Abstract: A multiplicity of defogging devices, each having a closed refrigeration system, are arranged in two rows on opposite sides of an elongated strip to be maintained free from fog. The direction of the jet of each individual defogging device is determined by the wind direction and the location of the device in relation to the rest of the defogging devices in its row. The strength of the jets (outlet force or velocity) of the defogging devices of each row is determined by the wind velocity. The ratio between the strength of the jets of the defogging devices on the leeward side of the covered region and the strength of the jets of the defogging devices on the windward side therof is higher than 1 and is increased with increasing wind velocity.