The use of the melting of ice to provide a reference temperature was first proposed by Robert Boyle (1627-91) and Robert Hooke (1635-1703). Using two reference points was suggested by Christian Huygens in 1665 (1).

This was unnecessarily extended to three reference points by Gabriel Fahrenheit (1686-1736). He proposed (rather arbitrarily) a zero for the freezing point of a brine solution, a value of 32 for the melting point of ice, and the body temperature at 100 units (this should be about 96, 100 is feverish). The centigrade scale based on the melting and boiling points of water was devised by Anders Celsius of Uppsala (1701-44). Later in the 18^th century the Kelvin scale was introduced, after Lord Kelvin proved that -273ºC was the absolutely lowest temperature of any material.

Alcohol was used as the working fluid of thermometers until superseded in about 1717 by mercury, which can be made more pure, is opaque, more immune to loss by evaporation, and is liquid over a wider range of temperatures.

(1) Sorbjan, Z. 1996. Hands-on Meteorology (Amer. Meteor. Soc.) 306pp.