gives him the desired clue, and, though colour-blind, he passes the test. The material is the best possible, as it will not fade like all dyed substances, and therefore all records made with one set of apparatus will be uniform. Again, a coloured light has none of the accessory qualities which enable the colour-blind to pass through other tests. Thus many dichromics will call the yellow glass red or green, who would not think of putting a yellow with a green or red wool, on account of the difference in luminosity. He will, in the same way, if told to pick out colours in the Classification Test to match the colour of the light shown, have to depend upon his colour-perception. This is a useful method with nervous and undecided candidates. The objection to it is that it cannot be carried out in the dark or in a dark room. The Test is not open to any of the objections which may be urged against the method of simply naming colours, because the character and intensity of the colour may be changed at will. The method is better than that of direct comparison, because the candidate is forced to use his colour-perception, and has to compare the colour seen with previous impressions of colour in his mind. By the use of neutral glasses, etc., I have obviated the fallacy of the method of naming colours (namely, that these can be distinguished by their saturation and luminosity), and forced the individual to depend upon his colour-perception, and not upon some other accessory quality of the object seen. No amount of coaching will enable a colour-blind person to pass this test, whilst almost any other may be passed in this way. I have tried on many occasions to coach a man so as to pass my lantern, and without success. The combinations are so numerous that the only result is to make the colour-blind man nervous and doubtful and more easily detected than before. This has occurred with men who could pass other tests with ease. The test also has a quality possessed by no other--namely, that of enabling the examiner to reject dangerous persons and dangerous persons only, the lower degrees of colour-blindness being allowed to pass.