1911 Encyclopædia Britannica/Speculum

SPECULUM, the Latin word for a mirror, employed more particularly for a metallic mirror used in a reflecting telescope. In early instruments metallic mirrors, made from an alloy of copper and tin, with the addition of a little arsenic or other metals to increase the whiteness, were customarily employed, but they have now been displaced by the more convenient silver-on-glass mirror (see Telescope). Various forms of specula are used in surgery for examining internal organs.