|This is a copy of the instrument that Galileo devised
to measure hot and cold during his Paduan period. Viviani, in his Vita di
Galileo, states that the thermoscope was conceived by Galileo in 1597. The
discovery of the instrument is confirmed by Benedetto Castelli in a letter
to Cesarini dated 20 September 1638, in which he describes the use of the
instrument. This consisted of a glass bottle of about the size of an egg,
with a long glass neck. This bottle was heated with the hands and then immersed
partially in a vessel containing a liquid. When the hands were removed from
the bottle, the liquid rose to a certain height in the neck, remaining above
the level of the liquid in the vessel. A similar instrument was devised by
Santorio in Venice in 1612. When Galileo was informed by Sagredo of the instrument
made by Santorio he protested and seems to have suspected that someone wanted
to rob him of the glory of the discovery.
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.