46 ROBERT M. YERKES AND JOHN B. WATSON 



We recommend that in all quantitative investigations of 

 color vision determinations be made (a) of the wave-length of 

 the stimuli by means of a first-class spectroscope or spectro- 

 meter,' and (b) of the intensity of the stimuli by means of a 

 good spectro-photometer and also, when grating or prism is 

 used, by the use of a radio -micrometer or a selenium cell.^ 



V. DESCRIPTION OF STANDARDIZED APPARATUS AND METHOD 

 FOR THE STUDY OF COLOR PERCEPTION 



The apparatus we have finally decided to recommend as a 

 standard for testing the color perception of animals was de- 

 scribed in an early form in the April, 1909, number of the Journal 

 of Comparative Neurology and Psychology, p. i. In that 

 form there were many objectionable features, such as the use 

 of silvered mirrors, the projection of colored beams upon im- 

 properly ground glass surfaces, etc., all of which have been 

 entirely eliminated in the present form.^* 



In its improved form the apparatus now affords: 

 (i) Means of selecting any two desired bands of homogeneous 

 spectral light of constant and known wave-lengths. Further- 

 more, (a) the energy of each band is known in C. G. S. units 

 and can be varied at will; (b) the distance between them is 

 adjustable; (c) their right-left position can be interchanged 

 at will. 



(2) Means of splitting any single chosen beam of monochro- 

 matic light into two parts, in such a way that the two beams 

 thus obtained are of the same wave-length, form and size, and 

 are equal in energy. At the same time, (a), (b) and (c) under 

 (i) apply here also. 



(3) The possibility of substituting for either of the mono- 

 chromatic bands a beam of white light of the same size and 

 form as the homogeneous chromatic bands. 



(4) The alteration of the saturation of any monochromatic 

 band by the admixture of white light of known energy. 



^ Further details are to be found on pp. 79-84, in the description of our stan- 

 dard procedure. 



^ See p. 79. 



^ On pp. 70-87 will be found a detailed description of the separate parts referred 

 to here, together with a statement of their cost and the places where they may 

 be obtained. 



