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

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                                intermediate between the densities of the medium containing 
it, the effect would be reversed, and the central spot, instead 
of black, would become white; and I have now the 
pleasure of stating that I have fully verified this prediction,
by interposing a drop of oil of sassafras between a prism 
of flint glass, and a lens of crown glass; the central 
spot seen by reflected light was white, and surrounded by a dark ring: it was 
however necessary to use some force, in order to produce a 
contact sufficiently intimate; and the white spot differed 
even at last <s>from<\s> in the same degree from perfect whiteness,
as the black spot usually does from perfect blackness.
The colours of mixed plates suggested to me an 
idea which appears to lead to an explanation of the 
dispersion of colours by refraction, more simple and satisfactory 
than that which I advanced in the last Bakerian lecture.
We may suppose that every refractive medium transmits 
the undulations constituting light in two separate 
portions, one passing through its ultimate particles, and the 
other through its pores; and that these portions reunite 
continually, after each successive separation, the one having 
preceded the other by a very minute but constant interval, 
depending on the regular arrangement of the particles of a 
homogeneous medium. Now, if these two portions were 
always equal, each point of the undulations resulting from their reunion 
would always be found half way between the places of the 
corresponding point in the separate portions; but, supposing 
                            
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Manuscript details

Author
Thomas Young
Reference
L&P/12/32
Series
L&P
Date
1800
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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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