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 silveron-glass mirror (see TELESCOPE) . Various forms of specula are used in surgery for examining internal organs .