1892-93.] Dr William Pole on Colour-Blindness. 107 
incandescent metals the red lithium line, the green thallium line, 
and the yellow sodium line appeared perfectly alike in colour, 
hut the two first slightly less bright than the last. It was, 
the author says, interesting to see how, after making mistakes 
with the defective eye, he always explained and corrected them by 
the aid of the normal one. 
As to the hue of the two colours, Hippel says: — “I have given the 
patient the yellow sodium, the blue indium, and the csesium lines 
alternately with the normal and the abnormal eye. I have always 
obtained the most definite assurance that the lines appear absolutely 
alike in hue, only to the blind eye a little weaker in luminosity. 
The two eyes behave in an analogous manner in regard to white ; 
one sees white exactly as the other does, only the dichromic one a 
little paler.” 
The neutral line was between h and F, but was difficult to 
define, it changed with the changing illumination ; with increasing 
brightness it went nearer to F ; with diminishing brightness nearer 
to h. The brightest parts in each colour were also difficult ; but 
after many trials they were for the yellow close beyond D, for the 
blue between F and G, rather nearer the latter. 
The author remarked that the defect must be congenital, because 
the nature of the colour-disturbance agreed perfectly with the 
congenital defect, and there was absolutely no symptom of any- 
thing wrong with the other eye. He said in conclusion : — “I see no 
possibility of bringing these facts into accord with the Young- 
Helmholtz hypothesis, without doing the greatest violence to it, 
and giving up its fundamental principles ; whereas they come 
easily within the scope of the Hering theory, to which they present 
no difficulty in any direction.” 
G. 
Extracts from Professor Holmgren’s Paper given to the Royal 
Society of London, 1881. 
A combination of a normal and an abnormal eye with the same 
brain is not impossible I have been fortunate enough to 
examine two such cases ; one a case of one-sided red-blindness. 
A one-sided colour-blind person has, through his normal eye, 
