252 Mr. A. S. Eve on the Ionization of 



These experiments, and those of A. Boltzmann, indicate 

 that the ionization over the ocean is about the same as that 

 over the land. 



The ionization in the air over land is generally attributed 

 to radium emanation and its successive products in the 

 atmosphere, and to the penetrating rays from the active 

 matter in the earth. I am not aware that any other adequate 

 cause has been suggested which will account for the pro- 

 duction o£ positive and negative ions near the earth's surface, 

 but there may be causes with which we are not at present 

 acquainted. 



Various experimenters have found that the relationship 

 q = an 2 does not hold good, probably owing to the presence 

 of dust and impurities in the air. Thus Mache and Rimmer * 

 find a— 4-6 XlO -6 for the air in a cave, and a= 2*1 x 10~ 6 

 for surface air. Whilst Townsend, McClung, and Langevin 

 find for dust-free air a = l*lxl0 -6 . But supposing that 

 we take any of these values as approximately correct for the 

 lower layers of the atmosphere, then, since n is about 1000, 

 we find q — 1'1 to 4*6. So that if a few ions per c.c. per 

 second are produced by active matter in the earth or air, the 

 ionization of the atmosphere over the land surface can be 

 satisfactorily explained. But Cooke has proved that the 

 penetrating radiation at Montreal produces about 4 ions 

 per c.c. per second in a brass vessel, and I have deduced 

 from this value an estimate of the amount of radium near 

 the earth's surface f, which is in fairly good agreement with 

 the amount determined by Strutt by more direct methods. 

 Again, an attempt to measure the ionization due to the 

 a rays from the active matter in the air leads to an estimate 

 of a few ions per c.c. per second %. Hence the ionization 

 of air over the land may be satisfactorily explained by the 

 active matter in the earth and atmosphere. 



A consideration of the production of ions in air over the 

 ocean presents several difficulties. The following is a list of 

 possible known causes, but there may be others with which 

 we are not at present acquainted : — 



(1) Emanation, and its successive products, rising from 

 radium contained in sea-water. 



(2) Penetrating radiation due to active matter in sea- 

 water. 



* Phys. Zeit. Sept. 15, 1906. 

 t Pbil. Mag. Sept. 1906. 

 \ Phil. Mag-. July 1905. 



