114 L. W. COLE 



an electric, i6 c.p., lamp (not shown in the figure) in a small 

 box fitted with milk-glass windows. This lamp aftbrded light 

 and warmth to the young chick during the intervals when it 

 was in the hover box, and gave to a small area in the middle of 

 this box approximately the temperature of the brooder in which 

 the chicks were reared. The result of this was that chicks placed 

 in O hovered near this lamp and thus rarely made, at either 

 end of the box, any sounds which might influence the chick in 

 the experiment box in its choice of a passageway back to O. 



The inclined planes, G, of box O were replaced, early in the 

 experiment, by two small platforms at the level of the floor of 

 the experiment box. From these platforms the chicks hopped 

 down directly to the floor of box O. This change was made 

 because it was found that while chicks very readily walk up an 

 inclined plane it is very difficult and apparently unnatural for 

 them to walk down such planes. This difficulty becomes evident 

 if one tries to imagine a man descending a steep incline with 

 his body leaning far forward. The inclined planes, therefore, 

 to the inconvenience of the experimenter, served rather to toll 

 the chicks in box O upward toward the small doors of the ex- 

 periment box than to give a means of descent for the chick 

 which was escaping from the latter box. The platforms obviated 

 this difficulty. 



The illumination box, 107.8 x 40.2 x 23.2 cm., was divided 

 lengthwise into two compartments by a light tight partition. 

 The inside dimensions of each compartment were 107.8 x 19.3 x 

 23.2 cm. Each of these compartments held an incandescent 

 lamp of the oval reflector type with frosted globe. These lamps 

 were mounted on slides so that they could be moved easily along 

 the millimeter scales, S. They were rated as of 50 c.p. When 

 photometered at the close of the experiments the lamp in the 

 right compartment had an intensity of 42.6 c.p., the one at the 

 left 41.2 c.p. By moving the lamps along their millimeter 

 scales they could be changed in position from 8.5 cm. to 103 

 cm. behind the opal glass screens, Nj and N3, so that a wide range 

 of intensities of illumination was available. 



As already stated, three difi^erent conditions of discrimination 

 were used. For the condition termed " easy " one screen was 

 illuminated by a lamp 33.5 cm. distant, the other screen was 

 not illuminated. For " medium " discrimination one lamp was 



