JoLY AND Smyth — Amount of Radium Emanation in the Soil. 151 



the observed ricliness in radium emanation extends no higher than 5 kilometres, 

 we find, at first sight, difficulty in accounting for the large aggregate of 

 emanation involved. 



In a vertical heiglit of 5 kilometres tliere is over eacli square metre of 

 the land-surface 80 X 10"'^ X 5000 gram radium-equivalent of emanation. 

 In 3'7 days half this amount breaks up. Tliere appears to be only one source 

 from wliicli it can be recuperated — tlie materials spread over the surface of 

 the land. This is the hypotliesis whicli first presents itself. Of the surface- 

 materials we may confine our attention to the soils ; the unbroken rock- 

 surfaces can make but a negligible contribution. The demand on tlie soils 

 is even more considerable tlian this fact implies. It appears highly probable 

 that the radium emanation observed to exist over tlie oceans must be, in part, 

 derived from the land. 



We may calculate from the known rate of break-up of the radium emana- 

 tion the amount which must leave in unit time each square metre of land- 

 surface. This will bo the average exhalation of emanation. We take the 

 atmosphere as radioactively homogeneous to a height of 5 kilometres, and 

 neglect non-productive areas on the land and the contribution of the land 

 to the ocean. 



The radioactive constant of the emanation is nearly 2 x 10"^ The quantity, 

 therefore, transforming each second in the atmosphere over each square metre, 

 expressed as the equivalent radium, is 4x lO-'x 2x 10° = 0-8x lO'^^ gram. 

 This amount must, on the average, exhale each second from each square 

 metre, or, say, 2880 x lO-^^ pm. ]iour. 



In order to investigate how far this condition might be fulfilled, we have 

 made experiments (a) on the amount of radium emanation contained in the 

 gases diffused through the soil, and (i) ou the amount escaping from the 

 surface of the soil. 



Experiments on ground-gases were begun in April this year (1911) at the 

 conclusion of a long spell of dry weather. The first series of observations were 

 carried out in the Park of Trinity College, Dublin. The method of experiment- 

 ing is easily understood. Au iron tube is closed at one end by a plug of pointed 

 iron. The tube is drilled with small holes just above the plug, the holes being 

 sloped both downwards towards the plug and inwards, iu passing through 

 the metal. This tube is driven to the required depth in the ground. The 

 holes above the conical point, in virtue of their sloping direction, do not get 

 clogged. The gases of the soil are withdrawn from the projecting end of the 

 tube, which is fitted with a rubber stopper and a leading tube of glass. This 

 glass tube is normally kept closed by rubber tube and pinch-cock. As the 

 iron tube has a clear bore of about 1'5 cms., an inner tube of brass, fitting 



