116 L. W. COLE 



light, its value as perceived by the human eye was not dark- 

 ness. This factor of reflected light was present throughout the 

 experiments and made the dift'erence in brightness of the two 

 screens, as judged by the experimenter, much less than that 

 indicated by the above ratio. Subjectively estimated the bright- 

 nesses of the two screens would stand, respectively, in the ratios 

 I : 20 for easy discrimination, i : 4 for medium, and i : 2 for 

 difflcult. 



A current of 2.1 amperes was supplied to the primary coil 

 of the inductorium. The interruptions were 44 ± 5 per second. 

 The positions of the secondary coil and the corresponding num- 

 ber of units of stimulation appear in table i.^ 



s 



TABLE I 



Position of Units of 



secondary stimulation 



6 220 



5 350 



4 480 



3 590 



Method of the experiments. As a- result of the experiments 

 with the first group of chicks, Nos. 1-6 inclusive, it was found 

 necessary to give all subsequent groups twenty trials in the 

 experiment box in order that they might learn both ways of 

 escape from it. The chick was first placed in compartment 

 A of this box. The door in the partition w^as opened and it 

 passed into compartment C. By drawing back the cardboard 

 shutter M' the small door, E, was opened through which the 

 chick escaped to the hover box. In the next trial it escaped 

 at the right and so on until the preliminary series had been 

 completed. 



There was no difference of brightness between the two screens 

 during the preliminary tests. During the first five of such tests 

 under the condition of easy discrimination there was no light 

 behind either screen, during the second five trials both lamps 

 were at 33.5 cm. and so on. During the first five tests of medium 

 discrimination both lamps were at 98.5 cm., during the second 

 five at 23.5 cm., and the distances 53.5 cm. and 23.5 cm. were 

 similarly used in the preliminary tests of the difficult discrimi- 

 nation. 



^ For the calibration of the inductorium used in these experiments see the paper 

 by Yerkes and Dodson, p. 467. 



