144 BAUER— SOLAR ACTIVITY AND [April 23. 



and winter Schuster had to make the plausible hypothesis that the 

 conductivity of the atmospheric regions was altered in the course 

 of the year by the variation in the supply of the ionizing agencies 

 coming from the sun. Schuster's currents are accordingly the 

 diurnal variation of those of our primary atmospheric field on which 

 we must depend, coupled with the earth's rotation, to furnish the 

 actual supply of energy required to produce and maintain a mag- 

 netic storm. 



The hypothesis above advanced for the formation of the primary 

 atmospheric electric currents must, at present, be regarded as a ten- 

 tative one. The precise determination of the characteristic features 

 of this electric field cannot be attempted until the completion of the 

 general magnetic survey of the globe. It ought to be pointed out, 

 however, that the theory advanced to account for our magnetic 

 disturbances is in no wise dependent upon the correctness of the 

 hypothesis as to the origin of the primary electric field. While we 

 do not know, at present, all we should like, we are sure of the 

 existence of this field and that is all the theory requires. 



In conclusion let me give you briefly another result obtained 

 from our analysis of magnetic disturbances, viz., that as to the 

 earth's magnetic permeability of which we have had thus far no 

 knowledge. Taking the magnetic permeability of air as unity, it 

 is found that for magnetizing forces on the order of 1/10,000 part 

 of a C.G.S. unit, the earth's average magnetic permeability is about 

 2. The probabilities are that this value may be somewhat increased 

 as the analysis progresses. 



