PART II. EXPERIMENTAL 



CHAPTER III 



Apparatus 



The work on visual acuity, as reviewed in the preceding chap- 

 ter, has been criticised primarily on the basis of method. One 

 general fact stands out when these experiments on visual per- 

 ception in the chick are viewed in their historical setting: the 

 methodological aspect has rapidly come to be the central feature 

 of the work. Beginning with loose observations in which ac- 

 curate description of method was either impossible or ignored, 

 the method has developed into a thoroughgoing scientific pro- 

 cedure. The early naturalistic observers raised questions for 

 the later scientific school to solve. The naturalists have con- 

 tributed a general orientation ; the experimentalists are solving, 

 one by one, the specific tasks involved. The apparatus used in 

 the present experimental study represents an important stage 

 in the development of technique for stud^dng detail vision. 

 Controllability w^as the primary aim in its construction. It 

 represents a definite standardization which has been previously 

 described in detail, hence my description will be a rapid sum- 

 mary. Supplementary to apparatus, but no less important, 

 is experimental method and technique to which a special chap- 

 ter will be devoted. 



The dark room-discrimination apparatus has been carefully 

 described in the report by Yerkes and Watson. In Chapter II, 

 the origin and development of the method has been set forth. 

 In figure 3 is presented an isometric view of the apparatus 

 showing the skeleton of the various parts when assembled for 

 work. That part of the mechanism labelled I is the experiment 

 box. The opposite end. III, is the light or source box. Between 

 the experiment box dindthesourc^hoKis the stimulus shifter, II. 



1. Experiment box 



An illustration of the experiment box appears as figure 4. 

 This section of the apparatus is made of one-half inch lumber, 



