LAURENS: MONOCHROMATIC LIGHTS. 281 
with other lights, 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, 
Fic. 5. Curves representing the percentages of movements toward blue when 
paired with the three other lights, when the lights are received through both the 
skin and the eyes ( ):. through the eyes only (----); and through the 
seanroniy (.. .u. = ). Wave-lengths as abseissae 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 = Yellow. 
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 
