and the Aurora JBorealis, 363 



In the equatorial plane this force becomes = 0. The electric 

 molecules situated in that plane move therefore vertically up- 

 ward, seeing that the component of the force A is the only 

 one which acts upon them. At the terrestrial poles (7=90) 

 B and A are alike equal to nil ; therefore the molecules si- 

 tuated in the parts themselves undergo no action from the 

 magnet. For all the other molecules, the distance r of which 

 from the centre of the earth is above or equal to 2p, the first 

 term of the expression (B) will be always positive. For the 

 molecules of the northern hemisphere (that is to say, for the 

 positive values of the latitude) the first term will be numeri- 

 cally higher than the second, and consequently the total ex- 

 pression will be positive ; for the southern hemisphere (that 

 is, for the negative values of /) the first term will be numeri- 

 cally lower than the second, and consequently the entire ex- 

 pression will be negative. For the same value of r, and at an 

 equal latitude, the expression f B) will have the same numeri- 

 cal value in both hemispheres ; but this value will be positive 

 in the northern, negative in the southern hemisphere. It 

 appears, then, from the expression (B) of the tangential com- 

 ponent of the force, that the electric molecules situated in the 

 terrestrial atmosphere or at the surface of the earth endeavour, 

 in the northern hemisphere, to approach the north pole, and 

 those situated in the southern hemisphere the south pole. The 

 vertical component (A) tends in the same way in both hemi- 

 spheres to move the molecules always further from the centre 

 of the earth in their course toward the terrestrial poles. 



We will now see what is the influence which these forces 

 are capable of exerting upon the electric state of the earth and 

 the atmosphere. The lower stratum of the air is a relatively 

 bad conductor ; and we assume at first the ideal case that its 

 conductivity is everywhere equal. The vertical component of 

 the magnetic force in question then tends to direct the aether 

 (positive electricity) from the earth to the air, the lower strata 

 of which consequently become charged with that fluid, while 

 the earth itself, which is a good conductor, incurs a deficit of 

 aether (that is, becomes electronegative). The magnetic force 

 being always in equally intense activity, and the earth rota- 

 ting with a constant velocity, a portion of the electric fluid is 

 soon conducted into the upper regions of the atmosphere, 

 where the conductivity is better. Arrived there, the electric 

 fluid is impelled towards the poles by the tangential component 

 of the magnetic force. The aether (positive electricity) in this 

 way accumulates in the atmosphere, while the earth itself suf- 

 fers a deficit of electricity (becomes electronegative). This 

 continues until the electric tension of the atmosphere is suffi- 



