182 Mr. Bew on Blindnefs. 
feels himfelf alarmed with new fenfations, that 
bear a ftrong relation to our ideas of light and 
colour; but which he finds it impoffible to de- 
feribe, becaufe he cannot fix on any comparative 
idea whereby to explain himfelf. Thefe dreams, 
my intelligent friend informs me, are always 
painful, and, as may naturally be expe&ed, the 
impreffions are extremely tranfient and unfatif- 
faflory. 
But it is not the blind only, who are unable 
to trace the various effe&s produced by light and 
colour. There are perfons, whofe organs of 
vifion are fo imperfedtly formed, that they can* 
not diftinguilh colours, though they fee the objects 
-perfeftly. In the Philofophical Tran factions 
we have an account of a man who knew no 
difference of colour whatever; and there is an in¬ 
genious perfon, within the circle of our acquaint¬ 
ance, whofe knowledge in Perfpeftive, as well 
as in the other branches of Natural Philofophy, 
is unqueftionable; yet who finds himfelf defici¬ 
ent in difeerning the difference of fome colours, 
which he knows to exilt, and v/hich are diftin- 
guilhable to perfect vifion. In particular, I think 
I have heard him mention, that the fenfation 
he felt, from the colours of brown and green, 
had no obvious difference, provided they were 
diffufed with equal degrees of intenfenefs. 
But thefe fpeculations, however curious and 
entertaining, were not the principal objefls I 
had 
