cyanometer

thumb|right|A cyanometer by Horace-Bénédict de Saussure (from the collection of ''Musée d'histoire des sciences de la Ville de Genève) thumb|right|An artwork in Ljubljana, Slovenia, inspired by a cyanometer A cyanometer (from cyan and -meter'') is an instrument for measuring "blueness", specifically the colour intensity of blue sky. It is attributed to Horace-Bénédict de Saussure and Alexander 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.

== History == thumb|Engraving of de Saussure's cyanometer, merely for illustrative purposes, published in the ''Memoires de l'Academie Royale des Sciences'' (1790) Horace-Bénédict de Saussure, a Swiss physicist and mountain climber, is credited with inventing the cyanometer in the 1760s. De Saussure's cyanometer was divided into colored, numbered sections, ranging from white to gradually darker shades of blue, dyed with Prussian blue and arranged in a circle. The cyanometers were manually produced with a predefined recipe of watercolor concentration for each section, and then distributed to friends and fellow naturalists to gather more observations. In an article from 1790, de Saussure presents an illustration of a wheel with 40 stops, though clarifies that it serves merely to give the reader "an idea of its form"; the actual cyanometer had 53 stops (or "degrees"), starting with white as 0 and black as 52.