"Pardon me," replied the professor, laughing also, "I never said you both did not. Had that been the case, you probably would not have been in opposition to each other. But I have been using my own eyes since we stood here, and I see which of you has the defect. One of you possesses the organ of colour (as we call it) in a full degree; the other does not possess it at all. It lies here." Dr. Macpherson raised his fingers to his eyebrow, and pointed out a spot near its middle. The colonel and Oliver Jupp immediately passed their fingers over their eyebrows, somewhat after the manner of a curious child. Oliver's eyebrows were prominent; the colonel's remarkably flat. "You can testify by experiment whether I am right or wrong, Colonel West; but I give it as my opinion that you are not able to distinguish colours." For some moments the colonel could not find his tongue. "I never heard of such a thing in all my life!" cried he. "Do you mean to say that I can see the blue sky" (turning his face upwards), "and not know it's blue?" "You know it is blue, and call it blue, because you have heard it so called all your life," returned the undaunted professor. "But, if half the sky were blue and half green, you would not be able to say which was the green half and which the blue." "That caps everything," retorted the colonel, in high good-humour. "It's a pity my wife can't hear this; she'd shake hands with you at once. She has, you must know, a couple of garden parasols: one green, the other blue. If she sends me indoors for the green, she says I bring her the blue; and if for the blue, I bring the green. She sets it down to inattention, and lectures me accordingly." "You could not have given us a better confirmation that my opinion is correct," said Professor Macpherson, glancing at the group around. "Your wife has set this down to inattention, you say, colonel. May I ask what you have set it down to?" "I? Not to anything. I never troubled myself to think about it." The learned gentleman rubbed his hands with satisfaction. "What you acknowledge is so true to nature, colonel! Those who, like you, are affected with colour-blindness, can rarely be brought to believe in their own defect. It is a fact that the greater portion of them _are not conscious of it_; they really don't know that they cannot distinguish colours. Some few have perhaps a dim idea that they are not so quick in that particular as others, but they never think of questioning the cause. To use your own expression, it does not trouble them. I understand you maintain that on the night of the accident the usual light was up--green?" "Yes," said the colonel. "They exhibit the green light always at Coombe Dalton station, to enforce caution, on account of the nasty turning just after passing it. I maintain, as you say, that the customary green light was shown that night."