Discover the Cyanometer, the Device Invented in 1789 Just to Measure the Blueness of the Sky

Eng­lish astronomer and physi­cist James Jeans’ 1931 essay “Why the Sky is Blue” has become a clas­sic of con­cise expos­i­to­ry writ­ing since it was first pub­lished in a series of talks. In only four para­graphs and one strik­ing­ly detailed, yet sim­ple anal­o­gy, Jeans gave mil­lions of stu­dents a grasp of celes­tial blue­ness in prose that does not sub­sti­tute nature’s poet­ry for sci­en­tif­ic jar­gon and dia­grams.

Over a hun­dred years ear­li­er, anoth­er sci­en­tist cre­at­ed a sim­i­lar­ly poet­ic device; in this case, one which attempt­ed to depict how the sky is blue. Swiss physi­cist Horace Béné­dict de Saus­sure’s 1789 Cyanome­ter, “a cir­cle of paper swatch­es dyed in increas­ing­ly deep blues, shad­ing from white to black,” Sarah Laskow writes at Atlas Obscu­ra, “includ­ed 52 blues… in its most advanced iter­a­tion,” intend­ed to show “how the col­or of the sky changed with ele­va­tion.”

Saussure’s fas­ci­na­tion with the blue­ness of the sky began when he was a young stu­dent and trav­eled to the base of Mont Blanc. Over­awed by the sum­mit, he dreamt of climb­ing it, but instead used his fam­i­ly’s wealth to offer a reward to the first per­son who could. Twen­ty-sev­en years lat­er, Saus­sure him­self would ascend to the top, in 1786, car­ry­ing with him “pieces of paper col­ored dif­fer­ent shades of blue, to hold up against the sky and match its col­or.”

Saus­sure was tak­en with a phe­nom­e­non report­ed by moun­taineers: as one climbs high­er, the sky turns a deep­er shade of blue. He began to for­mu­late a hypoth­e­sis, the Roy­al Soci­ety of Chem­istry Explains:

Armed with his tools and a small chem­istry set, he trekked round the val­leys and beyond. As his trips car­ried him ever high­er, he puz­zled about the colour of the sky. Local leg­end had it that if one climbed high enough it turned black and one would see, or even fall into, the void — such ter­rors kept ordi­nary men away from the peaks. But to Saus­sure, the blue colour was an opti­cal effect. And because on some days the blue of the sky fad­ed imper­cep­ti­bly into the white of the clouds, Saus­sure con­clud­ed that the colour must indi­cate its mois­ture con­tent. 

At the top of Mont Blanc, the physi­cist mea­sured what he deemed “a blue of the 39th degree.” The num­ber meant lit­tle to any­one but him. “Upon its inven­tion, the cyanome­ter rather quick­ly fell into dis­use,” as Maria Gon­za­lez de Leon points out. “After all, very lit­tle sci­en­tif­ic infor­ma­tion was giv­en.”

The tool did, how­ev­er, accom­pa­ny the famed geo­g­ra­ph­er Alexan­der von Hum­boldt across the Atlantic, “to the Caribbean, the Canary Islands, and South Amer­i­ca,” writes Laskow, where Hum­boldt “set a new record, at the 46th degree of blue, for the dark­est sky ever mea­sured” on the sum­mit of the Andean moun­tain Chimb­o­ra­zo. This would be one of the only notable uses of the poet­ic device. “When the true cause of the sky’s blue­ness, the scat­ter­ing of light, was dis­cov­ered decades lat­er, in the 1860s, Saussure’s cir­cle of blue had already fall­en into obscu­ri­ty.”

via Messy­Nessy/Colos­sal

Relat­ed Con­tent: 

A 900-Page Pre-Pan­tone Guide to Col­or from 1692: A Com­plete Dig­i­tal Scan

The Vibrant Col­or Wheels Designed by Goethe, New­ton & Oth­er The­o­rists of Col­or (1665–1810)

A Vision­ary 115-Year-Old Col­or The­o­ry Man­u­al Returns to Print: Emi­ly Noyes Vanderpoel’s Col­or Prob­lems

Josh Jones is a writer and musi­cian based in Durham, NC. Fol­low him at @jdmagness

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