Matter present in the AtmosphereA 99 



a known volume of the atmosphere, measured in terms of 

 the mass of radium required to maintain the supply constant. 



2. To ascertain if the natural ionization of the air can be 

 entirely attributed to the radioactive matter present in the 

 atmosphere. 



3. To determine the rate of formation of ions due to the 

 active matter in the air. 



4. To find the distance from which active matter can be 

 collected on a wire maintained at a high negative potential. 



I. On the Amount of Radioactive Matter present in the 

 Atmosphere. 



If a wire is raised to a high negative potential for two or 

 three hours in the open air, it is known that it collects active 

 matter from the air. The rate of decay of the activity of the 

 deposit thus obtained approximates closely to the rate of 

 decay of the matter similarly collected from the emanation 

 of radium. 



It is not necessary to repeat here the summary of evidence 

 collected by Professor Rutherford in the last chapter of 

 6 Radioactivity/ It appears certain that the radium in the 

 earth gives rise to radium-emanation in the atmosphere, and 

 that the emanation in turn disintegrates successively into the 

 three products of rapid decay, radium A, B, C. Bumstead 

 has accurately compared the decay of the active deposit 

 obtained from the air of Newhaven, Connecticut, and has 

 shown that it must be ascribed to radium. He has also 

 observed in the same locality the presence of thorium 

 emanation. It may be of interest to compare the rate of 

 decay of the active deposit obtained from the emanation 

 of radium, as given by Professor Rutherford in his Bakerian 

 Lecture *, w T ith the rate of decay of the active deposit 

 derived from the atmosphere in Montreal, as determined by 

 the present writer 



These results are shown in Table I. and in the curve 



(%. i). 



It is possible that some of the observed difference is due 

 to the presence in the air of active matter from radioactive 

 elements other than radium, such as thorium, but in any 

 case the difference is not large, and it may be partly 

 experimental. 



In order to measure the quantity of emanation present in 

 a given volume of the atmosphere, a simple method of 

 comparison was employed. A negatively-charged wire was 



* Phil. Trans. Roy. Soc. ser. A, vol. cciv. pp. 169-219. 

 H2 



