Effect of infrared radiation on the temperature shown by exposed thermometers

A thermometer to be examined is usually placed in a thermostat filled with water. In this condition, the thermometer is to show the same temperature, no matter whether it gets the heat from the surrounding water by conduction or from the enclosing walls by radiation. In the open field, however, the thermometer presents sometimes the erroneous temperature caused by the follwing facts. 1. Differently conditioned surroundings, for example, heat radiation from clouds overhead, obstacles nearby and atmospheric water vapors etc. 2. Dimension of the bulb, i.e. the relation of radiation to conduction differs by the radius of the thermometer bulb. 3. Wind velocity, which deprives of heat from the thermometer by conduction. Though the exact temperature of air is hardly obtainable by and means of the current instrument, the considerations above made are confirmed by thethermometer being subjected to the varied conditions.