452 BIOLOGY IN RELATION TO OTHER NATURAL SCIENCES. 



this tells us of the specific euergy of the visual apparatus. Whether 

 or not the faculty by which we see gray in the dark is one which we 

 possess in common with animals of imperfectly developed vision, there 

 seems little doubt that there are individuals of our own species, who, 

 in the fullest sense of tbe expression, have no eye for color; in whom 

 all color seuse is absent; persons who inhabit a world of gray, seeing 

 all things as they might have done had they and their ancestors always 

 lived nocturnal lives. In the theory of color vision, as it is commonly 

 stated, no reference is made to such a faculty as we are now discussing. 

 Prof. Hering, whose observations as to the diminished spectrum I 

 referred to Just now, who was among the first to subject the vision of 

 the fofalli/ color-blind to accurate examination, is of opinion, on that 

 and on other grounds, that the sensation of light and shade is a specific 

 faculty. Very recently the same view has been advocated on a wide 

 basis by a distinguished psychologist, Prof. Ebbinghaus.* Happily, as 

 regards the actual experimental results relating to both these main 

 subjects, there seems to be a complete coincidence of observation 

 between observers who interpret them difllerently. Thus the receut 

 elaborate investigaticms of Capt. Abneyt (with Gen. Festing), repre- 

 senting graphically the results of his measurements of the subjective 

 values of the different parts of the diminished spectrum, as well as 

 those of the fully illuminated spectrum as seen by the totally color-blind, 

 are in the closest accord with the observations of Hering, and have 

 moreover been substantially confirmed in both points by the measure- 

 ments of I)r. Konig in Helmholtz' laboratory at Berlin. J That observ- 

 ers of such eminence as the three persons whom 1 have mentioned, 

 employing different methods and with a different purpose in view, and 

 without reference to each other's work, should arrive in so complicated 

 an inquiry at coincident results, augurs well for the speedy settlement 

 of this long-debated question. At present the inference seems to be 

 that such a specific energy as Hering's theory of vision postulates actu- 

 ally exists, and that it has for associates thecolor-i)erceiviug activities 

 of the visual apparatus, provided that these are present; but that 

 whenever the intensity of the illumination is below the chromatic 

 threshold — that is, too feeble to awaken these activities — or when, as 

 in the totally color-blind, they are wanting, it manifests itself independ- 

 ently ; all of which can be most easily understood on such a hypothesis 

 as has lately been suggested in an ingenious pajDer by Mrs. Ladd 



* Ebbinghaus, "Theorie des Farbensehens," Zrifschr f. Psyclwl., 1893, vol. v, p. 

 145. 



tAbney aiuIFestiug, Color Photometry, Partiii. Phil. Trans., 1891, vol. clxxxiii, 

 A, p. 531. 



t Konig," Ueber den Helligkeitwerth der Spectralfarben bei verschiedeuer absoln- 

 ter Intensitiit," Beltriuje zur Psyohologie, etc., "Festschrift zu H. vou Helmholtz, 70, 

 Geburtstage," 1891, p. 309. 



