RELATIVE STIMULATING EFFICIENCY OF LIGHT 161 



The methods used and the results obtained may be elucidated 

 by a detailed description of one of the numerous similar experi- 

 ments performed. The animal used in this experiment was 

 designated butterfly "25." This insect was first tested in the 

 flash-frequencies mentioned above with the dark periods of the 

 intermittent light three tunes as long as the light periods : after 

 an interval of about 30 minutes it was tested with the dark periods 

 of the intermittent light equal to the light periods: finally after 

 another interval of about 30 minutes it was tested with the dark 

 periods only one-third as long as the light periods. 



With the ratio between the light and dark periods, 1/3, and 

 with a flash-frequency of 2 per second the average angle of deflec- 

 tion obtained for 20 trials was 23.3 degrees; with a flash- 

 frequency of 5 per second the average angle of deflection was 

 18.15 degrees; with a flash-frequency of 10 per second the 

 average angle of deflection was +2.45 degrees; with a flash- 

 frequency of 20 per second the average angle of deflection was 

 + 12.55 degrees; and with a flash-frequency of 30 per second the 

 average angle of deflection was +11.6 degrees (fig. 2). 



With the ratio between the light and dark periods, 1/1, and 

 with a flash-frequency of 2 per second the average angle of 

 deflection obtained for 20 trials was 13.15 degrees; with a 

 flash-frequency of 5 per second the average angle of deflection 

 was 3.05 degrees; with a flash-frequency of 10 per second the 

 average angle of deflection was +1.9 degrees; with a flash-fre- 

 quency of 20 per second the average angle of deflection was 

 +14.65 degrees; and with a flash-frequency of 30 per second 

 the average angle of deflection was +11.65 degrees (fig. 3). 



With the ratio between the light and dark periods, 3/1 and 

 with a flash-frequency of 2 per second the average angle of deflec- 

 tion obtained for 20 trials was 6.95 degrees; with a flash-fre- 

 quency of 5 per second the average angle of deflection was 

 +5.25 degrees; with a flash-frequency of 10 per second the 

 average angle of deflection was 1.4 degrees; with a flash- 

 frequency of 20 per second the average angle of deflection was 

 +6.75 degrees; and with a flash-frequency of 30 per second the 

 average angle of deflection was +4.95 degrees (fig. 4). 



