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A hygrometer [haɪˈɡrɒmɪtə] is an instrument used for measuring the moisture content in the atmosphere

Historical Development of Instruments that Measure Humidity

Hygrometer dew point DaniellHorace Bénédict de Saussure devised the first hair-tension hygrometer in 1783, but Leonardo da Vinci invented a version of the hygrometer as early as the late 1400s. Francesco Folli designed the first practical hygrometer in 1664, and John Frederic Daniell built the first dew-point hygrometer in 1820.

  1. Guillaume Amontons invented a type of hygrometer that was similar to a three-liquid barometer in 1687.
  2. James Hutton developed the first psychrometer in the late 1700s.
  3. Johann Heinrich Lambert first coined the name “hygrometer” in 1774.
  4. Robert Hooke, prolific inventor of the universal joint, balance spring and a prototype respirator, made improvements to hygrometers and barometers.

The above image shows a hygrometer from “A Text-book on Chemistry”. Which was published by John William Draper in 1861. This hygrometer by John Frederic Daniell (1790-1845) was intended to determine the dew point. The image and a description of this hygrometer can be found on page 52. The book is freely available at Google Books.