A thermometer for determining soil temperature. Two forms are in use. One consists of a glass tube bent at right angles, so that the bulb is held at a depth of 50, 100, or 200 mm, with the graduated portion of the tube remaining above and parallel with the ground surface. In the second type, for depths of 300 and 1 000 mm, the thermometer bulb is encased in wax within an outer tube. The whole may be withdrawn from the ground, with the wax acting to prevent any change in the reading while the observation is being made.