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 asin 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. Summary. 
The results obtained with balanced pairs of monochromatic lights 
are summarized in Table 11. 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. 
