in the Optical Phenomena of Mother of PearL 
in. On the causes of the Phenomena of Mother of Pearl, 
From a careful examination of the preceding facts, we must 
now' be prepared to infer, that all the peculiar phenomena of 
mother of pearl, as seen by reflection and transmission, are 
owing to a particular configuration of surface ; that the communis 
cation of these pr operties to other bodies, is the necessary consequence 
of the communication of its superficial structure ; and that none of 
the light IV hick is concerned in the production of these phenomena, 
has penetrated the surface of the mother of pearl. 
What this configuration of surface is, and in wdiat manner it 
generates the coloured images, are points of high interest, and 
of corresponding difficulty. The facts naturally lead us to 
conjecture, that the extraordinary reflections are produced by 
faces, either curved or rectilineal, slightly inclined to the 
general surface of the mother of pearl. In attempting to 
determine this point, I anticipated no assistance from micro- 
scopical observations, as it w'as contrary to all our notions 
of the action of bodies upon light, to imagine that a plate of 
mother of pearl reflecting an image as perfectly as the mirror 
of a telescope, could exhibit to the human eye any superficial 
irregularities. These anticipations however w'ere wholly 
erroneous. By the application of single microscopes with 
pow'ers of 200, 300, and even 400, 1 have discovered in almost 
every specimen of mother of pearl, an elementary grooved 
surface, which no polishing can modify or remove. This 
structure resembles very closely the delicate texture of the 
skin at the top of an infant's finger; or the lines parallel to 
the coast upon a map, by which the engraver marks the limits 
of the sea and land. When the mother of pearl has a regular 
