J.— PSYCHOLOGY 



221 



in a projection lantern. By means of an erecting prism, the beam of light 

 was thrown downwards on a table, after passing through the filter, and the 

 tests were placed on the part of the table so illumined. No other light 

 was admitted to the room. 



The first stage in the investigation was to determine the region of the 

 spectrum transmitted by each filter. This was done by the Drever- 

 Hilger Hue-Discrimination Spectrometer, and the following results were 

 obtained. The results from the Ilford filters only are given here : — 



Violet 

 Blue 



Blue-green 

 Green 



Yellow-green 

 Yellow . 

 Orange 

 Red . 



Ilford Filters. 

 End of spectrum to 480/^^ 



450^^ to 500/X|U, 



475/x/A to 530/x^ 



500^^ to 550;Uft. 



53o/x/i to 590/^^ 



555/z/x to 630/x/u, 



575/i/A to 690/x/x 



620|U,/i to extreme of spectrum 



The following table (Table III) shows the results for the Ishihara test 

 with the Ilford filters. The Wratten filters gave much the same results. 



Table III. 

 Ishihara Test with Ilford Filters. 



