. . "R(T) and R(To) are the resistances of the thermistor at T and To respectively; and B is a material constant for the material of the thermistor. ##EQU2## where ew is the ambient water vapor pressure in mb; Tc is the temperature of the carbon element in degrees centigrade; es is the saturation vapor pressure at Tc ; and RH is the relative humidity expressed as a decimal." . .