A hygrometer is an instrument used
to measure the moisture content or the humidity of air or any gas. The
best known type of hygrometer is the "dry and wet-bulb psychrometer", best
described as two mercury thermometers,
one with a wetted base, one with a dry base. The water from the wet base
evaporates and absorbs heat causing the thermometer reading to drop.
Using a calculation table, the reading from the dry thermometer and the
reading drop from the wet thermometer are used to determine the relative
Other kinds of
hygrometers use human hair (blond) to determine moisture content. These
are called mechanical hygrometers, based on the principle that organic
substances ( human hair) contract and expand in response to the relative
humidity. The contraction and expansion moves a needle guage. In 1783,
Swiss physicist and geologist, Horace Bénédict de Saussure
built the first hygrometer using a human hair to measure humidity.
Some hygrometers use the measurements
of changes in electrical resistance, using a thin piece of lithium chloride
or other semiconductor devices and measuring the resistance which is affected
Leonardo da Vinci built the first
crude hygrometer in the 1400s. Francesco Folli invented a more practical
hygrometer in 1664.
Robert Hooke invented the universal
joint, the iris diaphragm, and an early prototype of the respirator; invented
the anchor escapement and the balance spring, which made more accurate
clocks possible, invented or improved meteorological instruments such as
the barometer, anemometer, and hygrometer; and so on.
John Frederic Daniell
In 1820, British chemist and meteorologist,
John Frederic invented a dew-point hygrometer, which came into widespread
use. Daniel is best known for inventing the Daniell cell, an improvement
over the voltaic cell used in the early history of battery development.
Build your own hair hygrometer.
To Calibrate Your Hygrometer
How to calibrate your hygrometer
(for use with cigar boxes).
Weather Measuring Instruments
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