96 THE POPULAR SCIENCE MONTHLY. 



ble 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 undistin- 

 guishable ; 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 

 demarkation 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 maxi- 

 mum 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 diag- 

 nosis 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 bv 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 fre- 

 quently 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-blind- 

 ness would in course of time disappear, except as a rare anomaly. 



-+++- 



STALLO'S "CONCEPTS OF MODERN PHYSICS."* 



By W. D. LE SUEUK. 



" "FT is generally agreed," says Mr. Stallo, " that thought in its most 

 -L comprehensive sense is the establishment or recognition of rela- 

 tions between phenomena." All perception is of difference ; and two 



* From a criticism of " The Concepts and Theories of Modern Physics," in the " Cana- 

 dian Monthly." 



