152 WILLIAM L. DOLLEY, JR. 



stimulate it by handling. When the five trials were completed 

 a water glass was inverted over the insect to prevent its escape. 

 A pencil was then drawn along the trails made on the record 

 sheet : the direction of the rays of light was marked on it : and it 

 was replaced by a fresh sheet. A sectored disk with one-fourth 

 removed, rotating at the rate of 100 revolutions per second, was 

 next interposed in one of the beams, and the illumination in the 

 other beam was decreased by changing the position of its source 

 until the amount of light received from the two sources was equal, 

 as in the preceding tests, that from one, however, being inter- 

 mittent and that from the other continuous. The butterfly was 

 then given 5 consecutive trials just as in the preceding test. 

 After an interval of about five minutes, 5 more consecutive trials 

 were given with the flash-frequency of the intermittent light 60 

 per second. Similarly, tests were made with the flash-frequency 

 of the intermittent light 50, 40, 30, 20, 10, 5, and 2 per second re- 

 spectively. The results obtained may be illustrated by a detailed 

 description of a typical experiment. 



In this experiment the butterfly was first given 5 trials in two 

 beams of continuous light of equal illumination. It deflected 

 somewhat toward the source to its right, making an average 

 angle of +12.3 degrees with the line bisecting the angle made by 

 the two beams of light. It was then exposed to two beams of 

 equal illumination, one of them being of continuous and the other 

 of intermittent light. The flash-frequency of the intermittent 

 light was 100 per second. The organism made the same average 

 angle that it had made in two beams of continuous light of equal 

 illumination, +12.3 degrees. The insect was next given tests 

 in intermittent light of flash-frequencies of 60, 50, 40, and 30 

 per second. It made the following average angles respectively: 

 +4.4, +6, +19.8, and +15.6 degrees, thus reacting to inter- 

 mittent light of high flash-frequency in general as it did to con- 

 tinuous light. A test in intermittent light of a flash-frequency 

 of 20 per second followed. The butterfly made a much larger 

 average angle, +29.7 degrees, indicating that the stimulating 

 efficiency of intermittent light of this flash-frequency was greater 

 than that of continuous light. The effect of intermittent light of 



