Instruments

ROOM VII

The Galileo Museum preserves the only two telescopes built by Galileo that have come down to us. The specimen covered in leather with gold decorations was given by the Tuscan scientist to Grand Duke Cosimo II. The instrument consists of a framework of wooden slats onto which the covering leather is glued, originally red in color. At the ends of the tube, there are two small barrels that house the lenses, providing a magnification power of about 21 times.

The other specimen, made up of two wooden shells held together by metal wire and covered in paper, bears an annotation by Galileo near the objective about the focal length of the instrument. In this case, the magnification is about 14 times.

It was using telescopes of this kind that, starting from the summer of 1609, Galileo made the sensational celestial observations that made him famous.

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The compound microscope, made of cardboard, leather and wood, is inserted in an iron support with three curved legs. The outer tube is covered in vellum green decorated with gold tooling. There are three lenses (an objective, a field lens, and an eyepiece), all double-convex.

This very important instrument was said to have been built by Galileo, but is now more plausibly attributed to Giuseppe Campani. Johannes Faber, fellow of the Accademia dei Lincei, gave the name "microscope" (microscopio) to Galileo's "small eyeglass" (occhialino) in 1625.

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The thermoscope consists of an egg-sized glass with a long neck. The jar is heated with the hands and partially immersed, upside down, in a container filled with water. When the hands are removed, the water rises in the neck. The experiment demonstrated the changes in air density caused by temperature variations.

Vincenzo Viviani, in the Life of Galileo, states that the thermoscope was developed by the scientist in 1597.

ROOM VII

Long kept in the Uffizi Gallery, where it was observed and described by Cornelis Mejjer, this lodestone was re-armed by Mejjer to restore its original power. Mejjer also recalled that exceptional magnets such as this fetched exorbitant prices. Indeed, in 1609, Cosimo II had paid 100 doppie (i.e., 200 gold scudi) to buy—on Galileo's advice—an extremely powerful lodestone owned by Giovanfrancesco Sagredo in Venice. That magnet has been lost.

ROOM VII

The machine is built on the same principle as item inv. 998 and, like the latter, is known as an Archimedean screw, after the scientist who first designed such a device. A brass plate is hinged to a wooden base and its tilt can be adjusted by means of a sliding brass stirrup. The plate holds a glass tube closed at both ends by two brass stoppers and fitted with a handle. The stoppers carry small elastic strips holding a helical glass tube. Water is raised through the tube by rotating the handle. Provenance: Lorraine collections.

ROOM VII

Second-order lever inspired by a model proposed by Willem Jacob 's Gravesande in Physices elementa mathematica, experimentis confirmata (3rd ed., Leiden, 1742).

A turned column fixed to a profiled base carries the beam with a counterweight and two notches for shifting the fulcrum's position. A second column carries a pulley on which runs a cord connected to a weight serving as the effort. Two lead pans hanging from the lever act as the load. Fifteen nails dividing the beam into equal segments serve to vary the application of the load.

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Built in 1877 by the Florentine clockmaker Eustachio Porcellotti, this working model is based on the drawing (inv. 2433) of the Galilean invention by Vincenzo Viviani and Vincenzo Galilei.

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Brass instrument, undated and of unknown maker. The Jovilabe is certainly connected to Galileo's efforts to determine the periods of Jupiter's moons—whose discovery he announced in 1610 in Sidereus Nuncius—and to compute the times of their eclipses. Galileo immediately realized that eclipses of Jupiter's moons could provide a precise method to determine the longitude. The instrument is engraved with tables showing the mean motions of each of the four moons. Two connected disks of different diameters are rotated by means of a movable rod. They are used to create a "view from the Sun" of the movements of Jupiter's moons observed from the Earth (movements that seem irregular because of the heliocentric motions of the Earth and Jupiter). Galileo began the systematic study of the periods of Jupiter's moons in 1611, developing a micrometer for the purpose. The Pisan scientist compiled tables of the periods that he offered, with his telescopes, first to the King of Spain (1611, 1612, 1616, and 1627-1628), then to the States General of Holland (1637-1641). To convince his Spanish interlocutors that Jupiter and its moons could be observed on unstable ground, such as a ship's deck, Galileo designed a special helmet carrying a small telescope on a hinged mount. The device was named celatone (celata = "helmet" in Italian). In this second proposal, he also described the advantages of applying the pendulum to the clock. Despite the interest they aroused, neither of his proposals was accepted. Provenance: estate of Leopold de' Medici.

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This inclined plane, with five small bells and a pendulum, was devised to provide an experimental demonstration of the Galilean law of falling bodies. The apparatus makes use of another important physical principle discovered by Galileo: the isochronism of pendulums of equal length. This principle is demonstrated by the pendulum connected to the plane, which completes its oscillations in equal times. The experiment consists in releasing a small ball from the top end of the plane at the same time as the pendulum is swung. At each successive complete oscillation of the pendulum, the ball strikes one of the small bells placed along the inclined plane at increasing distances, arranged in the sequence of odd numbers. The experiment not only makes it possible to measure the increase in the distances traveled by a body in natural fall in successive and equal time intervals starting from the rest position; it also provides—thanks to the bell rings—an acoustic perception of the ball's constant acceleration during its fall.

No documents survive proving that Galileo performed this specific experiment. In the mid-nineteenth century, Giuseppe Bezzuoli—following the instructions of Vincenzio Antinori, director of the Museo di Fisica e Storia Naturale—represented in a fresco of the Tribuna di Galileo the Pisan scientist conducting an experiment to demonstrate the law of falling bodies by means of an inclined plane.