Fahrenheit, Gabriel Daniel (1686–1736)

Polish-born Dutch physicist who invented the first accurate thermometer in 1724 and devised the Fahrenheit temperature scale. Using his thermometer, Fahrenheit was able to determine the boiling points of liquids and found that they vary with atmospheric pressure.

Fahrenheit was born in Danzig (Gdańsk). He learned the manufacture of scientific instruments in Amsterdam from 1701, and spent ten years travelling round Europe, meeting scientists. In 1717 he became an instrumentmaker in Amsterdam, and remained in the Netherlands for the rest of his life.

Fahrenheit's first thermometers contained a column of alcohol which expanded and contracted directly, as originally devised by Danish astronomer Ole Römer in 1701. Fahrenheit substituted mercury for alcohol because its rate of expansion, although less than that of alcohol, is more constant. Furthermore, mercury could be used over a much wider temperature range than alcohol.

In order to reflect the greater sensitivity of his thermometer, Fahrenheit expanded Römer's scale so that blood heat was 90° and an ice–salt mixture was 0°; on this scale freezing point was 30°. Fahrenheit later adjusted the scale to ignore body temperature as a fixed point so that the boiling point of water came to 212° and freezing point was 32°. This is the Fahrenheit scale that is still in use today.