Measurements using a Pt-Rh heater strip in a high temperature X-ray diffractometer furnace show that the temperature indicated by a two-colour infra-red pyrometer directed at the upper surface of the strip is within fl “C of the temperature indicated by a Pt/Pt-lO%Rh (type S) thermocouple welded to the lower surface, over the temperature range from 600-l 100 “C. However, the temperature of a po...