The effect of wind, temperature, humidity and sunshine on the loss of heat of a body at temperature 98°F.

1. Diagrams are given showing isopleths of the cooling power of the air in millicalories per cm.2 per second for winds up to 30 m.p.h. and for temperatures from 0° to 90°F. for— (i) A “dry” body at 98°F. (ii) A “wet” body at 98°F. (a) For dry air. (b) For saturated air. (iii) A “wet” body at 98°F. for wet-bulb temperatures from 0° to 90°F. They are based on the formulae given by Hill. 2. The cooling power of the air at Croydon has been computed for each day of the year 1934, both for a dry body and for a wet body, and a frequency table is given showing the number of days in each month with different degrees of cooling power. In an exposed situation there is little difference on the average between the cooling power by day and by night. 3. The effect of reducing the wind to values similar to those ordinarily experienced in unexposed places has been examined for typical months. It is found that this smooths the differences and reduces the mean values of cooling power by about one-third. 4. The effect on cooling power in the daytime of solar and sky radiation is computed: in a warm summer month the gain of heat in the middle of the day exceeds the loss of heat by a body at 98°F. in a situation where the wind is only one quarter of that recorded at Croydon at 100 feet above the ground. The effect of loss of heat by outward radiation to sky and earth at night is shown to be generally insignificant compared with the losses due to convection and radiation to the surroundings at the temperature of the air. 5. The relation between cooling power and the terms hot, warm, cold, is examined and a scale suggested, which agrees with a scale independently proposed by Conrad. From this scale a scheme of terms appropriate to different conditions of temperature, wind, and cloud is arrived at. A further specification of terms in relation to wind temperature and wet-bulb temperature is also given.