328 



Contributions to the Study of Flicker. 



[May 14, 



vary the intensity of its illumination by the white light. We can, 

 therefore, by the help of what has already been said, deduce from the 

 above constants for each curve in fig. 4, the illumination of the disc 

 at each point of the spectrum considered, for it follows from the 

 nature of the curves in fig. 3, that each of the above seven constants 

 is of the form c + d log I, where c = 0*2560085, and d = 0-066283, 

 and I is the measure of the illumination to which the disc is exposed 

 in terms of the unit illumination already used. We have, therefore, 



for the violet curve 0-2660459 = 0-2560085 + 0-066283 x log I 

 whence I = 1-42 approx. Similarly for the other colours in the order 

 of the curves from left to right, we find I - 2-62, 4-50, 7 71, 13-22, 



