A cyanometer) is an instrument for measuring

Measuring instrument

In the physical sciences, quality assurance, and engineering, measurement is the activity of obtaining and comparing physical quantities of real-world objects and events. Established standard objects and events are used as units, and the process of measurement gives a number relating the item...

 'blueness', specifically the colour intensity of blue sky

Sky

The sky is the part of the atmosphere or outer space visible from the surface of any astronomical object. It is difficult to define precisely for several reasons. During daylight, the sky of Earth has the appearance of a pale blue surface because the air scatters the sunlight. The sky is sometimes...

. It is attributed to Horace-Bénédict de Saussure

Horace-Bénédict de Saussure

200px|thumb|Portrait of Horace-Bénédict de Saussure Horace-Bénédict de Saussure was a Genevan aristocrat, physicist and Alpine traveller, often considered the founder of alpinism, and considered to be the first person to build a successful solar oven.-Life and work:Saussure was born in Conches,...

 and Alexander von Humboldt

Alexander von Humboldt

Friedrich Wilhelm Heinrich Alexander Freiherr von Humboldt was a German naturalist and explorer, and the younger brother of the Prussian minister, philosopher and linguist Wilhelm von Humboldt...

. It consists of squares of paper dyed in graduated shades of blue and arranged in a color circle or square that can be held up and compared to the color of the sky.

de Saussure is credited with inventing the cyanometer in 1789. de Saussure's cyanometer had 53 sections, ranging from white to varying shades of blue (dyed (with Prussian blue

Prussian blue

Prussian blue is a dark blue pigment with the idealized formula Fe718. Another name for the color Prussian blue is Berlin blue or, in painting, Parisian blue. Turnbull's blue is the same substance but is made from different reagents....

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

Geneva

Geneva In the national languages of Switzerland the city is known as Genf , Ginevra and Genevra is the second-most-populous city in Switzerland and is the most populous city of Romandie, the French-speaking part of Switzerland...

, Chamonix

Chamonix

Chamonix-Mont-Blanc or, more commonly, Chamonix is a commune in the Haute-Savoie département in the Rhône-Alpes region in south-eastern France. It was the site of the 1924 Winter Olympics, the first Winter Olympics...

 and Mont Blanc

Mont Blanc

Mont Blanc or Monte Bianco , meaning "White Mountain", is the highest mountain in the Alps, Western Europe and the European Union. It rises above sea level and is ranked 11th in the world in topographic prominence...

. de Saussure concluded, correctly, that the color of the sky was dependent on the amount of suspended particles in the atmosphere.

Humboldt was also an eager user of the cyanometer on his voyages and explorations in South America.

The blueness of the atmosphere

Atmosphere

An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...

 indicates transparency and the amount of water vapour.

External links

• Saussure's cyanometer, from the Royal Society of Chemistry. Accessed Nov. 19, 2010. Includes a picture of the cyanometer.