Note 760 — ARTIFICIAL PEARLS.

[When the surface of pearl is examined with a microscope, it is found to be indented by a large number of delicate grooves, which by their effect upon the light give rise to the play of colours; and if impressions of them be taken upon wax, fusible metal, lead, balsam of Tolu, &c., the impressed surface exhibits the prismatic colours in the same manner as the pearl. This principle has been applied by Mr. Barton and others to the making of ornaments, in the form of buttons, artificial jewels, &c., by grooving the surface of steel with a very fine cutting machine. The theory of the production of the colours is this: the surfaces of the grooves, from their varied inclinations, reflect the incident white light at various angles, hence the correspondence of the luminous undulations is interrupted and some of them check or interfere with one another, others continue their course. Now, ordinary white light being a mixture of coloured rays, when some of these are checked or interfered with in their progress, the remainder continue their course and appear of that colour which results from the ocular impression communicated by them.]