The temperature vs time curve of a cooling or heating incandescent material is displayed either on a cathode ray oscilloscope or a strip chart recorder. Temperatures at which phase transitions occur are seen as discontinuities in the curves. The temperature‐sensing device is a photomultiplier tube. The sample is heated in an eddy current concentrator by induced radio‐frequency currents. Light from the sample is divided by a beam splitter between the phototube and an optical pyrometer which is used for temperature calibration. The temperature range displayed for a fixed starting temperature may be reduced by opposing the phototube's output voltage with an adjustable fixed voltage. Typical cooling curves are included.