Methods and Results of Measurements:-- A stick of steel was driven into the ground down to one meter depth, and a narrow pipe of aluminum or brass, closed at the upper end, was inserted and the hole covered by a board and earth. (See
Fig.3.) In Fig.2 the locations for the experiments are shown by x. Fig.1 gives the atmospheric temperatures at noon, October4-21,1955, when the experiments were carried out. About three hours after the above setting had been done, the gas in the hole was replaced by a bottle of water, and was collected, by driving sprayer for five minutes with apparatus as shown in Fig.5, in a can in which an autoradiographic plate was set. (See Fig.6.) The temperature in the hole was read by means of a maximum thermometer hung in the hole for ten minutes at one meter depth. Fig.7 shows the distribution of temperatures at one meter depth thus observed. Exactly twenty four hours after the above setting, the autoradiographic plate in the can (a quarter sized Fuji ET-2E plate, 15μ thick, for contact method) was developed. For developing, the plate was immersed in Ilford D-19 for fifteen minutes, then fixed with Fuji-fix for fifteen minutes, washed with running water for forty minutes, and dried. Then those autoradiographic plate was examined under the microscope of magnification ×280, to count the number of tracks of a-particles. The results obtained are shown in Fig.8. Underground Temperature Distribution:-- On the basis of the distribution of temperatures at one meter depth (Fig.7) and of other available boring data, the distribution of undergound temperatures is estimated as shown in Fig.9 (vertical section along the Misasa river).