3. _Special directions for conducting the test._--(1) The candidate should be seated at a distance of twenty feet from the lantern. (2) He should be asked to name the colour of the light produced by a coloured glass (1 to 6) alone, or in combination with another coloured glass or glasses, or with the modifying glasses (7 to 13). (3) A candidate should be rejected (i) if he call the red, green, or the green, red, in any circumstances; (ii) if he call the white light, in any circumstances, red or green, or vice versa; (iii) if he call the red, green, or white lights, black, in any circumstances. (4) A candidate who makes mistakes, other than those mentioned above, should be put through a very searching examination. It is not necessary to have the room absolutely dark; in fact, I prefer a certain amount of light. The examiner can, if he wish, make the test at night in the open air. The examiner should on no account conduct the examination on any regular plan, because the candidate, anxious to pass, finds out from persons who have already passed the order and method of the examination, and so, though colour-blind, might obtain a certificate. Any one of the glasses may be shown first, and the candidate required to name the colour of the light. The following will serve as an example of the method to be employed in testing a candidate. A red being shown, the candidate is required to name its colour. Then a blue or green may be substituted. It is best to use the largest aperture at first and to show all the colours on one disc. This will give confidence to the normal-sighted candidate, whilst most of the colour-blind will be detected. In the case of candidates who appear to be normal-sighted and yet very nervous, there is no harm in telling them after they have named all the colours on the disc correctly that this is the case. No comment should, however, be made on individual answers. Then one of the neutral, ground, or ribbed glasses should be inserted, not the slightest intimation being given to the candidate of the nature of the colour. He should be asked to name or describe the light, and the answer, if incorrect, together with his other replies, carefully recorded. The other glasses may then be shown, a combination of the neutral, ground, ribbed, and coloured glasses being used at irregular intervals. When the candidate has been examined with the largest aperture, the examiner can go through the same procedure with one of the smaller apertures. I have found the third aperture the one which is most generally useful. On account of the great diminution of total luminosity caused by the diminished area of the light source, the three smallest apertures can only be used in a dark room.