A cyanometer (from ''

cyan Cyan () is the color between green and blue on the visible spectrum of light. It is evoked by light with a predominant wavelength between 490 and 520 nm, between the wavelengths of green and blue. In the subtractive color system, or CMYK color ...

'' and '' -meter'') is an instrument for measuring " blueness", specifically the colour intensity of blue

sky The sky is an unobstructed view upward from the surface of the Earth. It includes the atmosphere and outer space. It may also be considered a place between the ground and outer space, thus distinct from outer space. In the field of astronomy, ...

. It is attributed to Horace-Bénédict de Saussure and

Alexander von Humboldt Friedrich Wilhelm Heinrich Alexander von Humboldt (14 September 17696 May 1859) was a German polymath, geographer, naturalist, explorer, and proponent of Romantic philosophy and science. He was the younger brother of the Prussian minister, p ...

. It consists of squares of paper dyed in graduated

shades of blue Varieties of the color blue may differ in hue, chroma (also called saturation, intensity, or colorfulness), or lightness (or value, tone, or brightness), or in two or three of these qualities. Variations in value are also called tints and sha ...

and arranged in a color circle or square that can be held up and compared to the

color of the sky The sky is an unobstructed view upward from the surface of the Earth. It includes the atmosphere and outer space. It may also be considered a place between the ground and outer space, thus distinct from outer space. In the field of astronomy, ...

History

De Saussure, a Swiss physicist and mountain climber, is credited with inventing the cyanometer in 1789. De Saussure's cyanometer had 53 sections, numbered cards, ranging from white to varying shades of blue (dyed with

Prussian blue Prussian blue (also known as Berlin blue, Brandenburg blue or, in painting, Parisian or Paris blue) is a dark blue pigment produced by oxidation of ferrous ferrocyanide salts. It has the chemical formula Fe CN)">Cyanide.html" ;"title="e(Cyani ...

) and then to black, arranged in a circle; he used the device to measure the color of the sky at

Geneva Geneva ( ; french: Genève ) frp, Genèva ; german: link=no, Genf ; it, Ginevra ; rm, Genevra is the List of cities in Switzerland, second-most populous city in Switzerland (after Zürich) and the most populous city of Romandy, the French-speaki ...

Chamonix Chamonix-Mont-Blanc ( frp, Chamôni), more commonly known as Chamonix, is a commune in the Haute-Savoie department in the Auvergne-Rhône-Alpes region of southeastern France. It was the site of the first Winter Olympics in 1924. In 2019, it had ...

, and

Mont Blanc Mont Blanc (french: Mont Blanc ; it, Monte Bianco , both meaning "white mountain") is the highest mountain in the Alps and Western Europe, rising above sea level. It is the second-most prominent mountain in Europe, after Mount Elbrus, and i ...

. De Saussure concluded, correctly, that the color of the sky was dependent on the amount of

particles In the physical sciences, a particle (or corpuscule in older texts) is a small localized object which can be described by several physical or chemical properties, such as volume, density, or mass. They vary greatly in size or quantity, from su ...

, water droplets and ice crystals, suspended in the atmosphere. Humboldt was also an eager user of the cyanometer on his voyages and explorations in South America.

Theory

The blueness of clear air in Earth's

atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...

is due to

Rayleigh scattering Rayleigh scattering ( ), named after the 19th-century British physicist Lord Rayleigh (John William Strutt), is the predominantly elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the ...

by nitrogen and oxygen molecules. Dry air is 78% nitrogen and 21% oxygen. Atmospheric water content ranges from 0% to 5%. When looking through clear air toward the

horizon The horizon is the apparent line that separates the surface of a celestial body from its sky when viewed from the perspective of an observer on or near the surface of the relevant body. This line divides all viewing directions based on whether i ...

, distant

sunlight Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is scattered and filtered through Earth's atmosphere, and is obvious as daylight when t ...

of all

wavelengths In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...

(colors) will generally undergo

Mie scattering The Mie solution to Maxwell's equations (also known as the Lorenz–Mie solution, the Lorenz–Mie–Debye solution or Mie scattering) describes the scattering of an electromagnetic plane wave by a homogeneous sphere. The solution takes the f ...

from spherical suspended particles. In an unpolluted sky, these spherical particles will primarily be liquid water condensed onto natural atmospheric dust grains. This is known as "wet

haze Haze is traditionally an atmospheric phenomenon in which dust, smoke, and other dry particulates suspended in air obscure visibility and the clarity of the sky. The World Meteorological Organization manual of codes includes a classification ...

". Therefore, in an unpolluted clear sky, wet haze adds white sunlight to blue Rayleigh-scattered light. More wet haze in the observer's

line of sight The line of sight, also known as visual axis or sightline (also sight line), is an imaginary line between a viewer/observer/spectator's eye(s) and a subject of interest, or their relative direction. The subject may be any definable object taken ...

results in a brighter and paler blue sky color. When looking toward the horizon, an observer looks through up to 40 times as much atmosphere compared to looking overhead. Therefore, more Mie scattering is seen when viewing parts of the sky closer to the horizon. A darker blue sky will be observed if less wet haze is in the observer's line of sight. This occurs when looking directly overhead and at a higher

altitude Altitude or height (also sometimes known as depth) is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The exact definition and reference datum varies according to the context ...

Notes

References

* *{{cite book , author = Hermann von Schlagintweit, Adolf Schlagintweit, title = Untersuchungen über die physicalische Geographie der Alpen in ihren Beziehungen zu den Phaenomenen der Gletscher, zur Geologie, Meteorologie und PflanzengeographieBarth , year = 1850 , page = 441 , url = https://books.google.com/books?id=yC4-AAAAcAAJ&pg=RA4-PA441 *

Lord Byron George Gordon Byron, 6th Baron Byron (22 January 1788 – 19 April 1824), known simply as Lord Byron, was an English romantic poet and Peerage of the United Kingdom, peer. He was one of the leading figures of the Romantic movement, and h ...

alludes to this device in his satirical verse epic

Don Juan Don Juan (), also known as Don Giovanni (Italian), is a legendary, fictional Spanish libertine who devotes his life to seducing women. Famous versions of the story include a 17th-century play, '' El burlador de Sevilla y convidado de piedra'' ...

(Canto IV, 112 ) as an ironical means of measuring the blue of

bluestocking ''Bluestocking'' is a term for an educated, intellectual woman, originally a member of the 18th-century Blue Stockings Society from England led by the hostess and critic Elizabeth Montagu (1718–1800), the "Queen of the Blues", including Eliz ...

ladies.

External links

Saussure's cyanometer
from the Royal Society of Chemistry. Accessed Nov. 19, 2010. Includes a picture of the cyanometer which now lives in the Bibliothèque de Genève, Switzerland.
''The Cyanometer Is a 225-Year-Old Tool for Measuring the Blueness of the Sky''
by Christopher Jobson
thisiscolossal.com
May 9, 2014. Atmospheric optical phenomena Meteorological instrumentation and equipment 1789 introductions 1789 in science Shades of blue Historical scientific instruments

History

Theory

See also

Notes

References

External links