Galileo’s scientific experiments, the uses he made of them, and the concepts he developed led directly to reexaminations of the traditional Aristotelian view of nature and laid the foundation for Newtonian mechanics.

Galileo was one of a number of scientists who questioned the Aristotelian view of the workings of nature and turned to experiment to find answers. His frequent discussions with friends and colleagues have led some to believe that many of his findings should be credited to a group effort. As important as his colleagues were, however, probably no one influenced Galileo’s scientific life more than did his musician father, Vincenzo Galilei. Science;experimentation
Galileo
Galilei, Vincenzo
Monte, Guidobaldo Marchese del
Santorio Santorio
Viviani, Vincenzio
Sarpi, Paolo
Galilei, Vincenzo
Viviani, Vicenzio
Santorio Santorio
Monte, Guidobaldo Marchese del
Sarpi, Paolo
Galileo

During 1588 and 1589, Galileo was at his father’s home in Florence and most likely worked with him on a problem that involved physics and music. It was commonly believed that the pitch of a plucked string depended directly on both the length and the tension of the string. Doubling the tension should raise the pitch one octave. Using strings of various lengths and under different tensions, the elder Galilei showed that the pitch did depend on the length of the string, but it depended on the square root of the tension. Questioning what was commonly accepted and appealing to experimentation became hallmarks of Galileo’s scientific career.

In 1581, Galileo enrolled at the University of Pisa to study medicine, but he soon changed to the study of mathematics Mathematics;Italy . According to Vincenzio Viviani, a student of Galileo’s and his first biographer, during Galileo’s own student days in 1583, while standing in the cathedral of Pisa, he happened to notice the chandelier swing with the air currents from an open window. He was amazed to note that the period with which the chandelier swung back and forth remained the same regardless of whether the chandelier swung in a smaller arc or a larger arc. He probably timed the period with his heartbeat.

Galileo later stated that the pendulum is isochronous, that is, that the period of the swing is the same, regardless of amplitude, no matter how large. He was in error on this point, for the pendulum is nearly isochronous only if the arc of the pendulum swing is small. (Grandfather clocks make use of such an isochronous pendulum to regulate their movement.) One of Galileo’s friends, a physician named Santorio Santorio, began using a short pendulum to time the pulse of patients in 1602. Galileo completed four years of studies at the University of Pisa but left without a degree in 1585. He returned to his father’s home, taught private students, and occasionally gave public lectures. Galileo admired the work of Archimedes greatly. He reconstructed Archimedes’ method of weighing an object in air and then weighing it in water to determine the object’s density and, therefore, the purity of the precious metal used. In doing so, Galileo devised a more accurate balance. He described it in a small booklet called La bilancetta
Bilancetta, La (Galileo) (c. 1586; the little balance). His balance had a vertical support for the pivot of a horizontal arm. The item to be weighed was suspended from one side of the arm, and a counterweight was suspended from the other side of the arm. The counterweight was moved along the arm until balance was achieved, and then its weight and distance from the pivot allowed the weight of the item to be computed. Galileo’s simple, but brilliant, improvement consisted of winding a fine wire around the counterweight arm so that the counterweight’s position could be very accurately located by counting the number of turns of wire from an index mark to the counterweight’s position. If the fineness of the wire “bedazzled the eye,” making it difficult to count turns, Galileo suggested running a lightly held, sharp stiletto along the turns and counting the clicks as the stiletto passed from turn to turn.

At the recommendation of Galileo’s friend and patron, Guidobaldo Marchese del Monte, Galileo was appointed to the chair of mathematics at the University of Pisa in 1589. Some of Galileo’s lecture notes from 1589 to 1592 were gathered into a collection referred to as De motu (c. 1590; On Motion
On Motion (Galileo) , 1960). In it, Galileo still used the Aristotelian concepts of natural and forced motions, but he proved Aristotle wrong on several points. He introduced the new concepts of infinitesimal forces and “neutral motion,” a precursor to the modern concept of inertia. He reported on his experiments with bodies falling in various media, and by casting the problem in terms of relative densities, he was able to avoid some of Aristotle’s errors. Physics

Around 1590, according to Viviani, Galileo dropped a large cannon ball and a musket ball from the Leaning Tower of Pisa simultaneously. The two hit the ground at nearly the same time, contrary to Aristotle’s prediction. While others before Galileo had done the same experiment and reached the same conclusion, Galileo’s public demonstration assured not only that his experiment was memorable but also that it countered false tradition.

After his father died in 1591, the financial responsibility for his brother and sisters fell to Galileo. Guidobaldo helped him obtain a better position at the University of Padua in 1592. Notes from his lectures from 1593 to 1600 were compiled for the collection Le meccaniche (c. 1600; On Mechanics
On Mechanics (Galileo) , 1960), considered the best work on simple machines up to that time. One of its gems is a clever proof based on balances: for a body on an inclined plane, the component of the weight acting down the plane is proportional to the sine of the angle of incline of the plane (to use modern terms).

In Aristotelian theory, heat and cold were fundamental properties that simply were. Until Galileo’s time it seems that people believed hot and cold could not, or should not, be measured. As early as 1592, Galileo built a crude thermometer by fusing a long glass tube “as fine as wheat straw” to a hollow glass egg. If the egg were warmed by cupping it in the hand and then inverted with the end of the tube in water, water would be drawn into the tube as the air in the egg cooled. If the egg was warmed or cooled, the water in the tube would fall or rise. Santorio marked a scale on the tube, making it a proper thermometer. While useful, this type of thermometer had the serious defect of depending not just on the temperature but also on atmospheric pressure.

Guidobaldo concentrated on practical applications of science and influenced Galileo to do the same. Galileo studied and taught about fortifications, and in 1597, he invented and began to manufacture a “military compass” that could be used to measure the elevation angle of cannon. It was engraved with tables and scales to show such things as the proper charge of powder for the cannon or the number of soldiers required for various formations.

The flight of a cannon ball is far too swift for the eye to determine its trajectory, but evidence found in Galileo’s notes, and in those of his intellectual companions, Guidobaldo and Paolo Sarpi, shows that around 1592, Galileo and Guidobaldo proved that the trajectory was a parabola. Their marvelously simple method was to cover a small brass ball with ink, fasten a sheet of paper to a board, and hold the board nearly upright. Then the ball was launched upward against the paper and allowed to trace out its path. They quickly recognized the inked curve as a parabola. The ascending and descending arcs of the trajectory were the same, contrary to Aristotle’s claim.

When Galileo recognized that the trajectory of a projectile was a parabola, he would have known by the parabola’s mathematical properties that the distance the projectile fell increased as the square of the time elapsed. Thus, he had all of the elements of “the law of the fall” but did not publish these results until many years later when he could present them as part of a coherent system.

Galileo was a true Renaissance figure. He was a good artist, wrote poetry, and played the lute and the organ. He was a hands-on scientist who performed experiments and constructed his own instruments. He was the only scientist of his time to gain international recognition in mathematics, physics, and astronomy. This enabled him to bring mathematics to physics and (eventually) bring physics to astronomy. In so doing, he helped place modern science firmly on course.

Ideally, science has a dual role: It approaches questions theoretically by soundly predicting the outcome of “events,” and then it proves those predictions through sound experiment and observation. Galileo’s experiments, backed by mathematical models and proofs, paved the way for Isaac Newton’s formulation of the three laws of motion.

• Galileo. On Motion, and On Mechanics. Madison: University of Wisconsin Press, 1960. Translated and introduced by I. E. Drabkin and Stillman Drake. A translation of and introductions and notes to Galileo’s De motu and Le meccaniche. Also includes illustrations. Part of the Medieval Science series.
• Drake, Stillman. Galileo Studies: Personality, Tradition, and Revolution. Ann Arbor: University of Michigan Press, 1970. An excellent look at Galileo and his character and his influence on science.
• Machamer, Peter, ed. The Cambridge Companion to Galileo. New York: Cambridge University Press, 1998. Twelve historians examine in depth Galileo’s place in the history of science. Suitable for all readers.
• Sharratt, Michael. Galileo: Decisive Innovator. Cambridge, Mass.: Blackwell, 1994. Examines Galileo’s ability as a scientific innovator who explored the natural world through varying means.
• Sobel, Dava. Galileo’s Daughter: A Historical Memoir of Science, Faith, and Love. New York: Penguin Books, 2000. An annotated compilation of letters written to Galileo by his daughter, Virginia, who took the convent name Sister Maria Celeste. It provides a warm look at Galileo the individual.

1462: Regiomontanus Completes the Epitome of Ptolemy’s Almagest

c. 1478-1519: Leonardo da Vinci Compiles His Notebooks

1543: Copernicus Publishes De Revolutionibus

1572-1574: Tycho Brahe Observes a Supernova

1600: William Gilbert Publishes De Magnete