Theory of the Flicker Photometer. 



307 



as are called for by our theory as it lias been worked out 

 here. The various straight lines are very nearly parallel. 

 Discussion of this discrepancy between oar theory and 

 experiment will be reserved till the next section. 



The third point studied was the behaviour of the eye 

 toward blue light at low intensities, for different sector 

 openings. The blue light was obtained by the use of a 

 monochromatic blue filter placed over the eyepiece j and the 

 illumination was lowered until the field appeared no longer 

 coloured, but grey. Observations were then made for three 

 angles, 30, 180, and 330 degrees, for four illuminations. 

 The resultant horizontal straight line plots of the data are 

 shown in fig. 8. The approximate symmetry which holds 



loq I 



"Critical frequency-log I data for blue light at low intensities, 

 for exposures of 30°, 180°, and 330°. 



tit high illuminations has entirely disappeared. These data 

 ■are plotted as well in fig. 4 along with the points prophesied 

 from the theory. It is evident that the new phenomenon 

 indicated is a reality, for the critical speed increases con- 

 tinuously as the opening is decreased, instead of returning 

 .toward zero as it does for higher illuminations. 



(e) .Discussion. 



The conflict between our theory and the data on the slope 

 ■of the critical frequency-log I lines for various angles is 

 perhaps due to the simplifying assumptions which we found 

 necessary in order to handle the case at all. We nave, in 

 fact, used practically the case of: a simple sine function 

 superposed on a steady stimulus, and this, as we have already 

 seen (Section 3), gives both from the theory and by experi- 

 ment, lines of slope varying with the relative magnitude of 



Y2 



