Roundel for use in optical experiments Product:Postcard King Henry IV of England

King Henry IV of England

Wolverhampton Wanderers 3 vs

towards two young ladies

Engraved by Thomas Hodgetts

Roundel for use in optical experiments Product:Postcard King Henry IV of EnglandPlate 9 figure 2 from the paper "New experiments on the ocular spectra of light and colours", by Robert Waring Darwin, Philosophical Transactions of the Royal Society, vol. 76 (1786), pp. 313 348. Roundel intended for use in exploring colour perception. In the written experiment circular pieces of silk are overlaid in the sequence blue (outer), yellow, pink, green and indigo (inner) with a central spot. "look steadily for a minute on this central