On the Vision of Colours. 39 
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 ex- 
plained 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 materially 
in other colours. They, like all the rest of us, were 
not aware of their actually seeing colours different 
from other people; but imagined there was great 
perplexity in the names ascribed to particular co- 
lours. I think I have been informed already of near- 
ly twenty persons whose vision is like mine. The 
family at Maryport consisted of six sons and one 
daughter; four of the sons were in the predicament 
in question. Our family consisted of three sons 
and one daughter who arrived 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 pa- 
rents 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 
