948 Proceedings of Royal Society of Edinburgh. [sess. 
Note on some generally accepted Views regarding 
Vision. By Dr W. Peddie. 
(MS. received June 29, 1905. Read July 17, 1905.) 
The following beliefs regarding vision meet with very general 
acceptance : — 
First. Very intense light of any wave-length produces prac- 
tically the sensation of whiteness. 
Second. Very weak light of any wave-length produces prac- 
tically the sensation of whiteness. 
Third. A coloured area of normal brightness retains its colour, 
though with diminished purity, when gazed at steadily for a 
long time. 
Fourth. Small, faintly luminous, objects are seen more easily 
by indirect vision than by direct vision. 
The first and second of these supposed facts are readily 
accounted for on any of the usual theories of vision. The 
Young-Helmholtz theory, for example, gives quite as easy an 
explanation of them as Hering’s theory gives. Yet the truth of 
these supposed facts is by no means a necessary result of any of 
the theories. In a recent paper “ On Colour-Vision by very Weak 
Light” ( Proc . Roy. Soc., B 508, 1905), Dr G. J. Burch describes 
experiments which lead him to the conclusion that the second 
statement is not necessarily true. In that paper he also refers 
to the first statement in the following words : “ In my paper 
on Artificial Colour-Blindness” {Phil. Trans., B vol. 191, 1899), 
“ I described experiments showing that Hering’s argument in favour 
of a black-white sensation is invalid, in so far as it rests on the 
statement that by intense light all colours tend towards white. 
For the apparent whiteness — in the green region, for instance — is 
only a transitory stage in the production of green blindness, and 
is reached when the green sensation is reduced to the strength 
of the underlying blue and red, the mixture of the three being 
