Color-blindness : remarks / by B. Joy Jeffries.

  • Benjamin Joy Jeffries
Date:
[1881]
Catalogue details

Licence: Public Domain Mark

Credit: Color-blindness : remarks / by B. Joy Jeffries. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    often are all these extraneous conditions absent for the pilot or tli e railroad engineer, when, from the color of light alone, instantaneous recognition of port or starboard danger or safety must be made to save collision, and which recognition is so certain for the normal eye that the lack of it can hardly be believed? Now, this apparatus of Professor Donders, in practical use in Holland, and directed by the Connecticut rules, enables us to exactly imitate the condition of seeing colored signals when there are no extraneous circumstances to help the decision of the pilot or engineer. If there is any value in the use of colored signals, then certainly there is danger in allowing those who cannot distinguish them by their color to steer our vessels or run our locomotives. The testing color-blind pilots or railroad employes who have been long in service, and fortunately for us escaped any very serious collisions, &c., is a very interesting psycho- logical study. As they cannot see their mistakes, they cannot believe in them. The red or green-blind see blue and yellow as we do ; therefore, by showing them two bright worsteds of these colors together, and telling them that in their examination they made as marked mistakes as to class these yellow and blue as the same, gives them, if they will believe us, some little conception of the gravity of their defect. But seeing is said to be believing, and as they cannot see as we do, they are not likely to believe as we do, since such belief means loss of occupation. Hence, we see at this time the great value of Donders’ apparatus. By it the medical examiner can perfectly prove to the interested laity, or inspectors, the pilot’s employers or friends, just how he is defective. Nothing is more convincing than the witnessing such an examination, properly conducted. The most skeptical have always admitted the danger, which they could not before appreciate, and which satisfied them so thoroughly that they never asked for further tests with signal- lanterns, &c. But a misuse of this test, as, in fact, of any, may equally perplex the medical examiner, render him doubtful of liis diagnosis, cause in the laity suspicion of the whole question of the existence of defect or danger from it, and confirm the examined in his belief that lie does see colors as the normal-eyed. All tests, therefore, must, in justice to the examined, be applied only by those thoroughly competent, whose education enables them to learn them and perfectly understand them when described by the expert. I would call the attention of the board to an addition I have made to Donders’ apparatus, by which, as you see, I can interpose a neutral- colored (London smoke, so-called, used for spectacles) glass, which will simply darken the colored light or the white light. Now it will be re- membered that red or green colors make a light darker to a color-blind in proportion to the amount of his defect and the depth of the pigment. Hence, when he sees a white light become darker by interposing a smoke-glass, lie immediately concludes that it is colored, and says red or green, according to circumstances. So darkening a pale-green glass » j will make it seem the same as red to him, and rendering a red one brighter will make it appear green to him. I do not know any way officials can be made to appreciate the peculiar danger of the defect better than by this arrangement, which so perfectly exposes the color- || blind’s exact condition of vision and shows how dangerous it is. When we remember that a slightly-smoky lantern, a little rain or fog or sleet, a dirty glass, or blurred eyesight from fatigue, exposure, or stim- ulants, cause the color-blind to mistake the signals, by changing their
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