In former days, not much more than a century ago, the existence of colour blindness, as it is now named, was a matter of great curiosity, and in the Philosophical Transactions of the Royal Society of 1777, the case of a shoemaker named Harris is described by a Mr. Huddart, who travelled all the way from London to the Midlands on purpose to see if all the alleged facts regarding the patient were true. Harris mistook orange for green, brown he called black, and he was unable to distinguish between red fruits and the surrounding green leaves. At first, colour blindness was called Daltonism, from the fact that the great chemist Dalton suffered from it, and investigated the variation which he found existed in his vision from that of the majority of his fellow-creatures. It was in 1794 that Dalton described his own case of colour blindness. He was quite unaware of his defect till 1792, when he was convinced of its existence from his observations of a pink geranium by candle-light. “The flower,” he says, “was pink; but it appeared to me almost an exact sky-blue by day. In candle-light, however, it was astonishingly changed, not having any blue in it; but being what I call a red colour which forms a striking contrast to blue.” He goes on to remark that all his friends except his _brother_ (mark this relationship), said: there was not any striking difference in the two colours by the two lights. He then investigated his case by the solar spectrum, and became convinced that instead of having the normal sensations, he only had two or at most three. These were yellow, blue, and perhaps purple. In yellow, he included the red, orange, yellow, and green of others, and his blue and purple coincided with theirs. He says, that “part of the image which others call red, appears to me little more than a shade or defect of light; after that, the orange, yellow and green seem _one_ colour, which descends pretty uniformly from an intense and a rare yellow, making what I should call different shades of yellow. The difference between the green part and the blue part is very striking to my eye, they seem to be strongly contrasted. That between the blue and purple much less so. The purple appears to be blue much darkened and condensed.” Dalton said a florid complexion looked blackish-blue on a white ground. Blood looked like bottle green, grass appeared very little different from red. A laurel leaf was a good match to a stick of sealing-wax. Colours appeared to him much the same by moonlight as they did by candle-light. By the electric light and lightning, they appeared as in day light. Some browns he called red, and others black. Mr. Babbage, in Scientific London (1874), gives an account of Dalton’s presentation at Court.