Essay · Plate VII

The seven colours were never merely decoration

A prism did not make colour beautiful; it made colour answerable to measurement.

In a darkened London chamber, the useful question was not whether a beam pleased the eye. It was whether its colours kept their order after passing through glass. The answer turned a familiar ornament of rain into an experiment one could repeat.

Order is the evidence

The red ray bent least; the blue travelled farther from its former course. That small, stubborn ranking made the spectrum a record rather than a flourish. Every interval carried a place, and every place could be tested against the next.