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XI. 



ON THE AMOUNT OP RADIUM EMANATION IN THE SOIL 

 AND ITS ESCAPE INTO THE ATMOSPHERE. 



By JOHN JOLY, Sc.D., F.R.S., 

 Professor of Geology and Mineralogy in the Univei'sity of Dublin, 



AND 



LOUIS B. SMYTH, B.A., 



Assistant to tlie Professor of Geology, Univ. Dubl. 



(Plath IX.) 



[Read, June 27. Received for Publication, Junk 27. Published, August 29, 1911.] 



To adequately review the development of the subject of the radioactivity of 

 tlie gases of the soils would dem.and much space ; nor is it necessary for the 

 statement of the observations which we liave to record upon this subject. A 

 brief sketch of the state of ovir knowledge will suffice. 



The pioneer observations of Elster and Geitel showed that a wire freely 

 exposed to the atmosphere and maintained at high negative potential had 

 condensed upon it a radioactive substance which could be removed by friction 

 or by solution, and whicli when brought into an electroscope much increased 

 the ionization. It is now well known that this active deposit is derived 

 from the break-up of radioactive emanations in the atmosphere. 



Tlie active deposit detected by Elster and Geitel has been observed in 

 many parts of the world, and at high altitudes on mountain tops. It lias 

 been found in rainwater and in snow. 



The early observations of Rutlierford and Allen in Canada' on the rate of 

 decay of the active deposit collected from the atmosphere by means of a 

 negatively electrified wire, were followed by many others sliowing that in 

 many cases the rate of decay indicated tliat tlie deposit is that arising from 

 the disintegration of the emanation of radium. Subsequent observations 

 showed that the active deposit upon the wire often behaved as if active 

 deposit from the emanation of thorium was also present. 



1 Phil. Mag., Dec, 1902. 



