A cyanometer (cyan-o-meter) aims to answer the question ‘how blue is the sky today?’ by assessing its blueness. Its inventor Bénédict de Saussure, considered as the founder of alpinism (mountaineering), was also the first man to climb the Mont Blanc.
In the 18th century, a Swiss physicist and inventor designed a tool to measure the blueness of the sky and unveil the secret of its hue variations. The cyanometer was born.
What for? Study, observation and comparison of the different shades of blue in the sky. Thanks to this important tool, we could understand that the color of the sky was linked to the presence of particles and water in the atmosphere.
Indeed: water absorbs the longest wavelengths composing natural light (red, orange, yellow), so only the short wavelengths (green, blue, purple) are reflected in water. Note that the infrared to ultraviolet spectrum of light is composed of the same colours as in a rainbow.
In short, the sky is blue because of the atmosphere. But how blue? Well, it depends on the atmosphere, the level of humidity, and that’s when the cyanometer makes his entry. Read more below.
Cyanometer on Wikipedia: ‘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.
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) and then to black, arranged in a circle; he used the device to measure the color of the sky at Geneva, Chamonix and Mont Blanc. 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 indicates transparency and the amount of water vapour.’
Source: Cyanometer @Wikipedia