150 



WILLIAM L. DOLLEY, JR. 



eral, as the difference between the illumination of the two beams 

 increased, for, as the last line in table 2 shows, the average angle 

 made in 20 trials when the light from the two sources was equal 



TABLE 2 



Showing the variation exhibited by a specimen of Vanessa (butterfly 14) in successive 

 trials under the same conditions. The numbers indicate the degree of deflection 

 from a line bisecting the 90 degree angle between two beams of continuous light. 

 "Plus," deflection toward right beam. If beams are of unequal illumination the 

 stronger one is to right of the insect. "Minus," deflection toward other beam 



was +5.35 degrees; when the illumination in one beam was 

 three-fourths that in the other the average angle of 20 trials was 

 +6.02 degrees; when the illumination in one beam was twice 

 that in the other the average angle was +12.45 degrees; and when 



