Pȳ-rōm'e-ter, n.

n. [Fr. pyromètre, from Gr. πῦρ, πυρός, fire, and μέτρον, measure.] An instrument for measuring degrees of heat above those indicated by the mercurial thermometer, constructed usually on the principle of registering, or measuring, by means of multiplying levers and a scale, the change in length of some expansible substance, as a metallic rod, when exposed to the heat to be measured.

☞ The name was first applied by Muschenbroek, and is still sometimes used to designate an instrument of this class invented by him for measuring the expansion of solid bodies by heat.