1904 - 5 .] Dr W. Peddie on some Views regarding Vision. 949 
equivalent to white by candlelight, and, therefore, by courtesy, 
white.” In the majority of the instances given in Dr Burch’s 
paper the region of the spectrum, in which the light used to 
produce blindness lies, is entirely blotted out, so that evidence of 
‘ whiteness ’ cannot appear. In the case of blinding by green 
light the region is not blotted out, and, between the red part of 
the spectrum on the one hand and the blue on the other, there 
is a narrow band of an indescribable neutral tint. This indicates 
practical whiteness in the green region when the strong blinding 
light is replaced by weaker light. Farther blinding may alter 
this condition, but does not affect the question whether the 
intense coloured lights do not themselves appear to be white. It 
would be of great interest, in the above case, to determine if 
mixture of the red and blue lights which occur on either side of 
the neutral band cannot give rise to a neutral light. There is no 
a priori reason why a mixture of lights should not be neutral to 
a blinded eye although they appear to it to be similar to lights 
which, when viewed by the eye in an unblinded condition, are 
not mutually complementary. It is known that apparent absence 
of colour in light viewed by a colour-blind eye does not prevent 
that light from exercising its property of complementariness ; 
so that lights which are complementary in normal vision are 
also complementary in abnormal vision. But the converse is 
often untrue. 
Whatever may be the case with regard to intense light, Dr 
Burch’s conclusion with regard to weak light seems to be fully 
supported. He finds that some hours of entire rest in darkness 
may be necessary to get rid of ‘dazzle-tints,’ that is, coloured 
luminosity in the eye due to previous exposure to light ; and that, 
when the dazzle-tints have entirely disappeared, “there is no 
interval between the threshold of light-sensation and the threshold 
of colour-sensation,” so that the feeblest visible light has its 
colour manifest. 
With regard to the third belief, Dr Burch’s statement as to 
the transitoriness of the stage of whiteness in blinding by intense 
light, would, if verified, prove a negative. A somewhat different 
phenomenon which I have observed points in the same direction. 
About three years ago I was making observations on after-images 
