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XVII. On Colour-Blindness. By William Pole, F.R.A.S., F.G.S., Mem. Inst. C.F., 
Professor of Civil Engineering, University College, London. Communicated hj 
Charles Manby, F.R.S. 
Eeceived March 24, — Eead April 7, 1859*. 
1. Mt object in this paper is to state my own case of Colour-Blindness, which I believe 
O'! aid to show that the general phenomena 
attendmg this defect of vision are more simple, uniform, and consistent than is generally 
supposed. ® ^ 
2. Some apology is perhaps necessary for a colour-bUnd person undertaking to treat 
even mdu-ectly, of the subject of colours; on which the views formed from his own expe- 
nence must necessarily be very Umited. It is not, however, my intention to trespass upon 
the provmce of the normal-eyed. All I wish to do is to give a statement, as explicit and 
accuiate as I can, of the facts connected with the sensations of myself and others simi- 
arly situated, leaving these facts to be discussed by others more competent to deal with 
them. 
And as far as the con-ect detennination of these facts is concerned, it seems to me 
that we, the colour-blind, are really in a better position for investigating their nature 
than the normal-eyed. 
Such an investigation must be based entirely on a comparison of the impressions 
expermnced respectively by two distinct classes of individuals. The normal-eyed person 
experiences one set of sensations, the colour-blind person a set entirely different; neither 
can see^ what the other sees; and each must therefore draw his ideas of the other’s 
impressions solely from the description communicated to him. 
Now in such case, supposing it is necessary for one of the parties so far to understand 
both sets of phenomena as to describe faithfully the difference between them it is 
evident that he will be most favourably situated who can procure the best testimony 
rom the other side ; and this is certainly the position of the colour-blind. The greatest 
difflcu ty in dealing with the subject has been hitherto, and still is, the limited td 
perfect nature of the evidence obtainable from those labouring under the defect; and 
y mall, only (as far as can at present be computed) about two or three in every 
19 ™ identical with a former paper by the anther, received June 7 and read June 
rtb 1 d f P- 1^2), which is here presented in an abridged and modiSed form 
anther in the iXL Maxwki's oolonr-top, made by thj 
