n. [ Pyro- + -meter: cf. F. pyromètre. ] 1. (Physics) An instrument used for measuring the expansion of solid bodies by heat. [ 1913 Webster ]

2. (Physics) An instrument for measuring degrees of heat above those indicated by the mercurial thermometer. [ 1913 Webster ]

☞ 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. [ 1913 Webster ]