THE PERCEPTION OF LIGHT AND COLOR. 



By Georges Lechalas 



Twenty years ago, while on a railway car, I accidentally made an 

 observation which strongly attracted my attention. Having held one 

 eye closed for a certain time, I reopened it during the passage of the 

 train through a tunnel. The consciousness of a profound inequality in 

 the vision of my two eyes led me to close them alternately, and I thus 

 verified not only that the sensitiveness of the eye previously closed was 

 greater than that of the other, exposed just before to the full light, 

 but also that there was a profound difference in the coloration of the 

 images. While in fact the image corresponding to the latter was quite 

 clearly yellowish, the other was white or even of a violet hue. This 

 violet tint, if real, could be explained by the phenomenon of contrast 

 with the yellow of the other eye; but it nevertheless persisted, not- 

 withstanding the fact that yellow light, thrown by a lamp on objects, 

 appeared white to an eye which had ceased to be adapted to solar light. 



This observation naturally leads to the hypothesis that color has only 

 a purely relative value, and that light of every color should appear col- 

 orless to an eye which has been in repose. To verify this hypothesis I 

 bandaged both eyes, and at the expiration of ten minutes I opened 

 them again in a room illuminated through a plate of blue gelatin. The 

 blue color was found to be much fainter, but quite distinguishable. 

 Repeating the experiment with a plate of red gelatin, no attenuation of 

 color was observed, although both eyes had been kept in darkness for 

 a still longer time. The hypothesis was thus disproved by experiment. 

 I did not continue the investigation, for which, besides, I was not prop- 

 erly equipped with apparatus. If I had better followed the trend of 

 scientific research I would have known that Dr. Charpentier, professor in 

 the medical faculty at Nancy, had already devoted himself to extremely 

 interesting studies of this class of phenomena, in which he was soon 

 followed by Dr. Parinaud; then the Germans entered the lists, and 

 to-day there exists an extensive scientific literature on the subject. It 

 possibly will not, therefore, be uninteresting to give a resume of the 

 conclusions thus far deduced from the experimental results obtained. 



1 Translated from Eevue des Questions Scientifiques, Louvain, April, 1899, pp. 

 476-504. 



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