1450,1481: Hygrometer - The book of science

Hygrometer
Hygrometer designs
Water witching
Commentary

Nicolaus de Cusa, Leonardo da Vinci atmospheric sciences

Hygrometer

Nicolas de Cusa observed
If someone should hang a good deal of wool,
tied together on one end of a large pair of scales,
and should balance it with stones at the other end
in a place where the air is temperate,
it would be found that the weight of the wool
would increase when the air became more humid,
and decrease when the air tended to dryness.
Leonardo da Vinci might have been the first to build one,
in which the bundle of wool,
absorbing more water
when the air was more humid,
gradually tipped the scale.

Hygrometer designs

Balancing a clod of dirt with a piece of charcoal.
Balancing a bundle of wool with a pile of stones.
Hanging a weight on the string of a lyre.
Chilling a cone to drip condensed moisture into a beaker.
Attaching a paper ribbon to a dial on a graduated scale.
Forcing mercury in an absorbent bag to move a liquid barrier in a tube.
Calling these “hygrometers” after the Greek word meaning moisture.
Attaching a hair under tension to a dial.
Comparing readings from wet-bulb and dry-bulb thermometers.
Calling these “psychrometer” after the Greek word meaning cold.
Determining the temperature at which a mirror fogs.
Drawing air through a silver thimble full of ether until the thimble dulls.
Ventillating wet-bulb and dry-bulb thermometers with a wind-up fan
or by swinging them in a circle over your head.

Water witching

If a teardrop were a potion,
then consider
where its magic
would come from.
It would come from the stars,
and from the earth,
and would be carried
by every germ of life,
empowering millions of lives
swimming in seas,
raining from clouds,
and flowing through leaves.
It shows your pain,
it shows you care,
it shows you’re a part
of life on earth.

Scientists have created many ways to measure humidity. Here is an incomplete chronology assembled from the readings below (not original work):

1450: Nicolaus de Cusa described the first hygrometer.
1481: Leonardo da Vinci implemented de Cusa's idea.
1625: Santorrio Santorre made a hygrometer by hanging a weight on the string of a lyre.
1650: Ferdinand II, the Grand Duke of Tuscany, invented the condensation hygrometer.
1664: Francesco Folli designed the first practical hygrometer, a paper-ribbon hygrometer.
1687: Guillaume Amontons invented a hygrometer similar to a three-liquid barometer.
1755: Johann Heinrich Lambert made a hygrometer, and in 1774 first coined the term “hygrometer.”
1783: Horace Bénédict de Saussure invented the hair hygrometer.
1799: John Leslie measured the humidity using a differential thermometer with a dry-bulb and a wet-bulb (a psychrometer).
Late 1700s: James Hutton invented the sling psychrometer.
1815: Joseph Louis Gay-Lussac derived the formula for calculating humidity from readings of the dry- and wet-bulb thermometers.
1818: Ernst August coined the name “psychrometer.”
1820: John Frederic Daniell invented the dew-point hygrometer.
1854: Henri Victor Regnault created a dew-point hygrometer using ether in a silver thimble.
1887: Richard Assmann invented the aspirated (ventillated) psychrometer.
1938: Dumore began research into developing the electric hygrometer.

See also in The book of science:

1643—Atmospheric pressure—Evangelista Torricelli, Blaise Pascal

Readings in wikipedia:

Other readings:

“Hygrometer: Leonardo da Vinci’s Weather Predictions,” Hubpages
“Hygrometer - Research Article from World of Invention,” BookRags
“Fun Science History about the Hygrometer...,” Hvacproforums
“Condensation hygrometer - Ferdinand II de”; Medici,” Museo Galileo
“Folli’s paper-ribbon hygrometer,” Museo Galileo
“Historical Development of Instruments that Measure Humidity,” Hygrometer.net
“Renault’s Hygrometer,” The University of Queensland Physics Museum
http://www.th-friedrichs.de/en/products/humidity/relative-humidity-psychrometer/aspiration-psychrometer-by-assmann/