RATE OF LEARNING IN THE CHICK 115 



at 23.5 cm., the r)ther at 98.5 cm., and for difficult discrimination 

 the lamps were placed respectively at 23.5 cm. and 53.5 cm. 

 from the screens. 



The experiment box was, as shown in the figure, somewhat 

 narrower than the illumination box. It was divided into two 

 compartments, A, 30 x 16.7 x 21.3 cm., and C, 46 (from parti- 

 tion B to the glass screens N 2 and N3), x 30 x 21.3 cm. A damp 

 pad of felt was placed on the floor of compartment A during the 

 experiments and a similar pad in compartment C extended from 

 the partition, B, to within 2 cm. of the electric wires. These 

 pads were used to moisten the feet of the chicks, for when dry 

 the horny epidermis served to protect the animals perfectly 

 from the electric stimulus. The opening, shown in the parti- 

 tion, B, between the two compartments was closed by a mesh 

 wire door which could be opened by lifting it vertically. That 

 half of the floor of compartment C which was nearest the screens 

 w^as wound with seventeen turns of phosphor bronze wire of 

 No. 20 A.S. gauge. The distance between the successive wires 

 was I cm. This wire was in circuit with the secondary coil 

 of the inductorium, I, and the circuit could be closed by means 

 of the electric key, K. A V-shaped partition divided the wired 

 portion of this compartment into two passageways, D and D'. 

 From these passageways two openings (of which one, marked 

 E, is shown) gave means of egress for the chick to the platforms 

 (see p. 113) and thence to the hover box, O. They were closed 

 by the cardboard shutters M and M'. 



The two opal flashed glass screens, Nj and N3, (Ni was not 

 used in the experiments) were each 12 cm. square. As already 

 stated, the lamps ^^'ere placed at different distances behind the 

 two screens so that the latter differed from each other in bright- 

 ness. Their relative brightnesses when photometered were 

 roughly as follows : 



For " easy " discrimination o' : 8 . 9 



For medium discrimination i :i3 . 7 



For difficult discrimination 1:5.1 



While one screen w^as not illuminated under the condition of 

 easy discrimination it had a surface of rather high reflecting 

 power and, since the experiments were made in diffused day- 



"" This screen was not illuminated. The zero is meant to indicate nothing more 

 than that fact. 



