The glass is now withdrawn, and the ordinary white light falls upon the skeins in my hand. They are a strangely variegated lot as now seen; we have green shades, yellows, and browns, and greys. Such a variety would tell me that I was colour deficient, but would not be, perhaps, decisive as to what was the exact character of the deficiency. For if the pink glass is placed in front of the lantern you will find the same matches, with one or two exceptions, might have been made. The blue-green glass is once more placed in the beam, and this time I match the pink skein with the wools. A certain number are picked out, and the audience will agree with me that the matches are fair ones. When, however, the glass is withdrawn from the light and we see what colours have been selected, we find that they consist of pale blues, mauves, pinks of various shades, and cerise, and violet. The red in the pink did not affect my eyes any more than would it the red-blind. I am evidently then in this light red-blind, for if the pink glass replaces the blue-green, the matches are impossible. While this coloured light is illuminating the heap I will make matches again. When made, the white light is again thrown on the selected skeins, and this time we have bluish-green and neutral tint together with pinks. The reason of this is evident, there is no green visible; the bluish-green contains besides blue a certain amount of yellow, which, in its turn, contains red, and the grey must be pink. To the green-blind, for reasons already given, the blue-green looks white, as does the pink, and therefore the two are matched together. The grey is also degraded white to him, and therefore he also matches that with them. The matches which the violet-blind would make can be well exemplified by placing in the beam of light a yellow glass, or a glass coated with collodion in which “brilliant yellow” has been dissolved. By this plan, then, we can in some measure produce the effect of colour blindness on ourselves, and very interesting it is to compare theory with the results obtained in this manner. There is no necessity to have recourse to the electric light for this purpose. If matches are made with such media held before the eyes in ordinary daylight, the same results will be obtained. I have often examined through these same media the matches made by the colour blind, and been able at once to settle the nature of the defective vision from which they were suffering. It must be remembered that the colours transmitted through these two glasses are not _absolutely like_ the whites which the two classes of colour blind see respectively, though they approach it.