Galileo Galilei

Galilei was born in Pisa in 1564, the son of Vincenzo Galilei, well known for his studies of
music, and Giulia Ammannati. Galileo studied medicine at the university of Pisa, but his real interests were always in mathematics and natural philosophy. He is chiefly remembered for his work on free fall, his use of the telescope and his employment of experimentation.

After a spell teaching mathematics, first privately in Florence and then at the university of Pisa, in 1592 Galileo was appointed professor of mathematics at the university of Padua (the university of the Republic of Venice). There his duties were mainly to teach Euclid’s geometry and standard (geocentric) astronomy to medical students, who would need to know some astronomy in order to make use of astrology in their medical practice. However, Galileo apparently discussed more unconventional forms of astronomy and natural philosophy in a public lecture he gave in connection with the appearance of a New Star (now known as ‘Kepler’s supernova’) in 1604. In a personal letter written to Kepler (1571 - 1630) in 1598, Galileo had stated that he was a Copernican (believer in the theories of Copernicus). No public sign of this belief was to appear until many years later.

In the summer of 1609, Galileo heard about a spyglass that a Dutchman had shown in Venice. From these reports, and using his own technical skills as a mathematician and as a workman, Galileo made a series of telescopes whose optical performance was much better than that of the Dutch instrument. The astronomical discoveries he made with his telescopes were described in a short book called Message from the stars (Sidereus Nuncius) published in Venice in May 1610. It caused a sensation. Galileo claimed to have seen mountains on the Moon, to have proved the Milky Way was made up of tiny stars, and to have seen four small bodies orbiting Jupiter. These last, with an eye on getting a job in Florence, he promptly named ‘the Medicean stars’.

Soon afterwards, Galileo became ‘Mathematician and [Natural] Philosopher’ to the Grand Duke of Tuscany. In Florence he continued his work on motion and on mechanics, and began to get involved in disputes about Copernicanism. In 1613 he discovered that, when seen in the telescope, the planet Venus showed phases like those of the Moon, and therefore must orbit the Sun not the Earth. This did not enable one to decide between the Copernican system, in which everything goes round the Sun, and the Tychonic (Tycho Brahe) one in which everything but the Earth (and Moon) goes round the Sun which in turn goes round the Earth. Most astronomers of the time in fact favoured the Tychonic system. However, Galileo showed a marked tendency to use all his discoveries as evidence for Copernicanism, and to do so with great verbal as well as mathematical skill. He seems to have made a lot of enemies by making his opponents look fools. Moreover, not all of them actually were fools.

In 1614, Father Tommaso Caccini denounced the opinions of Galileo on the motion of the Earth from the pulpit of Santa Maria Novella, judging them to be erroneous. Galileo therefore went to Rome, where he defended himself against charges that had been made against him but, in 1616, he was admonished by Cardinal Bellarmino and told that he could not defend Copernican astronomy because it went against the doctrine of the Church. In 1622 he wrote the Saggiatore (The Assayer) which was approved and published in 1623. In 1630 he returned to Rome to obtain the right to publish his Dialogue on the two chief world systems which was eventually published in Florence in 1632. In October of 1632 he was summoned by the Holy Office to Rome. The tribunal passed a sentence condemning him and compelled Galileo to solemnly abjure his theory.

He was sent to exile in Siena and finally, in December of 1633, he was allowed to retire to his villa in Arcetri, the Gioiello. Galileo’s sight was failing, but he had devoted pupils and amanuenses, and he found it possible to write up his studies on motion and the strength of materials. The book, Discourses on two new sciences, was smuggled out of Italy and published in Leiden (in the Netherlands) in 1638.

Galileo wrote most of his later works in the vernacular, probably to distance himself from the conventional learning of university teachers. However, his books were translated into Latin for the international market, and they proved to be immensely influential.

His health condition was steadily declining, - by 1638 he was completely blind, and also by now bereft of the support of his daughter, Sister Maria Celeste, who died in 1634. Galileo died in Arcetri on 8 January 1642. For the family of Galileo, see the genealogical tree. Within the Museo, Sala IV is entirely dedicated to Galileo and his studies; among other things are preserved the lenses, the inclined plane, the lodestone, the model of the application of the pendulum to the clock, several portraits and a relic.

Galileo’s contributions to science
The contributions made by Galileo to mechanics remain fundamental, despite the fact that this field of research met with less interest from the Medici Grand Dukes than Galileo’s astronomical discoveries, perhaps because it was less spectacular. Galileo’s investigations concerned the natural descent of bodies along planes of various inclinations, the formulation of the law which established the relationship between space traversed and time interval in free-fall, the isochronism of the oscillations of pendulums of equal lengths and, of particular importance, the motion of projectiles.

The observations of the sky which Galileo carried out with his telescope led to the discovery of the satellites of Jupiter and to Galileo’s increased adherence the Copernican System. The phenomena which were revealed little by little due to the increased possibility of larger lenses were described and illustrated by Galileo in Sidereus Nuncius. The periods and frequencies of appearances of the satellites of Jupiter were studied by Galileo in order to develop a method for determining longitudes at sea.

In the early years of the seventeenth century Galileo adapted a telescope for the viewing of extremely small objects. Between 1619 and 1624 he began to produce microscopes or “occhialini” as he called them. The Galileian microscope is made up of the tube of a telescope, of reduced size, furnished with two lenses. Galileo gave his “occhialino” to various people. He sent a letter to Federigo Cesi, accompanying the instrument, in which he explained the means by which it was focussed and the arrangement of objects for observation.

Viviani recounts that Galileo dedicated himself to research on heat at the end of the 16th century. The invention of the thermoscope seems, then, to belong to his Paduan period. This device was used to carry out experiments on the relationship between changes of temparature and variations of the level of the liquid. The work of the Accademia del Cimento which led to the birth of the Florentine thermometer had its origins in Galileo’s early research.

Between 1600 and 1609 Galileo devoted himself to studying magnetism, inspired by William Gilbert’s De magnete. He attempted to increase the strength of loadstones by means of special armatures. One of these (IV.8) was given to Grand Duke Ferdinand II by Galileo.