'Galileo's thermometer', 1592.
© Science Museum / Science & Society Picture Library
Detail of a replica made by Ad-Glas of Oklahoma, USA, c 1994, of the air thermoscope made by Galileo Galilei (1564-1642), the celebrated Italian scientist, in 1592. This was probably the first instrument made for the measurement of temperature and consisted of a long thin glas tube fitted with a bulb at one end which was heated to expel the air within it. The whole instrument was then inverted and placed in another vesel containing a liquid, usually water or wine. Changes of temperature were marked by the amount the liquid rose in the tube.