An Account of Some Cases of the Production ofColours, Not Hitherto Described. Thomas Young.

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                                its opposite side, and at last coinciding nearly in 
direction with the former portion; that, accordingly 
as both portions deviated more from a rectilinear 
direction, the difference of the length of their paths 
would become gradually greater and greater, and would 
consequently produce the appearances of colour usual 
in such cases; that, supposing them to be inflected 
at right angles, the difference would amount nearly 
to the diameter of the fibre, and that this difference 
must consequently be smaller as the fibre became smaller,
and, the number of fringes in a right angle becoming 
<s>fewer<s> smaller, that their angular distances would consequently 
become greater, and the whole appearance would be dilated.
It was easy to calculate, that for the light least inflected,
the difference of the paths would be to the diameter of 
the fibre, very nearly as the deviation of the ray, at any 
point, from the rectilinear direction, to its distance from 
the fibre.   MDCCCII 3E 389
I therefore made a rectangular hole in 
a card, and bent its ends so as to support a hair 
parallel to the sides of the hole: then, upon applying 
the eye near the hole, the hair of course appeared dilated 
by indistinct vision into a surface, of which the breadth 
was determined by the distance of the hair and the magni-
tude of the hole, independently of the temporary aperture of the pupil.
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Thomas Young
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An Account of Some Cases of the Production ofColours, Not Hitherto Described. Thomas Young., 1800. From The Royal Society, L&P/12/32



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