Visual Diffusirity. 



21 



This case is plotted in fig. 2, using the data of fig. 1, 

 taking 12 = 101!. The less intense image should be seen 

 later than the more intense by an interval which should 

 increase with decreasing intensity. If the observation is by 



Fiff. 2. 



SO 



'25 





/\ 







i 





/ \ 







I 







Logb H 



Time-interval between a high intensity and a low intensity image 

 (differing ten times in brightness), as calculated from the data of fig. 1. 



blue light, which goes over into rod vision at the lowest 

 intensities, this interval again decreases, becoming zero when 

 the diffusivity is constant and the same for both images. 

 This is the case represented. 



2nd Case. 



Two colours, red and blue, of the same intensity. 



• • (6) 



• • (7) 



<B~ *B= .„ T , J - :. !„„. T , !■ ' • • ( 8 ) 



/-n, — 



i 



JL 



ce — 



a log I + b ' 



*B<= 



1 

 clogl-fd' 



/, 



1 



a < c ; b<d, 



c log I + d a log I -f b ' 



This case is plotted in fig. 3, again using the data of fig. 1. 

 For all intensities shown on the plot the blue image will be 

 seen later than the red. At high intensities the interval will 

 be smaller than at low. At very low intensities, where the 



