ACCIDENTS BY RAIL AND SEA. 193 



the sample color. But we do not venture to lay this down as a principle, 

 for, if it should be proved that these individuals can generally distinguish 

 the light of colored lanterns with sufiflcient accuracy, this does not prove 

 that it is so in ev^ery case, and especially not at every distance required 

 in the service. This is why we know nothing better to advise than to 

 refer all such cases to competent specialists, as long as the transition 

 period of which we have spoken lasts. 



In the examination of doubtful cases submitted to my judgment, I 

 determined according to several of the methods mentioned in one of the 

 preceding chapters. In general, these persons were all subjected to a 

 trial according to the methods of Seebeck and of Maxwell, and an exami- 

 nation by means of the visual perimeter and of colored shadows, as well 

 as the lanterns of my invention and colored glasses. These last means 

 have capacity especially in view, and they are very suitable for the ob- 

 ject, when it is desired to investigate those who have been already dis- 

 covered, by my method of Berlin wool, as having a defective chromatic 

 sense. 



The light of colored lanterns and illuminated surfaces generally, con- 

 veniently arranged and methodically used, may serve especially in such 

 cases to enlighten us as to the faculty of the person, examined for appre- 

 ciating colored signals. Our experiences of this kind have shown us that 

 the majority of color-blind railway employes, however much practice they 

 have had, are utterly incapable of recognizing and distinguishing the 

 regulation colors of lanterns, especially when they are employed in the 

 shades which are not most commonly in use in the service. This applies 

 not only to the completely red and green blind, but also to the incom- 

 pletely blind. These last require the most circumstantial investigation, 

 and it is not to be assumed that the lower degrees can stand the trial; they 

 may often, it is true, distinguish the signal-lights at a short distance 

 with sufiicient accuracy, but they do not succeed at a comparatively 

 greater distance. As the places where the trials are usually made do 

 not command such distances as railways for observing signals, signal- 

 lights cannot of course be used for these trials. They are replaced by 

 small illuminated surfaces, which, seen from a suitable distance, produce 

 exactly the same effect as lanterns at a great distance. Such surfaces 

 are made by placing a screen with a suitable opening covered with a 

 colored glass before the flame of a lamp. This is enough to show how 

 to dispose of the case in question. 



C— EFFORTS TO CONCEAL OR TO FEIGN COLOR-BLINDNESS. 



We have announced that none of the kinds of color-blindness we have 

 in view in this work could escape discovery by our method. But this, 

 of course, assumes that the subject does his best in the trial and acts in 

 good faith. If it happen that one persists either in concealing a conscious 

 color-blindness or for some other motive, in not giving the least informa- 

 tion by act or word it is evident that the examination must fail from this 

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