125 
1892-93.] Dr William Pole on Colour-Blindness. 
pressions are in themselves not recognisable as mixed. Why there- 
fore is it necessary to assume that these simple final effects can 
only arise from the simple first causes by the intervention of mixing- 
operations ? Where are the difficulties of comprehension which are 
removed by the assumption of fundamental colours ? 
The author then states the various reasons which have prompted 
the assumption of fundamental colours, and shows that the facts are 
capable of explanation without them. 
He does not deny that it is possible to produce all colours (mixed 
with white) by mixtures of three, of which one is arbitrarily 
chosen ; but this is no reason to justify giving them the name of 
fundamental colours. He admits the ingenuity and elegance of the 
theories, but believes that many of the industrious labours, especially 
in regard to colour-blindness, which are carried on in all directions, 
would produce more results of permanent value for science if they 
were not based so dogmatically on particular theories. 
Some of the most accurate investigations on colour-blindness 
show cases that cannot properly be grouped under either of the 
hypotheses. They go the easiest with Hering’s, which gives the 
idea (so well corresponding with the facts) of pairs of colours. But 
it appears very possible that the affection for which “ red-green 
blindness ” is a very suitable name, if taken in a sufficiently wide 
interpretation, really embraces a whole series of different kinds, 
including the red and the green blindness of Helmholtz. 
The author’s object is not to set up a new theory, but to weaken 
the undue reliance on the old ones, so that the freedom of inves- 
tigation may not on all sides be limited and cramped thereby. 
AC. 
Investigations hy Drs Konig and Dieterici, 1883 to 1886. 
Some of the most elaborate investigations we have on colour 
vision were made about this period by Dr Konig and Dr Dieterici, 
two pupils and collaborateurs of Professor von Helmholtz. The 
experiments appear, indeed, to have been made partly under his 
guidance ; he presented accounts of them to the Berlin Academy ; 
and he has incorporated many results of them in his own book. 
They are, therefore, eminently worthy of attention. 
