Answer · confidence: partial
How did people in the 1800s measure sky blue, and what did they use?
Research question: How did people in the 1800s measure how blue the sky was before modern instruments existed, and what did they use?
The records show that the instrument people used was the cyanometer, which de Saussure invented in the 1780s, before the 1800s 1. It was a colour chart of blue hues running from very light blue to dark blue 5, with 52 hues arranged on a graded circular scale 13, and it was calibrated against a companion instrument for air transparency 8. It relied on the observer's eyesight and ability to discern shades, not an objective quantity such as pigment concentration 11. Humboldt used it during his South American travels to measure the intensity of the sky's blue 4, and Arago built a different cyanometer based on chromatic polarisation 6. The facts do not describe the modern instruments that the question contrasts with, nor give the detailed procedure for taking readings.
Checked 2026-10-18. Only documented and supported facts are used.
Dig deeper on this questionSources
[1] supported
In the 1780s, de Saussure invented the cyanometer, an instrument for measuring the blueness of the sky.
"In the 1780s, de Saussure invented the cyanometer that was subsequently used by Humboldt on his research travels."Material Blue (2017)
[2] supported
The cyanometer was used to determine how blue the sky was at different altitudes.
"It served to determine the blueness of the sky at various altitudes."Material Blue (2017)
[3] documented
Horace Benedict de Saussure invented the cyanometer to get a relative measure of how blue the sky was.
"To get a relative measure onhow blue the sky was, de Saussure invented a device he called cyanometer."How Blue is the Sky? : Horace B. de Saussure and his cyanometer – its invention, use and legacy (2020)
[4] documented
Before modern instruments, Alexander von Humboldt used Horace Bénédict de Saussure's cyanometer during his South American travels to measure the intensity of the sky's blue.
"During his travels in South America, Humboldt used Saussure’s cyanometer to determine the intensity of the blue colour of the sky."Himmelsblau. Bemerkungen zum Thema „Farben“ in Humboldts Alterswerk Kosmos. Entwurf einer physischen Weltbeschreibung (2015)
[5] supported
The cyanometer was a colour chart of blue hues, running from very light blue to dark blue.
"It is a colour chart containing dierent hues of blue, starting with very lightblue, ranging all the way to dark blue."How Blue is the Sky? : Horace B. de Saussure and his cyanometer – its invention, use and legacy (2020)
[6] supported
François Arago invented a different cyanometer, based on chromatic polarisation, which Humboldt later discussed with him.
"Later he corresponded about this instrument with his friend François Arago who had invented a cyanometer based on chromatic polarisation."Himmelsblau. Bemerkungen zum Thema „Farben“ in Humboldts Alterswerk Kosmos. Entwurf einer physischen Weltbeschreibung (2015)
[7] supported
While climbing the Alps, de Saussure noticed that the sky looked darker and more intensely blue at higher altitudes, which motivated his measurement.
"When deSaussure climbed the Alp mountains he noticed that the sky turned darkerwith a more intense blue, at higher altitudes."How Blue is the Sky? : Horace B. de Saussure and his cyanometer – its invention, use and legacy (2020)
[8] supported
The cyanometer was a paper instrument designed by Horace Bénédict de Saussure to measure the blueness of the sky, and it was calibrated against a companion instrument for air transparency.
"paper instruments designed to measure, respectively, the blueness of the sky and the transparency of the air (Fig. 3) —the students were able to grasp how much the two were entwined, the former being calibrated on the latter"Experimenting with History (2023)
[9] supported
Saussure's cyanometer was the instrument used to gauge sky blue, and Humboldt shared this interest in the sky's blue with Saussure and other figures such as Goethe and Caspar David Friedrich.
"The present paper focuses on Humboldt’s interest in the blue colour of the sky, which he shared with artists, writers and scientists like Johann Wolfgang von Goethe, Christian Gottfried Lichtenberg, Caspar David Friedrich and Horace Bénédict de Saussure."Himmelsblau. Bemerkungen zum Thema „Farben“ in Humboldts Alterswerk Kosmos. Entwurf einer physischen Weltbeschreibung (2015)
[10] supported
The cyanometer gave a recordable measurement of the sky's blueness at the time of each observation.
"With this simple device de Saussurecould get a recordable measurement on how blue the sky was at the timefor the observation."How Blue is the Sky? : Horace B. de Saussure and his cyanometer – its invention, use and legacy (2020)
[11] documented
The cyanometer measured sky blueness by relying on the observer's eyesight and ability to discern shades of color, not on an objective quantity such as a concentration of pigment.
"how their making relied not on supposed objective quantities, such as a concentration of pigment, but on the eyesight of the observer and their ability to discern different shades of colors"Experimenting with History (2023)
[12] supported
Saussure's cyanometer was used by Horace Bénédict de Saussure, an eighteenth-century savant, to quantify atmospheric phenomena.
"One project aimed at reproducing some instruments designed and used by the eighteenth-century savant Horace Bénédict de Saussure to quantify natural phenomena pertaining to the physics of the atmosphere."Experimenting with History (2023)
[13] supported
Horace-Bénédict de Saussure invented the cyanometer, a simple gauge with 52 hues of blue arranged from light to dark on a graded circular scale, to measure how blue the sky is.
"He invented a rather simple gage that consisted of 52 different hues of blue arranged from light to dark on a gradated circular scale."Cyanometer — Colour Studies
[14] documented
The cyanometer was a simply constructed measuring instrument used to determine the blueness of the sky.
"The cyanometer is a simply constructed measuring instrument that enables a determination of skyblue."Himmelblau – das Cyanometer des <i>Horace-Bénédict de Saussure</i> (1740–1799) (2011)
[15] supported
The cyanometer helped confirm that the colour of the sky changes with elevation.
"His device, called a cyanometer, helped to confirm that the sky’s colour changed with the elevation."Cyanometer — Colour Studies
[16] supported
Simultaneous cyanometer readings differed by altitude: a whiter shade of 7 at Geneva versus a dark blue of 1–2 from the summit.
"Simultaneous measurements gave a whiter shade of 7 at Geneva but a dark blue of 1–2 from the summit."Sixteen shades of blue; the use of a digital camera as a cyanometer (2026)
[17] documented
The cyanometer consisted of a circular color scale running in equal steps from white through blue (Prussian blue) to black.
"It consists of a color-scale that is arranged circularly going in equal steps from white to blue (Prussian blue) and finally into black."Himmelblau – das Cyanometer des <i>Horace-Bénédict de Saussure</i> (1740–1799) (2011)
[18] documented
Its inventor, Horace-Bénédict de Saussure, held that the sky's azure depended on the amount of opaque vapors in the atmosphere linked to meteorological phenomena.
"According to its inventor - Horace-Bénédict de Saussure - the azure is determined by the amount of so called opaque vapors in the atmosphere associated with meteorological phenomena."Himmelblau – das Cyanometer des <i>Horace-Bénédict de Saussure</i> (1740–1799) (2011)