results appeared in the Edinburgh Philosophical Journal in 1820.
An
elaborate examination of the microscopic structure of shells was
undertaken many years ago by the late Dr. W. B. Carpenter, and some
valuable results obtained as to the nature of the nacreous varieties.
Microscopic
examination of a thin section of nacre shows that the surface is
traversed by numerous delicate lines ; in some cases almost straight,
while in others they are crumpled and corrugated. These lines are
produced by the outcrop of thin laminae running more or less obliquely
to the surface. It appears that Sir David Brewster regarded them as the
edges of hard calcareous layers, alternating with softer membranous
laminae ; the latter being more readily worn away, would naturally form
grooves, while the former being hard, would stand out as alternating
ridges. Dr. Carpenter, however, regarded the lines on the nacre as the
plaited edges of a single membranous layer.
Whatever
be the exact nature of the lineation, it is certain that the
iridescence is due to the interference of light reflected from the
undulations of the delicately-grooved surface.
When a piece of Mother-ef-Pearl is digested in
