Mr. Scott has described, in the Philosophical Transactions, his own defect in perceiving colours. He states that he does not know any _green_ in the world; that a _pink_ colour and a _pale blue_ are perfectly alike; that he has often thought a _full red_ and a _full green_ a good match; that he is sometimes baffled in distinguishing a _full purple_ from a _deep blue_, but that he knows light, dark, and middle _yellows_, and all degrees of _blue_ except _sky-blue_. “I married my daughter to a genteel, worthy man, a few years ago; the day before the marriage, he came to my house dressed in a new suit of fine cloth clothes. I was much displeased that he should come, as I supposed, in _black_, and said that he should go back to change his colour. But my daughter said, No, no; the colour is very genteel; that it was my eyes that deceived me. He was a gentleman of the law, in a fine, rich, claret-coloured dress, which is as much black to my eyes as any black that ever was dyed.” Mr. Scott’s father, his maternal uncle, one of his sisters, and her two sons, had all the same imperfection. Dr. Nichol has recorded a case where a naval officer purchased a _blue_ uniform coat and waistcoat with _red_ breeches to match the blue, and Mr. Harvey describes the case of a tailor at Plymouth, who on one occasion repaired an article of dress with _crimson_ in place of _black_ silk, and on another patched the elbow of a _blue_ coat with a piece of _crimson_ cloth. It deserves to be remarked that our celebrated countrymen, the late Mr. Dugald Stewart, Mr. Dalton, and Mr. Troughton, have a similar difficulty in distinguishing colours. Mr. Stewart discovered this defect when one of his family was admiring the beauty of a Siberian crab-apple, which he could not distinguish from the leaves but by its form and size. Mr. Dalton cannot distinguish _blue_ from pink, and the solar spectrum consists only of two colours, _yellow_ and _blue_. Mr. Troughton regards _red ruddy pinks_, and brilliant _oranges_, as _yellows_, and _greens_ as _blues_, so that he is capable only of appreciating _blue_ and _yellow_ colours.