‘J’écartai du ciel l’azur, qui est du noir…’
– Arthur Rimbaud, ‘Delirium’

WANDERING AROUND the Musée d’art et d’histoire on a visit to the Swiss city of Neuchâtel, I stopped for a while in front of the monumental painting Effet de soleil sur les Hautes Alpes du Valais en face de la chaîne du Mont-Rose, 1843–44. It was the work of Alexandre Calame (1810–64), a Swiss painter who made Alpine scenes his calling card. White-capped mountains formed an extended backdrop to a range of bare brown slopes guarding an untroubled turquoise lake, the entire upper half of the painting being given over to a clear blue sky depicted in subtle gradations of that colour. It was the sky rather than the barren scene of rocks and mountains which caught my eye, and the empirically informed way in which Calame had rendered its nuances as the bleu bleuet became powdery and then deepened into ultramarine and cyan above the range of snow-covered peaks in the distance.

What the German poet and mining engineer Novalis called ‘atmosphereology’ had matured by the nineteenth century into meteorology – a new science that caught the public imagination. Every new science comes with its own instruments, and one that was popular in Calame’s day was the cyano­meter. It was an invaluable device for landscape artists too. This simple handheld analogue instrument registers the intensity of blueness of the atmosphere. It had been developed a generation before by the remarkable eighteenth-century Swiss geologist and inventor Horace-Bénédict de Saussure, and became well-known ...