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LXXII. On the Amount of Radium Emanation in the 

 Atmosphere near the Earth's Surface. By A. S. Eve, M.A* 



T T has been proved by Elster and Geitel that a negatively- 

 JL charged wire, exposed for a few hours in the air, receives 

 a radioactive deposit similar in character to the quick-changing 

 products of radium. Radium is known to be widely dis- 

 tributed among the constituents of the earth's crust. More- 

 over, there is evidence that the emanation from the radium 

 in the earth escapes into the atmosphere. From the emanation 

 arise the active deposits of radium in the atmosphere. The 

 radioactive changes in the air and soil account for the 

 ionization of the air ; and important electric and meteoro- 

 logical effects result, the characters of which are at present 

 imperfectly understood. 



It is, then, important to form an estimate of the amount of 

 emanation in the atmosphere, expressed in terms of the 

 quantity of radium required to keep the supply constant. 

 Throughout this paper the cubic metre, and one-billionth 

 <(10 -12 ) gram of pure radium will be adopted as units of 

 measurement. By " pure " radium is meant that which 

 generates 110 gram-calories per hour per gram of radium. 



The first attempt to measure the amount of radium emana- 

 tion in the atmosphere was made by the present writer |, by 

 an indirect method, in the following manner : — On the ground 

 in the Campus of McGrill University was placed a large zinc 

 cylinder, of known volume, with closed ends. Along the 

 axis was a wire, charged negatively to 10,000 volts, on which 

 was collected the active deposit from the air in the cylinder. 

 The activity of this deposit was measured by a gold-leaf 

 electroscope, which was calibrated by means of the active 

 deposit collected on a wire from the emanation obtained from 

 a standard solution of radium of known strength. By this 

 comparative method it was found that a cubic kilometre ot 

 air contained the active deposit which could be obtained 

 from the emanation arising from *14 gram of pure radium 

 bromide. In other words, one cubic metre of air near the 

 earth's surface, at the place of measurement, appeared to 

 contain the emanation from 82 x 10~ 12 grams of pure radium. 

 But there was no definite evidence of the existence of the 

 emanation ; its presence was inferred, not proved. There 

 was also an objection to the method. The active deposit 

 collected on a charged wire fluctuates largely in magnitude ; 



* Communicated by the Author. A preliminary note on this paper 

 appeared as a Bulletin of the Royal Society of Canadaj 21st June, 1907 

 (Ottawa). 



t Phil. Mag. July 1905. 



