Colour Measurement and Mixture

As dusk erases the colours of an autumn garden, a glow-worm still shines among the flowers. Why can the eye see its tiny light when the blossoms have lost theirs?

In this late-nineteenth-century study, Sir William de Wiveleslie Abney begins with familiar sights to uncover a difficult question: what is colour, and how can it be measured? Light reflected from a flower depends on its surface and its illumination; what we see also depends on the eye. Abney sets out to control these shifting conditions, then to give colour measurable constants—hue, luminosity and purity—using experiments with spectra, pigments and mixed lights. The task is more than naming shades: it is finding a standard for a sensation that changes with both the light and the observer. Can colour be made to yield numbers without losing its wonder?

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