TESTS OF NATURAL AND CULTURE PEARLS.—A simple optical method of distinguishing the Japanese “culture” pearls from wholly natural pearls is described by Dr. F. E. Wright in Journ. Washington Acad. Sci., 1923, vol. 13, p. 282. In a bead of mother-of-pearl, such as is always used for the nucleus of the “culture” pearls, the nacreous layers are not concentric to the surface, but are approximately plane, being parallel to the surface of the shell from which the bead was cut. Now normal to this surface the reflecting power, and consequently also the opacity, is at a maximum; whilst at 900 from this direction (that is, looking along the laminae) there is a minimum of reflection and of opacity. A “culture” pearl when viewed in a strong reflected light (for example, with the observer's back to the sun) shows at the opposite poles of one diameter a small bright spot due to the light reflected from the laminae of the enclosed bead of mother-of-pearl. In a strong beam of transmitted light (arranged in a closed box with lens and mirror, the pearl resting in a circular aperture) the “culture” pearl shows two positions of maximum opacity, whilst the natural pearl is the same in all positions. A third method, which is applicable also to “culture” pearls containing a real pearl as nucleus, is given by an examination of the walls of the hole drilled through the pearl. The pearl is illuminated by a strong side light and a minute bead melted on the end of a gold wire is inserted in the bore to act as a reflector, which is viewed under the microscope.