Galileo’s thermometer also worked as a barometer. Santorio^2 was actually a friend of his.  He worked out an air thermometer, which used colored liquid that moved based on the expansion of air.  Daniel Fahrenheit was the one who first implemented a fixed scale to the thermometer, which he set to be the melting point of water at the base and the heat of the typical human body as the upper end.  This was later changed to be the boiling point of water.  It’s sort of neat to know where the fahrenheit scale came from, though.