ACCIDENTS BY RAIL AND SEA. 189 



1. He rejects one after the other, the foreign shades, so that the correct 

 remain, which is often only the sample skein. He is shown what mistake 

 he has made. Names are used to remind him that one class of green 

 may be yellow-green and another blue-green; and to induce him to 

 avoid them, he is advised only to select skeins of the same shade as the 

 specimen, although they be lighter or darker, and have neither more 

 yellow nor blue than that. If his first error arose only from a miscon- 

 ception or want of practice in handling. colors, he begins generally to 

 understand what he has to do, and to do properly what is required of him. 



2. Or else he selects and rejects immediately the skein of the sample 

 itself. This proves that he sees the difference of color. He is then 

 shown the skein as the only correct one, and asked to repeat the trial in 

 a more correct manner. He is again put on the right track as just before, 

 and the trial proceeds rightly, unless the error arise from a defect in 

 the chromatic sense. Many seem, however, to experience a natural diffi- 

 culty in distinguishing between yellow-green and blue-green, or the dull 

 shades of green and blue. This difficulty is, however, more apparent 

 than real, and is corrected usually by direct comparison. If the method 

 requiring the name of the color to be given is used, a number of 

 mistakes may be the result. If a skein of light green and light blue 

 alone are presented to him, asking him to name them, he will often call 

 blue, green, and green, blue. But if in the first case a blue skein is 

 immediately shown him, he corrects his mistake by saying this is blue 

 and that green. In the last case, it happens so mutatis mutandis. This 

 is not the place for an explanation. It must suffice to say that the error 

 is corrected by a direct comparison between the two colors. 



There is, according to the theory, one class of the color-blind — violet- 

 blind — who, in consequence of the nature of their chromatic sense, and, 

 therefore, notwithstanding the comparison, cannot distinguish blue and 

 green. But our method has nothing to do with this class of the color- 

 blind, because such are not dangerous on railways. 



{&) Another process. — If the one examined place by the side of the sam- 

 ple a shade, for instance, of yellow-green, the examiner places near this 

 another shade, in which there is more yellow, or even a pure yellow, re- 

 marking at the same time that if the first suit, the last must also. The 

 other usually dissents from this. He is then shown, by selecting and 

 classing the intermediate shades, that there is a gradation which will 

 diverge widely if logically carried out as he has begun. The same 

 course is followed with colors of the blue shades, if the blue-green were 

 first selected. He sees the successive gradations, and goes through 

 with this test perfectly if his chromatic sense is correct. 



To ascertain further whether he notices these additions, or the tints of 

 yellow and blue in the green, we can take ourselves the yellow-green and 

 blue-green to ask him if he finds this to be so. We can judge by his 

 answer of his sense with regard to these shades, and the object of this 

 investigation is accomplished. 



