Py*rom"e*ter (?), n. [Pyro- +
-meter: cf. F. pyromètre.] 1.
(Physics) An instrument used for measuring the expansion
of solid bodies by heat.
2. (Physics) An instrument for
measuring degrees of heat above those indicated by the mercurial
thermometer.
&fist; It is usually constructed so as to register the change which
the heat to be measured produces in the length of some expansible
substance, as a metallic rod, or in the intensity of a thermo-electric
current.