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 the day before the wedding the bridegroom came to his house in a full suit of black, as he thought. He was greatly displeased to see him appear in mourning on such an occasion, and took an opportunity to remonstrate with him on the subject. But what was his surprise to hear his daughter exclaim, in loud tones of counter remonstrance, that she had rarely seen her lover in a coat of such a pretty colour, and that her father's eyes must deceive him on this as on many other occasions. Scott's father, his maternal uncle, one of his sisters, and two of his sons had the same defect of sight. Dr. Mitchell mentions the case of a naval officer who for his ordinary uniform chose a blue coat and waistcoat and red trousers, fully believing that they were all of the same colour. A tailor of Plymouth, also mentioned by Dr. Mitchell, mended a black silk waistcoat with a piece of crimson, and another put a red cloth collar to a blue coat. Several celebrated men have suffered from colour-blindness. Amongst them may be mentioned Dugald Stewart, the great philosophical writer; John Dalton, the originator of the atomic theory; and Troughton, the philosophical instrument maker. Dugald Stewart first discovered the defect on hearing a member of his family admire the contrast of colour between the leaves and fruit of a Siberian crab-tree, while he could see no difference between them, except in point of form and size. John Dalton could not distinguish blue from crimson, and he could only see two colours, blue and yellow, in the prismatic spectrum. Troughton could see no difference between dark crimson, bright orange, and yellow—in fact, he could only distinguish blue from yellow.

In an article on this subject, published in the Magasin Pittoresque for 1846, a Swiss physician gives some interesting examples, which are worth repeating. In the solar spectrum obtained by passing a ray of light through a triangular prism, and which is composed of