2. A reflector of polished metal, especially one used in
reflecting telescopes. See {Speculum metal}, below.
3. (Surg.) An instrument for dilating certain passages of the
body, and throwing light within them, thus facilitating
examination or surgical operations.
4. (Zo["o]l.) A bright and lustrous patch of color found on
the wings of ducks and some other birds. It is usually
situated on the distal portions of the secondary quills,
and is much more brilliant in the adult male than in the
female.
{Speculum metal}, a hard, brittle alloy used for making the
reflectors of telescopes and other instruments, usually
consisting of copper and tin in various proportions, one
of the best being that in which there are 126.4 parts of
copper to 58.9 parts of tin, with sometimes a small
proportion of arsenic, antimony, or zinc added to improve
the whiteness.