Discoveries
The cyanometer
Horace-Bénédict de Saussure made a painted circle of blues so the colour of the sky could be named as a number. The instrument is slight. The question it asked is not.
Discovery
There are instruments that force a new fact into the world, and instruments that only give a name to something everyone already looks at. The cyanometer belongs to the second kind. Horace-Bénédict de Saussure, late in the eighteenth century, painted a circle of blues, from white to a near-black indigo, and took it into the open air. The sky was asked to match a number.
The sky was asked to match a number.
A scale instead of a mood
The point was not to make the sky more beautiful. The point was to stop treating blue as a mood. Travellers already knew that the colour changed with height, weather, and the hour. What they lacked was a way of saying how much. De Saussure’s circle made the change comparable: a reading on the lake, a reading on the ridge, a reading after rain.
The published plate of 1790 is only a sketch of the idea. The working instruments had more stops. Even so, the engraving is enough. It looks almost like a game, a painted wheel a child might cut from card. That slightness is part of its force. Someone had to decide that the colour of the air was worth measuring.
What remains interesting is not the number itself. It is the courtesy of looking twice. The sky does not become a different sky because a circle of paint is held against it. It becomes a sky that can be written down.