Note 46 — THE TRAVELS OF MARCO POLO

Yule’s colour-blindness was one of the cases in which Dalton, the original investigator of this optical defect, took special interest. At a later date (1859) he sent Yule, through Professor Wilson, skeins of coloured silks to name. Yule’s elder brother Robert had the same peculiarity of sight, and it was also present in two earlier and two later generations of their mother’s family—making five generations in all. But in no case did it pass from parent to child, always passing in these examples, by a sort of Knight’s move, from uncle to nephew. Another peculiarity of Yule’s more difficult to describe was the instinctive association of certain architectural forms or images with the days of the week. He once, and once only (in 1843), met another person, a lady who was a perfect stranger, with the same peculiarity. About 1878–79 he contributed some notes on this obscure subject to one of the newspapers, in connection with the researches of Mr. Francis Galton, on Visualisation, but the particulars are not now accessible.