Atmosphere due to Radioactive Matter. 



27 



in the past few years, yet we may concentrate the best results 

 together, ascertain the measure of success attained by the 

 radioactive theory of the ionization o£ the atmosphere, and 

 indicate those outstanding difficulties which require farther 

 explanation and investigation. 



At the outset it may be stated that the radioactive theory 

 of atmospheric ionization holds the field, and that in most 

 respects it appears sufficient and satisfactory. Yet there are 

 some particulars in which this theory is detective or lacking, 

 so that either there may be causes still undetermined, or our 

 knowledge of the ascertained causes must be incomplete. 

 Also we will consider only normal atmospheric conditions, 

 and not such abnormal ones as thunder-storms — recently 

 explained by Simpson as sometimes due to vertical air 

 currents causing the breaking of water-drops with the well 

 known consequent ionization. 



In this paper the value of the electronic charge e will be 

 taken as 4*6 x 10~ 10 electrostatic unit, and all numerical 

 results will be given on that understanding. Also the value 

 of a, the coefficient of recombination of small ions, will be 

 taken as 3420e or 1*57 x 10~ 6 , at standard temperature and 

 pressure. When the ionization is steady, there will be the 

 well-known relation q = an 2 between q the rate of production 

 of ions and n the number of small ions actually present, in 

 each case per cubic centimetre. So that we have the following 

 table for the corresponding values of q and n. 



?• 



n. 



?• 



n. 



1 



800 



5 



1784 



1-57 



1000 



6 



1960 



2 



1131 



6-28 



2000 



3 



1386 



9 



2400 



4 



1600 



14-13 



3000 



Unfortunately these simple relations rarely if ever exist in 

 the atmosphere, because many small ions become transformed 

 into large ions owing to the presence of water vapour, dust, 

 mist, smoke, or other physical impurities in ihe atmosphere. 

 Recombination is thus delayed, and the number of ions 

 present is exceedingly variable and hard to determine. Other 

 difficulties arise when we seek to determine q, the rate of 



