But this is not all with a dyed fabric, for
here the light is not simply reflected light; part of it has traversed
the upper layers of that coloured body, and is then reflected from the
interior, losing a portion of its coloured rays by absorption. This
reflected coloured light is always mixed with a certain amount of white
light reflected from the actual surface of the body before penetrating
its uppermost layer. Thus, if dyed fabrics are examined by the
spectroscope, the same appearances are generally observed as with the
solution of the corresponding colouring matters. An absorption spectrum
is in each case obtained, but the one from the solution is the purer,
for it does not contain the mixed white light reflected from the
surfaces of coloured objects. Let us now take an example. We will take a
cylinder glass full of picric acid in water, and of a yellow colour. Now
when I pass white light through that solution and examine the emerging
light, which looks, to my naked eye, yellow, I find by the spectroscope
that what has taken place is this: the blue part of the spectrum is
totally extinguished as far as G and 2/3 of F.
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