I saw this and had to share: A cyanometer is an instrument for measuring the intensity of blue in the sky. Its invention in 1789 is attributed to the mountain climber and physicist Horace-Bénédict de Saussure and Alexander von Humboldt. De Saussure's cyanometer consists of 53 sections, numbered cards, ranging from white to different shades of blue (tinted with Prussian blue) and then to black, arranged in a circle. The idea of ​​recording the hues of the sky occurred to him on one of his trips climbing Mont Blanc. He, as well as other mountain climbers, had noticed that as they climbed higher, the sky became a darker blue. Saussure demonstrated that the sky darkened as one ascended. He was also convinced that the color of the sky was an optical effect and argued that, since the blue faded subtly into the white of the clouds, the color must be an indicator of the moisture content of the air.
De Saussure concluded that the color of the sky depended on the amount of particles, water droplets and ice cry…