Roundel for use in optical experiments Size:XL: 80 x 80cm Campbell (second from the left)

Campbell (second from the left)

One putto holds a scroll bearing the legend: 'Ecce Philosophorum Princeps'

View of Blackfriars Bridge and St Paul's Cathedral

Interior view of the theatre

Roundel for use in optical experiments Size:XL: 80 x 80cm Campbell (second from the left)Plate 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