Departures of note

In 1768 the Académie published a 1765 paper by Patrick d'Arcy on the duration of visual impressions. He built a mill in his garden that whirled a burning coal, measured the time for one rotation when it appeared as a full fiery circle from about 50 m in the dark, and, with an observer who had better eyesight, recorded a mean duration of 0.13 seconds.

Patrick d'Arcy planned further experiments to test differences among individuals, colors, viewing distances and light intensity. His experiments are linked to persistence‑of‑vision theories that later influenced devices such as the thaumatrope and the development of cinematography, though many historians have overlooked his work.