166 WILLIAM L. DOLLEY, JR. 



energy emitted in a unit of time are of equal stimulating efficiency. 

 For example, intermittent light of a flash-frequency of 20 per 

 second produced by a disk with one-fourth removed and light 

 of the same flash-frequency produced by a disk with one-half 

 removed are of equal stimulating efficiency. Yet the latter of 

 these two lights emits four times the amount of light energy 

 in one second that the former does. 



Table 6 also shows that the stimulating efficiency of the lights 

 used depends on the ratio between the duration of the light and 

 dark periods. This is evident when the members of each of the 

 groups in this table are studied. For example, in group I are 

 placed those lights of a flash-frequency of 30 per second and in 

 group VI are placed those lights of a flash-frequency of 2 per 

 second. Any difference in stimulating efficiency between the 

 members of each group is therefore not due to differences in 

 flash-frequency for this factor is the same in all. Hence dif- 

 ferences in stimulating efficiency between the members of each 

 group must be due to the ratio between the duration of the light 

 and dark periods. In the first two groups the order of the 

 stimulating efficiency of the lights of the three ratios is as follows : 

 1/3, 1/1, and 3/1, i.e., in each of the first two groups the inter- 

 mittent light in which the ratio of the duration of the light to 

 the dark periods is 1/3 is of the highest stimulating efficiency, 

 and the intermittent light in which the ratio of the duration of 

 the light to the dark periods is 3/1 is of the lowest stimulating 

 efficiency. Similarly, in the last three groups the order of the 

 stimulating efficiency of the lights of the three ratios is as follows : 

 3/1, 1/1, and 1/3. This shows that the stimulating efficiency of 

 the intermittent light used in the experiments depends on the 

 ratio between the duration of the light and dark periods and that 

 the effect of the ratio is reversed at lower flash-frequencies. 



VII. INFLUENCE OF MECHANICAL STIMULATION AND PREVIOUS 

 EXPERIENCE ON THE REACTIONS OF VANESSA TO LIGHT 



When two paths made under the same conditions differ in 

 the angle made with the rays of light it indicates a change in the 

 physiological state of the organism. Two factors were dis- 



