ME. W. POLE ON COLOUE-BLINDNESS. 325 
any physical defect of the visual organs. My own eyesight is very sensitive to minute 
differences of tone or hue in regard to those colours which I can see. 
C. The third variety is the only one with which we have now to do. It is a real phy- 
sical defect in vision, of a milder character than the first kind, but much more common; 
and its outward manifestation is a natural inability to distinguish between many of the 
colours most marked and distinct to normal eyes. It is yet an open question what 
degrees of severity may exist in this defect; but its most complete form is that called 
dichromic vision, of which my own case is a very perfect example. 
6. I was bom in 1814. My eyesight, in every other respect but that of colour, is 
remarkably good. I am very fond of bright colours, and of scenes and pictures that 
contain them. 
I believe I was about eight or ten years old when the mistaking of a piece of red cloth 
for a green leaf betrayed the existence of some peculiarity in my ideas of colour ; and as 
I grew older, continued errors of a similar nature led my friends to suspect that my eye- 
sight was defective ; but I myself could not comprehend this, insisting that I saw colours 
clearly enough, and only mistook their names. 
I was articled to a cml engineer, and had to go through many years’ practice in 
making drawings of the kind connected with this profession. These are frequently 
coloured, and I recollect often being obliged to ask, in copying a dravfing, what colour’s 
I ought to use ; but these difficulties left no permanent impression, and up to a mature 
age I had no suspicion that my vision was different from that of other people. I 
frequently made mistakes, and noticed many cu’cumstances in regard to colours which 
temporarily perplexed mef; but I still adhered to my first opinion, that I was only at 
fault in regard to the names of colours, and not as to the ideas of them ; and this opinion 
was strengthened by observing that the persons who were attempting to point out my 
mistakes, often disputed among themselves as to what certain hues of colour ought to 
be called. 
I was nearly thirty years of age, when a glaring blunder, persisted in by me in oppo- 
sition to the positive evidence of others, led me seriously to suspect that my vision of 
colours must be defective ; and this suspicion once admitted, it was soon confirmed and 
strengthened by further observation. I cannot recollect what process of investigation I 
followed, but I succeeded in determining, from my own case, the general facts now 
known to characterize the defect, and made out its principal feature to be an insensi- 
bihty to one of the primary colours. I subsequently became acquainted with the 
* I use the word hue always to denote a distinct variety of colour. The variations in illumination or 
shade which may be given to any hue by its mixture with white or black, I call tones. The light tones pro- 
duced by diluting it with white are technically called “ tints the dark ones formed by darkening it with 
black are called “ shades.” Thus the addition, to any pigment, of white or black will only alter its tone ; 
the addition of any other colour will alter its hue, 
I recollect in particular, having wondered why the beautiful rose light of sunset on the Alps, which 
threw my friends into raptures, seemed all a delusion to me. 
MDCCCLIX. 2 X 
