Researches in Colour Vision and the Trichromatic Theory. By Sir William de W. Abney Pp. xi + 418 + 5 plates. (London: Longmans, Green and Co., 1913.) Price 21s. net.

It can perceive full color in images which, according to classical theories, should be monochromatic The eye has recently been found to be an instrument of wonderful and unsuspected versatility.