A dewpointmeter comprises a detecting element or probe, a thermocouple adapted to determine the temperature of the probe, means for directing a flow of cooling air at the probe, and an electrical circuit extending to the probe and adapted to be completed by condensate formed on the probe, there being a motor driven regulator adapted to control the rate of flow of cooling air directed at the probe, which motor is adapted to be driven in accordance with the current flowing through the circuit.