METALLIC mirrors have been known from very early times, and references to them are scattered through ancient literature. They were frequently elaborately decorated, and many of them possess the greatest interest as objects of art. Looking-glasses coated with an amalgam of quicksilver and tin came into use about the middle of the fifteenth century, but it is not known by whom they were originally invented. The details of their manufacture were, for long”, carefully guarded as trade secrets, and were not made public until about a hundred years later. The process then described is in all essentials that still employed, wherever it has not been abandoned on account of the danger to workers from mercurial poisoning. Tin amalgam mirrors were most extensively used during the latter half of last century, but at the present time in England and Germany they are no longer made, as mirrors obtained by the actual deposition of metallic silver upon glass have displaced them.