Notes on experimental technique and apparatusthe phenolic section of the specimen cage, because the thermal instabilities would be restricted to a short length on either side of the liquid nitrogen level. The apparatus attains thermal equilibrium in about 1 h at liquid nitrogen temperature and is then stable for periods up to 5 h. The drift in a 'null' experiment wherein the specimen was not loaded was less than 2 x in h-' over a period of more than 5 h. A creep rate of min-I for a 1 in gauge length specimen requires an extension of 6 x in in 1 h. Such requirements are well within the capabilities of the apparatus.Abstract Small globe thermometers, about half the diameter of the normal (15 cm) instrument, equilibrate quickly and are useful in assessing mean radiant temperature in restricted surroundings. The reduction in sensitivity is not serious. Relations are derived that allow the radiant and convective components of the heat exchange of spheres of different sizes to be predicted.

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