with
hardened steel dies upon which the delicate lines had been engraved.
Nothing can better illustrate the nature of the optical phenomena
presented by nacre, or Mother-of-Pearl, than their artificial
reproduction by Barton's method.
It
is therefore demonstrated that the iridescent colours of nacre are
produced by the light reflected from the corrugated surface, resulting
in that beautiful appearance by which the very atoms of the substance
seem as if lit up by colour; now at one end of the solar spectrum where
violet, blue and green rays predominate, and now at the other end where
red, orange and yellow unite in such harmonious blending as to produce
the most pleasing offects.
This
nacre then composes the whole interior of the shell, and is the same
secretion which in the Pearl has assumed a more or less globular form :
between nacre and Pearls, therefore, there is virtually only the
difference of the form of deposition.
The
Mother-of-Pearl shell lies on the sea bottom, usually inclined at an
angle of 20 degrees, with the flat valve downwards, although it is
frequently found reversed. In young shells, more particularly the
black-edged variety, there is a byssus or bunch of strong fibres which passes through the hinge or
