Sir William Fergusson’s (1808-1877) Speculum is the best known of this class of instruments. Initially constructed of glass, the outer wall of which is first covered with a layer of polished tin foil, silver or mercury, and covered with India rubber over which a coat of black varnish is evenly spread to produce a mirror surface on the inner wall. A relatively scarce and fine example of Fergusson’s model in white porcelain, or very opaque milk-glass, unsigned and in EC.