42 



ROBERT M. YERKES AND JOHN B. WATSON 



The formulae of Parker and Day. — The following formulae 

 were devised for the study of the reactions of organisms to 

 chromatic stimuli in the Zoological Laboratory of Harvard 

 University, but for obvious reasons they were not employed. 

 We present them as given to us by Professor G. H. Parker, 

 with his comments. 



Thick- 

 ness of 

 layer in 

 Color mm. 



Blue 



20 



Aqueous solution 



Methylene blue 



Grams of 



substance Range 

 in I 300 cc. in 



of solution spectrum 



o. 65 420-470 /^/^ 



Green 



20 



"Napthol yellow S 

 Lichtgrtin F. S. 

 .Napthol green B 



3-25 

 . 39 490-580 M/A 



•39 



rNapthol yellow S 

 Yellow 20 i Napthol green B 



iPonceau P. R. 



3-25 

 •39 560-650 p-H- 

 . 20 



Red 



rPonceau P. R. 

 20 < Napthol green B 



IFormyl violet S 4 B. 



[3.00 



. 20 600-720 H-f^? 



"All of these were used as single solution ray filters in plate 

 glass containers, with the thickness of layer 20 mm. Tests 

 with the radiomicrometer indicated that about one-third of 

 the energy transmitted by these solutions was invisible (prob- 

 ably for the most part infra-red) . We could find no satisfactory 

 way to prevent this transmission of the invisible rays and there- 

 fore abandoned the use of filters in connection with studies 

 of the influence of chromatic stimuli." 



The formulae of Greene. — We have tested the following form- 

 ulae, supphed by Mr. Willard Greene, and discovered that they 

 may be used to advantage for certain experiments with animals. 

 Several of them are very similar to those given by Professor 

 Parker. We have used our solutions, how^ever, in layers 10 mm. 

 instead of 20 mm. in thickness. 



