Two nude resting men were exposed for two-hour periods to each of 25 dry environments, with air temperatures ranging between 12.8° C and 49.1° C and wind speeds between 0.67 m/sec and 4.94 m/sec. The mean radiant temperature of the surroundings was kept equal to the air temperature. Rates of radiant and convective heat exchange were measured directly, separately and continuously. The men had reached a thermal steady state after 105 min in the warm environments, but not in the cold environments. Graphs are presented to show the effect of ambient temperature and wind speed on the radiation and convection rates attained after 105 min, as well as on metabolic rate, sweat evaporation rate, rectal temperature and mean skin temperature. These graphs revealed some important aspects of the behaviour of man's thermal control system. In particular the physiological conductance increased with increasing ambient temperature and then “saturated” at an ambient temperature near 35° C. This saturation resulted in a constant difference between rectal temperature and mean skin temperature irrespective of the environmental conditions.
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Mitchell, D., Wyndham, C.H., Atkins, A.R. et al. Direct measurement of the thermal responses of nude resting men in dry environments. Pflugers Arch. 303, 324–343 (1968). https://doi.org/10.1007/BF00596389