McLaren and Murdock [2] noted hysteresis effects in the AufPt thermocouple amounting to 20-50 mK at the Sb and Ag points, and attributed it to differential thermal expansion of Pt and Au. Such effects, observable as a difference in the measured temperature profile in a fixed-point cell, depending on the direction of immersion (insertion or withdrawal), were overcome by using a stress- relieving coil at the thermocouple junction. McLaren and Murdock used coils consisting of about five turns of Pt wire of diameter 1/4 of that of the thermoelements, i.e. about 0.13 ram, a design adopted by others for the Au/Pt and Pt/Pd thermo- couples (see Table 1). In addition, they used a lead harness for the flexible section of thermocouple just beyond the alumina insulator to minimize deformation of wires during assembly and whilechanging the immersion within a furnace. For greatest benefit, a bar clamp was included. The expansion coefficients of various elements are given in Fig. 4, which includes data for high- density polycrystalline alumina. Clearly, the ther- mal expansion of Au is twice that of Pt, but equally, it is more than twice that of alumina. For measurements with a thermocouple mounted verti- cally, as it would be in a standard fixed-point cell, the relative expansion of the alumina will have little effect, provided the bore is large enough, perhaps > 1 mm, and a stress-relieving coil is used. However, the effect of any expansion relative to