772 



SCIENCE. 



[N. S. Vol. IX. No. 231. 



lately perfect at the wool- test. He can 

 match wools with incredible precision at 

 any distance away ; he is, nevertheless, 

 color-blind. This case is typical of a class 

 of persons with eyes abnormally acute for 

 differences in color, but yet with only two 

 fundamental sensations instead of three. 



In the second place, I have had among 

 my students those who possessed perfect 

 color-vision for near objects or bright ob- 

 jects, but who were practically color-blind 

 for weakly illuminated or distant objects. 

 These persons possess the typical three 

 fundamental color sensations, but have one 

 of them weaker than the normal. A per- 

 son of this kind may pass the wool-test 

 with the utmost perfection if the test is 

 performed close by, but will fail if the 

 wools are removed to a distance of 20 or 30 

 feet. This peculiar defect I take the liberty 

 of terming ' color-weakness.' The first stu- 

 dent of this kind that I examined passed 

 the wool-test close at hand and yet was un- 

 able to distinguish red and green lanterns 

 a few hundred yards away. Cases similar 

 to this have been reported by the British 

 Marine Examiner, Edridge-Green. Among 

 other cases he quotes a letter from an engi- 

 neer containing the following statement : 

 " I have been on the railway for thirty 

 years and I can tell you the card-tests and 

 wool-tests are not a bit of good. Why, sir, 

 I had a mate that passed them all, but we 

 had to pitch into another train over it. He 

 couldn't tell a red from a green light at 

 night in a bit of a fog." 



To eliminate both these classes of persons 

 we must have a method of testing on quite 

 different principles from the usual ones. 



In the first place, the sorting of delicate 

 shades of colors, according to likeness, must 

 be replaced by naming certain fundamental 

 and familiar colors. The sorting of wools is 

 a quite unusual and perplexing task to a 

 man brought up in a railway j'ard and on 

 shipboard. It puts a nervous man at quite 



a disadvantage ; it furnishes the unsuc- 

 cessful candidate with the excuse that the 

 judgment required was so unlike any he 

 had made before that he failed from nervous- 

 ness ; and, finally, it is not a guarantee that 

 all who pass ai"e not color-blind. The nam- 

 ing of colors should — as Bonders proposed 

 — be rigidly required. The engineer or the 

 pilot in his daily routine is not called upon 

 to match colors , but to decide whether a 

 light is red, green or white ; he should be 

 tested on just this point. The color-blind 

 student referred to above who can pass the 

 wool-test to perfection fails at once when 

 called upon to name the wools. The nam- 

 ing of delicate and perhaps unusual shades 

 should, however, not be requii-ed ; the 

 colors to be named should be the three fa- 

 miliar ones : red, green and white, so 

 manipulated that every possible chance for 

 confusion is presented. 



The second necessity for eliminating 

 danger is that of an absolutelj' certain test 

 which shall detect both the color-blind and 

 the color-weak. Acting on the basis of 

 suggestions from the work of Bonders and 

 of Edridge-Green, I have devised a test 

 that meets this requirement as well as the 

 first one. 



The instrument* which I have invented 

 may be termed the ' color sight tester ' or 

 the ' color sense tester.' In general appear- 

 ance it resembles an ophthalmoscope. On 

 the side toward the person tested. Fig. 1, 

 there are three windows of glass, numbered 

 1 , 2 and 3, respectively. The opposite side of 

 the tester. Fig. 2, consists of a movable disk 

 cai-rying twelve glasses of different colors. 

 As this disk is turned by the finger of the 

 operator the various colors appear behind 

 the three windows. At each movement of 

 the disk the subject calls off the colors seen 



* For those interested in obtaining the Color-Sight 

 Tester I will say that I have made arrangements to 

 have it made by the Chicago Laboratory Supply and 

 Scale Co., Chicago. 



