Apparatus has been developed to accurately measure electrical resistivity as a function of temperature at high temperatures for metals and alloys. The resistivity of 0.254 mm diam tantalum wire has been measured between the temperatures 1170 and 2860 K. Temperature measurements were taken with an automatic optical pyrometer, a twohyphen;color ratio pyrometer, and a tungstenndash;rhenium thermocouple. The temperature observations were made under simulated blackbody conditions, in accordance with the blackbody calculations of deVos. The 2ndash;3percnt; agreement with the tantalum data previously published indicates that the apparatus performs satisfactorily.
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