Note 105 — Chapter IV · ADOLESCENCE—1844 TO 1847—ÆT. 13-16.

So far as I can recall the order in which his ideas on this subject were developed, the phenomena of complementary colours came first, then the composition of white light, then the mixture of colours (not of pigments), then polarisation and the dark lines in the spectrum, and about the same time “the art of squinting,” stereoscopic drawing, etc., then colour-blindness, the yellow spot on the retina, etc.