Room IV may be described as a small Galileo Museum. Some precious original instruments of Galileo are preserved here: a specimen of the geometric and military compass, the objective lens of the telescope used by Galileo in January 1610 to observe Jupiter's moons for the first time, and the jovilabium, based on the Pisan scientist's observations and drawings. There are also a model of the thermoscope (predecessor of the modern thermometer), the armed magnets used by Galileo for his researches on magnetism, and even the embalmed middle finger of his right hand, transformed into an emblematic relic. Educational models illustrate fundamental Galilean research on mechanics. Such models were built at the Museo di Fisica e Storia Naturale founded in Florence by Grand Duke Peter Leopold in 1775.