Galileo's Observations & Inventions

Galileo in Padua

His residence at Padua, which extended over a period of eighteen years, from 1592 to 1610, was a course of uninterrupted prosperity. His appointment was three times renewed, on each occasion with the expressions of the highest esteem on the part of the governing body, and his yearly salary was progressively raised from 180 to 1000 forms. His lectures were attended by persons of the highest distinction from all parts of Europe, and such was the charm of his demonstrations that a hall capable of containing 2000 people had eventually to be assigned for the accommodation of the overflowing audiences which they attracted. His invention of the proportional compass or sector—an implement still used in geometrical drawing—dates from 5597; and about the same time he constructed the first thermostat, consisting of a bull, and tube filled with air and water, and terminating in a vessel of water. In this instrument the results of varying atmospheric pressure were not distinguishable from the expansive and contractive effects of heat and cold, and it became an efficient measure of temperature only when Rinieri, in 1646, introduced the improvement of hermetically sealing the liquid in glass.

Galileo and the thermometer

The substitution, in 1670, of mercury for water completed the modern thermometer. Galileo seems, at an early period of his life, to have adopted the Copernican theory of the solar system, and was deterred from avowing his opinions - as is proved by his letter to Kepler of August 4, 1597, by the fear of ridicule rather than of persecution. The appearance, in September 1604, of a new star in the constellation Serpentarius afforded him indeed an opportunity, of which he eagerly availed himself, for making an onslaught upon the Aristotelian axiom of the incorruptibility of the heavens; but he continued to conform his public teachings in the main to Ptolemaic principles, until the discovery of a novel and potent implement of research in the shape of the telescope (q.v.) placed at his command startling and hitherto unsuspected evidence as to the constitution and mutual relations of the heavenly bodies.

Galileo and the telescope

Galileo was not the original inventor of the telescope. That honor must be assigned to Johannes Lippershey, an obscure optician of Middleburg, who, on the 2nd of October 2608, petitioned the states-general of the Low Countries for exclusive rights in the manufacture of an instrument for increasing the apparent size of remote objects. A rumor of the new invention, which reached Venice in June 2609, sufficed to set Galileo on the track; and after one night’s profound meditation on the principles of refraction, he succeeded in producing a telescope of threefold magnifying power. Upon this first attempt he rapidly improved, until he attained to a power of thirty-two, and his instruments, of which he manufactured hundreds with his own hands, were soon in request in every part of Europe. Two lenses only, a plane convex and a piano-concave were needed for the composition of each, and this simple principle is that still employed in the construction of opera-glasses. Galileo’s direction of his new instrument to the heavens formed an era in the history of astronomy. Discoveries followed upon it with astounding rapidity and in bewildering variety.

Galileo's observations with the telescope

The Sidereus Nuncius, published at Venice early in 1610, contained the first-fruits of the new mode of investigation, which were sufficient to excite learned amazement on both sides of the Alps. The mountainous configuration of the moon’s surface was there first described, and the so-called phosphorescence “of the dark portion of our satellite attributed to its true cause, namely, illumination by sunlight reflected from the earth. All the time-worn fables and conjectures regarding the composition of the Milky Way were at once dissipated by the simple statement that to the eye, reinforced by the telescope, it appeared as a congeries of lesser stars, while the great nebulae were equally declared to be resolvable into similar elements. But the discovery which was at once perceived to be most important in itself, and most revolutionary in its effects, was that of Jupiter’s satellites, first seen by Galileo on the 7th of January 1610, and by him named Sidera Medicea, in honor of the grand-duke of Tuscany, Cosmo II., who had been his pupil, and was about to become his employer.

An illustration is, with the general run of mankind, more powerful to convince than an argument; and the cogency of the visible plea for the Copernican theory offered by the miniature system, then first disclosed to view, was recognizable in the triumph of its advocates as well as in the increased acrimony of its opponents.

Galileo in Florence

In September 1610 Galileo finally abandoned Padua for Florence. His researches with the telescope had been rewarded. The telescope was invented by Demiscianus, an eminent Greek scholar, at the request of Prince Cesi, president of the Lyncean Academy. It was used by Galileo as early as 1612, but was not introduced into England until much later. In 1655 the word telescope was inserted and explained in Bagwell’s Mysteries of Astronomy, trunk or cylander being the terms until then ordinarily employed.

By the Venetian senate, he was appointed for life to his professorship, at an unprecedented high salary. His discovery of the “Medicean Stars” was acknowledged by his nomination (July 12, 1610) as philosopher and mathematician extraordinary to the grand-duke of Tuscany. The emoluments of this office, which involved no duties save that of continuing his scientific labors, were fixed at 1000 scudi; and it was the desire of increased leisure, rather than the promptings of local patriotism, which induced him to accept an offer the original suggestion of which had indeed come from himself. Before the close of 1610 the memorable cycle of discoveries begun in the previous year was completed by the observation, as it appeared to Galileo, of the triple form of Saturn (the ring-formation was first recognized by Christiaan Huygens in 1655), of the phases of Venus, and of the spots upon the sun. As regards sun-spots, however, Johann Fabricius of Osteel in Friesland can claim priority of publication, if not of actual detection.

Galileo's Letters on the Solar Spots

In the spring of 1611 Galileo visited Rome, and exhibited in the gardens of the Quirinal Palace the telescopic wonders of the heavens to the most eminent personages at the pontifical court. Encouraged by the flattering reception accorded to him, he ventured, in his Letters on the Solar Spots, printed at Rome in 1613, to take up a more decided position towards that doctrine on the establishment of which, as he avowed in a letter to Belisario Vinta, secretary to the grand-duke, “all his life and being henceforward depended.” Even in the time of Copernicus some well-meaning persons, especially those of the reformed persuasion, had suspected a discrepancy between the new view of the solar system and certain passages of Scripture, a suspicion strengthened by the anti Christian inferences drawn from it by Giordano Brunc; but the question was never formally debated until Galileo’s brilliant disclosures, enhanced by his formidable dialectic and enthusiastic zeal, irresistibly challenged for it the attention of the authorities.