Physiologists consider that there are two kinds of colour-blindness,—one where only two colours are seen, the other where more than two are perceptible. Daubeny Turberville, an oculist of Salisbury, mentions a case of the former, in which a young girl, like the Maryport shoemaker mentioned by Brewster, could only distinguish between black and white, everything between the two being of different shades of grey. This girl, singularly enough, could see to read in twilight a quarter of an hour after her companions. This sharpness of sight appears to be not at all uncommon amongst those who are colour-blind. Spurzheim mentions the ease of a whole family who were afflicted in the same way as Turberville’s patient. All the male members of Troughton’s family were equally incapable of distinguishing any colours but blue and yellow. The cases of colour-blindness where more than two colours are distinguishable, are much more common. Goethe, the great German poet, who dabbled a great deal in optics, knew two young men who, although they possessed powerful sight, and could distinguish between white, black, grey, yellow, and orange, were at a loss when the shades between dark red and rose-colour were in question. A piece of dried carmine appeared bright red to them, and a faint carmine hue on a white shell, and a rose-leaf, light blue; the leaves of trees and grass appeared yellow, and they confounded rose-colour, blue, and violet together. Goethe supposed them to be incapable of perceiving blue and its several hues, and called their defect by a high sounding Greek name, _akyanoblepsy_, or blue-blindness. Péclet mentions two other persons, also brothers, who likewise were incapable of distinguishing between blue, violet, and rose-colour. Like Professor Whewell, they confounded the dull scarlet of the trousers of the French infantry with the leaves of the trees. Yellow appeared to them more brilliant than any other colour. Doctor Sommer and his brother could not distinguish between red and its derivatives and other colours; they could only distinguish between yellow, blue, white, and black. Doctor Nicholl mentions a child that could only see red, yellow, and blue, in the spectrum. It could distinguish green, but called it brown when it was dark, and pink when it was pale. The same physiologist knew a man who called red green, and brown dark green. A young lady who was an amateur artist, could not perceive a piece of scarlet cloth hanging on a hedge that was close to her, although others could see it plainly half a mile off. One day she gathered, as a great curiosity, a lichen which she supposed to be of a bright scarlet hue, but which was in reality of a beautiful green. Another time she could see no difference between carmine and prussian blue. A gardener living at Clydesdale, who began life as a weaver, was compelled to give up his first trade because in daylight he confounded all light colours; yellow and its varieties he could distinguish