RELATIVE STIMULATING EFFICIENCY OF LIGHT 173 



of continuous light; at flash-frequencies of 5 and 2 per second 

 it is lower than that of continuous light; and at flash-frequencies 

 of 10, 100, 60, 50, and 40 per second it is approximately equal 

 to that of continuous light. 



3. The stimulating efficiency of intermittent light of relatively 

 low flash-frequency depends on the ratio between the duration 

 of the light periods and the dark periods. At flash-frequencies 

 of 30 and 20 per second, intermittent light in which the ratio 

 between the light and the dark periods is 3/1 is less efficient than 

 light in which this ratio is 1/3 and 1/1. At these flash-fre- 

 quencies the efficiency of the latter two sorts of light is appar- 

 ently equal. At flash-frequencies of 10, 5, and 2 per second 

 intermittent light in which the ratio between light and dark 

 periods is 3/1 is more efficient than light in which this ratio is 

 1/1, and this light in turn is more efficient than light in which 

 the ratio is 1/3. 



4. Some specimens of Vanessa exhibit great variation in then* 

 reactions to light. This variation is shown to depend, in part at 

 least, upon previous experience. Mechanical stimulation pre- 

 ceding exposure to light may cause butterflies to react more 

 strongly to weak light than to strong light. It may also cause 

 them to react more strongly to intermittent light of low flash- 

 frequency than to continuous light of equal illumination. More- 

 over, butterflies after having reacted for some time to certain 

 light conditions may continue to react in the same manner after 

 the light conditions are suddenly changed. 



REFERENCES 



ABNEY, W. DE W. 1907 Treatise on photography. 10th ed. London, pp. 425- 



AUBERT, H. 1864 Physiologic der Netzhaut. Breslau. 



BAADER, E. G. 1891 Ueber die Empfindlichkeit des Auges gegen Lichtwechsel. 



Dissertation, Freiburg, pp. 38. 

 B ABLER, ADOLF 1911 Ueber die Verschmelzung von zwei nacheinander erfol- 



genden Lichtreizen. Arch. f. d. ges. Physiol., cxliii, 245-251. 

 BLAAUW, A. H. 1909 Die Perzeption des Lichtes. Rec. des Travaux Botan- 



iques Neerlandais, v, 209; Review in Bot. Cent., 1910, cxiii, 353-356. 

 BLOCH, A. M. 1885 Experiences sur la vision. Compt. Rend, de la Soc. de 



Biol., xxxvii. 

 BRUCKE, E. 1864 Ueber den Nutzeffect intermittirender Netzhautreizungen. 



Wiener Berichte, xlix, II, 128. 



