Mr Dalton on the Vision of Colours. 95 



vations upon them by day-light and candle-light : the result 

 was exactly conformable to my expectation. 



It then appeared to me probable, that a considerable num- 

 ber of individuals might be found whose vision differed from 

 that of the generality, but at the same time agreed with my 

 own. Accordingly, I have since taken every opportunity to 

 explain the circumstances amongst my acquaintance, and have 

 found several in the same predicament. Only one or two I 

 have heard of who differ from the generality and from us also. 

 It is remarkable that, out of twenty-five pupils I once had, to 

 whom I explained this subject, two were found to agree with 

 me ; and, on another similar occasion, one. Like myself, they 

 could see no material difference betwixt pink and light blue by 

 day, but a striking contrast by candle-light. And, on a fuller 

 investigation, I could not perceive they differed from me mate- 

 rially in other colours. They, like all the rest of us, were not 

 aware of their actually seeing colours different from other peo- 

 ple ; but imagined there was great perplexity in the names as- 

 cribed to particular colours. I think I have been informed 

 already of nearly twenty persons whose vision is like mine. 

 The family at Maryport consisted of six sons and one daugh- 

 ter; four of the sons were in the predicament in question. 

 Our family consisted of three sons and one daughter who ar- 

 rived at maturity ; of whom two sons are circumstanced as I 

 have described. The others are mostly individuals in families, 

 some of which are numerous. I do not find that the parents 

 or children in any of the instances have been so, unless in one 

 case. Nor have I been able to discover any physical cause 

 whatever for it. Our vision, except as to colours, is as clear 

 and distinct as that of other persons. Only two or three arc 

 short-sighted. It is remarkable that I have not heard of one 

 female subject to this peculiarity. 



From a great variety of observations made with many of 

 the above-mentioned persons, it does not appear to me that 

 we differ more from one another than persons in general do. 

 We certainly agree in the principal facts which characterize 

 our vision, and which I have attempted to point out below. 

 It is but justice to observe here, that several of the resemblan- 

 ces and comparisons mentioned in i lie preceding part of tlu^ 



