290 bulletin: museum of comparative zoology. 



reactions to balanced pairs of lights of different wave-lengths. By 

 referring to Table 10, it will be seen that the two generators A and B 

 delivered lights that were very similar in effect, the differences in the 

 percentages of reactions to one or the other of a given pair being 

 hardly noticeable, and not constant for either. The decrease in the 

 percentage of positive responses between blue and red shown here was 

 very slight, there being 98 % of positive responses in the blue, 96 % 

 in the green, 92 % in the yellow, and 84 % in the red, the decrease 

 between the yellow and red being the greatest of that between any 

 pair of lights adjacent to each other in the spectrum. This decrease 

 from blue to red was, however, sufficient to bring out very clearly a 

 gradually increasing percentage of indifferent reactions, there being 

 about eight times as many indifferent reactions in red as in blue. 



These results served to confirm the belief that the spectroscopic 

 and photometric readings of the different lights had been sufficiently 

 accurate as a means of keeping constant the radiant energy contained 

 in each light. 



By way of summarizing these results it may be said that the two 

 generators gave out lights that were very similar in effect, and that 

 therefore the combining of the results of two sets of trials in which the 

 same lights occurred, but from different generators, was a legitimate 

 procedure. 



C. Smumary. 



The results obtained with balanced pairs of monochromatic lights 

 are summarized in Table 1 1 . These may be briefly stated as follows : 



1. The results obtained with balanced pairs of monochromatic 

 lights agree in all essential respects with those obtained with single 

 monochromatic lights. 



2. Blue, green, and yellow lights produced positive responses of a 

 marked degree; red light resembled darkness, or called forth only a 

 very slight positive response. 



3. Blue light was the most effective stimulus; and green, yellow, 

 and red formed a series of decreasing effectiveness, corresponding 

 roughly to their distribution in the spectrum. 



4. In any pair of balanced lights the larger percentage of responses 

 was toward the light which in the spectrum was nearer the blue end. 



5. In effectiveness the light nearer the blue end of the spectrum, in 

 the several pairs of lights tried, did not correspond very closely to that 

 of the pairs of lights as determined by their distances apart in the 

 spectrum. 



