1892-93.] Dr William Pole on Colour-Blindness. 
127 
colours appeared to coincide, with a maximum at about 455. The 
curves of various kinds are copied in Helmholtz’s work, pages 358 
and 367. 
The next thing was to endeavour to test the applicability to 
these facts of Young’s theory of three fundamental sensations. 
But in order to do this they found it necessary to adopt a new and 
extended view of their nature. 
The general plan had been to consider the three before-mentioned 
“ elementary sensations ” R, G, and V, taken from the spectrum, 
as the “fundamental ” ones. But the authors had reason' to think 
that the result would be better if they endeavoured to find other 
colours for the purpose, and to assume the spectral hues as all ob- 
tained by mixture from these. This was not an entirely new" idea, 
as in 1859 both Clerk-Maxwell and myself had found that the red 
which was invisible to dichromic vision (and which, therefore, was 
considered as fundamental) was extra-spectral ; and others had sus- 
pected the general mixed nature of the spectral colours. 
The fundamental sensations had to be the same in number as the 
elementary ones, and connected w"ith them by linear equations of 
the form 
aR -1- 5G -}- cV 
a + b + c 
The object Konig and Dieterici had in view, as they expressed it, 
was to ascertain whether, among the infinite number of possible 
fundamental colours, they could find three such that a person who 
could only see light and shade should have one of them ; a 
dichromic person should have two of them ; and a normal eye all 
three of them. They w^ere obliged to give up the first condition, 
but after much intricate calculation they found colours that would 
comply with the conditions for dichromic and normal vision. 
It must suffice to give the results of the painstaking labours in 
searching for these fundamentals. They were ultimately settled as 
follows : — 
(1) A red, inclining more to purple than the extreme end of the 
spectrum. 
(2) A green of wave-length about 505. 
(3) A blue of wave-length 'about 470. 
