636 Supply of Radium Emanation from Soil to Atmosphere. 



Dec. 8, 18, 24. (In the case of Aug. 24-26 the maximum 

 and minimum respectively may quite possibly have occurred 

 together on Aug. 25.) Maxima in the exhalation curve also 

 occur on Nov. 16 and Mar. 3 accompanied by wind. The 

 only remarkable exceptions occur on Sept-. 15 and Feb. 28, 

 and in both these cases there is a considerable drop in the 

 emanation content of the soil-gas in the next experiment. 

 It will be noticed that for the month of December the ground- 

 gas curve exhibits a remarkable series of oscillations. These 

 seem to be due to the fact that between the 4th and 24th of 

 that month there were five severe gales, besides several 

 lesser storms. 



It is probable that when a gust of wind moves over the 

 surface of the soil it exerts suction on the soil capillaries. 

 The soil-gas, rich in radium emanation, is sucked out, and, 

 when suction ceases, is replaced by dilute gas. Thus escape 

 of emanation is caused by wind. The dilution of the upper 

 parts of the soil-gas as regards emanation steepens the 

 emanation concentration gradient, and thus increases the 

 rate of upward diffusion. This would account for the deple- 

 tion at 50 cm. so often accompanying storm in the experi- 

 ments. 



It is interesting to notice that the soil-gas curve attains its 

 highest value on 31st January — the first experiment per- 

 formed with the ground frozen. This may, perhaps, be 

 attributed to the fact that the frozen surface prevented the 

 escape of emanation. The high figure obtained on the same 

 day for the escape of emanation may probably be accounted 

 for by the fact that the collecting tin had to be pressed into 

 the frozen soil, thus breaking the hard crust. We should 

 expect a great outflow at this point, owing to the increased 

 amount accumulated just below the surface. 



In the following experiment the ground was harder, and 

 the collector was driven in with a hammer. Perhaps it did 

 not go deep enough to pierce the frozen crust, then pre- 

 sumably thicker. The exhalation result is the. lowest re- 

 corded. On the 4th Feb. the collector was only pressed into 

 the snow until it touched the frozen ground. 



A number of high readings occur from Dec. 30th to 

 Jan. 9th on the soil-gas curve. These seem to be due to the 

 fine, calm weather, accompanied by a heavy water-logged 

 soil, which would hinder the escape of emanation. 



As noticed in the previous experiments, rain tends to choke 

 the soil capillaries and cause an accumulation of emanation 

 below the surface. To observe this, we must examine the 

 ■gas curve at points where the wind f'nctor does not 



