I9I0.] TERRESTRIAL MAGNETIC DISTURBANCES. 143 



Examining the results to date from actual observations, a gen- 

 eral agreement is found with the hypothesis — the electric currents 

 in the atmosphere not only follow the general direction prescribed, 

 but have a magnetic field whose axis is actually found displaced 

 from that of the earth through an angle of 32° to the west and 

 south. If we examine into the various effects of the primary 

 electric field, many of the phenomena disclosed by the observations 

 in atmospheric electricity, e. g., relation to barometric changes, give 

 additional support to the theory above set forth. 



The mechanical efifect of the currents induced in the atmosphere 

 will be to increase the velocity of the earth's rotation or more likely 

 to cause a displacement of the earth's magnetic axis eastward. We 

 thus have introduced one of the several systems which together 

 cause the secular variation of the earth's magnetism. This subject, 

 as well as the conversion of electrical into thermal energy and the 

 possible meteorological consequences thereof cannot be entered into 

 here. So likewasemere reference can be made to the subject of 

 the possible vertical earth-air electric currents, which the theory 

 discloses and which I have already partially investigated. Thus 

 far only the effects of the primary circulation of the atmosphere 

 have been considered ; manifestly there will be other effects from 

 the secondary motions of the atmosphere. 



If the primary atmospheric electric field is brought about electro- 

 dynamically as explained, then it is reasonable to suppose that any 

 periodic or spasmodic fluctuation in the general motions of the 

 atmosphere will result in a corresponding change in the electric 

 field, which in turn may give rise to a variation observed in ter- 

 restrial magnetism and atmospheric electricity. Now Schuster had 

 previously shown that the diurnal variation of the earth's magnetism 

 corresponded precisely to what would result from Foucault currents 

 electro-dynamically induced by the daily oscillatory movements of 

 the atmosphere with reference to the earth's lines of magnetic force. 

 The motion of the air currents it was necessary to suppose for the 

 production of the electric currents corresponded precisely to that 

 as indicated by the diurnal oscillation of the barometer. To explain 

 the difference of the effects on the magnetic needle between summer 



