202 ELEMENTS OF STATIC ELECTRICITY. 



any portion of the earth's surface, must produce a 

 corresponding change in the stratum of least resistance, 

 in the atmosphere above it; and that a transfer of 

 electricity must occur between this electrified atmos- 

 pheric area, and the surrounding atmosphere, lying in 

 the same horizontal plane, either from it or to it, as the 

 earth's surface below is positive or negative. 



We have, in the aurora, the exact fulfillment of all 

 these conditions. A high earth potential, in the polar 

 regions, must result from the currents flowing in from 

 the warm region ; and produce, by induction, a corre- 

 sponding negative potential in the atmosphere. And, 

 in the belts where these ice-bound polar regions join 

 the warmer region, the principal electric action must 

 take place; producing the auroral arches of white light : 

 while the electricity radiating in opposite directions, 

 north and south from the arch, produces the streamers, 

 beams, rays, bands, and coronas ; as the electric action 

 at different points has greater or less intensity, or meets 

 with varying resistance. 



Confirmatory evidence of this view is found in the 

 fact, shown by the chart on page 200, that within the 

 torrid and north frigid zones, where a comparatively 

 even temperature exists, the aurora is not seen ; and 

 also in the shifting position of the auroral belt with 

 change of temperature, as already mentioned. 



The east and west earth currents must also exercise 

 their inductive influence, giving rise, probably, to the 

 transverse undulations observed in the streamers and 

 curtain formations. And the resultants of these cur- 

 rents, and the north and south currents, are seen in the 

 bands and streamers which often assume a diagonal 

 direction, northwest and southeast, or otherwise. 



