LAURENS: MONOCHROMATIC LIGHTS. 



281 



with other Hghts, were only a little higher than those toward the dark 

 when these lights were used singly; in other words, the negative re- 

 sponses to blue, green, and yellow, when paired with red light, were 

 almost the same as when these lights were used singly. Red light 

 can be said, therefore, to have had only very little, if any, effect in 

 the production of positive responses, when used in pairs with other 

 lights, while blue, green, and yellow were distinctly effective in this 

 respect. 



Although for each pair of lights, there were always positive responses 

 to the blue, or to the light which in the spectrum was nearer the blue, 



Fig. 5. Curves representing the percentages of movements toward blue when 

 paired witli the three other liglits, when tlie lights are received tlirough both the 



skin and the eyes ( ) ; tlirough the eyes only ( ) ; and through the 



skin only ( ) . Wave-lengtlis as abscissae and percentages of movements 



as ordinates. Points marked on axis of abscissae are the positions of the wave- 

 lengths of the middle band of each light. B = Blue; G = Green; R = Red; 

 Y = YeUo.w. 



still the distribution of effectiveness, as seen in the percentage of 

 responses to the light of shorter wave-lengths in any pair, did not follow 

 closely the distribution of the several lights in the spectrum. Never- 

 theless, when the blue light was paired in sequence with the other 

 three lights, it was found that the percentage of positive responses 



