Watson, Color Vision iti Monkeys. 5 



intensity of either color, and the absolute intensity of both may be 

 altered at will ? In investigating this problem, we ought to be able 

 to find totally color blind animals, red-green blind animals, animals 

 with normal color vision, if such differences in sensitivity exist. 

 After the problem has been solved, color theories based upon the 

 phylogenetic development of a photo-chemical molecule will or will 

 not have bases in fact, 



2. How nearly identical in wave length may any two colors 

 be and still afford a basis for, the animal to discriminate between 

 them (the qualitative 'difference linien', D.L.) ?^ 



3. How nearly identical in intensity may two bands of the same 

 wave length be and still afford a basis for discrimination (the D.L. 

 for intensity) ? 



4. Do the different parts of the spectrum possess different thresh- 

 old values (stimulus limen, R.L.) ? 



5. Is the spectrum of a given animal wider or narrower than 

 the average width of the spectrum of man ? 



Description of Appaeatus. 



As Figs. 1 and 2 show, the light apparatus is made upon the 

 principle of a spectrometer. Fig. 1 shows, in order, the arc, A, 

 the condensing lens, Lj, the slit, S^, the collimating lens, L.2, the 

 prism, P, the mirror, ilf^, and the lens, L3, (all are enclosed in a 

 system of dark boxes). 



The arc is an ordinary hand-feed arc. The direct 220 v. current 

 supplying the arc is furnished by the university power-house. This 

 curxent is very steady and uniform. The positive (cored) carbon 

 is placed horizontally and in the axis of the optical system. The arc 

 is so arranged that it can be adjusted by the experimenter in the 

 adjoining room at K (Fig. 2). Two long rods, BE, extending 

 from the are into the experimental room permit this. AC in Fig. 1 

 shows the gearing system by means of which the long rods are 

 brought into connection with the short feeding rods of the arc. 

 After practice the experimenter can control the arc at K through 



^In the apparatus to be described, a double image prism would afford the 

 conditions for this test. 



