274 



BACON. 



to this cause alone. In order to explain the maintenance of the large positive 

 charge which generally exists in the upper atmosphere, there must be a strong 

 ionization of the upper air, a condition which may possibly be due to ionizing 

 radiations emitted by the sun. 



However, there are several statements in the recent literature of 

 radioactivity which seem to point to the idea that there also may be 

 other factors than radioactive processes which help to cause the observed 

 ionization of the air. Thus Eutherford and Allan, 10 working in Canada, 

 found that in winter, with the ground frozen and deeply covered with 

 snow, and the wind blowing from the north over snow-covered fields, 

 there was quite as much, and, in many cases, more ionization of the 

 air than in summer in the same place. 



This fact is difficult to reconcile with the idea of radioactive emanation 

 escaping into the atmosphere from the pores of the earth, and is much 

 easier to explain on the basis of a sunlight ionization, or of a secondary 

 ionization of the air due to snow sublimation and an intermediate forma- 

 tion of hydrogen peroxide. 



Elster and Geitel, 17 who made extensive studies on the effects of 

 meteorologic conditions on the radioactivity of the atmosphere, sum- 

 marized their conclusions in the following table : 



No. 



Weather. 



Rate of 

 leak of ' 

 charge. 



Fog, wind southeast 



Fine rain, mist 



Clear, air very transparent . 



3.77 

 3.18 

 8.58 

 Sky half overcast, air very transparent! 13. 67 



Rate of 

 leak of 

 charge. 



2. 64 



3. 02 

 9.82 



13. 83 



It is a curious coincidence, if nothing more, that days when the sky 

 is about half overcast are days such as No. 4, when the chemical activity 

 of the sun is greatest on reactions like the blackening of "silver salts, 

 the decomposition of oxalic acid under the influence of uranium salts, 

 and on the ionization of the air by tropical sunlight, in short, on 

 reactions effected by the ultra-violet portion of the sun's spectrum. 



If the radium emanation in the atmosphere and the penetrating radia- 

 tion due to radium in the earth are together the main causes of the 

 ionization of the atmosphere near the surface of the earth, then it might 

 be expected that the ionization over the land would be greater than that 

 over the sea. The experimental evidence at present obtainable indicates 

 that radium is present in sea water to a markedly less extent than in 

 the sedimentary rocks on land ; and since the radium emanation decays to 

 half its value in five days, the wind is unable to transport the emanation 



'"Phil. Mag. (1902), (6), 4, 704. 

 17 Ann. d. Phijs. (1900), 2, 425. 



