Some new apparatus. 105 A suitable arrangement of tbe colors gives direct simultaneous comparisons of reds, greens, and grays of different shades. The well-known confusion by color-blind persons of dark greens with reds, greens with gray, etc., are exactly imitated, and the instrument gives a decisive test for color-blindness. Its peculiar advantage, however, lies in the fact that it presents reds, greens, and grays simultaneously in a large number of different shades of intensity. The light of a green lantern, as it appears to a color-weak person at different distances, is simulated by the red behind the different grays ; at the same time a white light is also changed. The color-weak per¬ son to whom weak green is the same as gray (white at a distance) is utterly confused and thinks that the weakened green is gray (white) and the dark gray is green. The actual test is performed in the following manner : The tester is held toward a window, but not in the bright sunlight, at about 2^ feet from the person tested. The operator begins with any chance position of the glasses, and asks the person tested to tell the colors seen through the three glasses, Nos. 1, 2, and 3. He answers, for example, “No. 1 is dark red ; No. 2 is gray ; No. 3 is green.” The operator records from the back of the tester the letters indicating what glasses were actually used. Suppose he finds that A, D, and G were opposite the glasses Nos. 1, 2, and 3 he records : A 1, dark red ; D 2, gray; G 3, green. The disk is then turned to some other posi¬ tion, the colors are again named, and the operator records the names used. For example, the result might be : “No. 1 is dark green ; No. 2 is white ; No. 3 is red.” and the record would read: G 1, dark green ; J 2, white ; A 3, red. Still another record might give ; J 1, dark gray ; A 2, red ; D 3, medium gray. Similar records are made for all combinations. Of course, the person tested knows nothing concerning the records made. The blank thus filled out is forwarded to the chief inspector for railway or marine service. A comparison with a table containing the true colors for each position determines whether the test has been passed or not. The records can be taken by any one, and, on the supposition that the record has been honestly obtained and that the instrument has not been tampered with after leaving the central office, the compari¬ son is likewise mechanical. There is none of the skillful manipula¬ tion required in the wool test and none of the uncertainty attaching to its results. The only instruction given to the subject is, “Name the colors ” ; the results render the decision with mechanical cer¬ tainty.