Moscow-Leningrad, 1948, p. 21). Those who blindly followed the opinions of the authorities, without wishing to study the phenomena of nature themselves, Galileo called “servile minds” and considered them unworthy of the title of philosopher and branded them as “doctors of rote-learning.” However, limited by the conditions of his time, Galileo was not consistent; he agreed with the theory of dual truth and allowed divine first cause.

Galileo’s talents were not confined to science; he was a musician, a painter, a lover of the arts, and a brilliant man of letters. His scientific treatises, a large number of which were written in the Italian vernacular although Galileo had a complete mastery of Latin, can also be categorized as works of art in terms of the simplicity and clarity of exposition and the brilliance of literary style. Galileo did translations from Greek into Latin, studied the ancient classics and poets of the Renaissance (the works Notes toAriosto and Considerationson Tasso), spoke at the Florentine Academy on questions pertaining to the study of Dante, and wrote a burlesque poem, Satire of the Toga Wearers. Galileo was the coauthor of A. Salvadori’s canzone On the Medicean Stars —satellites of Jupiter discovered by Galileo in 1610.


Le opere, national ed., vols. 1-20. Florence, 1890-1909.
Pensieri, mott e sentenze. Selections from the national edition, edited by A. Favaro. Florence, 1910.
Le opere. Florence, 1933 (Scritti letterari, vol. 9).
In Russian translation:
Dialog o dvukh glavneishikh sistemakh mira ptolomeevoi i kopernikovoi. Moscow-Leningrad, 1948.
Besedy i matematicheskie dokazatel’stva, kasaiushchiesia dvukh novykh otraslei nauki, otnosiashchikhsia k mekhanike i mestnomu dvizheniiu. Moscow-Leningrad. 1934.
“Rassuzhdenie o telakh, prebyvaiushchikh v vode, i tekh, kotorye v nei dvizhutsia.” In the collection Nachala gidrostatiki. Moscow-Leningrad, 1933.
“Poslanie k Franchesko Ingoli.” In the collection Galileo Galilei (1564-1642). Moscow-Leningrad, 1943.
Izbrannye trudy, vols. 1-2. Moscow, 1964.


Galileo Galilei (1564-1642). Sbornik, posviashchennyi 300-letnei godovshchine so dnia smerti. Moscow-Leningrad, 1943. (Articles by S. I. Vavilov, A. N. Krylov, and others.)
Vygodskii, M. Ia. Galilei i inkvizitsiia. Moscow-Leningrad, 1934.
Olschki, D. Istoriia nauchnoi literatury na novykh iazykakh, vol. 3.Moscow-Leningrad, 1933. (Translated from German.)
Kuznetsov, B. G. Galilei. [Moscow] 1964.
Galilei Galileo (1564-1642). Ukazatel’ literatury. Moscow, 1940.
Cervini, M. Galileo Galilei. Antologia. Torino, 1952.
Nel quarto centenario della nascità di Galileo Galilei. Milan [1966].
Boffito, G. Bibliografia Galileiana. [Roma] 1943.

S. I. VAVILOV (article from the 2nd edition of the Great Soviet Encyclopedia, with some deletions)