Roundel for use in optical experiments Size:XL: 80 x 80cm the purple martin

the purple martin

View of Blackfriars Bridge and St Paul's Cathedral

Campbell (second from the left)

( Mr Punch)

Two dogs are seen at left

Roundel for use in optical experiments Size:XL: 80 x 80cm the purple martinPlate 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