Modification of Vernon's globe thermometer and its calibration in terms of physiological strain

Six men wearing shorts performed treadmill work in about 150 climatic chamber experiments at several temperatures of Vernon's globe thermometer (tg) from 25 to 50 degrees C. Each tg was produced partly by an equal air temperature (ta) and a mean radiant temperature (MRT), partly by a lowered ta (minimum 5 degrees C) and an MRT elevated up to about 80 degrees C above the ta. With an increasing MRT and lowered ta, respectively, body temperature, heart rates, and sweat losses decreased significantly. In another 55 experiments physiologically equivalent combinations of ta and MRT were derived. According to the results a modified globe thermometer was built. It reduced the errors of Vernon's instrument by about 75%. The remaining error of 25% was due to changes in air velocity between 0.5 and 2 m.s-1. The applicability of simple instruments like globe thermometers is obviously limited for the description of physiologically equivalent conditions of unequal ta and MRT at various air velocities.