Copy of the instrument to measure heat and cold invented by Galileo during his stay in Padua. Vincenzo Viviani, in his Vita di Galileo [Life of Galileo], states that the thermoscope was designed by Galileo in 1597. This is confirmed by Benedetto Castelli in his letter of September 20, 1638, to Ferdinando Cesarini, in which he describes the use of the instrument. 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. Santorio had built a similar instrument in Venice in 1612.