Page:Popular Science Monthly Volume 21.djvu/104

96  of distinguishing between the impressions of wave-lengths which lie relatively near together as regards their vibration numbers. It will be noticed, as an important fact, that there is confusion only of those colors which lie toward the same end of the spectrum. Red and green, for instance, are the colors which are most commonly undistinguishable; blue and yellow less commonly; but no instance is on record in which red and blue, or green and yellow, were constantly confounded. It seems from the examinations thus far made that the color-blind make, as a rule, distinctions between only two classes of color-sensations. A most intelligent color-blind man, whom I recently examined with the spectrum, saw it only as two colors—the line of demarcation being sharply at the blue-green junction, all to the right was blue, all to the left was what he called red. He could distinguish no line of separation between the red, green, and yellow, and the maximum of intensity was at the yellow, as is the case with normal eyes. As Mauthner says, there are no fixed rules which serve us for a diagnosis between red-and green-blindness. The two colors are confused, but how are we to know which is the one correctly perceived? The individual who is found to be green-blind by one method of examination is often found to be red-blind by another, and in some cases to have a shortening of the red end of the spectrum. Moreover, the red-blind can not unerringly pick out the greens, nor the green-blind the reds.

If, as we believe, a large number, perhaps a majority of the cases of congenital color-blindness are cerebral rather than retinal, and due more to a want of education of the color-sense than to any anatomical defect, a plan for the diminution or eradication of color-blindness would be by no means chimerical. The fact that women are less frequently color-blind than men we consider most probably due to the circumstance that their faculty for color is in more active and constant use, and for this reason has become more highly developed, and has been transmitted as a sexual peculiarity from mother to daughter. It seems, therefore, quite reasonable to suppose that if boys could have their color-sense educated to the same extent as girls, and the process were continued through a number of generations, the defect of color-blindness would in course of time disappear, except as a rare anomaly.



T is generally agreed," says Mr. Stallo, "that thought in its most comprehensive sense is the establishment or recognition of relations between phenomena." All perception is of difference; and two