ACCIDENTS BY KAIl. AND SEA. 183 



sense, but to depend finally upon the character of the person examined. 

 One of intelligence, with a quick, practical mind, is examined in less 

 than a minute. In this time, in fact, a normal eye could easily find the 

 four or five skeins of the same color as the sample, and the color-blind 

 make a sufficient number of characteristic mistakes to thoroughly 

 establish the diagnosis. It is clear that a method such as ours affords 

 the opportunity in connection with the investigation of the chromatic 

 sense of learning much of all the peculiarities relating to the use of 

 our senses. This is why we maintain the principle that it is nec- 

 essary to leave to the activity of the hands the task of revealing the 

 nature of the sensations, and to have recourse to the tongue only for 

 verification when there is need of more information. The combina- 

 tion of the action of the eye and hands, which plays in general so 

 important a part in the training and use of the senses, is also of 

 great consequence in this examination. An attentive examiner, espe- 

 cially if he have already acquired some experience, can draw im- 

 portant conclusions from the manner m which the other executes 

 his task, not only and directly with regard to the nature of his chro- 

 matic sense, but generally as to his intelligence and character, and 

 especially in some cases as to his previous training and exercise in the 

 use of colors, and his skill in recognizing them. The examination 

 affords us also the opportunity of making psychological observations, 

 which contribute in a great measure in giving us a clear idea of the 

 nature of the chromatic sense. A practiced examiner can often detect 

 color-blindness by the first gesture, and make his diagnosis before the 

 end of the trial. He can, according to the manner in which the task is 

 performed, form a judgment of a feeble chromatic sense in instances which 

 are proved correct by the final result. He also can and must see whether 

 the result is erroneous simply on account of a misunderstanding or a 

 want of intelligence, just as he can see whether the really color-blind 

 succeeds, in a certain degree, from much previous exercise or a consid- 

 erable amount of caution. In short, the method supplies us with all 

 necessary information, so that by an examination made with its assist- 

 ance, a defective chromatic sense, no matter of what kind or in what 

 degree, cannot escape observation. As we have already said, the prin- 

 ciple of our method is that the test is confined to one color. 



The faculty possessed by the eye of distinguishing colors and that of 

 defining the degrees of light and color (of '^ saturation") are relatively 

 very difierent; but these special faculties have this in common, that they 

 have their maximum activity in a certain intermediary region of abso- 

 lute intensity of light and their minimum at the two limits of this region. 

 Just as we experience the most difficulty in distinguishing between the 

 shades of intensity of light by a very feeble or very strong illumination, 

 so it is difficult for us to distinguish colors slightly or strongly luminous, 

 or the deepest and the lightest. It is, therefore, necessary to select as 

 a suitable color for discovering a feeble chromatic sense either the light- 



