METHODS OF STUDYING VISION IN ANIMALS 17 



III. DESCRIPTION OF STANDARDIZED APPARATUS AND METHOD 

 FOR THE STUDY OF LIGHT, SIZE, FORM, AND DIS- 

 TANCE PERCEPTION 



Without wishing to dictate to any experimenter either details 

 of apparatus or methods of experimentation, we present the 

 following description of a mechanical device and of an experi- 

 mental procedure which in our experience yield excellent results. 



I. Light or "brightness " apparatus 



This apparatus consists of three chief parts: (i) A light 

 box, fig. I, A; (2) an experiment box suited to the animal to 

 be tested, fig. 4; and betw^een the two (3) a stimulus adapter, 

 fig. 3, by means of which two illuminated areas are simultane- 

 ously exposed to view. 



The wooden light box. A, is divided into two compartments, 

 C and D, by the partition, B. The sides, ends, and partition of 

 the box are I inch planed and seasoned lumber. The inside 

 dimensions are as follows: length, 3 meters; width (between 

 sides) 52 cm.; depth, 30 cm. The bottom is if inch planed 

 stock, do welled and glued. It is made 2 feet longer than the 

 box, as a provision for the support of the experiment box. 



To the middle partition of the box are hinged two lids, E 

 and F, of | inch lumber.' The edges of the box and lids are 

 grooved and rabbeted. When the lids are closed the two com- 

 partments, C and D, are light-tight with respect to one another. 



Two cast-iron carriages, G and H, carry incandescent lamps 

 which serve as sources of photic stimuli. Each carriage rides 

 on a pair of steel tracks, I J and KL, placed on the floor of its 

 compartment. 



To the floor of each compartment is attached a Starrett 

 (Athol, Mass.) steel tape, M and N, from which the position 

 of the source of light may be read directly in millimeters. 



In order that daylight, instead of artificial light, may be 

 used when it seems desirable, a hole 12.7 cm. in diameter is 

 cut in the end of each compartment. These holes are fitted 

 with Aubert diaphragms as shown at O and P, fig. i. 



The completed apparatus carries a system of ball-bearing 

 pulleys, cords, and levers (not shown in fig. i) by means of 



^ The drawing for fig. 1 was made while the lids were hinged to the sides. Later 

 it was found desirable to hinge them to the middle partition. We recommend 

 the latter form of construction. 



