102 Dr. "W. Pole on some unpublished 



"Nash Manor, June 1859." 

 " The great peculiarity of my case is that it has existed in my 

 family, as far as we have been able to trace, for generations, and 

 has always skipped over the female branches, although, as in my 

 own case, it has been transmitted through them. 

 " My brother has the same peculiarity of vision. 

 " I have long been convinced that I really see but three colours, 

 viz. blue, yellow, and white, and the absence of all colour, black. 

 By taking the water-colours gamboge, Prussian blue, and Indian 

 ink, I can produce all the colours I see in Nature. I form my 

 reds, greens, and browns by combinations of yellow and black ; 

 pinks and crimsons by light and dark blue. The rainbow appears 

 to me to be composed of but two well-defined and distinct bands, 

 stripes, or colours, the one shaded from light to dark blue, aud the 

 other shaded from light to dark yellow.'" 



"E. C. Nicoll-Cabne." 



I visited these gentlemen on the 14th of July, 1859. They 

 had never before been subjected to any precise or quantitative 

 experiments, and I am glad to have the opportunity of record- 

 ing the actual facts of their vision. Both brothers took part 

 in the examination, and their colour-impressions, so far as 

 I could tell, appeared precisely similar. 



I also examined a Mr. Lloyd, a middle-aged gentleman of 

 good intelligence, but not pretending to scientific knowledge ; 

 and a fourth example was Mr. Parry, a professional chemist, 

 whose case was peculiarly useful as forming the greatest con- 

 trast with mine. 



In all these cases I followed the same plan. After a pre- 

 liminary examination with the Chevreul circle and "gammes," 

 I obtained their matches with the revolving-disk tests, in the 

 manner described for myself in par. 19 of my paper. I have 

 collected the whole of the equations at the end of this article, 

 and I have added the case of Mr. Simpson, who was tested 

 by Prof. Clerk Maxwell about the same time, with, I believe, 

 the same colours. 



I am also able to add to these, by indirect evidence, another 

 case of great celebrity, namely that of John Dalton. Sir 

 John Herschel was good enough to suj^mit for my examination 

 the data he had obtained from Dalton, as mentioned in the 

 well-known letter of 1 833 ; and I had no difficulty in estab- 

 lishing the general similarity between Dalton's vision and 

 my own, subject to certain variations of the kind I am now 

 considering *. And, further, I found some data by which to 

 estimate roughly the nature and extent of these variations. 

 He had pointed out samples of red and green silk, which 



* See ' Contemporary Review,' May 1880, for further particulars. 



