center of the pyrolytic graphite body 12 however then the rate of temperature change measured by the thermocouple will not necessarily be the average rate of temperature change in the pyrolytic graphite body 12 although the illustrated embodiment has been discussed in connection with a thermocouple 11 capable of taking convective and radiative heat flux measurements it is to be understood that a gauge measuring radiative heat flux only could be used with for example a sapphire window to transmit only radiation to the gauge the following example serves to explain embodiments of the present invention in more detail the example is not to be construed as being exhaustive or exclusive as to the scope of this invention a gauge was prepared having a type k thermocouple embedded in the center of a pyrolytic graphite body the gauge had dimensions measuring 1 27 cm 0 5 inch in height h 1 27 cm 0 5 inch in length l and 0 48 cm 0 19 inch in width w the bore into which the gauge was inserted was filled with boron nitride then baked to dry the gauge the gauge was subject to a known incident radiation flux of 200 w cm 2 and data was recorded at.