The Collaborative International Dictionary of English v.0.48:

Pyroscope \Pyr"o*scope\, n. [Pyro- + -scope: cf. F. pyroscope.]
   (Physics)
   An instrument for measuring the intensity of heat radiating
   from a fire, or the cooling influence of bodies. It is a
   differential thermometer, having one bulb coated with gold or
   silver leaf. [R.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

pyroscope
    n 1: a pyrometer that uses the color of the light emitted by a
         hot object [syn: optical pyrometer, pyroscope]