THE THRESHOLD OF VISION FOR DIFFERENT COLOURED LIGHTS. 
101 
In fig. 4 the logarithms of the energy at the threshold are plotted against the 
deviations (colour) for W., while in fig. 5 the corresponding curves for B. are given. 
In the case of W. the curve corresponding to the fovea is very much higher, i.e., the 
threshold is higher that for the peripheral curves, and with the intensity of spectrum 
used the central curve could not be traced beyond SSN 35 on the blue side. In the 
case of B., however, the foveal curve is lower than any of the others, showing that for 
this observer the threshold is lower at the fovea than for any other part of the retina, 
while all the curves can be traced right down to SSN 10 . For W. as we proceed out¬ 
wards from the fovea the threshold values, except in the red, rapidly decrease, 
indicating an increasing sensitiveness, up to 5 degrees, there being a slight decrease at 
p 2 
