Firstly, he was a Quaker, and would not wear a sword, which is an indispensable appendage to ordinary Court-dress. Secondly, the robe of a Doctor of Civil Laws was known to be objectionable on account of its colour--scarlet, being one forbidden by the Quakers. Luckily, it was recollected that Dalton was affected with that peculiar colour blindness which bore his name, and that as cherries and the leaves of a cherry-tree were to him of the same colour, the scarlet gown would present no extraordinary appearance. So perfect evidence was the colour blindness, that the most modest and simple of men, after having received the Doctor’s gown at Oxford, actually wore it for several days in happy unconsciousness of the effect he produced in the street. The rest of the description we need not reproduce. Both the above cases we shall see shortly come under the category of red-blindness in the Young theory. Recent investigations tell us that such colour blindness is by no means rare, nor can it have been then. Statistics, derived from carefully carried out examinations made in various parts of the world by an approved method of testing, show that about four out of every hundred males suffer from some deficiency in colour perception, but that so far as the more limited statistics regarding them are to be depended upon, only about four out of every 1000 women suffer in the same manner. Colour blindness in a healthy subject is usually hereditary, and is always congenital. It is curious to trace back in some instances the colour blindness, where it is to be found, in a family. It often happens that colour blindness--as the gout is said to do--skips a generation. This is usually traced to the fact that the generation skipped is through the mother. Thus, the maternal grandfather may be colour blind, as may be the grandsons, but the mother will very frequently have perfectly normal vision for colour. On the other hand, the paternal grandfather may have defective colour perception, and this may be inherited both by the grandsons and the father. The remark made by Dalton regarding his brother’s eyesight points to the fact that his own colour blindness was probably hereditary. Deaf mutes, Jews and Quakers, seem to be more liable to colour blindness than other people, statistics giving them 13·7, 4·9, and 5·9 as the percentages. It may be well to point out that the deficiency in colour perception to which we are alluding is totally distinct from that which may arise from disease. This last form has such marked characteristics of its own that it can at once be distinguished from the congenital form.