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

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                                4 When the hair approached so near to the direction of the mar-
gin of a candle that the <s>light reflected from or very obliquely <\s> inflected light was sufficiently.
<s>and therefore expressly [?], could reach the eye <\s> copious to produce a sensible effect, the fringes 
began to appear, and it was easy to estimate the proportion 
of their breadth to <s>that of <\s> the apparent breadth of the 
hair, across the image of which they extended. I found 
that six of the brightest red fringes, nearly at equal 
distances, occupied the whole of that image. The 
breadth of the aperture was 66/1000, and its distance 
from the hair, 8/10 of an inch; the diameter of the 
hair was less than 1/500 of an inch; as nearly as I 
could ascertain, it was 1/600. Hence we have [11/1000 for 
the deviation of the first red fringe at the distance 8/10,
and as 8/10:11/1000::1/600:11/480000, or] 1/43636 for the difference 
of the routes of the <s>redlight <\s> red light where it was most 
intense. The measure deduced from Newtons experiments 
is 1/39200. I thought this coincidence, with only an 
error of one ninth of so minute a quantity, sufficiently perfect to warrant com-
pletely the explanation of the phenomenon, and even to 
render a repetition of the experiment unnecessary: for there 
are several circumstances which make it difficult to calculate 
much more precisely what ought to be the result of the <s>admeasurement <\s> measurement.
When a number of fibres of the same kind, as,
for instance, a uniform lock of wool, are held near 
to the eye, we see an appearance of halos surrounding 
a distant candle; but their brilliancy, and even their existence 
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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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